Report on the Radiolaria/Phaeoconchia

by Ernst Haeckel

Order IV. PHÆOCONCHIA, Haeckel, 1879.

Definition.—Phæodaria with a bivalved lattice-shell, composed of two free opposite valves (a dorsal and a ventral), between which the central capsule is enclosed.

Family LXXXIII. Concharida, Haeckel, 1879 (Pls. 123-125).

Concharida, Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Phæodaria with a bivalved lattice-shell, which is spherical or lenticular, and composed of two equal or unequal boat-shaped valves, a dorsal and a ventral. The valves bear neither an apical latticed cupola or galea, nor hollow radial tubes. The central capsule is placed in the aboral half of the shell-cavity, and so enclosed between both valves, that its three openings lie in the open frontal fissure between them (the astropyle on the oral pole of the main axis, the two parapylæ on both sides of its aboral pole, at right and left).

The family Concharida and the two following closely allied families, the Cœlodendrida and Cœlographida, compose together the most remarkable and interesting suborder of Phæoconchia (or "Phæodaria bivalva"), differing from all the other Radiolaria in the possession of a bivalved lattice-shell, composed of two separate valves, like the shell of a Brachiopod. The central capsule is so enclosed between the two fenestrated valves that its three openings lie in the horizontal open (frontal) fissure between them, the astropyle or main-opening on the oral pole of the main axis; the two secondary openings or parapylæ on the two sides of its aboral pole, at right and left. The plane in which the three openings lie is therefore the frontal plane, dividing the entire body into a dorsal and a ventral half. The two valves, accordingly, must be considered as dorsal and ventral valves (as in the Brachiopoda), and the symmetrical halves of each valve as right and left. These halves may be always easily distinguished, since the oral pole of each valve is constantly different from the aboral pole. The voluminous phæodium always lies in the oral half, and the central capsule in the aboral half of the shell-cavity, whilst the calymma encloses the whole shell.

The Concharida differ from the other two families of bivalved Phæodaria in the absence of the apical galeas, and the branched hollow tubes arising from them. Each of these two cupolas, which are at the opposite poles of the sagittal axis (one cupola on the apex of each valve), is in the Cœlographida connected by a simple or double frenulum with a peculiar rhinocanna, or an open nasal tube directed towards the mouth; whilst the cupolas of the Cœlodendrida possess neither a rhinocanna nor a frenulum. The three families of Phæoconchia may therefore represent a phylogenetical series, the common root of which are the Concharida. From these are developed the Cœlodendrida by development of an apical cupola or galea on each valve, and of hollow radial tubes arising from it; whilst the Cœlographida are developed from the latter by production of a rhinocanna on the base of each cupola, and of one or two frenula connecting the former with the latter.

All the Concharida described in the following pages (seven genera and thirty species), are perfectly new to science, and not a single form of this interesting family was known before the explorations of the Challenger. Some species (mainly of the genera Conchidium and Conchopsis) are by no means rare, and are found in great numbers at some stations of the tropical seas (in the Pacific as well as in the Atlantic). All described species are closely allied, agree in the majority of characters, and are easy to distinguish from all the other Radiolaria. Some few forms of Concharida, however, form a direct passage to the Cœlodendrida.

Regarding the probable origin of the Concharida (and therefore also of all other Phæoconchia derived from the latter), two different hypotheses are possible. They have either been derived directly from the skeletonless Phæodina, by development of a bivalved lattice-shell; or they may be derived from Phæodaria with a simple spherical lattice-shell (Castanellida), by the halving of this latter, or its splitting into two hemispherical valves; the former hypothesis is more probable than the latter.

The two valves of the lattice-shell (Pls. 123-126) must in the Concharida (as in all other Phæoconchia) be distinguished as dorsal and ventral, and may therefore be compared with the two valves of the Brachiopoda, not with those of the Lamellibranchia. This important morphological distinction is expressed by the constant position of the central capsule within the shell-cavity. The capsule always exhibits the character of the "Tripylea" and has three tubular openings, placed in the frontal or lateral plane of the unicellular body. In the same plane lies the open frontal fissure between the two valves, and the three openings are so disposed in it that the large anterior main-opening (or the astropyle) is placed on the oral pole of the main axis, whilst the two accessory small lateral openings or parapylæ are placed on both sides of the aboral pole, at the right and left. Therefore in a dorsal or ventral view all three openings are visible (Pl. 123, figs. 1, 8a); in the usual lateral view, however, from the right or left side, only two openings are visible, the astropyle on the anterior, and one parapyle (right or left) near the posterior pole of the main axis (Pl. 123, figs. 8, 9; Pl. 124, figs. 6, 10). The posterior view (from the aboral pole) shows the two parapylæ, at right and left; in the anterior view (from the oral pole) the astropyle may be visible, but usually it is completely hidden in the dark voluminous phæodium. This latter envelops sometimes nearly the whole capsule as an opaque conglomeration of green or brown phæodella (Pl. 123, figs. 8, 9); but usually the phæodium fills up the anterior (oral) half of the shell-cavity, whilst the capsule occupies the posterior (aboral) half (Pl. 124, figs. 6, 10).

The dorsal shell-valve is in almost all Phæodaria smaller or somewhat different in shape from the ventral valve, and this difference is often very striking (Pl. 124, figs. 3-16); but in a few species both valves are so similar, that I could not discover any certain difference. This equality of the two valves occurs mainly in those Concharida which pass over into the Cœlodendrida; in these latter as well as in the Cœlographida, both valves are usually equal in size and form. Whilst the main axis (or the longitudinal axis of the body) in the two latter families of Phæoconchia seems to be normally vertical (in the living and freely floating body), in the living Concharida it is probably horizontal, so that the larger and heavier ventral valve lies below the smaller and lighter dorsal valve.

The geometrical fundamental form of the body is therefore in the Concharida dipleural or bilaterally symmetrical, and we distinguish in it the same three dimensive axes, as in all other dipleural forms. On the anterior or oral pole of the main axis (or longitudinal axis) lies the mouth of the shell, and behind it the phæodium; on the opposite posterior or aboral pole lies the hinge of the shell (comparable to the shell-hinge of the Brachiopoda) and in front of it the central capsule. The sagittal (or dorso-ventral) axis, determining the height of the shell, has on its dorsal (or upper) pole the apex or highest point of the dorsal valve, on its ventral (or lower) pole the apex or lowest point of the ventral valve. The two poles of the frontal (lateral or transverse) axis are equal and are determined by the two parapylæ of the capsule, and the corresponding points of the shell-fissure between both valves. Usually the main-axis is the longest, the frontal axis the shortest, and between both the sagittal axis.

In regard to the three dimensive planes which are determined by these three axes, perpendicular to one another, they are rarely of nearly equal size (as in some subspherical species), usually the sagittal plane (separating the right and left halves of the body) is the largest; the cinctural or equatorial plane (separating oral and aboral halves) is the smallest, and the frontal or lateral plane (separating dorsal and ventral halves) is intermediate in size. The relation of the three perimeters of these three planes corresponds to that proportion; the sagittal perimeter (in which the keel of the compressed valves lies) is the largest; the cinctural or equatorial perimeter (separating the anterior phæodium and the posterior central capsule) is the smallest, and the frontal or lateral perimeter (in which the fissure between the valves lies) is intermediate in size.

The general form of the single valves is very varied in the different species, in the majority boat-shaped or hat-shaped, more or less laterally compressed, in a few forms hemispherical. In Conchopsis (Pl. 125) and Conchoceras (Pl. 124, figs. 15, 16) the lateral parts of the valves (right and left) are vaulted, whilst their median parts are so strongly compressed that they form a sharp sagittal keel, and then the shell in the dorsal or ventral view appears spindle-shaped (Pl. 123, fig. 8a; Pl. 125, fig. 8). Often the frontal margins of the valves are somewhat constricted (Pl. 124, fig. 7).

The junction between the two valves of the shell is always loose, but not so loose as in the two following families. In the Cœlodendrida and Cœlographida the two valves are either perfectly free and separated by a frontal zone of jelly, or in very loose contact on the frontal margins. In the Concharida, however, the margins of both valves seem to be usually in contact, and their connection is effected in a double way. In the subfamily Conchasmida (comprising the genera Concharium and Conchasma, Pl. 123, figs. 1-6) the lateral margins of both valves are smooth, not dentated, and fit one into another like the two parts of a box, or like the two valves of a Diatom (Navicula). In the second subfamily, however, Conchopsida (comprising the five other genera, Pls. 124, 125), the lateral margins of the valves are dentate, usually provided with a series of numerous strong conical teeth, and the teeth of both valves so catch into one another, that their union is rather firm (like the margin of the shells of Tridacna, Pecten, and other Lamellibranchiata). Besides, a more solid junction is often effected on the posterior or aboral part of the margins, which we shall call the hinge. Here often peculiar strong teeth catch one into another, and in the majority of species two aboral spines are developed, the caudal horns (a dorsal and a ventral); these are very large in Conchoceras (Pl. 124, figs. 15, 16). But a peculiar and most interesting kind of junction is effected in some Concharida by a true ligament between the valves (Pl. 123, figs. 8, 9; Pl. 125, fig. 2). This ligament is always placed on the aboral hinge, is of dark brown colour, and is not dissolved by mineral acids unless long applied. It may preserve the connection of the posterior parts of both valves, when their anterior parts are removed one from another, just as in the Brachiopoda. I observed this interesting ligament mainly in the genus Conchopsis, but not in all species, and it is not yet certain whether it is a constant organ in these and some other Concharida.

In the majority of Concharida the lateral margins of the two valves project slightly inwards into the cavity, and in some species of Conchopsis these inner borders are so broadened that they form a broad, horizontal, fenestrated inner shelf, comparable to the deck of a boat or to the velum of the Hydromedusæ or Craspedotæ (Pl. 125, fig. 9). In this case the velum surrounds the ovate aperture through which the two lobes of the central capsule (dorsal and ventral) enter into the cavity of both valves.

The mouth of the shell lies on the oral pole of the main axis, and is therefore opposed to the aboral hinge. The two valves are here usually more or less emarginate, so as to form a transverse mouth with an upper and a lower lip (Pl. 124, figs. 6, 7, 11). The form of these two lips is often very different and characteristic of particular species (Pl. 124, figs. 3, 15, 16). The mouth remains in many species constantly open, even when the frontal fissure is closed (figs. 7, 16). Since the centre of the shell mouth lies in the prolongation of the proboscis arising from the operculum of the central capsule, probably the main stream of sarcode, issuing from the latter, becomes protruded by the former.

Apophyses of the shell (besides the teeth of the margins) are completely wanting in three genera, Concharium, Conchellium, and Conchopsis (Pl. 123, figs. 1-4, 7; Pl. 125). The four other genera possess free apophyses or spines, which we call horns. They are probably important as the beginnings of those large hollow tubes which are characteristic of the two following families, Cœlodendrida and Cœlographida. We distinguish two different forms of horns, apical horns on the poles of the sagittal axis, and caudal horns on the aboral pole of the main axis; the former probably correspond to the sagittal tubes and the latter to the caudal tubes of the two following families. Apical horns are found in a single genus only, Conchonia (Pl. 124, figs. 10-14). Here either on one pole or on poles of the sagittal axis a horn is developed, usually curved backwards. Sometimes the base of this conical horn is inflated and fenestrated, and may represent the beginning of the formation of the galea or apical cupola of the Cœlodendrida.

The two caudal horns are opposite on the aboral hinge of the shell, one arising from the posterior end of each valve. Usually they are short and thick, pyramidal, the ventral horn larger than the dorsal (Pl. 124, figs. 3, 6). Rarely the two caudal horns are fenestrated at the base and reach a considerable size, as in Conchoceras (Pl. 124, figs. 15, 16).

The walls of the bivalved shell usually exhibit in the Concharida a rather solid shape and regular structure, with an elegant network of regularly arranged pores. But in some species the walls of the shell become very thin and fragile, and assume the same shape (with very irregular network), as in the Cœlodendrida and Cœlographida. The pores are usually small and numerous, circular, often hexagonally framed (Pl. 125, figs. 4-6). They pierce the thick shell-wall either in a radial or in an oblique direction. Sometimes each pore is armed with six radial teeth (Pl. 123, fig. 7a). At other times each pore represents an oblique ampullaceous canal, dilated in its middle part, with two narrow openings (Pl. 125, figs. 5a, b, c, 6). The pores are so arranged in the majority of species that they form regular curved series, which are separated by prominent crests, and converge towards the poles of the main axis. Usually the marginal pores (along the frontal margin of the valves) are much smaller (compare Pls. 123-125).

The central capsule of the Concharida, very well preserved in numerous specimens of the Challenger collection, constantly possesses the same situation and structure. It is always enclosed in the aboral or posterior half of the shell-cavity, whilst the oral or anterior half is filled up by the phæodium. The free spaces between both and between the inner surface of the shell are completely filled up by the jelly of the calymma, which also covers the whole shell as a thin outer jelly-envelope. The form of the central capsule is sometimes nearly spherical, usually somewhat compressed in the direction of the main axis, and sometimes also in the direction of the frontal axis (Pl. 123, figs. 1-9). In some species it becomes bilobed, with an upper dorsal and a lower ventral lobe, and in some others it becomes triangular (Pl. 125, fig. 7). Its two membranes (inner and outer) are often separated by a broad colourless interval, containing a clear fluid or jelly (Pl. 123, figs. 8, 9). The nucleus is usually about half as large as the central capsule and ellipsoidal, its longer axis lying in the sagittal diameter of the body. Several specimens (of different genera) contained two separate nuclei, one placed in the dorsal, the other in the ventral half of the capsule (Pl. 124, fig. 6). This duplication of the nucleus is probably the preparation for the division of the capsule. The division will be probably effected in the frontal plane, so that each half of the bisected capsule gets one nucleus and one valve, and the other valve becomes newly formed (in a way similar to that in the bivalved Diatomaceæ). The astropyle, or the main-opening of the capsule, is closed by a radiate operculum, from which arises a tubular proboscis; this lies in the main axis of the body, is directed towards the anterior mouth of the shell, and surrounded by the phæodium. The two shorter tubes of the paired parapylæ, or the accessory lateral openings, lie on the posterior or caudal side of the capsule, at right and left, and are directed half backwards, half outwards (towards the frontal fissure between the valves, Pl. 123, figs. 1, 8a).

The phæodium exhibits in all Concharida the same characteristic shape, and represents a dark conglomeration of phæodellæ, filling up the anterior or oral half of the shell-cavity. Usually it is bilobed, divided into a dorsal and a ventral lobe or wing, which fills up the corresponding valve of the shell (Pl. 123, figs. 8, 9). The phæodium is commonly more voluminous than the capsule, and surrounds its anterior half, more rarely it encloses nearly the entire capsule (Pl. 124, figs. 6, 10). Its colour is usually olive, sometimes more greenish, at other times more brownish, in some species nearly black. The phæodellæ, or the roundish granules which compose the phæodium, exhibit the same shape as in all other Phæodaria (compare above, p. 1535). Sometimes peculiar rather oblong nucleated cells are scattered in great numbers between the phæodellæ, probably parasites or symbiontes (Pl. 123, figs. 7-9, 9a).

Synopsis of the Genera of Concharida.

