Second Geological Survey of Pennsylvania. Report of Progress/PPP/Ceratiocaridae from the Chemung and Waverly groups of Pennsylvania
CERATIOCARIDÆ
FROM THE
CHEMUNG AND WAVERLY GROUPS OF PENNSYLVANIA.
By Chas. E. Beecher.
The literature upon the subject of the palæozoic phyllopods is comparatively very meager and fragmentary. An occasional discovery of a few specimens, as in the present instance, has resulted in the publication of one or more new forms, but nothing has led to a compilation and review of the palæozoic forms of the whole order. The trilobita forming the bulk of palæozoic crustacea, and including such varied forms and numerous species, have received much attention from palæontologists, so that a nearly complete monograph of this order is now possible; while of the American ostracoda, merostomata, and phyllopoda, but little is yet known which would furnish materials for an exhaustive monograph of the fossil species.
In the present paper several new forms are presented and considerable structural detail is here first given for the genus Echinocaris, Whitfield}}, which it is hoped will add to our knowledge of the zoölogical relations of this and allied genera.
Bibliographical History.
1839.—The first palæozoic fossils of this order were found in England and published by Sir R. Murchison. Professor L. Agassiz considered them as fin-spines of fishes, and reffered them to the genus Onchus. Only the separated portions of the trifid rail were then known, and this reference was not unnatural.
1850.—These fragments were ascribed to Pterygotus and constituted as a sub-genus Leptocheles by Professor McCoy. In the same publication he proposes the genus Ceratiocaris, and describes two species.
1851.—The following year these species are again described by Prof. McCoy and properly classed with the Phyllopoda, which has since been the receptacle for all fossil forms of a similar nature.
1852.—In 1852, Professor Hall made the first announcement in America of the discovery of fossils similar to those described by Prof. Agassiz as Onchus murchisoni, and described the species Onchus deweyi, from the Niagara group of New York. (Pal. N. Y. Vol. ii, p. 320.)
1853.—M. J. Barrande pointed out the essential identity of the fossils described under the names of Onchus and Leptocheles, with the telson and movable spines of Ceratiocaris, and suggests that these names are superfluous.
Since this time a number of new genera have been established both in America and abroad, of which only those will here be noticed which lead directly to the species of the present paper.
1863.—In the 16th Report of the New York State Cabinet of Natural History, Professor Hall described four species of this order and referred three of them to the genus Ceratiocaris. Two of these have since been recognized as having been described from different portions of individuals of the same species, and are now united under one species.
1876.—In 1876 the same author again illustrated these species and refered to one as Ceratiocaris (Aristozoe) punctatus, and suggested that the specimens designated as Ceratiocaris armatus were probably identical with it. (Illustrations of Devonian Fossils, pl. 23.)
1879.—Dr. A. S. Packard recognizes the importance of Nebalia and its fossil allies and their relations to the decapods, and proposes the order Phyllocarida for their reception. (Zoölogy American Science Series, p. 703.)
1880.—Professor R. P. Whitfield in 1880 (Am. Jour. Sci., vol. xix) described three allied species from the Devonian of Ohio and established the genus Echinocaris, which is to include also, the species Ceratiocaris (Aristozoe) punctatus, Hall.
The present paper furnishes one new species belonging to the genus Echinocaris and two related genera considered as new to science, under which are described four species.
Besides the crustaceans of the type of Ceratiocaris, Professor J. M. Clarke has shown (Am. Jour. Sci., Vols. xxiii and xxv, 1882–3,) that the Devonian series furnishes another distinct but allied group belonging to the prototype Discinocaris, Woodward. For the reception of these species he has erected the genera Spathiocaris and Dipterocaris.
1883.—In "A Monorgraph of the North American Phillopod Crustacea," Dr. A. S. Packard reviews the genera of the family ceratiocaridiæ and enumerates the described species.
Terminology.
In the use of descriptive terms for the different members of these crustaceans, it has been deemed advisable to adhere to the established nomenclature, with perhaps a few slight introductions and variations. The terminology used is explained by the following diagram.