I. Subfamily Conchasmida. Lateral edges of the two valves smooth, without teeth.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Valves without sagittal keel, nearly hemispherical or slightly compressed.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Aboral hinge without horns,	720. Concharium.
				Aboral hinge with two horns (one on each valve),	721. Conchasma.
II. Subfamily Conchopsida. Lateral edges of the two valves dentate, with a series of prominent teeth on both sides. The teeth of both valves catch one into another.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Valves without sagittal keel, nearly hemispherical or slightly compressed.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Aboral hinge without horns,	722. Conchellium.
				Aboral hinge with two horns. No apical horn,	723. Conchidium.
				Aboral hinge with two horns. Apex also with a horn,	724. Conchonia.
		Valves with a sharp sagittal keel, strongly compressed on both sides, boat-shaped.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Aboral hinge without horns,	725. Conchopsis.
				Aboral hinge with two horns (one on each valve).	726. Conchoceras.

Subfamily 1. Conchasmida, Haeckel.

Definition.—Concharida with the lateral margins of the two valves smooth, without interlocking teeth.

Genus 720. Concharium,^[1] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Concharida with the lateral margins of the valves smooth, without sagittal keel and without horns on the hinge.

The genus Concharium is the simplest and the most primitive form of all Concharida; it may be regarded as the common ancestral form of the whole family. The entire shell is usually almost spherical, without horns or teeth, and may be regarded as a Castanella which is bisected or broken into two equal hemispherical halves. The lateral margins of the two hemispherical valves are smooth, without teeth, and catch one into the other like the two valves of a Diatom, or the two halves of a bivalved box. Concharium agrees in this simple shape of the frontal margins with the following genus Conchasma, and represents with it the small subfamily Conchasmida.

1. Concharium bivalvum, n. sp. (Pl. 123, figs. 2, 2a).

Shell spherical, smooth. Diameter in all directions nearly the same. Borders of the two hemispherical valves circular, smooth, about twice as broad as the pores. In the half frontal perimeter of the shell (along the right and the left border of each valve) twenty-two to twenty-four pores, in the half sagittal perimeter (in the middle line of each valve) eighteen to twenty-two pores, in the half equator (in the cinctural perimeter of each valve) twenty to twenty-two pores. All pores circular, of the same size, twice as broad as their bars.

Dimensions.—Length of the shell (longitudinal diameter) 0.35, height (sagittal diameter) 0.34, breadth (lateral diameter) 0.33.

Habitat.—North Atlantic, west of Madeira, Station 354, depth 1675 fathoms.

2. Concharium nucula, n. sp. (Pl. 123, fig. 3).

Shell pear-shaped, with costate surface. Oral face somewhat truncated, broader than the aboral face. Its longitudinal diameter about one-fifth longer than the two other diameters. Borders of the two valves ovate, smooth, about as broad as the pores. In the half frontal perimeter of the shell twenty-two to twenty-four pores, in the half sagittal perimeter eighteen to twenty, in the half equator sixteen to eighteen. Pores irregularly roundish, three to four times as broad as the bars. The pores are so disposed in meridional rows that the crests between the rows converge towards the two poles of the sagittal axis.

Dimensions.—Length of the shell 0.2, height 0.18, breadth 0.16.

Habitat.—South Atlantic (west of Tristan da Cunha), Station 332, depth 2200 fathoms.

3. Concharium diatomeum, n. sp. (Pl. 123, fig. 1).

Shell nearly spherical, slightly lenticular, somewhat compressed in dorso-ventral direction; the sagittal diameter therefore somewhat shorter than the two others. Borders of the two hemispherical valves nearly circular, quite smooth, about as broad as the length of the largest pores. In the half frontal perimeter of the shell forty-four to fifty pores; in the half sagittal perimeter twenty to twenty-four; in the half equator thirty to thirty-three. Pores different in form and size; the marginal pores small, nearly circular; the dorsal and ventral pores oblongish-hexagonal, twice as long as broad, about four to six times as long as the bars, regularly arranged in transverse rows.

Dimensions.—Length of the shell 0.22, height 0.21, breadth 0.2.

Habitat.—Tropical Atlantic, near Sierra Leone, Station 348, depth 2450 fathoms.

4. Concharium bacillarium, n. sp. (Pl. 123, fig. 4).

Shell walnut-shaped, with panelled surface; oral and aboral face of the same form. Its longitudinal diameter about one-fifth longer than the two other diameters. Borders of the two cup-shaped valves elliptical, smooth, with a prominent edge, about as broad as the larger pores. In the half frontal perimeter of the shell fifty to fifty-five pores, in the half sagittal perimeter thirty-six to forty, in the half equator also thirty to forty. Pores hexagonally framed. The pores are tapering in size from the sagittal plane towards the valve-margins, and so regularly arranged in meridional rows that the crests between the latter converge towards both poles of the longitudinal axis.

Dimensions.—Length of the shell 0.2, height 0.15, breadth 0.15.

Habitat.—Tropical Atlantic, off St. Helena, Station 340, depth 1500 fathoms.

5. Concharium fragilissimum, n. sp.

Shell subspherical, very thin-walled and fragile. Diameter in all directions nearly the same. Oral and aboral face scarcely different. Margins of the hemispherical valves extremely thin and hyaline. Pores irregularly roundish, of very different sizes and unequal forms. The fragile shell of this species differs in general shape from that of all other Concharida, and is like that of the Cœlodendrida (Pl. 121, fig. 3), but exhibits neither an apical cupola or galea, nor radial tubes arising from it. It may be perhaps a young specimen of Cœlodendrum.

Dimensions.—Diameter of the shell 0.22, of the pores 0.002 to 0.02.

Habitat.—Mediterranean, Portofino (Haeckel), surface.

Genus 721. Conchasma,^[2] n. gen.

Definition.—Concharida with the lateral margins of the valves smooth, without sagittal keel, but with two caudal horns on the hinge (a dorsal and a ventral).

The genus Conchasma is closely allied to the preceding Concharium, and has the same hemispherical valves with smooth margins, without teeth; but it differs from the latter in the development of two caudal horns or posterior spines on the aboral hinge, one horn on the aboral end of each valve. The three species of this genus were all found in great depths of the Antarctic Ocean, in Diatom ooze, between 1260 and 1975 fathoms, at Stations 152 to 157.

1. Conchasma radiolites, n. sp. (Pl. 123, fig. 5).

Shell nearly spherical, somewhat compressed on both sides; the dorsal valve smaller, flatter and shorter than the ventral valve. In the half sagittal perimeter of the shell twenty to twenty-two pores, in the half frontal perimeter twelve to fourteen, in the half equator eighteen to twenty. All pores nearly of the same size, circular, hexagonally framed, scarcely as broad as the bars. The two horns of the hinge are four-sided pyramidal, of different sizes; the ventral horn (of the larger valve) two to three times as long as the dorsal horn (of the smaller valve); the latter twice as long as a pore.

Dimensions.—Length of the shell 0.16, height 0.15, breadth 0.14.

Habitat.—Antarctic Ocean, Station 154, depth 1800 fathoms.

2. Conchasma sphærulites, n. sp. (Pl. 123, fig. 6).

Shell nearly spherical, somewhat compressed on both sides, the frontal diameter therefore somewhat shorter than the two others. Both valves nearly of the same size, hemispherical, their borders smooth, twice as broad as the largest pores. In the half sagittal perimeter of the shell twenty-eight to thirty pores, in the half frontal perimeter twenty to twenty-two, in the half equator twenty-four to twenty-six. Size of the pores increasing from the borders towards the top of the valves. One series of very small pores along the frontal free margin of each valve. Pores roundish-polygonal, three to four times as broad as the bars. The two horns of the hinge are of equal size, four-sided pyramidal, and twice as long as the larger pores.

Dimensions.—Length of the shell 0.18, height 0.18, breadth 0.16.

Habitat.—Antarctic Ocean, Station 152, depth 1260 fathoms.

3. Conchasma hippurites, n. sp.

Shell nearly spherical, scarcely compressed. The frontal diameter equal to the two others. Both valves equal. In the half sagittal perimeter of the shell thirty-two to thirty-four pores, in the half frontal perimeter twenty-four to twenty-six, in the half equator twenty-six to twenty-eight. All pores of nearly equal size, circular, polygonally framed, twice as broad as the bars. The two horns of the hinge are large, three-sided pyramidal, the ventral horn twice as long as the dorsal, and four to six times as long as one pore.

Dimensions.—Length of the shell 0.22, height 0.21, breadth 0.2.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

Subfamily 2. Conchopsida, Haeckel.

Definition.—Concharida with the lateral margins of the two valves dentate, the teeth of both catch one into another.

Genus 722. Conchellium,^[3] n. gen.

Definition.—Concharida with the lateral margins of the valves dentate, without sagittal keel and without horns on the hinge.

The genus Conchellium and the four following genera represent together the subfamily Conchopsida, differing from the Conchasmida in the dentate lateral margins of the two valves. These are armed with a series of strong, conical teeth, and catch one into another just as the two valves of many Lamellibranchiata and Brachiopoda do (Pl. 124, figs. 1-16). Conchellium is the simplest form among the Conchopsida, since the valves are hemispherical, and possess neither a sagittal keel nor projecting horns.

1. Conchellium tridacna, n. sp. (Pl. 123, figs. 7, 7a).

Shell nearly spherical, finely tuberculated, the sagittal diameter somewhat longer than the two others. Borders of the two hemispherical valves smooth in 0.2 of the oral, and 0.1 at the aboral part, dentated in the remaining 0.7 part; on one side of each valve fourteen to sixteen very strong and long teeth, all nearly of the same size, about one-fourth as long as the shell-radius. In the half frontal perimeter of the shell (on one border of each valve) twenty-five to thirty pores, in the half sagittal perimeter thirty-five to forty, in the equator twenty-five to thirty. Pores circular, hexagonally framed, of equal size (except some smaller rows along the fissure), twice as broad as the bars. On the conical inside of each funnel-like pore six small spinules, between every three neighbouring pores a triangular facette (fig. 7a).

Dimensions.—Length of the shell 0.34 to 0.38, height 0.38 to 0.42, breadth 0.32 to 0.36.

Habitat.—North Pacific, Stations 250 to 253, depth 2740 to 3125 fathoms.

2. Conchellium hippopus, n. sp.

Shell nearly spherical, in the lateral perimeter (along the girdle-fissure) somewhat constricted. Borders of the two hemispherical valves semicircular, smooth in 0.3 of the oral, and 0.2 of the aboral part, dentated only in the remaining 0.5 middle part; on one side of each valve seven to eight very strong and long teeth, increasing in size towards the mouth, the longest (foremost) teeth nearly one-third as long as the shell-radius. In the half frontal perimeter of the shell (along one border of each valve) twenty-four to twenty-eight pores, in the half sagittal perimeter thirty-two to thirty-six, in the half equator twelve to fourteen. Pores circular, twice to three times as broad as the bars, smaller along the fissure.

Dimensions.—Length of the shell 0.06, height 0.065, breadth 0.055.

Habitat.—Central area of the Tropical Pacific, Station 274, depth 2750 fathoms.

Genus 723. Conchidium,^[4] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Concharida with the lateral margins of the valves dentate, without sagittal keel and apical horns, but with two caudal horns on the hinge (a dorsal and a ventral).

The genus Conchidium is the most common form of all Concharida, and some of its species occur in great numbers in the tropical zone of the Pacific and the Atlantic, on the surface as well as at various depths. It differs from the preceding Conchellium, its ancestral form, in the development of two caudal horns, or two strong pyramidal spines which arise from the posterior end of the valves; the dorsal horn usually is smaller than the ventral.

1. Conchidium terebratula, n. sp. (Pl. 124, figs. 1, 2).

Shell subspherical, smooth; both valves of nearly equal size and form, hemispherical. The three dimensive axes of the body are almost equal. Margins of the valves dentate in nearly the whole periphery; on each side of one valve eleven or twelve strong conical teeth, all of the same size. Aboral hinge with two short and stout four-sided pyramidal horns of equal length. Mouth with two equal short lips. Pores of the shell subregular, circular, three to four times as broad as the bars, in the dorsal valve twice as large as in the ventral valve.

Dimensions.—Diameter of the shell 0.24 to 0.28.

Habitat.—Central Pacific, Stations 270 to 274, surface, and at various depths.

2. Conchidium thecidium, n. sp. (Pl. 124, fig. 6).

Shell subspherical, slightly compressed on both sides. Dorsal valve somewhat smaller than the ventral, of similar form. Principal axis of the shell somewhat longer than the sagittal, and this longer than the frontal axis. Margins of the valves smooth in the oral quarter, strongly dentate in the remainder; on each side of one valve eight or nine very large triangular teeth, half as long as the height of the valve. Aboral hinge with two unequal, stout, four-sided pyramidal horns; the dorsal horn half as long at the ventral. Mouth with two unequal lips, the upper shorter than the lower. Pores of the shell subregular, hexagonal, three to four times as broad as the bars. The figured specimen, well preserved, contained in the central capsule two nuclei, one in the dorsal, the other in the ventral half.

Dimensions.—Length of the shell 0.28 to 0.33, height 0.27 to 0.3, breadth 0.22 to 0.24.

Habitat.—South Pacific, Station 292, depth 1600 fathoms.

3. Conchidium rhynchonella, n. sp. (Pl. 124, fig. 3).

Shell with three different dimensive axes in the proportion = 6 : 5 : 4. Ventral valve semi-ovate, larger than the humpbacked dorsal valve. Margins of the valves dentate almost in the whole periphery; on each side of one valve twelve or thirteen strong conical teeth. Aboral hinge with two very unequal horns, the dorsal much smaller than the pyramidal ventral. Under lip of the mouth emarginate, much larger than the acute upper lip. Pores subregular, circular, twice as broad as the bars.

Dimensions.—Length of the shell 0.3, height 0.25, breadth 0.2.

Habitat.—North Pacific, Stations 244 to 253, surface, and at various depths.

4. Conchidium dimerella, n. sp.

Shell laterally compressed, very similar to the preceding, but differing in the following characters:—Proportion of the three axes = 7 : 5 : 4. Ventral valve hemispherical, larger than the humpbacked dorsal. Margins of the valves dentate in the middle half only, whilst the anterior and posterior quarters are smooth; on each side of one valve six or seven strong conical teeth. Ventral horn of the aboral hinge very large, pyramidal, one-third as long as the shell and three times as long as the dorsal.

Dimensions.—Length of the shell 0.35, height 0.25, breadth 0.2.

Habitat.—North Pacific, Station 236, surface.

5. Conchidium leptæna, n. sp. (Pl. 124, figs. 4, 5).

Shell laterally compressed, with three different dimensive axes of the proportions = 4 : 3 : 2. Ventral valve larger than the dorsal, both semi-ovate. Margins of the valves dentate along the lateral sides; on each side of one valve nine or ten conical teeth, the middle of which are smaller. Aboral hinge with two unequal short horns; the dorsal rudimentary. Under lip of the mouth pointed, much larger than the truncate upper lip. Pores circular, about twice as broad as the bars.

Dimensions.—Length of the shell 0.2, height 0.15, breadth 0.1.

Habitat.—Central Pacific, Stations 271 and 272, surface, and at various depths.

6. Conchidium argiope, n. sp. (Pl. 124, figs. 7-9).

Shell laterally compressed, with three different dimensive axes of the proportion = 6 : 5 : 3. Both valves nearly equal. Margins of the shell dentate along the lateral fissure, on each side of one valve thirteen or fourteen thin conical teeth. Aboral hinge with two equal, short, pyramidal horns. Mouth with two equal short lips. Pores subregular, circular, twice as broad as the bars.

Dimensions.—Length of the shell 0.2, height 0.17, breadth 0.1.

Habitat.—Tropical Atlantic, Stations 341 to 349, surface, and at various depths.

7. Conchidium magasella, n. sp.

Shell laterally compressed, with two equal valves, very similar to the preceding species, but differing in the following characters:—Proportion of the three axes = 6 : 4 : 3. Margins of the valves with smaller and more numerous teeth; on each side of one valve sixteen to eighteen short conical teeth. Pores smaller and more numerous, about as broad as the bars.

Dimensions.—Length of the shell 0.24, height 0.16, breadth 0.12.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface.

8. Conchidium productum, n. sp.

Shell laterally compressed, prolonged, with two equal valves, similar to the two preceding species, differing in the following characters:—Proportion of the three axes = 3 : 2 : 1. Margins of the valves smooth in the anterior and posterior quarter, dentate in the middle lateral half; on each side of one valve ten to twelve strong conical teeth. Horns of the aboral hinge prolonged, conical, half as long as the shell, the ventral somewhat larger than the dorsal. Pores regular, circular, twice as broad as the bars.

Dimensions.—Length of the shell 0.25, height 0.15, breadth 0.08.

Habitat.—North Atlantic, Station 354, surface.

Genus 724. Conchonia,^[5] n. gen.

Definition.—Concharida with the lateral margins of the valves dentate, without sagittal keel, but with an apical horn on the poles of the sagittal axis, and with two caudal horns on the hinge (a dorsal and a ventral).

The genus Conchonia is closely allied to the preceding Conchidium, its ancestral form, but differs from this and from all other Concharida in the development of horns on the poles of the sagittal axis. These are probably of great morphological importance, since they represent the beginnings of the hollow tubes arising from the poles of the sagittal axis in all Cœlodendrida and Cœlographida. In one of the three observed species each valve possessed an apical or sagittal horn, whilst in the two other species one valve only was provided with a horn. Since I observed one specimen only of each species, I cannot say whether this difference is important and of constant generic value.

1. Conchonia diodon, n. sp. (Pl. 124, figs. 10-12).

Shell laterally compressed, with two very unequal valves. Dorsal valve smaller, hat-shaped, on the apex with a fenestrated protuberance which is similar to the galea of the Cœlodendrida, and bears a short, conical, backwardly-directed horn. Ventral valve larger, boat-shaped, without apical horn. Aboral hinge with two pyramidal, horizontal, caudal horns of different sizes, the dorsal smaller than the ventral. Lateral margin of each valve on one side with twelve to fourteen strong conical teeth (fig. 12). Lips of the narrow mouth thickened (fig. 11).

Dimensions.—Length of the shell 0.3, height 0.27, breadth 0.21.

Habitat.—Tropical Atlantic, Station 342, depth 1445 fathoms.

2. Conchonia triodon, n. sp. (Pl. 124, figs. 13, 14).

Shell laterally compressed, with two very unequal valves. Dorsal valve (fig. 14) larger, hat-shaped, on the apex with a large pyramidal horn which is half as long as the shell, curved and directed backwards. Ventral valve (fig. 13) smaller, boat-shaped, without apical horn. Aboral hinge with two pyramidal caudal horns of different sizes, the dorsal horn twice as long as the ventral. Lateral margin of each valve on one side with twelve to fifteen conical teeth. Perhaps the larger horned valve (fig. 14) may be the ventral, and the opposite smaller hornless (seen from above in fig. 13) the dorsal valve.

Dimensions.—Length of the shell 0.21, height 0.17, breadth 0.12.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Conchonia tetrodon, n. sp.

Conchura tetrodon, Haeckel, 1882, Manuscript.

Shell subspherical, with two nearly equal hemispherical valves, which are very thin-walled and similar in structure to those of the Cœlodendrida, with very irregular roundish pores of different shapes and sizes (compare Pl. 121, fig. 3). Lateral margins of the valves with very numerous and irregular, thin, bristle-shaped teeth, similar to those of some Cœlographida (compare Pl. 127, fig. 8). Aboral hinge with two equal, conical, caudal horns, which are straight, parallel, and half as long as the shell. Two similar straight conical horns are opposed on the poles of the sagittal axis, and arise from the apex of the two valves. This remarkable species may perhaps better represent a separate genus, Conchura, forming a direct transition to the ancestral form of the Cœlodendrida, Cœlodoras; it differs from the latter in the absence of a galea or hollow conical cupola on the apex of each valve, and in the solid, not hollow structure of the horns.

Dimensions.—Diameter of the shell 0.24, length of the two sagittal horns 0.1, of the two caudal horns 0.12.

Habitat.—Indian Ocean, Cocos Islands (Rabbe), surface.

Genus 725. Conchopsis,^[6] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Concharida with dentate lateral margins and a sharp sagittal keel of the compressed valves, without horns on the hinge.

The genus Conchopsis and the following Conchoceras differ from the other Concharida in the strong lateral compression of the shell, so that each valve is provided in the sagittal plane with a sharp prominent keel, comparable to the dorsal and the anal fin of fishes. These compressed shells are in general twice to three times as large as the more roundish and keelless shells of the five preceding genera. The sculpture of the fenestrated valves is extremely elegant. Conchopsis possesses at the aboral hinge not the two prominent caudal horns, which mark the following genus Conchoceras, but in some species a peculiar ligament connects the aboral ends of both valves.

1. Conchopsis orbicularis, n. sp. (Pl. 125, fig. 3).

Shell subcircular, lenticular, strongly compressed on both sides, nearly as high as long, its sagittal perimeter nearly circular; frontal and cinctural perimeter spindle-shaped. Borders of the two boat-shaped valves smooth in 0.4 of the oral part, and in 0.1 of the aboral part of their length, strongly dentated in the remaining 0.5 middle part; about twenty-five slender, straight teeth on each side of one valve, size of the teeth increasing from the aboral towards the oral pole. In the half lateral perimeter of the shell (along the right and the left borders of each valve) sixty to sixty-five pores, in the half sagittal perimeter (along the keel of each valve) eighty to eighty-five pores, in the half equator sixty to sixty-five pores.

Dimensions.—Length of the shell 0.53, height 0.55, breadth about 0.2.

Habitat.—South Atlantic, west of Tristan da Cunha, Station 333, depth 2025 fathoms.

2. Conchopsis compressa, n. sp. (Pl. 125, figs. 7, 8).

Shell lenticular, strongly compressed on both sides; proportion of its longitudinal diameter to the sagittal and lateral = 10 : 9 : 3, its sagittal perimeter elliptical (fig. 7), cinctural and frontal perimeter spindle-shaped (fig. 8). Borders of the two boat-shaped valves smooth in 0.3 of the oral, and 0.3 in the aboral part, dentated in the remaining 0.4 middle part; about forty to forty-four very slender teeth of equal size on one lateral edge of each valve. In the half frontal perimeter of the shell (along the border of the valve) sixty-four to sixty-eight pores, in the half sagittal perimeter (along one valve-keel) seventy to eighty pores, in the half equator forty-four to forty-eight pores. Ventral and dorsal pores linear, three to four times as long as the circular, lateral pores.

Dimensions.—Length of the shell 0.6 to 0.8, height 0.55 to 0.72, breadth 0.2 to 0.3.

Habitat.—North Pacific, between 30° and 40° north latitude (between Japan and San Francisco), in depths from 2000 to 3000 fathoms frequent, Stations 241 to 252.

3. Conchopsis carinata, n. sp. (Pl. 123, fig. 8).

Shell subcircular, lenticular, in the central half slightly compressed, nearly spherical, in the peripheral half strongly compressed, with a broad, hyaline, smooth keel on the sagittal plane. Borders of the two valves smooth in the 0.2 of the oral, and 0.1 of the aboral part, strongly dentated in the remaining 0.7 middle part; about fifty slender teeth of equal size on one lateral edge of each valve. In the half lateral perimeter of the shell about forty-five to fifty pores, in the half sagittal perimeter sixty-five to seventy, in the half equator thirty-two to forty pores. The pores are arranged in parallel curved rows, which are separated by high denticulate crests. Aboral hinge with a strong ligament.

Dimensions.—Length of the shell 0.6 to 0.7, height 0.55 to 0.65, breadth 0.35 to 0.45.

Habitat.—South Atlantic (east of Patagonia), Station 318, depth 2040 fathoms.

4. Conchopsis lenticula, n. sp. (Pl. 123, fig. 9).

Shell subcircular, lenticular, strongly compressed on both sides, with a sharp and broad hyaline keel in the sagittal perimeter. Borders of the two valves smooth in 0.3 of the oral, and 0.2 of the aboral part, strongly dentated in the remaining 0.5 middle part; about thirty strong, conical teeth on the lateral edge of each valve. In the half lateral perimeter of the shell fifty to fifty-five pores, in the half sagittal seventy to seventy-five, in the half frontal forty to forty-five pores. The large central capsule of this species fills up the posterior half of the shell-cavity, the dark green phæodium the anterior half; the latter contains numerous peculiar, longish, nucleated cells (fig. 9a), parasites or symbiontes (?). Aboral hinge of the shell with a strong ligament.

Dimensions.—Length of the shell 0.7, height 0.6, breadth 0.3.

Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

5. Conchopsis pilidium, n. sp. (Pl. 125, fig. 9).

Shell ovate, lenticular, compressed on both sides, with a broad, wing-like sagittal keel. Proportion of its longitudinal diameter to the sagittal and lateral = 6 : 5 : 3. Sagittal perimeter elliptical. Borders of the two hat-like valves smooth in 0.15 of the oral, and 0.2 of the aboral part, strongly dentated in the remaining 0.65 middle part; about twenty-five to thirty teeth of nearly equal size on one side of each valve. In the half lateral perimeter of the shell (along one border of each valve) forty-five to fifty pores, in the half sagittal perimeter (on the keel of one valve) seventy to seventy-five pores, in the half equator thirty-six to forty pores. Each pore is surrounded by a hexagonal frame. The opening of each valve in this species is bordered and partly closed by a broad, horizontal diaphragm or velum, like the deck of a boat; it is broadest on the oral side.

Dimensions.—Length of the shell 0.78 to 0.8, height 0.66 to 0.7, breadth 0.3 to 0.4.

Habitat.—South Atlantic, between Buenos Ayres and Tristan da Cunha, Stations 324 to 334, at depths between 1715 and 2900 fathoms.

6. Conchopsis aspidium, n. sp. (Pl. 125, figs. 1, 2).

Shell scutiform, strongly compressed on both sides, in the centre only lenticular, in the periphery wing-like, keeled. Proportion of the longitudinal diameter to the sagittal and frontal = 6 : 5 : 2. Sagittal circumference in the oral half semicircular, in the aboral half pentagonal, two acute corners jutting out near the aboral hinge, one corner in the keel of the dorsal, the outer in the keel of the ventral valve. Borders of the two boat-shaped valves smooth in 0.3 of the oral part, and in 0.1 of the aboral part, strongly dentated in the remaining 0.6 middle part; about thirty-five teeth in one side of each valve, larger on both ends than in the middle. In the half frontal perimeter of the shell sixty to sixty-five pores, in the half sagittal perimeter eighty to eighty-five, in the half equator of the shell forty to fifty pores.

Dimensions.—Length of the shell 0.55 to 0.65, height 0.5 to 0.55, breadth 0.2 to 0.22.

Habitat.—North Pacific, Stations 243 and 244, depth 2800 to 2900 fathoms.

7. Conchopsis navicula, n. sp. (Pl. 125, figs. 4-6).

Shell pear-shaped, compressed on both sides, in the sagittal periphery keeled. Proportion of the longitudinal diameter to the sagittal and lateral = 4 : 3 : 2. Its sagittal perimeter nearly ovate. Borders of the two boat-shaped valves smooth in 0.3 of the oral, and 0.15 of the aboral part, strongly dentated in the remaining 0.55 middle part; teeth conical, of nearly equal size. In the half frontal perimeter of the shell (along one border of each valve) forty to forty-five pores, in the half sagittal fifty-four to fifty-six pores, in the half equator thirty-two to thirty-six pores. Each pore is surrounded by a hexagonal frame, and pierces the shell in an oblique direction, dilated in the middle part (figs. 5, 6). Shell very thick-walled, several longitudinal crests on both sides of the keel of each valve. Hinge very strong, usually with a broad ligament between the two unequal aboral lips of the hinge.

Dimensions.—Length of the shell 0.8, height 0.6, breadth 0.4.

Habitat.—South Pacific, Station 293, depth 2025 fathoms.

Genus 726. Conchoceras,^[7] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Concharida with dentate lateral margins and a sharp sagittal keel of the compressed valves, and with two caudal horns on the hinge (a dorsal and a ventral).

The genus Conchoceras has the same lenticular keeled and laterally compressed shell as the preceding ancestral genus Conchopsis, but is distinguished from it by the development of two large caudal horns on the aboral hinge. It bears therefore the same relation to the latter as Conchidium does to Conchellium.

1. Conchoceras caudatum, n. sp. (Pl. 124, fig. 15).

Shell lenticular, slightly compressed; proportion of the longitudinal diameter to the sagittal and lateral = 6 : 5 : 4; sagittal and cinctural perimeter ovate, frontal perimeter elliptical. Free margins of the two boat-shaped valves dentate nearly in the whole perimeter; in one lateral border of each valve eleven or twelve very large conical teeth, the largest of which are nearly half as high as the valve. On the aboral hinge of the shell two divergent, very large horns, four-sided pyramidal, acute, straight, at the base perforated by a few large pores. The dorsal horn (of the smaller valve) is somewhat shorter than the ventral horn (of the larger valve). The apical distance of both horns is somewhat greater than their length, and about half the length of the shell. In the half frontal perimeter (along one border of each valve) thirty-two to thirty-four pores, in the half sagittal perimeter thirty-four to thirty-eight, in the half equator thirty to thirty-three. The pores are smaller near the girdle-fissure, irregularly quadrangular, and arranged in longitudinal rows, which are separated by meridional crests, and converge towards both poles of the main axis.

Dimensions.—Length of the shell (without the horns) 0.24 to 0.26, height 0.20 to 0.22, breadth 0.16 to 0.18; length of the horns 0.1 to 0.13.

Habitat.—Eastern part of the Tropical Atlantic, near the Equator, Station 348, depth 2450 fathoms.

2. Conchoceras cornutum, n. sp. (Pl. 124, fig. 16).

Shell lenticular, strongly compressed on both sides; proportion of the longitudinal axis to the sagittal and lateral = 4 : 3 : 2. Sagittal perimeter ovate, frontal perimeter elliptical, cinctural perimeter spindle-shaped. Free margins of the two keeled valves in the oral third smooth, in the remaining part strongly dentate; ten or eleven large teeth on one lateral border of each valve, the largest about half as high as the valve. On the aboral hinge of the shell two fenestrated apophyses which bear two stout, strongly curved horns, like pincers; the dorsal horn (of the smaller upper valve) is shorter and less curved than the ventral horn (of the larger lower valve). The lips of the mouth (at left on fig. 16) are also unequal, the upper lip emarginate. In the half frontal perimeter of the valve twenty-two to twenty-four pores, in the half sagittal perimeter twenty-eight to thirty, in the half equator twenty to twenty-two. The pores are separated by high parallel crests and arranged in longitudinal rows, which converge towards the aboral hinge.

Dimensions.—Length of the shell (without the horns) 0.36 to 0.4, height 0.27 to 0.3, breadth 0.2 to 0.22; length of the horns 0.16 to 0.22.

Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms.