It has been suggested that the so-called "optic spots" of McCoy and other authors may only be frontal bosses, and not connected with vision. In recent forms such as Apus there are three eyes one of which is double [Baird], other genera show one (double) or two. In the species furnished with a rostrum the eyes were probably stalked. None of the genera of the present paper have yielded any evidence of a rostral plate, and it is doubtful if such an appendage will be discovered. The tubercle, as indicated above, is one of the most constant features of the carapace in all of the species and must have a special significance. In a number of specimens examined, by the writer, under the microscope a subcircular depression is observed at or near the summit of this tubercle as in the ocelli of Eurypterus, etc. The fact that facets cannot be discerned is no criterion of their absence in the animal, for numerous trilobites and Eurypterus have as yet revealed no evidence of the compound character of their eyes, and on the other hand many species have large and distinct facets. It has also been noticed by Professor McCoy that this spot on the carapace is darker in the fossil than the general surface of the carapace, indicating the presence of pigment in the animal at this point. In the specimens of Elymocaris siliqua, Tropidocaris bicarinata and T. interrupta of the present paper this character is well marked.
 |
Explanation of Fig. 1. |
| 1. Anterior margin. | |
| 2. Furrow limiting the cephalic region. | |
| 3. Lower or ventral margin of valve. | |
| 4. Dorsal-line or hinge. | |
| 5. Posterior margin. | |
| 6. Articulating surface of somite. | |
| 7. Fimbria or setæ. | |
| 8. Crenulated inner margin of spine for the attachment of setæ. | |
| 9. Caudal plate. | |
| 10. Abdominal segments. | |
| 11. Thoracic portion of the valve extending to the furrow limiting the cephalic area. | |
| 12. Longitudinal ridge. | |
| 13. Nodes on the thoracic area. | |
| 14. Cephalic region. | |
| 15. Nodes and elevations. | |
| 16. Eye tubercles and optic spots. |
Geological Range.
The following table gives the distribution of the described species of the genera Echinocaris, Elymocaris and Tropidocaris. It is seen that the number of species reached its maximum in the Chemung group, which would naturally be expected from the almost total disappearance of the order Trilobita at the close of the deposition of the Hamilton group.
Besides the species of the list here given, I have seen two undescribed species of Echinocaris, from the Chemung group, of New York; also a large form belonging to the genus Elymocaris, from the Hamilton group of western N. Y.; and another species, probably belonging to the latter genus, from the same horizon in the central part of the State.
| Hamilton. | Genesee Sl. | Portage. | Chemung. | Waverly. | ||
| Echinocaris, Whitfield. | ||||||
| punctata, Hall, | ✕ | |||||
| longicauda, Hall, | ✕ | |||||
| sublevis, Whitfield, | ✕✕✕ | |||||
| pustulosa, Whitfield, | ✕✕✕ | |||||
| multinodosa, Whitfield, | ✕✕✕ | |||||
| socialis, Beecher, | ✕ | |||||
| Elymocaris, Beecher. | ||||||
| siliqua, Beecher, | ✕ | |||||
| Tropidocaris, Beecher. | ||||||
| bicarinata, Beecher, | ✕ | |||||
| interrupta, Beecher, | ✕ | |||||
| alternata, Beecher, | ✕ | |||||
Order PHYLLOCARIDA, (Packard, 1879.)
Family Ceratiocaridæ, Salter, 1860.
Genus ECHINOCARIS, Whitfield, 1880.
(Am. Jour. Sci., Vol. XIX, p. 34, 1880.)
Echinocaris punctata.
Plate I, Figs. 13–16.
Ceratiocaris? punctatus, Hall. Sixteenth Rep. N. Y. State Cab. Nat. Hist., p. 74. 1863.
Ceratiocaris armatus, Hall. Sixteenth Rep. N. Y. State Cab. Nat. Hist., p. 72. 1863.
Ceratiocaris armatus, Hall. Illustrations of Devonian Fossils. Explanation of Pl. 23, Figs. 4, 5. 1876.
Ceratiocaris (Aristozoe,) punctatus, Hall. Illustrations of Devonian Fossils. Expl. Plate 23, Fig. 7. 1876.
Echinocaris punctatus, (Hall,) Whitfield. Am. Jour. Sci., 3d Ser., Vol. XIX, p. 7. 1880.
Capapace obliquely subovate in outline; widest just posterior to the middle, width about two-thirds of the greatest length, which is four-fifths of the free segments of the abdomen; compressed on the anterior half, becoming regularly convex over the posterior portion.
Dorsal line straight, about equal to the width of the valves, situated anteriorly, so that one-third the length of the valves projects beyond the posterior extremity of the hinge.
Margins distinctly marked by a thickening of the test, rounded in front, making a broad curve along the lower edge of the valve, more rapidly curving around the lower posterior portion, and extending in nearly a straight line to the extremity of the dorsal line.