Family LXXXIV. Cœlodendrida, Haeckel (Pl. 121).

Cœlodendrida, Haeckel, 1862, Monogr. d. Radiol., p. 360.

Definition.—Phæodaria with a bivalved lattice-shell, composed of two hemispherical valves, a dorsal and a ventral. A conical cupola or a pyramidal galea arises from the apical pole of both valves, therefore at the opposite poles of the sagittal axis. Rhinocanna and frenula wanting. Three or more hollow radial tubes arise from each valve and are symmetrically disposed. Sometimes their branches form an outer bivalved mantle. The central capsule is so enclosed between the two inner valves, that its three openings lie in the open frontal fissure between them.

The family Cœlodendrida differs from the preceding Concharida (its probable ancestral group) in the development of a conical galea or pyramidal cupola on the apical pole of each valve, and of three or more hollow radial tubes arising from each galea. They do not possess, however, the peculiar sagittal nasal tube or rhinocanna, which is constantly developed from the base of each cupola (and connected with its apex by a frenulum) in the following family, the Cœlographida. These latter differ also from the former in the constant possession of prominent verticillate styles.

The family Cœlodendrida was founded in 1862 in my Monograph (p. 360) and represented hitherto only by two species of the genus Cœlodendrum, there described (p. 361, Taf. xiii. figs. 1-3, and Taf. xxxii. fig. 1). This first description, however, contained some errors, which were afterwards (in 1879) corrected by Richard Hertwig; this author also gave the first accurate description of the central capsule and its three openings. In the rich collection of the Challenger, the Cœlodendrida are represented by four genera, but only seventeen species, some of which, however, are cosmopolitan and very common, particularly Cœlodendrum.

The two valves of the lattice-shell, dorsal and ventral, are either hemispherical, or somewhat more flatly vaulted or cap-shaped. They are never connected in the equatorial zone of the body, as I supposed in my Monograph (1862, loc. cit.); but they are separated by the girdle-fissure, a free circular equatorial interval, in which lie the three openings of the enclosed central capsule. Though the two valves, therefore, have no direct connection, they are, however, always opposed so accurately, that their equal free circular edges correspond exactly one to the other, so that the apex of each valve lies in one pole of the sagittal axis. From this apex there arises on each valve an irregular conical or three-sided pyramidal cupola, the galea (Pl. 121, figs. 3, 4, 8). The Cœlodendrida differ in the possession of this galea from the Concharida, and agree with the Cœlographida; but they never exhibit the peculiar rhinocanna or nasal tube, which arises from each galea in the latter family.

The siliceous lattice-plate of the two valves, and of the galea arising from them, is very thin and fragile, and its irregular roundish pores are extremely variable in size, number, and disposition. Sometimes the pores are so small and so scarce, that the plate appears nearly solid. At other times the siliceous plate seems to be really solid, and covered by a network of thin crests, the small dimples between which give to it the appearance of being fenestrated. Often the pores or the dimples are wanting in the central part of each valve, while they are very numerous and dense in the peripheral part. The same may be said of the lattice-plate of the galea, which is sometimes nearly solid, at other times richly fenestrated. The Cœlodendrida agree in this structure with the following family, the Cœlographida, and differ from the preceding family, the Concharida, in which the siliceous wall of the two valves is much thicker, and perforated by regular circular or roundish pores.

The galea or conical cupola in the apex of the two valves ("der kegelförmige Aufsatz" of the German authors) has in all Cœlodendrida a triangular base and an irregularly conical or nearly three-sided pyramidal form. Its cavity is about one-third or one-fourth as large in diameter as the cavity of the hemispherical valve upon which it rests. The galea is relatively smaller and more irregularly formed than in the Cœlographida, and differs essentially from that of the latter in the constant absence of a rhinocanna; there are also wanting, therefore, the characteristic frenula, which connect the nasal tube with the apex of the galea. The cavity of the galea probably always communicates with that of the valves by pores in the separating siliceous plate, and is besides pierced by irregular pores in its outer wall, very variable in form, size, and number, but it does not communicate with the cavity of the hollow radial tubes, from which it is separated by a thin, solid, siliceous plate.

The hollow radial tubes which arise from the galea in the Cœlodendrida do not seem to possess that constant regularity in number, origin, and disposition, which is found in the following family, and there serves for distinction of genera. In my first description of the Cœlodendrida (1862, loc. cit., p. 362), I pointed out this irregularity, and mentioned that the number of radial tubes arising from each galea varies from three to eight; the total number therefore amounts to from six to sixteen, the same minimum and maximum numbers which we shall encounter also in the radial styles of the following family. But whilst it is easy to determine the position and relation of these hollow tubes in the Cœlographida, owing to the constant sagittal position of their rhinocanna, this task is very difficult in the Cœlodendrida, where the rhinocanna is wanting. In the most frequent cases there arise from each galea three or four tubes, more rarely five or six, and very rarely seven or eight. The simplest and probably the original case is the development of three tubes, two of which are paired (divergent on the right and left), while the third is odd, lying in the sagittal plane. Perhaps these three primary tubes may be compared to the three cortinar feet of the Nassellaria, so that we may regard the two paired anterior as pectoral, and the odd posterior as a caudal tube. Usually the two paired or pectoral tubes arise from two corners of the triangular base of the galea, whilst the third odd or caudal tube does not arise from the third corner of the base, but more or less above it, and often even from the highest point or the apex of the galea. In the majority of species observed, this odd sagittal tube is forked even at its origin, so that two divergent tubes (an anterior and a posterior) arise from the apex of the galea (Pl. 121, figs. 3, 8). More rarely the two paired or pectoral tubes are also forked at the base, so that three pairs of tubes arise from each galea, and the total number of tubes amounts to twelve. Very rarely four separate tubes or four pairs of tubes arise from each galea, viz., two from the two anterior corners of the basal triangle, one from the posterior corner, and one from the apex of the galea. It is possible that this difference in the origin, furcation, and number of the hollow radial tubes may be employed for the distinction of genera of Cœlodendrida, in the same manner as it is employed in the next following family, the Cœlographida. But I have not been able, in spite of numerous and accurate examinations, to demonstrate in the former the same regularity in number and arrangement of the tubes as in the latter. It seems that these relations here are very variable, even in one and the same Species, and not yet fixed.

It is, however, probable, on the other hand, that the primary tubes (all or partly) are identical to the Cœlodendrida and Cœlographida. This is most probably the case with the posterior odd or caudal tube, which seems to be never wanting, and in both families is developed in the form of a dichotomous brush (never in the form of a verticillate style). Possibly also the two paired pectoral tubes are homologous in both families.

The hollow tubes are perfectly simple and unbranched only in one genus, Cœlodoras, which is probably the common ancestral form of both families, and which may have been derived from Concharium by development of a galea and tubes on the sagittal apex of the valves. All the other Cœlodendrida have branched spines, and the ramification is constantly dichotomous, or repeatedly forked. There never occur in this family those characteristic "styles," or verticillate prolonged tubes, which we find in all Cœlographida. Usually the cylindrical tubes are slightly curved and forked even near their base. The furcation is repeated a variable number of times in the different species. In the largest species each tube becomes a brush with more than one hundred terminal bristles.

We divide the Cœlodendrida into two subfamilies, according to the different development of the distal branches of the hollow tubes. In the Cœlodorida all the branches of the tubes remain free and are never connected by anastomoses, so that the surface of the bivalved skeleton is protected by the free radial distal branches of the tubes. In the larger species of Cœlodendrum (e.g., Cœlodendrum furcatissimum, Pl. 121, fig. 1), the numerous branches of the dichotomous tubes form a dense thicket, similar to that in the Cœlotholida.

In the second subfamily, Cœlodrymida, the distal branches of the tubes are connected by numerous anastomoses, and compose either a simple lattice-plate on the surface of the skeleton (Cœlodrymus), or a thicker envelope of spongy framework (Cœlodasea). The lattice-mantle so produced is always bivalved, and its two outer hemispherical valves (dorsal and ventral) correspond exactly to the two inner valves, from which arise the hollow tubes. The free margins of the two external mantle-valves come externally into contact in the equatorial plane of the body, in which the girdle-fissure lies internally between the two central shell-valves. The free edges of the two external mantle-valves, opposed to one another in the circle of the equator, seem usually to catch one into another in the same way as the corresponding mantle-valves of the Cœloplegmida are loosely connected (Pl. 128, figs. 1, 7). A true concrescence between the two valves seems never to take place.

The two subfamilies of Cœlodendrida therefore exactly correspond to the two subfamilies of the following family, the Cœlographida. The Cœlodorida and Cœlotholida form in a similar way a thicket, by dichotomous ramification of the hollow tubes, all the branches of which remain free. The Cœlodrymida and Cœloplegmida, on the other hand, form an outer lattice-mantle by anastomosing branches. The latter two subfamilies, of course, have been derived correspondingly from the two former, and the common ancestral form of all four is probably Cœlodoras, derived from the Concharida.

Though the two corresponding subfamilies in both groups are very similar, they are, however, separated by important hereditary characters. All Cœlodendrida (the Cœlodorida without a mantle as well as the Cœlodrymida with a mantle) possess no rhinocanna and no frenula on the galea, and they never develop prominent verticillate styles; the surface of their calymma is probably always spherical or subspherical. All Cœlographida, however (the Cœlotholida without a mantle as well as the Cœloplegmida with a mantle), possess a rhinocanna and frenula on the galea, and always develop prominent verticillate styles; the surface of their calymma is probably always symmetrically polyhedral.

The superficial armature of the skeleton in the Cœlodendrida is rather simple, and by no means so manifold and differentiated as in the more highly developed Cœlographida. The thin terminal branches of the hollow tubes are in the Cœlodorida closed at the distal end, and armed with a variable number of short teeth (Pl. 121, fig. 2), or with a spinulate terminal knob, or a corona of recurved hooks (ibid., figs. 5-7). In the Cœlodrymida, however, where the distal ends of the branches by anastomosing form the lattice-mantle, the spherical surface of this latter is armed with numerous thin spathillæ or radial bristles (often zig-zag or spinulate), and each bristle usually bears at the distal end a small anchor with two, three, or four recurved teeth; the outer convex edge of these teeth is usually smooth, the inner concave edge denticulate. All these ramules and branches of the tubes (also the thinnest terminal threads) are hollow, and filled up by jelly.

The central capsule of the Cœlodendrida does not lie outside the two central valves (as I supposed in my first description, in 1862, being deceived by the dark enveloping phæodium, Monogr. d. Radiol., Taf. xxxii. fig. 1), but it is enclosed between the two valves, as in the preceding and the following family. The first accurate description of it was given by Richard Hertwig in 1879 (loc. cit., p. 95, Taf. x. fig. 3). Its constant position between the two lattice-valves (dorsal and ventral) is such, that its three openings lie in the frontal plane, in the open fissure between the valves. The astropyle or the main-opening, with the radiate operculum and the tubular proboscis arising from it, lies on the anterior (or oral) pole of the main axis, whilst the two lateral accessory openings, or parapylæ, lie on both sides of the posterior (or aboral) pole, to the right and left. The position of the capsule is therefore the same as in the preceding Concharida (Pls. 123-125), and the following Cœlographida (Pls. 126-128). The large nucleus, enclosed in the central capsule, is usually half as broad, and contains numerous nucleoli.

The calymma, or the extracapsular jelly-veil, is in the Cœlodendrida usually spherical, very voluminous, and includes the entire skeleton, the thicket of the Cœlodorida as well as the lattice-mantle of the Cœlodrymida. Only the outermost terminal branches of the tubes in the former, and the radial bristles and spathillæ on the surface of the latter, remain free and project beyond the surface of the calymma. The phæodium is usually very large, three to four times as broad as the central capsule, and envelops it often completely. Usually it envelops only the anterior half of it, and the proboscis (Pl. 121, figs. 1, 9). Often numerous green, brown, or blackish phæodellæ are scattered through the whole calymma, and sometimes accumulate in a superficial layer on its surface. The galea of both valves is usually also filled up by the phæodium.

Synopsis of the Genera of Cœlodendrida.

I. Subfamily Cœlodorida. Hollow tubes, arising from the galea of both valves, simple or dichotomously branched; the branches always free, not anastomosing. No outer lattice-mantle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Tubes simple, not branched,	727. Cœlodoras.
		Tubes forked or dichotomously branched,	728. Cœlodendrum.
II. Subfamily Cœlodrymida. Hollow tubes, arising from the galea of both valves, dichotomously branched; the branches anastomose and form an outer bivalved lattice-mantle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Lattice-mantle simple; its meshes lying in a spherical surface,	729. Cœlodrymus.
		Lattice-mantle spongy; its meshes lying in different planes,	730. Cœlodasea.

Subfamily I. Cœlodorida, Haeckel.

Definition.—Cœlodendrida without an external bivalved lattice-mantle, with simple or branched hollow tubes, the terminal branches of which are free, not anastomosing.

Genus 727. Cœlodoras,^[8] n. gen.

Definition.—Cœlodendrida without external lattice-mantle, with simple, not branched, radial tubes, which arise separately from the galea.

The genus Cœlodoras is the simplest form of the Cœlodendrida, and may be regarded as the common ancestral form of this and of the following family. It differs from all other members of these two families in the simple shape of the hollow radial tubes which arise from the galea, and are neither branched nor forked; the galea is very small, a flat triangular cap. Cœlodoras may be derived immediately from Concharium or Conchonia (p. 1723), by development of the galea and the radial tubes.

1. Cœlodoras hexagraphis, n. sp.

Three straight, cylindrical, equidistant hollow tubes arise divergent from the three corners of each galea, and are about as long as the diameter of the valves, at the distal end armed with a spinulate knob. The odd sagittal (or caudal tube) is directed backwards, the two paired (or pectoral) tubes, forwards.

Dimensions.—Diameter of the valves 0.16, length of the tubes 0.2.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Cœlodoras octographis, n. sp.

Four hollow cylindrical tubes, slightly curved, arise divergent from each galea, and are about one and a half times as long as the diameter of the valves, at the distal end knob-shaped, and armed with four crossed, recurved teeth. Two anterior (or pectoral) tubes arise from the two frontal corners of the galea basis, and diverge forwards to right and left. Two posterior tubes (a sagittal and a caudal) arise from the posterior corner of each galea, and diverge in the sagittal plane backwards.

Dimensions.—Diameter of the valves 0.2, length of the tubes 0.3.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Genus 728. Cœlodendrum,^[9] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 801.

Definition.—Cœlodendrida without external lattice-mantle, with branched radial tubes, the hollow branches of which are free and never connected by anastomoses.

The genus Cœlodendrum is the first described form not only of the family Cœlodendrida, but of all Phæoconchia or bivalved Phæodaria; it is also the most common form of this group, and represented by ten different species, some of which are cosmopolitan, very common, and widely distributed. In my first description of Cœlodendrum I confounded it erroneously with some forms of Cœlodasea and Cœlographis, the separated fragments of which I had found entangled between the branches of the former. The first figures of Cœlodendrum are given in my Monograph, in 1862, Taf. xiii. figs. 1-3 (not 4) and Taf. xxxii. fig. 1 (not 2 and 3). Cœlodendrum has been derived from Cœlodoras by furcation and repeated dichotomous ramification of the hollow radial tubes which arise from the galea.

Subgenus 1. Cœlodendridium, Haeckel.

Definition.—Ramification of the hollow tubes regularly dichotomous, each branch being forked again; therefore the two terminal ramules of the last branches equal.

1. Cœlodendrum ramosissimum, Haeckel.

Cœlodendrum ramosissimum, Haeckel, 1862, Monogr. d. Radiol., p. 363, Taf. xiii. figs. 1-3. Cœlodendrum ramosissimum, R. Hertwig, 1879, Organism. d. Radiol., p. 93, Taf. x. figs. 3, 12.

Terminal branches regularly forked, with two equal, smooth, nearly straight or slightly curved fork-branches, diverging at right angles; their end-knobs with four crossed (or sometimes five or six) short recurved teeth.

Dimensions.—Diameter of the spherical skeleton 1.2 to 1.8, of the two central valves 0.2 to 0.25.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; many Stations, surface and at various depths.

2. Cœlodendrum spinosissimum, n. sp. (Pl. 121, fig. 7).

Terminal branches regularly forked, with two equal, smooth, straight, fork-branches, diverging at right angles, their end-knobs echinoidal, subspherical or club-shaped, with numerous short radial thorns.

Dimensions.—Diameter of the skeleton 2 to 2.2, of the two central valves 0.25 to 0.03.

Habitat.—Tropical Atlantic, Stations 346 to 349, surface.

3. Cœlodendrum furcatissimum, n. sp. (Pl. 121, fig. 1-4).

Terminal branches regularly forked, with two equal, smooth, straight, or slightly curved fork-branches, diverging at acute angles; their end-knobs very small, with three short, diverging, conical teeth.

Dimensions.—Diameter of the skeleton 2 to 2.5, of the two central valves 0.3 to 0.4.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific; many Stations, surface, and at various depths.

4. Cœlodendrum bifurcum, n. sp.

Terminal branches regularly forked, with two equal, smooth, more or less curved fork-branches, diverging at acute angles; their end-knobs thin, with two slender, parallel, bristle-shaped teeth.

Dimensions.—Diameter of the skeleton 0.6 to 0.8, of the two central valves 0.1 to 0.15.

Habitat.—North Pacific, Stations 252 to 256, surface.

5. Cœlodendrum gracillimum, Haeckel.

Cœlodendrum gracillimum, Haeckel, 1862, Monogr. d. Radiol., p. 364, pl. xxxii. fig. 1.

Terminal branches regularly forked, with two equal, spinulate, curved fork-branches, diverging at obtuse angles and covered with numerous small thorns; their end-knobs cap-shaped, with a corona of six to eight small recurved teeth. In one specimen of this species (in 1859) I found entangled the fragments of Cœlographis gracillima, figured in Taf. xxxii. figs. 2, 3, loc. cit. I supposed at that time, erroneously, that the latter belonged to full-grown specimens of the former.

Dimensions.—Diameter of the skeleton 1 to 1.2, of the valves 0.15 to 0.2.

Habitat.—Mediterranean (Messina), surface.

6. Cœlodendrum lappaceum, n. sp.

Terminal branches regularly forked, with two equal, spinulate, straight or slightly curved fork-branches, diverging at acute angles and covered with small recurved hooks; their end-knobs large, conical, with a prominent apex and a basal corona of six to eight recurved teeth.

Dimensions.—Diameter of the skeleton 1.5 to 1.8, of the valves 0.22.

Habitat.—South Pacific, Stations 285 to 295, depth 1500 to 2600 fathoms.

Subgenus 2. Cœlodendronium, Haeckel.

Definition.—Ramification of the hollow tubes more or less irregular, mainly in the periphery; the terminal ramules of the last branches unequal.

7. Cœlodendrum cervicorne, n. sp. (Pl. 121, fig. 8).

Terminal branches irregularly ramified, with unequal, smooth, curved ramules, diverging at obtuse angles, their end-knobs echinoidal, small, with short, diverging, conical thorns.

Dimensions.—Diameter of the skeleton 1 to 1.2, of the valves 0.2.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

8. Cœlodendrum digitatum, n. sp.

Terminal branches irregularly ramified, with unequal, spinulate, straight ramules, diverging at acute angles; the two last fork-branches digitate, each with five diverging finger-shaped ramules, lying in a meridian plane; their end-knobs conical, pointed, with a corona of recurved hooks.

Dimensions.—Diameter of the skeleton 1.6, of the valves 0.24.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface.

9. Cœlodendrum flabellatum, n. sp. (Pl. 121, fig. 6).

Terminal branches flabellate, irregularly ramified, each of the last two fork-branches being divided into four or five diverging straight branches of different lengths; usually the last eight or ten ramules lie in a meridional plane; their end-knobs cap-shaped, with a corona of recurved teeth.

Dimensions.—Diameter of the skeleton 2.0 to 2.5, of the valves 0.25 to 0.3.

Habitat.—North Pacific, Station 235 to 240, surface.

10. Cœlodendrum serratum, n. sp. (Pl. 121, fig. 5).

Terminal branches flabellate, irregularly ramified like the preceding species; it differs from this in the strong compression of the broad, saw-shaped, terminal branches; the two opposite edges (placed in the meridional plane of the flabellum) are finely serrated; their end-knobs with a corona of diverging teeth.

Dimensions.—Diameter of the skeleton 3.0 to 3.2, of the valves 0.3 to 0.36.

Habitat.—Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

Subfamily 2. Cœlodrymida, Haeckel.

Definition.—Cœlodendrida with an external bivalved lattice-mantle, produced by the anastomosing branches of the hollow radial tubes.

Genus 729. Cœlodrymus,^[10] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Cœlodendrida with an external bivalved lattice-mantle, produced by the anastomosing terminal branches of the hollow tubes, which are connected in a spherical face.

The genus Cœlodrymus, and the following closely allied genus Cœlodasea, represent together the small subfamily Cœlodrymida, differing from the Cœlodorida in the possession of an outer bivalved lattice-mantle. They exhibit therefore the same relation to the latter, that in the following family the Cœloplegmida bear to the Cœlotholida. The bivalved spherical mantle is composed of a simple lattice-plate in Cœlodrymus, of a spongy framework in Cœlodasea; the anastomosing branches of the hollow radial tubes become connected in the former in a spherical face, in the latter in the form of a spongy framework.

1. Cœlodrymus ancoratus, n. sp. (Pl. 121, figs. 9, 10).

Network of the mantle loose, with large, irregular, polygonal meshes; the terminal branches of the forked trees, which communicate at the spherical surface of the calymma, and compose the mantle, are smooth. Spherical surface covered with very numerous and thin zigzag radial filaments, which are about as long as the galea, and bear at the distal end an anchor with two recurved teeth, denticulate at the concave proximal edge (fig. 10).

Dimensions.—Diameter of the spherical lattice-mantle 2 to 2.5, of the valves 0.3 to 0.4.

Habitat.—South-Eastern Pacific (off Juan Fernandez), Station 300, depth 1375 fathoms.

2. Cœlodrymus lappulatus, n. sp.

Network of the mantle rather dense, with numerous and small irregular polygonal meshes; the terminal branches of the forked trees, which compose the mantle, are spinulate. Spherical surface densely studded with very numerous spinulate, radial filaments, which are about half as long as the galea, and bear at the distal end an anchor with four crossed recurved teeth, denticulate at the concave proximal edge.

Dimensions.—Diameter of the spherical lattice-mantle 2.5 to 3, of the valves 0.4 to 0.5.

Habitat.—South-Western Pacific (east of New Zealand), Station 169, depth 700 fathoms.

3. Cœlodrymus echinatus, n. sp.

Network of the mantle very dense, with very numerous and small irregular roundish meshes; the terminal branches of the forked trees, which compose the mantle, are spiny. Spherical surface studded with very numerous, thin, radial bristles, which bear no anchor at the distal end.

Dimensions.—Diameter of the spherical lattice-mantle 1.8, of the valves 0.22.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

Genus 730. Cœlodasea,^[11] n. gen.

Definition.—Cœlodendrida with an external spongy lattice-mantle, produced by the anastomosing branches of the hollow tubes, which are connected in different heights.

The genus Cœlodasea differs from the preceding Cœlodrymus in the spongy structure of the outer bivalved mantle. The hollow branches of the radial tubes of Cœlodendrum, which anastomose in Cœlodrymus only on the spherical surface of the calymma, and form a simple lattice-sphere, become connected in Cœlodasea in different planes (laterally and terminally), and therefore form an irregular spongy framework. The latter exhibits therefore to the former a relation similar to that which Spongoplegma bears to Carposphæra among the Sphæroidea.

1. Cœlodasea ramosissima, Haeckel.

Cœlodendrum ramosissimum (partim), Haeckel, 1862, Monogr. d. Radiol., p. 363, Taf. xiii. fig. 4.

Spongy framework of the spherical bivalved mantle very dense and thick, produced by very numerous, irregular anastomoses of the lateral and terminal branches, which arise from the hollow tubes. The last and thinnest terminal branches are forked, as seen in the radial section of fig. 4 (loc. cit.), their ends are closed and armed with some very small denticles (not open, as figured in fig. 4). In my Monograph I had confounded this species with Cœlodendrum ramosissimum, which however, may possibly be its ancestral form.

Dimensions.—Diameter of the spongy spherical mantle 2 to 2.5, of the central valves 0.15.

Habitat.—Mediterranean (Messina), surface.

2. Cœlodasea spongiosa, n. sp.

Spongy framework of the bivalved mantle rather loose, not nearly so thick and dense as in the preceding species. The last and thinnest terminal branches are prolonged into denticulate, zigzagged, radial filaments, which bear at their distal end an anchor with two recurved teeth (similar to Cœlodrymus ancoratus, Pl. 121, figs. 9, 10).

Dimensions.—Diameter of the spongy spherical mantle 3 to 3.2, of the central valves 0.24.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

Family LXXXV. Cœlographida, n. fam. (Pls. 122, 126-128).

Definition.—Phæodaria with a bivalved lattice-shell, composed of two hemispherical valves, a dorsal and a ventral. A conical cupola or a helmet-shaped galea arises on the apical pole of each valve, therefore on the opposite poles of the sagittal axis. The cavity of the galea communicates with the sagittal rhinocanna, a peculiar nasal tube, which rests upon the valve, and is connected with the galea by a simple or double frenulum; its opening being directed towards the proboscis. Three or more branched hollow radial tubes arise from each valve, and are symmetrically disposed. Sometimes their branches form an outer bivalved mantle. The central capsule is so enclosed between the two inner valves, that its three openings lie in the open frontal fissure between them.

The family Cœlographida, the last family of the Phæodaria, exhibits the highest degree of morphological development, not only in this group, but among all Radiolaria. They attain also the greatest size of all members of the class, since the diameter of their body is sometimes more than 20 mm., and in a few species even more than 30 mm. The complexity of their structure attains at the same time such a high degree, that they may be regarded as the most complicated, and (in a morphological sense) as the most highly developed of all Protozoa. Nevertheless their body always remains a single cell, and is closely allied to the preceding Cœlodendrida; they differ from the latter mainly in the development of a peculiar new organ, the "rhinocanna," or "nasal tube." This is a hollow tube placed in the sagittal plane, arising from the base of each galea, and is connected with its apex by a simple or double frenulum. Between the oral openings of the two opposed rhinocannæ (one dorsal and one ventral) lies the proboscis of the central capsule.

The first observed species of Cœlographida was Cœlographis gracillima, some parts of which (but not the entire skeleton) were figured in my Monograph (1862, Taf. xxxii. figs. 2, 3). But I confounded these with Cœlodendrum gracillimum, in the branched hollow trees of which the fragments of the former were entangled. I detected this error afterwards, when I had the opportunity of the observing some complete specimens. The first description of a complete skeleton was given in 1882 by O. Bütschli, who examined a large specimen of Cœlothamnus davidoffii, captured by Davidoff in the Mediterranean (Zeitschr. f. wiss. Zool., Bd. xxxvi. p. 486, Taf. xxxi.). In the rich collection of the Challenger I was able to distinguish not less than nine genera and twenty-six species of Cœlographida, but the majority of their large and most fragile skeletons were more or less injured, or quite broken. It was, therefore, of the highest importance for the minute study of this difficult group, that Dr. John Murray, during his expedition to the Færöe Channel (in 1882, in H.M.S. "Triton"), discovered in the Gulf Stream the beautiful Cœloplegma murrayanum, and brought up home hundreds of well-preserved specimens (Pl. 127). Only by the complete examination of this excellent material it was possible to answer many difficult questions as to their morphology, and to correct the errors in my description and in that of Bütschli.

We divide the family Cœlographida into two rather different subfamilies, which may afterwards be separated as two divergent families, the Cœlotholida (Pl. 122) and Cœloplegmida (Pls. 126-128). Both groups may be easily distinguished at a glance, since the numerous branches, arising from the hollow radial tubes, remain constantly free and independent in the former, and represent a spiny thicket, whilst in the latter they constantly become united, and by anastomosing form a peculiar "mantle," or outer envelope of delicate network. But besides, there are other and more important differences between the two groups. The peculiar hollow tube, arising from the base of the galea on each valve, which is filled with phæodella, and which we call the rhinocanna, develops in the Cœlotholida on its open mouth two paired lateral frenula (right and left), which connect it (like two lateral bridges) with the base of two paired hollow main tubes (the "frontal tubes"). In the Cœlospathida, however, the mouth of the rhinocanna develops a single odd frenulum only (in the sagittal plane), and is connected by it with the base of an odd, single, hollow main tube, directed forwards, the "nasal style."

The central bivalve lattice-shell, from which the galea and the tubes arise, exhibits in the Cœlographida essentially the same form and structure as in the preceding Cœlodendrida. The only (but important) difference between them is indicated by the constant presence of the peculiar rhinocanna in the former, whilst this is always absent in the latter. The two valves of the shell, dorsal and ventral, are either hemispherical or somewhat flatter, sometimes nearly cap-shaped, and formed of an extremely delicate and irregularly fenestrated plate of silica, as in the Cœlodendrida. As in the latter, so also in the Cœlographida both valves are of similar form and usually of equal size, but sometimes the dorsal is a little smaller than the ventral valve. The remarkable difference which Bütschli describes in his Cœlothamnus davidoffii, and the inverse origin of the three tubes in both valves (loc. cit., Taf. xxxi; figs. 2, 4), depends upon an error of observation, produced by the artificial inversion of one valve, and the dislocation of their natural arrangement. The valves are never in direct contact, but separated by the equatorial fissure or girdle-cleft, in which the girdle zone of the enclosed central capsule and its three openings lie freely (Pl. 127, figs. 4, 5; Pl. 128, fig. 2). The free margins of both valves, which are opposite to one another, and bound the girdle-cleft, are always equidistant, so that the cleft in the whole equatorial circumference is of equal breadth. The margins are usually irregularly denticulate, sometimes armed with longer bristles (Pl. 127, fig. 8), more rarely smooth (fig. 5). The delicate lattice-work of the valves is always irregular and very variable, usually with numerous small and unequal pores, sometimes rudimentary, so that the valves appear partly solid and hyaline. The size of the valves is usually between 0.2 and 0.5 (in diameter).

The galea (g) or the apical cupola, which arises from the vaulted apex of each valve (or its sagittal pole) is more developed in the Cœlographida than in the preceding Cœlodendrida, and differs from the latter in the peculiar rhinocanna arising from its base, and in the single or double frenulum, connecting the open mouth of the rhinocanna with the odd or paired main tube arising from the galea. The two opposite galeæ lie therefore on the poles of the sagittal axis of the bivalve shell, and are so symmetrically disposed in the sagittal plane, that the open mouths of their rhinocannæ are directed towards the oral pole of the main axis, and nearly come in contact with the proboscis arising from the radiate operculum of the central capsule (Pl. 127, figs. 4, 5).