The cephalic portion of the carapace is distinctly marked by a furrow beginning at a point a little anterior to the middle of the dorsal line, curving outward and extending to a point on the lower anterior margin of the valve. This area, therefore, occupies the upper anterior portion of each valve, and is of a broad triangular form with curved sides. It is ornamented by a large rounded elevation, narrow towards the dorsum, broad and convex towards the lower portion, and occupying nearly one-half of the entire area. Near the center of the limiting furrow and just anterior, is a strong abruptly elevated node carrying the optic spot, which is usually marked by a slight depression on the summit of the node. There is also a small node in each valve adjacent to the dorsal line, near the posterior apex of the area.
The thoracic portion of the carapace is marked by two large tubercles, a long, sharp, doubly curved ridge, and a row of small nodes along the dorsal line. One of these tubercles is elliptical in outline, oblique, and situated near the middle of the anterior end, back of the optic node. The other elevation is elongate, with its longest diameter at right angles to the hinge, and marked by a small subcentral node. The ridge extends near the lower portion of the valve, concave to the margin along the anterior half of its extent, recurving and nearly following the contour of the lower posterior margin of the valve.
One specimen has been observed which preserves the mandibles in situ, and is represented in Fig. 16 of Plate I. The mandibles are broad and gibbous on the anterior portion becoming narrow below; furnished on their inner edge with a low of denticles; situated near the center of the carapace, and are nearly one-third the length of the valves.
Abdomen tapering towards the posterior end, composed of six exposed segments, having a total length of one-fourth greater than the length of the carapace. The segments increase in length towards the posterior segment, which has a length equal to two of the anterior segments, and is twice as long as wide; while the anterior somites have a greater width than length. The anterior dorsal margin of each is thickened and arched backwards; the posterior margin is furnished with from four to six strong spines, which project over the articulation of the succeeding segment. On the two anterior joints these spines are much shorter, appearing only as nodes. The ventral side is without spines, but is furnished with broad articulating faces. These characters indicate a great freedom of motion in the parts of the abdomen and account for the many positions in which this member is found.
Telson short and broad, flat and quadrangular on the ventral side; triangular and carinated on the dorsal side, and produced into a long, slender spine, having a length about equal to twice that of the posterior segment of the abdomen. To the ventral side of the caudal plate are articulated two movable spines, about equal in length to the spiniform extension of the telson. These spines are grooved along their lateral margins, and marked by a carina on their dorsal face.
Test thin, somewhat thickened on the margins and dorsal line of the carapace, and at the articulations of the abdominal segments; ornamented over the entire surface of the carapace, mandibles, abdomen, and tail with minute granules or pustules, which give a punctate appearance to the whole.
The specimen represented in Fig. 13 of Plate I has a length, exclusive of the tail spines, of 57 m m. The carapace measures 30 m m. in length, 20 m m. in breadth, and 18 m m. along the hinge-line. The segments of the abdomen, beginning with the anterior one, measure respectively 3.5, 3.7. 4, 4, 5, and 8.5 m m. in length,—showing that the posterior segment is more than twice the length of any of the first four segments. The three posterior ones, commencing with the distal segment, have diameters of 5.5, 7, and 8 m m. respectively. The left valve of this species figured in the 16th Rept. N. Y. State Cab. Nat. Hist. has a greatest length of 55 m m., with a breadth of 37 m m. The three abdominal segments figured in the same publication also belonged to a much larger individual than any noted in the present description.
This species differs from E. sublenis, Whitfield, (Am. Jour. Sci., Vol. XIX, p. 36,) in the more numerous nodes and tubercles of the carapace, the curvature and direction of the ridge along the thoracic portion, and in its more elongated abdominal segments. The same characters serve to distinguish it from E. pustulosa, Whitfield, (loc. cit.,) with the addition of a marked difference in the surface ornamentation, which in that species is distinctly pustulose. It is readily distinguished from E. socialis, in its larger size, less conspicuous and differently located nodes, and in the more simple character of the ornamentation.
This well-marked species occurs in the shales of the Hamilton group at several localities in the central portion of the State of New York. It is here introduced for the sake of comparison, and for a better elucidation of the characters of the following species. I am indebted to Professor James Hall, for the permission to examine and figure specimens of this species, belonging to the New York State Museum, at Albany. These collections furnish conclusive evidence of the identity of the abdomen and telson, referred to Ceratiocaris armatus, with the carapace described as Ceratiocaris? punctatus.