The size and form of the galea are very variable, even in one and the same species. The volume of its cavity is generally about as great as that of the hemispherical valve from which it arises, sometimes larger, at other times smaller. Its fundamental form is constantly dipleuric or bilateral, since the radial hollow tubes arise symmetrically on both its sides, and the rhinocanna proceeding from its base determines the sagittal plane. Usually the galea has the form of a vaulted helmet, the convex crest of which is inclined towards the mouth (Pl. 127, figs. 4, 5, 8, 9). Its anterior or apical part is broad and truncated in the Cœlotholida, more or less conical in the Cœlospathida; sometimes it assumes nearly the form of a bilateral three-sided pyramid, at other times it is more pear-shaped (Pls. 126-128). The thin siliceous wall of the galea has the same irregular and delicate network as the valve from which it arises, and sometimes the small irregular pores are also here reduced, so that the wall becomes partly solid. In some cases the thin, solid, siliceous plate of the galea and of the valve is covered by an irregular delicate network of crests; the dimples between these crests may be easily confounded with true pores.

The cavity of the galea is filled with phæodella and does not communicate with the cavity of the shell-valves, nor with the cavity of the radial tubes filled by jelly; it is closed towards the latter and the former by a thin solid plate of silex. Bütschli (1882, loc. cit., p. 488) describes in Cœlothamnus a large circular opening (Taf. xxxi. figs. 2a, 4a), and states that this is a direct communication between the cavities of the valves and of their galeas which are called by him "der dreiseitige kastenförmige Aufsatz" (ε). This error was caused by the fact that he observed the valves from the apical face only. The apparent opening of communication does not exist, and is the optical section of the rhinocanna, the shortened walls of which he describes as "trapezförmige Kiesellamelle" (γ); the two lateral edges of the latter ("die seitlichen Zipfel," δ) are the paired frenula, which connect the open mouth of the rhinocanna with the base of the two frontal tubes.

The "rhinocanna or nasal tube" (Pl. 126, figs. 1, 4; Pl. 127, figs. 4-9t) is a very remarkable organ which is common to all Cœlographida (without any exception), and distinguishes them markedly from all the other Radiolaria, and particularly from the closely allied Cœlodendrida in which we find no trace of it. The rhinocanna is a cylindrical or three-sided prismatic hollow tube, which lies in the sagittal plane, on the outer surface of each valve, arises from the base of the galea, and is directed towards the proboscis of the central capsule. The two opposite rhinocannæ open on each side of the latter (Pl. 127, figs. 4-9m), and usually this "nasal mouth" or the anterior opening of the nose is somewhat dilated or even funnel-shaped. The posterior opening of the nose passes directly over into the base of the cavity of the galea.

Usually the rhinocanna is densely filled up by dark phæodella, which enter by this channel into the cavity of the galea (Pl. 127, figs. 4, 5, 9). Sometimes the entire phæodium is enclosed in the two galeæ and their rhinocannæ (figs. 5, 9), whilst at other times a great part of the phæodium lies outside of their cavities, and surrounds the proboscis of the mouth, or even the anterior half of the central capsule (fig. 4). The length of the cylindrical rhinocanna is usually about equal to that of the galea, whilst the diameter of the latter is from three to five times as great as that of the former. The structure of the thin wall is the same in both. The fine reticulation (fig. 8) is produced either by true, very small and irregular pores, or by a fine network placed on the solid thin wall. We may distinguish on each rhinocanna an outer or distal convex face, which is opposite to the proximal concave face of the galea, and an inner concave or proximal face, which rests immediately upon the convex outer face of the shell-valve; a thin solid lamella of silica here completely separates the cavities of the valve and of the rhinocanna resting upon it.

The "frenula or nasal suspensoria" (Pl. 127, figs. 4-9b) are thin ligaments of silica, which connect the nasal mouth (m) with the base of the main tubes arising from the galea; they are, therefore, also common to all Cœlographida, and an exclusive and marked attribute of this family. They are, however, different in the two subfamilies of this group, corresponding to the different origin of the odd or paired main tubes. In the Cœloplegmida (Pls. 126-128) from the apex of each galea arises an odd main style, the nasal style (g 1), and its base is connected with the nasal mouth by an odd frenulum (b). In the Cœlotholida however (Pl. 122) the large nasal odd style is always wanting, and there arise two paired frontal tubes from the two corners of the truncate frontal face of the galea; therefore two paired frenula are developed (a right and a left), and these, converging towards the nasal mouth, connect its distal corner with the base of the two frontal tubes.

The odd frenulum of each valve of the Cœloplegmida lies therefore in the sagittal plane, whilst the two paired frenula of the Cœlotholida lie on both sides of it, to the right and left. The frenula seem to be supporting columellæ or pillars, which support the fragile skeleton, and mainly effect a fixed prop for the fragile galea. In the Cœlotholida the frenula are often rather broad and irregularly fenestrated lamellæ of silica (Pl. 122, fig. 2), whilst in the Cœloplegmida they are usually thin ligaments, fenestrated only at the broadened ends, which are inserted inside on the distal apex of the nasal mouth, and outside on the base of the nasal main styles.

The large hollow tubes which arise from the galea of all Cœlographida, are very variable in number, size and shape, but are always richly branched and symmetrically arranged in the dorsal and the ventral valve of the shell. They exhibit an important difference in the two subfamilies of the group; in the Cœlotholida all the branches, and also the thin terminal ramules, are free, without any junction; in the Cœloplegmida, however, they communicate by frequent anastomoses, and the connected terminal ramules form on the surface of the calymma an outer lattice-mantle of very delicate network. Another marked difference between the two families is indicated by the origin and site of those main tubes which are connected with the rhinocanna by a frenulum. In the Cœloplegmida an odd, very large main tube (the nasal style) arises from the anterior apex of each galea and bears on its base an odd frenulum. This nasal style and its frenulum is altogether wanting in the Cœlotholida, where two paired main tubes (the frontal tubes) arise from the lateral corners of the truncate anterior side of the galea, and are connected with the mouth of the rhinocanna by two paired convergent lateral frenula.

We distinguish in all Cœlographida two different forms of hollow branched tubes, which we will call "brushes" and "styles." The brushes are dichotomously branched from the base, not verticillate; their distal ramules remain separate in the Cœlotholida and compose the spiny surface, of the peculiar "fork-thicket" whilst in the Cœlographida they become connected by frequent anastomoses and form the outer "lattice-mantle." The styles however are much longer projecting over the surface of the thicket or the mantle, and are not dichotomously branched, but verticillate, or armed with cruciate or alternately cruciate pairs of branches; the larger branches of the styles may be again dichotomously branched like the brushes; whilst the free prominent parts of the styles are always verticillate or cruciate-pinnate. The brushes are identical with the hollow tubes of the Cœlodendrida, whilst the styles are peculiar forms of apophyses, wanting in the latter.

The minimum number of hollow tubes which arise from each valve is three, and these are probably homologous with the three primary tubes of the Cœlodendrida. Two of these are paired (right and left), whilst the third is odd and lies in the sagittal plane; they have the same position as in the tripodal Nassellaria, and may therefore bear the same names, the two paired anterior or pectoral tubes being divergent forwards, the odd or caudal tube being bisected backwards (so in the Cœlotholida, Pl. 121). The odd caudal tube (probably identical with the odd tube of the Cœlodendrida) is always a brush, dichotomously branched, and never prolonged into free style. The two paired frontal or pectoral tubes, however are usually prolonged into two long verticillate styles. The basal origin also of these three primary tubes is different. The two pectoral or anterior paired tubes always arise from the galea itself whilst the posterior odd or caudal tube usually arises behind the galea from the valve (Pl. 127, figs. 4-8, g 6).

Since these three primary tubes the odd caudal and the paired pectoral, are probably homologous in all Cœlographida and Cœlodendrida, they have a great morphological importance, similar to the three primary feet of the Nassellaria. All other tubes arising from the valves must be regarded as secondary apophyses, since they are not constant in all members of the two families, but present only in some of them. All the Cœlotholida observed (a small number of species only) possess no secondary tubes, but only the three primary; whilst all Cœloplegmida possess one or more secondary tubes, and one of these is constant, viz., the odd nasal style, directed towards the mouth, and arising as the foremost from the apex of the galea (Pl. 127, figs. 4-8, g 1).

The maximum number of tubes observed, which arise from each valve in the Cœloplegmida, is eleven; five of these are odd and placed in the sagittal plane of the body, viz.:—(A) the primary caudal tube (Pl. 127, figs. 4-8, g 6); (B) an odd procaudal tube, arising between the caudal and the sagittal tube; (C) the sagittal tube, placed either in the sagittal axis of the body or near it (often prolonged into a sagittal style, Pl. 128, fig. 1); (D) an odd postnasal tube, arising between the sagittal and the nasal tube; (E) the odd nasal tube, constant in all Cœloplegmida, and connected at its base by the odd frenulum with the rhinocanna (Pl. 127, figs. 4-8, g 1). All other tubes occurring in the Cœloplegmida are paired, and symmetrically arranged on both sides of the sagittal plane, at right and left; their maximum number is three pairs, viz.:—(F) the paired pectoral tubes (as the foremost), directed forwards; (G) the paired frontal or lateral tubes, placed either in the frontal axis of the valve, or in a neighbouring axis, directed towards the right and left pole (Pl. 127, figs. 4-8, g 4 and g 5); (H) the paired tergal tubes, directed backwards (constant in all Cœloplegmida). The origin of these tubes is rather variable, since they arise in nearly allied species, sometimes independently of one another, at other times united at the base. But a closer comparison of them in the different species will demonstrate their homology, caused by constant heredity.

The terminal ramules of the brushes, which form the subspherical "fork-thicket" in the Cœlotholida, the outer "lattice-mantle" in the Cœloplegmida, are constantly armed at the distal ends either with spathillæ or with anchor-pencils, bunches of those most elegant spinulate threads, which bear at the free end an anchor, or a whorl of two, three, or four recurved teeth (Pl. 122, fig. 8; Pl. 127, fig. 10; Pl. 128, figs. 1, 6). The pencils are usually dichotomously branched, their threads zig-zag or delicately serrate, often armed with very small recurved denticles, and the anchor teeth (commonly three or four) are usually smooth on the convex outer, serrate on the concave inner edge. The entire surface of the subspherical thicket in the Cœlotholida, and of the polyhedral lattice-mantle in the Cœloplegmida, is armed with thousands of those most elegant spathillæ, or anchor-pencils.

The "fork-thicket" of the Cœlotholida is identical with that of the Cœlodendrida, and is composed only of the innumerable dichotomous branches of the hollow tubes. It envelops the two central valves and the enclosed central capsule in the same way as in the Cœlodendrida. But the Cœlotholida differ from these latter in constantly possessing a rhinocanna and two frenulæ. The entire form of this thicket, which in the few species observed was never complete, but always more or less destroyed, is usually probably subspherical or polyhedral, sometimes cordate or kidney-shaped. Its surface is densely studded with thousands of spathillæ. Its diameter is about four to eight times as great as that of the enclosed bivalve shell.

The "lattice-mantle" of the Cœloplegmida, which replaces in this subfamily the fork-thicket of the Cœlotholida, is always produced by the anastomoses of the distal ramules of the brushes, and of those branches of the styles which do not proceed over the surface of the mantle. Its network is always very irregular, and composed of polygonal meshes of very different sizes. Usually it is quite simple, and may be compared with the cortical shell of the Disphærida. More rarely it is more or less spongy. Its surface is densely studded with thousands of spathillæ or anchor-pencils. The entire form of the lattice-mantle is always symmetrically polyhedral, since its dorsal and ventral halves are symmetrically developed on both sides of the equatorial plane, and therefore correspond perfectly to the enclosed smaller halves of the central bivalve shell. The two valves of the lattice-mantle (dorsal and ventral valves) are never really united and grown together, but are in loose contact in the equatorial plane; here the free edges of both valves catch into one another by means of free ramules (Pl. 128, figs. 1, 7). This loose connection is similar to what occurs in the Conchopsida (or in the Concharida with dentate edges), but never so regular. The special form of the polyhedral lattice-mantle depends on the number, arrangement, and development of the styles, which proceed over its surface; it preserves the polyhedral form of the calymma, on the surface of which it is deposed.

The characteristic styles of the Cœlographida (which are never found in the preceding Cœlodendrida) are longer hollow tubes, symmetrically disposed on both valves. They are prominent over the surface of the fork-thicket in the Cœlotholida, of the lattice-mantle in the Cœloplegmida. They bear in these latter a peculiar terminal coronet on their distal end, whilst in the former this end is armed with large pencils of spathillæ. The styles may be forked once or twice at their base, but in their greatest part they are verticillate, and not dichotomously branched like the brushes. The lateral branches of the styles are usually very numerous and regularly cruciate in alternating opposite pairs. In the odd nasal style, e.g., the first and third pairs of opposite lateral branches usually lie in the frontal plane, the second and fourth in the sagittal plane, perpendicular to the former, and so on. A similar regular disposition of the lateral branches is found also in other styles, but not in all. There are certain styles in which the lateral branches are not opposite in pairs, but alternate or verticillate, and others in which they represent unequal branches of forks, so that each single segment of the branched style represents the stouter branch of a fork, and the appertaining lateral branch the thinner branch of the fork. Further accurate examinations are required to recognise the different laws of the ramification of the styles in the different forms of Cœlographida. The lateral branches of the styles are usually again dichotomously branched inside the lattice-mantle, and their distal ends pass over into its network. But the verticillate or cruciate branches, which arise from the free part of the styles outside the lattice-mantle, are always armed with the same elegant pencils of spathillæ which cover the surface of the fork-thicket in the Cœlotholida, the surface of the lattice-mantle in the Cœloplegmida. These pencils also are often regularly opposite in pairs, and the pairs alternate in two planes perpendicular one to another (Pl. 128, figs. 1, 4).

The terminal coronets are peculiar ornaments which protect the distal ends of the styles in the Cœloplegmida, whilst in the Cœlotholida these are armed with the usual pencils of spathillæ (Pl. 122, fig. 8). Each coronet is usually produced by the double, triple, or quadruple furcation of the free distal end of the style; therefore composed of four, eight, or sixteen terminal branches, which, on account of their peculiar form and function, we may call "fingers." More rarely the ramification of the coronets is more or less irregular, and sometimes the number of the fingers exceeds twenty or even thirty.

In the majority of species eight fingers are regularly disposed (Pl. 127, figs. 1-3; Pl. 128, figs. 1-8). Often too sixteen occur, rarely four only. Sometimes the fingers are placed nearly in one plane and form a hand. The form of the fingers is very variable and most characteristic of the individual species. Very often they have the shape of a human finger, and are smooth, spinulate, or armed with recurved hooks. The distal end of each finger often again bears a small coronet or a spathilla (Pl. 128, figs. 5-9), and sometimes it is arrow-shaped (Pl. 126, fig. 2a). All these apophyses of the terminal coronets as well as the anchor-pencils of the mantle and the finest branches of the tubes, are hollow and filled up by jelly.

The different number and arrangement of the styles offers the best means for the distinction of genera in the Cœlographida. The minimum number is six (Cœlographis, Pl. 126, fig. 1), the maximum number sixteen (Cœlothamnus, Pl. 122, fig. 3, and Cœlagalma, Pl. 126, fig. 4). Since the arrangement of the styles in both valves is constantly symmetrical, the fundamental form of the whole body is in all Cœloplegmida "amphithect," as in the Ctenophora. The longitudinal or main axis of the body is vertical, with two distinct poles; the proboscis of the central capsule and the two rhinocannæ are directed upwards, towards the oral pole; the caudal tube of each valve is directed downwards, towards the aboral pole. The two other axes of the body are unequal, horizontal, and perpendicular one to the other; each has two equal poles. On the poles of the sagittal axis lie the galeæ of the dorsal and ventral valves; on the poles of the frontal axis lie the two secondary openings or parapylae of the central capsule. The frontal fissure or the large cleft between the dorsal and ventral valves of the skeleton lies in the vertical frontal plane of the body, which is perpendicular to the vertical sagittal plane; the equatorial plane, however, is horizontal.

The central capsule of the Cœlographida exhibits the same shape and position as in the preceding Cœlodendrida. It is subspherical, slightly depressed in the direction of the main axis, and lies enclosed between the two central valves of the lattice-shell. Its three constant openings lie in the frontal plane, and therefore in the frontal fissure between the two valves. The astropyle, or the main-opening of the capsule, lies on the oral pole of the main axis, and its radiate operculum (d) is directed upwards; the curved proboscis arising from it (o) is prominent between the mouths of the two opposed rhinocannæ. The two lateral parapylæ or accessory openings lie on both sides of the aboral pole, on the right and left (Pl. 127, figs. 4-6). The large spheroidal or somewhat lenticular nucleus (n) is usually about half as broad as the capsule, and contains numerous nucleoli. The protoplasm around the nucleus contains many vacuoles, and in the oral part of the capsule (between nucleus and operculum) often numerous groups of crystals (Pl. 127, figs. 4-6k, 7). The double membrane of the central capsule exhibits the same shape as in the other Phæodaria.

The calymma, or the extracapsular jelly-veil, is in the Cœlographida very voluminous, and includes the entire skeleton, the fork-thicket of the Cœlotholida, the lattice-mantle of the Cœloplegmida, and also the prominent large styles. Only the distal ends of the latter (with the terminal coronets), and the anchor pencils, covering the surface of the thicket and the mantle, seem to project over the surface of the calymma. The entire form of the latter is therefore a symmetrical polyhedron. The phæodium fills up a small part only of the calymma, and is usually enclosed in the two galeæ and their rhinocannæ (Pl. 127, figs. 5, 9), but often also a part of the phæodium is scattered around the oral half of the central capsule.

Synopsis of the Genera of Cœlographida.

I. Subfamily Cœlotholida. Rhinocanna of each valve with two paired lateral frenula. The distal ends of the dichotomous brushes are not united by anastomoses, and form an outer bivalved fork-thicket.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	Eight paired styles (four on each valve),			731. Cœlotholus.
		Twelve paired styles (six on each valve),			732. Cœlothauma.
		Sixteen paired styles (eight on each valve),			733. Cœlothamnus.
II. Subfamily Cœloplegmida. Rhinocanna of each valve with an odd sagittal frenulum. The distal ends of the dichotomous brushes are united by anastomoses, and form an outer bivalved lattice-mantle.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Mantle with six styles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	One odd and two paired styles on each valve,	734. Cœlographis.
		Mantle with eight styles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Two odd and two paired styles on each valve,	735. Cœlospathis.
		Mantle with ten styles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	One odd and four paired styles on each valve,	736. Cœlodecas.
		Mantle with twelve styles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Two odd and four paired styles on each valve,	737. Cœlostylus.
		Mantle with fourteen styles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	One odd and six paired styles on each valve,	738. Cœloplegma.
		Mantle with sixteen styles.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Two odd and six paired styles on each valve,	739. Cœlagalma.

Subfamily 1. Cœlotholida, Haeckel.

Definition.—Cœlographida with two paired lateral frenula on each galea, and with free terminal branches on the hollow radial tubes, without an external lattice-mantle. Eight to sixteen long styles are prominent over the surface of the fork-thicket, which is composed of the caudal brush and the dichotomous basal branches of the styles.

Genus 731. Cœlotholus,^[12] n. gen.

Definition.—Cœlographida with two paired lateral frenula on each galea, without external lattice-mantle, armed with eight styles (two pairs of styles on each valve).

The genus Cœlotholus and the two following genera form together the subfamily Cœlotholida, the hollow tubes of which do not communicate by anastomosing branches, and therefore form no lattice-mantle, as in the following subfamily Cœloplegmida. Another important difference between these two subfamilies of Cœlographida is found in the arrangement of the main tubes and their connection with the rhinocanna. In all Cœlotholida a pair of divergent frontal styles arise from the truncate oral side of each galea, and are connected with the mouth of the rhinocanna by two lateral convergent paired frenula (right and left); whereas the characteristic odd nasal style, which in all Cœloplegmida arises from the sagittal apex of each galea and is connected with the mouth of the rhinocanna by an odd sagittal frenulum, is always wanting. The total number of long verticillate styles, which project over the outer surface of the fork-thicket, is eight in Cœlotholus, whilst it is twelve in Cœlothauma, and sixteen in Cœlothamnus. The two latter may be derived from Cœlotholus, as the common ancestral genus of this subfamily.

1. Cœlotholus octonus, n. sp. (Pl. 122, figs. 1, 2).

Eight styles of equal length, regularly zig zag, twice as long (in their free part) as the diameter of the loose fork-thicket. Anchor-pencils gradually tapering from the proximal towards the distal end. Each of the four primary frontal tubes (to the right and left of each valve) is simply forked, and the pectoral (anterior) branch of each tube is so diametrically opposed to the tergal (posterior) tube of the other side, that they form together a double cross.

Dimensions.—Diameter of the whole body 12, of the fork-thicket 2.5.

Habitat.—South-Eastern Pacific, Station 300, depth 1375 fathoms.

2. Cœlotholus cruciatus, n. sp.

Eight styles of equal length, straight, twice as long (in their free part) as the diameter of the dense fork-thicket. Anchor-pencils of about equal size throughout their whole length. Each of four primary frontal tubes is divided into two equal, widely divergent branches; the anterior branches of the right side are diametrically opposed to the posterior branches of the left side, so that all eight together form a double cross.

Dimensions.—Diameter of the whole body 20, of the fork-thicket 4.0.

Habitat.—South-Western Pacific (off Sydney), Station 164A, depth 1200 fathoms.

3. Cœlotholus ancoratus, n. sp.

Eight styles of different lengths, slightly curved. Anchor-pencils gradually tapering from the proximal to the distal end. Each of the four primary frontal tubes is divided into two divergent branches of different lengths; the anterior (or pectoral branch) twice as long (in the free part) as the diameter of the fork-thicket, the posterior (or tergal branch) three times as long.

Dimensions.—Diameter of the whole body 20, of the fork-thicket 3.2.

Habitat.—Indian Ocean (Sunda Strait), Rabbe, surface.

Genus 732. Cœlothauma,^[13] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Cœlographida with two paired lateral frenula on each galea, without external lattice-mantle, armed with twelve styles (three pairs of styles on each valve).

The genus Cœlothauma differs from the preceding Cœlotholus, its ancestral form, in the possession of twelve long, prominent styles, six of which are opposite in three pairs on each valve. In the single species observed each of the four main tubes (opposite in pairs on the frontal corners of the two galeæ) is simply forked, as in Cœlotholus; but whilst in this latter all eight styles remain simple, in Cœlothauma the anterior (or pectoral) branch only is simple, the posterior (or tergal) branch is again forked.

1. Cœlothauma duodenum., n. sp. (Pl. 122, figs. 3-5).

Twelve styles straight, of different lengths. Two short bilateral main tubes arise opposite in pairs from the two frontal corners of each galea, and are divided into an anterior and posterior branch. The anterior or pectoral branch is simple, and twice as long as the diameter of the fork-thicket. The posterior or tergal branch is again forked near the base, and its two divergent branches are three times as long as the diameter of the fork-thicket. All twelve styles are densely studded with anchor-pencils of nearly equal size.

Dimensions.—Diameter of the whole body 21, of the fork thicket 3.5.

Habitat.—South-Western Pacific (east of New Zealand), Station 169, depth 700 fathoms.

Genus 733. Cœlothamnus,^[14] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Cœlographida with two paired lateral frenula on each galea, without external lattice-mantle, armed with sixteen styles (four pairs of styles on each valve).

The genus Cœlothamnus differs from its ancestral form, Cœlotholus, in the duplication of the number of long verticillate styles, which are prominent over the surface of the dense fork-thicket. Whilst in Cœlotholus each frontal main tube (arising from the frontal corner of the galea at right and left) is divided into an anterior or pectoral, and a posterior or tergal style, in Cœlothamnus each of these two divergent main styles is again forked, so that the total number of projecting and radially diverging styles amounts to sixteen. One Mediterranean species of this genus, Cœlothamnus davidoffii, has been already described by Bütschli in 1882 (Zeitschr. f. wiss. Zool., vol. xxxvi. p. 486, Taf. xxxi.). Though its description on the whole is accurate, some important errors, which may be here corrected, are to be met with. The two central valves of the lattice-shell (dorsal and ventral) are symmetrically equal in size and in form, as in all other Cœlographida; the different forms and the inverse arrangement of the two valves, described by Bütschli (pp. 488, 491), were effected by an artificial dislocation and inversion. The peculiar opening α, which, according to his opinion, was supposed to bring about a direct communication between the cavities of the galea and its valve, is in reality the optical section of the rhinocanna, the two convergent frenula of which (γ) he figured, but did not recognise. Cœlothamnus attains the greatest size among all Radiolaria; the diameter of the body in Cœlothamnus maximus amounts to 33 mm.

1. Cœlothamnus bivalvis, n. sp. (Pl. 122, figs. 6-9).

Sixteen styles all of equal length, about three times as long (in their free part) as the diameter of the dense fork-thicket. The size of the anchor-pencils tapers from the proximal to the distal end. Each of the four primary frontal tubes (which arise in opposite pairs from the frontal corners of the two galeæ) is twice forked, and so produces four styles.

Dimensions.—Diameter of the whole body 18, of the fork-thicket 2.4 to 3.0.

Habitat.—North Atlantic, Canary Islands, Station 354, surface.

2. Cœlothamnus davidoffii, Bütschli.

Cœlothamnus davidoffii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 486, Taf. xxxi.

Sixteen styles all of equal length (?), about four times as long (in their free part) as the diameter of the fork-thicket. The size of the anchor-pencils is nearly equal throughout their entire length. (Compare the careful description of this species by Bütschli.)

Dimensions.—Diameter of the whole body 15, of the fork-thicket 1.8.

Habitat.—Mediterranean (Villafranca, near Nice), Davidoff, surface.

3. Cœlothamnus sedecimalis, n. sp.

Sixteen styles straight, of different sizes. The pectoral or anterior branch of each frontal main tube is simple, and twice as long as the diameter of the large fork-thicket. The tergal or posterior branch is forked at the base, and its anterior branch is again forked in the middle part, so that three long divergent styles arise from each tergal tube. The hindermost of these is the longest, three times as long as the diameter of the fork-thicket. All anchor-pencils have nearly equal size.

Dimensions.—Diameter of the whole body 22, of the fork-thicket 5.2.

Habitat.—South Pacific, Station 166 (west of New Zealand), depth 275 fathoms.

4. Cœlothamnus maximus, n. sp.

Sixteen styles straight, of different sizes. The four frontal main tubes are already forked at the base, so that from each frontal corner of the two galeæ two divergent tubes, an anterior or pectoral and a posterior or tergal, arise. Each of these is again forked, and each branch prolonged into a very long verticillate style. The hindermost style of each side is the longest, twice as long as the foremost, and one and a half times as long as the two intermediate styles. The size of the anchor-pencils decreases in the distal third of the styles.

Dimensions.—Diameter of the whole body 32, of the fork-thicket 7.5.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Subfamily 2. Cœloplegmida, Haeckel.

Definition.—Cœlographida with an odd sagittal frenulum on each galea, and with an external bivalved lattice-mantle, produced by the anastomosing branches of the hollow radial tubes. Six to sixteen long styles are prominent over the surface of the mantle, and bear terminal coronets.

Genus 734. Cœlographis,^[15] n. gen.

Definition.—Cœlographida with an odd sagittal frenulum on each galea and an outer lattice-mantle, armed with six styles (one odd and two paired styles on each valve).

The genus Cœlographis is the simplest form of the Cœloplegmida, or of those Cœlographida in which the branches of the arborescent tubes are united on the surface of the calymma, and form a delicate bivalved lattice-mantle. In all these Cœloplegmida an odd nasal main style is developed on the apex of the galea, and this is connected by an odd sagittal frenulum with the mouth of the rhinocanna, Cœlographis differs from the other Cœlographida in the minimum number of coronal styles, viz., three on each valve, an odd anterior (nasal) and two paired posterior (tergal).

1. Cœlographis regina, n. sp. (Pl. 126, figs. 1a-1c).

Shell-mantle twice as long as broad, its frontal perimeter isosceles triangular, with a triangular excision at the base, its sagittal perimeter slenderly ovate. Nasal odd style twice as long as the paired tergal styles, the former with ten to twelve, the latter with five to six alternate-cruciate pairs of lateral branches. Terminal coronets (on the free distal ends of the styles) palmate, with ten to twelve spinulate, irregular, finger-shaped branches (fig. 1d).

Dimensions.—Length of the shell 5.6, breadth 2.7.

Habitat.—South-Eastern Pacific (off Juan Fernandez), Station 297, depth 1775 fathoms.

2. Cœlographis sagittella, n. sp.

Shell-mantle one and a half times as long as broad, its frontal perimeter arrow-shaped, isosceles triangular, with a deep concave excision at the base, its sagittal perimeter slenderly ovate. Nasal odd style one and a half times as long as the paired tergal styles, the former with fourteen to sixteen, the latter with eight to nine verticils of branches. Terminal coronets three times forked, with eight subregular, broad and spinulate, finger-shaped branches.

Dimensions.—Length of the shell 6.4, breadth 4.2.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Cœlographis hexastyla, n. sp.

Shell-mantle one and a half times as long as broad, very similar to the preceding species, its frontal perimeter isosceles triangular, with a flat basal excision. Nasal odd style one and a third times as long as the paired tergal styles, the former with fourteen to sixteen, the latter with ten to twelve verticils of branches. Terminal coronets with four forks in the form of a cross, and eight divergent spinulate fingers.

Dimensions.—Length of the shell 4.2, breadth 3.1.

Habitat.—North Pacific, Station 259, depth 2225 fathoms.

4. Cœlographis gracillima, Haeckel.

Cœlodendrum gracillimum (partim) Haeckel, 1862, Monogr. d. Radiol., Taf. xxxii. figs. 2, 3.

Shell-mantle one and a third times as long as broad, similar to the three preceding species, its frontal perimeter isosceles triangular. Nasal odd style one and a half times as long as the two paired tergal styles, the former with eleven or twelve, the latter with seven or eight pairs of branches. Terminal coronets irregularly dichotomously branched, with twelve to sixteen spinulate fingers. The network of the mantle is also spinulate (loc. cit., fig. 3). This species was formerly confounded by me with Cœlodendrum gracillimum (loc. cit., fig. 1), since I found a fragment only of the former entangled in the branch-work of the latter (1859, in Messina). Afterwards (in 1877) I observed a complete specimen in Corfu.

Dimensions.—Length of the shell 3.2, breadth 2.4.

Habitat.—Mediterranean (Messina, Corfu), surface.