The specimen Fig. 16, Plate I, is the only one yet observed in this genus showing the mandibles and their position. In 1865 Professor Henry Woodward, of the British Museum, described and figured a specimen of Ceratiocaris papilio which preserved the mandibles and showed the position which they occupy in the carapace. These two examples add materially to our knowledge of the characters of this group, and with the nearly entire specimens described in this and in the succeeding species, furnish us with material for a comparison with their recent ally—Nebalia.
Some of the specimens are covered with numerous examples of a small species of Crania, which from the perfect preservation of the Echinocaris were probably attached during the life of the crustacean. The shales carrying these remains are highly charged with other fossils, among which are fragments of fishes, Beyrichia, Leperditia, Phacops, Homalonotus, Orthoceras, Nautilus, Loxonema, Pleurotomaria, Bellerophon, Platyostoma, numerous species and genera of lamellibranchiata, with a few species of brachiopods and bryozoans.
Associated with numerous specimens of E. punctata are frequently found mandibles or jaws of the form represented in Figs. 9–11 of Plate II. These are evidently of crustacean origin and although somewhat similar in form to the mandibles undoubtedly belonging to E. punctata, they probably belong to a species otherwise unknown. In general form they are triangular with a broad flat manubrium for articulation or the attachment of muscles. Inner or masticating side arched laterally, concave to the dorsal side of the carapace. Crown lunate, broadest anterior to the middle, and furnished with a row of usually six, more or less, bicuspid denticles. The denticles become more prominent and acute towards the posterior extremity of the crown, where they are also somewhat oblique, while anteriorly they are broad and obtuse. The test forming the crust of the mandible reaches a thickness of more than one mm. over the denticles, but becomes very thin over the expansions of the sides and on the manubrium. For this reason very few of the specimens preserve more than merely the row of denticles.
M. J. Barrande has figured and described several specimens of a similar nature and has referred them to the genus Ceratiocaris from their association with species of this genus in the Silurian of Bohemia. It is therefore probable that these portions of the animal do not furnish sufficient generic character to be of importance.
Formation and localities.—In the shales of the Hamilton group; at Delphi, Pratt's Falls, and the shore of Cayuga lake, New York.
Echinocaris socialis, n. sp.
Plate I, Figs. 1–12.
Carapace convex, obliquely ovate in outline, widest posterior to the middle, length about one-third greater than the width. Dorsal line straight, oblique, having a length of more than one-half the longest diameter of the valves. Margins thickened, carinated, curving outwards over the anterior end of the valves at nearly right angles to the direction of the hinge, continuing in a broad curve to the lower posterior end, where the margin is abruptly rounded, thence extending in nearly a straight line to the hinge.
Cephalic region triangular in each valve, distinctly limited by a furrow extending from the center of the dorsum, curving outwards and downward to the anterior margin, and occupying about a fourth of each valve. This area is ornamented in each valve with a prominent rounded tubercle at its posterior dorsal apex; and a large rounded elevation occupying the whole anterior end of the valve, making in all four prominent elevations on the cephalic area. The optic node is situated on the lower side of the largest tubercle and adjacent to the limiting furrow.
The thoracic portion of the valve is ornamented with an elongate tubercle near the middle of the anterior portion, produced into a nodose ridge following the contour of the lower margin and dying out before reaching the posterior end. A similar tubercle, but situated transversely, is found in the upper dorsal portion, and is continued in a nodose ridge adjacent to the dorsal line, and along the posterior margin of the valve. In the center of the area partially enclosed by these two ridges is a less prominent longitudinal row of minute nodes forming a third carina.
The valves are also ornamented with minute irregular tubercles on the summits of all the elevated portions of the valves, a single row appearing along the three ridges and around the extreme margin of the posterior portion.
Abdomen composed of six naked segments, which become more elongate towards the telson. Somites cylindrical, marked by a thickened rim on the anterior end; ornamented with four or more spinose nodes across the middle of the dorsal side, and by a row of smaller retral spines or nodes around the posterior dorsal margin.
Caudal plate short, triangular, produced behind into a slender, acute, carinate spine, having a length equal to one-half the abdomen; also two lateral movable spines, extending as far as the prolongation of the telson. Test thin.
The largest carapace observed has a length of 18 mm., and a width of 10 mm. A single cercopod belonging to a large individual has a length of 25 mm. A small entire example has a total length of 16 mm., of which 6 mm. pertain to the carapace, 6 mm. to the abdomen, and 4 mm. to the telson and spine.
This species is more highly ornamented than any yet described, and is the only one of the genus observed in the rocks of the Chemung group in Pennsylvania. It somewhat resembles E. pustulosa, Whitf., but has more nodes and ridges ornamenting the carapace, and is without the entirely pustulose surface of that species. E. sublevis, Whitf., has but a single row of spines on each abdominal somite, and the lateral ones are of considerable length.
The series represented in Figs. 1–4 of Plate I, shows the different positions of the abdomen in relation to the carapace, which have been observed, and illustrates the great flexibility of this portion of the animal. Fig. 1 represents the abdomen extending in the direction of the longer axis of the carapace, and probably shows the normal position of the parts. In Fig. 2 the abdomen is elevated above the dorsum. Fig. 3 shows the valves open, with the abdomen closely curved around the posterior end of the left valve. The specimen represented in Fig. 4 has the position of the abdomen the reverse of Fig. 1, extending obliquely from between the anterior ends of the valves. Specimens in the first and second of these positions are represented on the piece of rock shown in Fig. 12, which also illustrates the abundance of specimens in some portions of the shales. The single fragment in question contains the remains of fifteen separate individuals, nine of which are shown on the side represented in the figure.
The specimens of Elymocaris siliqua, and Tropidocaris bicarinata, which have been thus far found, are associated with this species.
Besides the remains of the crustaceans here described, there are also several fragments in the collections from these shales which belong to other forms of crustacea, but are too obscure to furnish satisfactory information as to their nature and characters. In addition to the crustaceans are numerous species of lamellibranchiata in the same occurrence; also one or two species of brachiopoda, an Orthoceras and the teeth and scales of fish.
The data furnished by the specimens of E. punctata and E. socialis fix the number of naked abdominal segments in the genus at six.
Formation and locality.—In the shales at the base of the Chemung group as exposed at Warren, Pa.; belonging to the upper strata of the series when considered in relation to the entire thickness of the group in New York and Pennsylvania.
ELYMOCARIS, nov. gen.
[Ἐλυμος, siliqua; χαρις, caris.]
Carapace bivalve, dorsal line nearly equaling the length of the valves. Valves elongate, longitudinally sub-quadrangular or sledge-shaped, extending posteriorly slightly beyond the hinge-line. Margins thickened, regularly curving from the anterior extremity of the hinge, making a broad sweep along the lower margin, rapidly curving around the lower posterior end, and extending to the hinge.
Cephalic region marked by a distinct optic node near the anterior end of the valve, behind which are two low, broad elevations. Thoracic portion regularly convex. Rostrum unknown.
Abdomen composed of two naked segments. Telson consisting of a short broad spine, with two strong lateral spines, which are crenulated along their inner margins for the attachment of fimbria.
Test thin and without special ornamentation in the typical species of the genus, which shows only vascular striæ along the margins of the valves, and over the segments of the abdomen.
This genus differs conspicuously from Echinocaris in the form and ornamentation of the valves, and in the number and character of the segments of the abdomen. In the outline of the valves it is very similar to Tropidocaris, and is distinguished by the absence of the strong longitudinal ridges presented by the species of that genus.
Elymocaris siliqua, n. sp.
Plate II, Figs. 1, 2.
Carapace regularly convex, pod-shaped, dorsal line straight, somewhat shorter than the greatest length of the valves. Valves elongate, longitudinally sub-quadrangular or rhomboidal in outline; lngth equal to more than twice the greatest width. Margins thickened, regularly curving outwards and backwards over the anterior end. extending in a broad curve along the lower margin. rapidly recurving around the lower posterior portion. and continuing concave and obliquely forward to the extremity of the hinge, mak- in: the hinge-line appear as slightly produced. The cephalic area occupies the anterior third of the valves, and is marked at its base by two broad flattened oval eleva- tions, of which the lower one is somewhat the larger. Optic node prominent. situated above the middle of the area.
Thoraic region convex over the anterior portion, becom- ing liattened on the posterior half. without nodes or ridges.
{{sc|Abdomen having at length of less than half that of the valves, composed of two naked cylindrical segments. The posterior segnient is one-third longer than wide, somewhat larger at its anterior end, Anterior segment partially con- cealed hy the carapace in the specimen described. The margins are slightly thickened.