5. Cœlographis triangulum, n. sp.

Shell-mantle about as long as broad, its frontal perimeter equilateral triangular, without basal excision, with three equal straight sides. Nasal odd style and the two paired pectoral styles nearly of equal length, each with ten to twelve alternate-cruciate pairs of lateral branches. Terminal coronets umbrella-shaped, composed of eight equal, simply forked branches.

Dimensions.—Length of the shell 3.6, breadth 3.4.

Habitat.—South Pacific, Station 293, depth 2025 fathoms.

Genus 735. Cœlospathis,^[16] n. gen.

Definition.—Cœlographida with an odd sagittal frenulum on each galea and an outer lattice-mantle, armed with eight styles (two odd and two paired styles on each valve).

The genus Cœlospathis differs from the preceding Cœlographis in the possession of four coronal styles on each valve. Two of these are odd and lie in the sagittal plane, viz., the constant vertical nasal style (directed towards the mouth), and the horizontal sagittal style, which is placed in the equatorial plane, in the sagittal axis of the body. The two other styles are paired and identical with the tergal styles of Cœlographis, directed backwards, and divergent to right and left.

1. Cœlospathis ancorata, n. sp. (Pl. 128, figs. 1-7).

Shell-mantle one and a half times as long as broad, its frontal perimeter isosceles triangular; its zonal perimeter square, its sagittal perimeter nearly rectangular, with a concave excision on the oral side (fig. 1). Odd nasal styles of both valves divergent in the sagittal plane (each with fourteen to sixteen pairs of branches), three times as long as the odd sagittal styles (each with three or four pairs) and twice as long as the paired tergal styles (each with four to six pairs of branches). Terminal coronets (on the free distal end of the styles) three times forked, each with eight slender, widely divergent fingers, which are curved, zig-zag, and armed with alternating recurved hooks; at the end of each finger a verticil of four to six small recurved teeth (fig. 5).

Dimensions.—Length of the shell 2 to 3, breadth 1.2 to 2.1.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

2. Cœlospathis octostyla, n. sp. (Pl. 128, fig. 8).

Shell-mantle one and a third times as long as broad, very similar to the preceding species; but differing from this in the following characters: the odd nasal styles bear ten to twelve pairs of branches, and are twice as long as the odd sagittal and the paired pectoral styles, which are nearly equal in size (each with five or six pairs of branches). The eight fingers of the terminal coronets are less divergent and curved than in the preceding species, and each finger bears at its end a verticil of four to six divergent, slender teeth, which are not recurved (fig. 8).

Dimensions.—Length of the shell 2.2 to 2.6, breadth 1.7 to 1.9.

Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

3. Cœlospathis octodactyla, n. sp. (Pl. 128, fig. 9).

Shell-mantle about as long as broad, in the frontal perimeter nearly isosceles triangular, very similar to the two preceding species; it differs from them in the following characters: all eight styles have nearly equal size, and each bears six to eight pairs of branches. The eight fingers of the terminal coronets diverge nearly in one plane, and are not curved in a zigzag manner, but armed with alternate, slender, recurved hooks, which are larger than in the two preceding species, and geniculate at the base; the distal end of each finger bears a verticil of eight to ten very small divergent teeth, which are not recurved (fig. 9).

Dimensions.—Length of the shell 2.4, breadth 2.2.

Habitat.—North Pacific, Station 252, surface.

Genus 736. Cœlodecas,^[17] n. gen.

Definition.—Cœlographida with an odd sagittal frenulum on each galea and an outer lattice-mantle, armed with ten styles (one odd and four paired styles on each valve).

The genus Cœlodecas is closely allied to Cœlographis, but differs from it in the development of a new pair of styles on each valve. These are placed between the odd nasal and the paired tergal styles, are usually directed laterally, parallel to the frontal axis of the body, and may therefore be called frontal or lateral styles. The total number of coronal styles is therefore ten.

1. Cœlodecas sagittaria, n. sp. (Pl. 126, figs. 2a, 2b).

Shell-mantle one and a half times as long as broad; its frontal perimeter pentagonal, with a deep median incision at the base; the two oral sides of the pentagon twice as long as the two lateral sides, and one and a half times as long as the base. Sagittal perimeter ovate; equatorial perimeter subcircular. Nasal odd style of each valve with fourteen to sixteen pairs of branches, one and a half times as long as the paired frontal styles (each with eight to nine pairs), and twice as long as the paired tergal styles (each with four to six pairs of branches). Terminal coronets (on the free distal ends of the styles) richly branched, each with thirty to forty thorny fingers, which bear a conical point with recurved teeth, like an arrow.

Dimensions.—Length of the shell 3.2, breadth 2.1.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

2. Cœlodecas decastyla, n. sp.

Shell-mantle one and a third times as long as broad; its frontal perimeter pentagonal, with a slight incision on the base; the two oral sides of the pentagon as long as the base, and one and a half times as long as the two lateral sides. Nasal odd style of each valve with ten to twelve pairs of branches, about twice as long as the four paired frontal and tergal styles, each of which bears five or six pairs. Terminal coronets three times forked, each with eight straight, spinulate, slightly divergent fingers, shaped like a human finger.

Dimensions.—Length of the shell 3.6, breadth 2.7.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

3. Cœlodecas pentagona, n. sp.

Shell-mantle about as long as broad; its frontal perimeter nearly regular pentagonal, with five equal sides. Nasal odd style of each valve with six to eight pairs of branches scarcely longer than the four paired frontal and tergal styles, each of which is provided with four to six pairs. Terminal coronets irregularly branched, each with twelve to sixteen slender curved fingers, which bear at the distal end a spinulate knob.

Dimensions.—Length of the shell 2.6, breadth 2.4.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Genus 737. Cœlostylus,^[18] n. gen.

Definition.—Cœlographida with an odd sagittal frenulum on each galea and an outer lattice-mantle, armed with twelve styles (two odd and four paired styles on each valve).

The genus Cœlostylus is characterised by the possession of twelve coronal styles; it is closely allied to Cœlospathis, and differs from this in the development of a new pair of styles on each valve. These are placed between the odd nasal and the odd sagittal style of each valve, they are directed forwards, and may therefore be called "pectoral styles."

1. Cœlostylus bisenarius, n. sp. (Pl. 126, fig. 3a, 3b).

Shell-mantle one and a third times as long as broad; its frontal perimeter pentagonal, with a deep median incision at the base; the two oral sides of the pentagon about as long as the basal odd side, and half as long as the two lateral sides. Sagittal perimeter (fig. 3a) octagonal; the three paired lateral sides of the bilateral octagon about equal, and somewhat shorter than the basal and oral odd sides. Equatorial perimeter rounded square. Nasal odd style of each valve with twelve alternate-cruciate pairs of lateral branches, about twice as long as the two paired pectoral styles (each with four pairs), and the odd sagittal style (with six pairs); the two paired tergal styles bear eight pairs and are longer than the latter, shorter than the nasal style. All styles are more or less curved, divergent, and at the distal end four times forked, bearing a terminal coronet with sixteen spinulate fingers (fig. 3b).

Dimensions.—Length of the shell 4.2, breadth 3.2.

Habitat.—Indian Ocean (Madagascar), Rabbe, surface.

2. Cœlostylus flabellatus, n. sp.

Shell-mantle one and a half times as long as broad, very similar to that of the preceding species. It differs from this mainly in the peculiar form of the twenty-four terminal coronets, which are flabellate and very similar to the terminal branches of Cœlodendrum flabellatum (Pl. 121, figs. 5, 6). I formerly supposed, therefore, that both forms belonged to one and the same species. But though I had no complete specimens of the two species, I was afterwards led to the opinion that one and the same peculiar form of terminal branches is here produced by adaptation to similar conditions in two very different genera. Each coronet is a flat flabellum, placed in a meridian plane, and composed of eight pairs of spinulate branches as figured, loc. cit., in figs. 5 and 6. The cap-shaped distal end of each finger is armed with eight to twelve recurved teeth.

Dimensions.—Length of the shell 3.8, breadth 2.6.

Habitat.—North Pacific, Station 252, surface.

Genus 738. Cœloplegma,^[19] n. gen.

Definition.—Cœlographida with an odd frenulum on each galea and an outer lattice-mantle, armed with fourteen styles (one odd and six paired styles on each valve).

The genus Cœloplegma, distinguished by the possession of fourteen coronal styles, is closely allied to Cœlodecas, but differs from it in the development of a new pair of styles on each valve. These are placed between the odd nasal and the paired frontal styles, are directed forwards, and may therefore be called pectoral styles, corresponding to those of Cœlostylus.

1. Cœloplegma murrayanum, n. sp. (Pl. 127, figs. 1-13.).

Shell-mantle about as long as broad, its frontal perimeter subcircular, or slightly pentagonal, with five convex sides, its sagittal perimeter also nearly circular. Odd nasal style with six to eight, the paired pectoral styles with two or three, lateral styles with three to five, and tergal styles with six to nine pairs of branches. The central capsule constantly contains masses of crystals (figs. 4-7). Terminal coronets (on the free distal ends of the styles) three times furcate, each with eight simple and short fingers. This interesting species, discovered by Dr. John Murray in August 1882, during the expedition of H.M.S. "Triton," in great numbers in the Gulf Stream, off the Færöe Channel, is very variable and connected by numerous transitional forms with the following closely allied species. (Compare the following note.)

Dimensions.—Length of the shell 1.6 to 2.2, breadth 1.5 to 2.1.

Habitat.—North Atlantic, Gulf Stream, off the Færöe Channel, in depths between 40 and 200 fathoms, John Murray.

2. Cœloplegma tritonis, n. sp. (Pl. 127, figs. 2-13).

Shell-mantle one and a quarter times as long as broad, its frontal perimeter heptagonal, with seven concave sides (fig. 2), its sagittal perimeter ovate, its zonal perimeter nearly square (fig. 3). Odd nasal style with twelve to fourteen, the paired pectoral styles with three to four, lateral styles with six to eight, and tergal styles with eight to ten pairs of branches. Coronets three times forked, each with eight terminal branches, bearing a small spinulate knob. This remarkable species, in external appearance very different from the preceding, is connected immediately with it by numerous transitional varieties; both species represent the opposite terminal poles of a long series of "Darwinian metamorphic forms." If only the two specimens, figured in Pl. 127, figs. 1 and 2, were known, every one would distinguish them as two widely different species. But the careful comparison of numerous intermediate forms demonstrates that there is no "missing link" in this long and remarkable chain. The careful comparative study of these very variable and most highly developed Cœlographida may be regarded as a strong argument for the theory of descent, and explains the true "origin of species."

Dimensions.—Length of the shell 1.8 to 2.5, breadth 1.5 to 2.1.

Habitat.—North Atlantic, Gulf Stream, off the Færöe Channel, in depths between 40 and 200 fathoms, John Murray.

3. Cœloplegma tetradecastylum, n. sp.

Shell-mantle one and a third times as long as broad, its frontal perimeter heptagonal, with seven concave sides. Similar to the preceding species, differs from it mainly in the prolonged nasal style, which bears sixteen to eighteen pairs of branches, and is about three times as long as each of the six paired styles, each of which bears five to six pairs of branches. Coronets three times forked, each with eight terminal branches, armed with scattered spines, and bearing a knob with three recurved hooks.

Dimensions.—Length of the shell 3.2, breadth 2.4.

Habitat.—Tropical Atlantic, Stations 335 to 342, surface.

4. Cœloplegma atlanticum, n. sp.

Shell-mantle one and a half times as long as broad, its frontal perimeter ovate. Similar to Cœloplegma murrayanum (Pl. 127, fig. 1), differs from it in the different length of the styles; the nasal odd style (with eighteen to twenty pairs of branches) is about twice as long as the lateral styles (with ten to twelve pairs), and three times as long as the pectoral and tergal styles (with six to eight pairs). Coronets four times forked, each with sixteen terminal branches, armed with recurved spines, and bearing a cross of four curved hooks.

Dimensions.—Length of the shell 2.5, breadth 1.7.

Habitat.—South Atlantic, Station 318, depth 2040 fathoms.

Genus 739. Cœlagalma,^[20] n. gen.

Definition.—Cœlographida with an odd sagittal frenulum on each galea and an outer lattice-mantle, armed with sixteen styles (two odd and six paired styles on each valve).

The genus Cœlagalma represents the highest degree of development among the Cœlographida, and exhibits the maximum number of coronal styles in this family, viz., sixteen (eight on each valve). Two of these are odd (as in Cœlospathis and Cœlostylus), viz., the longitudinal anterior nasal style, and the horizontal sagittal style. The six others are paired (as in Cœloplegma), viz., two anterior or pectoral, two lateral or frontal, and two posterior or tergal styles. Since Cœlagalma in this highest developed armature exceeds all the other Cœloplegmida, and exhibits at the same time the utmost complexity in structural detail, it may be regarded as one of the most perfect forms not among the Phæodaria only, but among all Radiolaria.

1. Cœlagalma mirabile, n. sp. (Pl. 126, figs. 4, 4a).

Shell-mantle one and a half times as long as broad, its frontal perimeter (fig. 4a) heptagonal, with seven concave sides, its sagittal perimeter octagonal, its equatorial perimeter hexagonal (fig. 4b), the corners of the polygons are marked by the sixteen prominent styles. Nasal odd style longer; and sagittal odd style shorter, than the six paired styles of each valve; the two pectoral styles are directed forwards, the two lateral styles are nearly opposed in the horizontal frontal diameter, while the two shorter tergal styles are directed backwards. The terminal coronets (at the distal ends of the sixteen styles) are four times forked, with sixteen equal spinulate fingers, each finger at the distal end with eight recurved teeth. The entire surface of the bivalved latticed mantle is densely studded with hundreds of most elegant anchor-pencils, so that the external appearance of this beautiful species becomes one of the most wonderful among Radiolaria.

Dimensions.—Length of the shell 5.4, breadth 3.6.

Habitat.—Central area of the Pacific, Station 271, depth 2425 fathoms.

1. Concharium = Small mussel; κογχάριον.
2. Conchasma = Bivalved shell-fish; κογχάσμα.
3. Conchellium = Small bivalved mussel; κογχέλλιον.
4. Conchidium = Similar to a bivalved mollusc; κογχίδιον.
5. Conchonia = Bivalved shell like a mussel; κόγχη, ὄνια.
6. Conchopsis = Similar to a bivalved shell-fish or mussel; κόγχη, ὄψις.
7. Conchoceras = Mussel with horns; κόγχη, κέρας.
8. Cœlodoras = Hollow spear; κοίλος, δόρας.
9. Cœlodendrum = Hollow tree; κοίλος, δένδρον.
10. Cœlodrymus = Forest of hollow trees, κοίλος, δρυμός.
11. Cœlodasea = Hollow thicket, κοίλος, δάσεα.
12. Cœlotholus = Hollow cupola; κοίλος, θόλος.
13. Cœlothauma = Hollow wonder; κοίλος, θαῦμα
14. Cœlothamnus = Hollow thicket; κοίλος, θάμνος
15. Cœlographis = Hollow style; κοίλος, γραφίς.
16. Cœlospathis = Hollow whorl; κοίλος, σπαθίς.
17. Cœlodecas = Shell with ten hollow styles; κοίλος, δεκάς.
18. Cœlostylus = Hollow style; κοίλος, στύλος.
19. Cœloplegma = Hollow framework; κοίλος, πλέγμα.
20. Cœlagalma = Hollow ornament: κοίλος, ἄγαλμα.