Telson consisting of a stout triangular spine flattened on the ventral side. rounded above, and marked by a longitud- inal varina along the middle. Lateral spines longer than the extension of the telson, flattened; margins thickened; marked by two sharp longitudinal ridges on the dorsal face. The inner edges of the movable spines are crenulate for the attachment of setæ
Test thin, not exceeding 110 mm. in thickness, minutely xvrinkled over the surface ol' the valves. except on their margins and the abdominal segments which are ornarnented with line curving strize or vascular markings.
An entire left valve has a greatest length of 23 mm., width 10 mm., and hinge-line 20 rum. In a specimen preserving a portion of the valves with the abdomen and its apppendages the valves have :1 width of 11 mm., and the length from the distal extremity of the telson to the insertion of the abdomen with the carapace measures 20 mm.
The three specimens of this species observed, present such marked differences from any described form, that it seems advisable to arrange them under a new generic desig- nation. The presence of crenulations along the inner margins of the lateral spines of the tail show that it was fur- nished with fimbria, similar to those illustrated for Dithyrocaris neptuni, Hall, in Iillustrations of Devonian Fossils, explanation of Plates XXII, XXIII. The other characters are very different, however, from that genus, i11 the absence of an anterior sinus for the reception of the rostral plate, the want of a strong ridge on the valves, the posterior spiniform projection of the lower posterior end of the valve. and in the number of abdominal segments. The posterior spines of Dithyrocaris are not a mere prolongation of the upper snrface of the valves but are produced by the extension of the infolded thickened rim of the lower side of the valves.
Formation and locality. In the lower arenaceous and micaceous shales of the Chemung gimip, as exposed at Warren, Pennsylvania.
TROPIDOCARIS,_ NOV GEN.
[ζροπις , carrina, χαρις caris.] Carapace bivnlve, semi ovate or semi-ellipitcal in outline, obliquely truncated behind. Dorsal line straight nearly equal to the length of the valves. Valves about twice as long as wide. ornamented with one or more strong longitu- dinal ridges. Cephalic region indicated by broad, rounded elevations on the anterior ends of the valves. or by differ- ence in convexity from the remainder of the carapace. Optic node well-marked, and in the species known. is situated on one of the smaller secondary ridges. Rostrum not observed Two seginents of the abdomen are known, which are cyl- indrical and without nodes or spines. The extent of the telson and appendages has not been observed. The species described show a range of from 15 to 40 nun. in the length of the carapace.
This genus differs in the form and ornamentation of the car- apace from Ceratiocaris Its relations with Elymocaris are quite apparent in the outline of the valves and probably equal number of segements in the abdomen. The succcessive appearance of three distinct species having a similarity of ornamentations from widely separated horizons indicates a permanence of of character which is of generic importance. The three species in question also illustrate in a very satis- satisfactory manner the sucessive appearance of higher types in the same genus. Beginning-with T.bicarinata at the base of the Uheinung group as exposed at Warren. Pennsylva- nia, we have a species exhibiting but two strong longitu- tlinal ridges on each valve. Ascending in the series of rocks at the same locality, and near the uppermost beds of the Chemung group. is found T. interrupta, the valves of whit-h are eavh ornamentetl with front four to live strong rarime and several shorter intermediate ridges. Three hun- dered and fifty feet higher in the series, in sandstones of the Waverly group. occur the examples of T. allernata, which slum' a still farther increase in the number of longitudinal ridges on the carapace. and with a still greater variation from their alternating size and ornamentation.
The species of this genus are conspicuously different from Echinocaris in their more elongate valves, the strong ridges of the carapace, and in the absence of spines or nodes on the abdomen, which is also probably composed of fewer segments.
Trorpicaris Bicarinata,n.sp.
Plate 11, Figs 3-5.
Carpace elongate. senii-elliptical obliquely truncated behind. Dorsal line extending nearly the entire length of the valves. Valves quite convex transversely; length from two and one-half to three times tl1e width. In mature in- dividuals. the greatest width is across the center of the length of the valves. Anterior end pointed. Margins reg- ularly curving from the anterior extremity of the hinge. to the lower posterior end. thence rapidly curving inwards, and extending concave and slightly oblique, to the ex- tremity of the hinge-line. The margins are strengthened by a thickening of the test, forming a rounded striated ridge, which extends the entire circumference of the valves.
Cephalic region occupying about one-fourth the area of the carpace, indicated by a slight change in the convexity of the valves and by several low, obscure elevations. The valves are each ornamented with two strong, longitudinal ridges extending nearly their entire length. The ridge nearer the dorsal line commences near the apex of the valve, following adjacent and parallel to the dorsal line to the base of the Cephalic area, and then diverging, extends almost to the posterior end of the valve, at about one-third the width of the valve from the hinge. The lower ridge also starts from the apex of the valve and is slightly carved, convex to the lower margin. This latter ridge is much more elevated and stronger, than the upper one, a11d is situated midway between it and the lower margin of the valve. The optic node is at the posterior extremity of a small Carina, between the two prominent ridges, extending to the base of the cephalic area.
Surface of the carapace marked by fine sharp irregular striæ. which are more conspicuous over the cephalic area and margins of the valves than on the thoracic portion.
Abdomen cylindrical, gradually tapering to the posterior end. But two segments are known, of which the anterior has a length equal to its transverse diameter; and in the posterior segment the length is twice the diameter. Lower edges thickened, anterior margins furnished with a rim for articulation with the adjacent segment. Surface marked by curved strife, which meet along the dorsal side.
Telson short and strong, produced into a spine of which the entire length is not known. Lateral spines not observed.
Test comparatively strong on the margins of the valves. the ridges of the carapace, and the ends of the abdominal segments.
The largest valves observed have a length of 39 mm., and a width of 14 mm. A small valve has a length of 15 mm., with a breadth of about 6 mm. Two segments of an abdomen measure respectively 3.5 and 6 mm. in length.
This species is distingushed from T. interrupta and T. alternata, by having only two prominent ridges on each valve. The apices of the valves in T. interrupta mucronate, and in T. alternata ridge is stronger and and crenulated along its summit, none of which characters appear in the present species.
The description of the abdomen is taken front a specimen 2 PPP. which, although not found attached to a carapace, is referred to this species on account of the similarity in sur- face ornamentation and from its association with specimens of the carapace of this species.
Formation and locality. In shales at the base of the Chemung group, as exposed at Warren, Pa.
Tropiidocaris Interrupta, n. sp.
{{c|Plate II, Fig. 6.
Carapace semi-oval in outline, obliquely truncated be- hind. slightly mucronate in front. Dorsal line straight, somewhat shorter than the greatest length of the valves. Valves regularly convex, widest in the middle, length more than twice the greatest breadth. Lower and anterior mar- gins regularly curving to the lower posterior end of the valve, which is abruptly rounded, and from whence the margin is concave to the extremity of the hinge.
Cephalic area marked by a slightly greater convexity than the remainder of the valve, and showing two or three obscure rounded elevations. Optic spots indicated by a swelling or tubercle on one of the short ridges extending from the apex of the valves. Valves ornamented with three strong ridges which extend the entire length, and by three or four similar ridges extending more than one half the length of the valves. Also on the cephalic region there are from four to five smaller carinæ which extend less than half the length of the valve. Abdomen, telson and append- ages unknown.
Test thin, slightly thickened around the margins of the valves.
The right valve described has a greatest length of 23 mm., a width across the middle of about 10 mm., and the dorsal line measures 21 mm.
The carapace of this species somewhat resembles that of T alternata, but in that species the ridges regularly alter- nate in size and the stronger ones are ornamented with a double series of minute pits along their summits. The greater number of carinae on the valves readily distinguishes it from T bicarinala.
In its geological position this species occurs about two hundred and fifty feet higher in the Chetnung series than the beds carrying T. bicarinata, and about three hundred and fifty feet below the beds in the Waverly group. in which are found T alternata. These beds of the Chemung and Waverly groups at Warren are conformable and in uninterrupted succession.
Formatin and locality.—In soft shales belonging to the Chemung group as exposed at an elevation of three hundred feet above the Alleghany river at Warren, Pa.
Tropidocaris Alternata, n. sp.
Plate I1 Figs. 7, 8.
This species is represented in the present collections by two imperfect left valves_which do not admit of an extended description. The carapace is elongate, at least twice as long as wide. and quite convex. The cephalic region is marked by two broad, rounded elevations on the lower anterior end of the valve, and by a prominent node produced by a swell~ ing and elevation of one of the secondary ridges. which cur- ries the optic spot.
Valves furnished with seven or more very prominent, longitudinal ridges, alternating in size, and continuing the Whole length of the thoracic portion of the carapace. On the line separating the cephalic :iron these ridges are more or less interrupted. but again appear and continue appar- ently to the apex of the valve. The stronger ridges are or- namented along their summits with a double row of minute pits, while the intermediate one are simple and sharp. Ab- domen and telson unknown.
Distinguished from T. interrupta by the alternating char- acter of the longditudinal ridges of the the carapace. One of the specimens figured shows the imprint of the plates of an echinoderm which was bedded with it.
Formation and locality.—In the sztndstones of the Wa- verly group at Warren, Pennsylvania, associated with nu- merous species of brachiopda, lamnellibranchiata, gastero- poda, and other fossils.
EXPLANATION OF PLATES.
Plate I.
Echinocaris socalis,Beecher.
| Fig 1. | A small example with the abdomen directed posteriorly, in a line with the-longer axis of the carapare. |
| " 2. | A similar specimen, in which the abdomen is elevated above the dorsnln. |
| " 3. | An individual with the valves opened and the abdomen closely curving around the posterior margin of tl1e left valve. |
| " 4. | Similar to the preceding. but with the abdomen protruded in front of the valves. |
| " 5. | An example preserving the carapace and four naked segments, showing the form and ornamentation of these parts of the test. |
| " 6. | A carapace with the valves opened, showing the distinct furrow limiting the cephalic and thoracic portions, the optic spots indicated by dotted lines. and the nodose ridges and elevations ornamentingthe valves. |
| " 7. | A smaller Carapace, presenting immature characters. belonging to a young example. |
| " 8. | Fragment preserving three abdominal segments, the telson and lateral spines showing the form and ornamentation. |
| " 9. | Two segnients of another fragment, enlarged to two diameters, to show the ornamentation and nature of the articulating surfaces. |
| " 10. | A small telson with tl1e attached lateral spines, showing their form and longitudinal carinæ. |
| " 11. | A piece of shale with an impression of the caudal plate, and with one of the lateral spines, belonging to a large individual. |
| Fig. 12. | A fragment of shale preserving the remains of fifteen young individuals, nine of which are to be seen on the side represented in the figure. Chemung group ; Warren, Pa. |
Echinaris Punctata | |
| Page 6. | |
| Fig 13. | A nearly entire individual showing the form and relation of the parts, and the number of naked abdominal segments. |
| " 14. | An enrolled specimen, with the valves partially opened and the abdomen extended along the ventrum. The specimen shows in a very satisfactory manner the optic spots, the number and distribution of the nodes, and the limits of the cephalic region. |
| " 15. | id. Lateral view, showing the position of the abdomen in this example. The specimen is flattened, and does not represent the normal convexity of the valves. |
| " 16. | The ventral side of zu. specimen preserving the mandibles in situ. Hamilton group ; New York. |
| PLATE II. | |
| Elymocaris siliqua,Beecher. | |
| Page 13. | |
| Fig 1. | A specimen wanting the anterior portion of the carpace, but preserving the abdomen and telson, with its appendages. |
| " 2. | The carnpace with the valves sepearted, showing their form with the rounded elevations and optic nodes on the Cephalic portion. Chemung group ; Warren, Pa. |
| Tropidocaris bicarinata,Beecher. | |
| Page 16 | |
| Fig.3. | A carapace with the valve opened and the test somewhat broken, showing the eye-tubercles and a pair of longitudinal ridges on each valve. |
| " 4. | The right valve of a smaller individual. |
| " 5. | Two segments of the abdomen with a. portion of the telson attached, showing the form and ornamentntion of the somites. Chemumg group ; Warren, Pa. |
| Tropidocaris interrupta,Beecher. | |
| Page 18. | |
| Fig.6. | A right valve of this species showing the form and ornamentation. Chemung group , Warren, Pa. |
| Tropidocaris alternata, Beecher. | |
| Page 19. | |
| Fig. 7. | An imperfect left valve. preserving the longitudinal ridges, and showing the tubercles and optic node on the cephalic portion. |
| " 8. | A fragment of a large left valve, bearing the impress of the plates of an echiuoderm. Waverly group ; Warren, Pa. |
| Mandibles. | |
| Page 9. | |
| Fig. 9. | A specimen preserving the mannbrium, and showing the number and character of the denticles. |
| " 10. | The inner edge of a smaller example. |
| " 11. | The crown of a large specimen with the denticles well-preserved and showing its arched and lunate form. Hamilton group; New York. |
