Quarterly Journal of the Geological Society of London/Volume 33/On the Agassizian Genera Amblypterus, Palæoniscus, Gyrolepis, and Pygopterus
What is an Amhlypterus? What is a Palæoniscus? How do we distinguish them? What special reasons have we for referring any of our smaller Carboniferous fishes to the one or the other genus? These are questions to which, I fear, few collectors of Carboniferous fossils could offer very definite answers, and for the very good reason that the definitions of these two genera, which are found in the works usually consulted by palæontologists, are, it must be owned, of a somewhat unsatisfactory nature.
Gyrolepis and Pygopterus also are terms frequently met with in lists of fossils from British Carboniferous localities. But by what characters do we distinguish Gyrolepis as a genus? Or what are the special marks which justify us in assuming any of our larger Carboniferous Palæoniscidæ to be generically identical with the Pygopteri of the Magnesian Limestone and Kupferschiefer? Here, again, we shall find our subject enveloped in an obscurity which can only be dispelled by fresh and careful original observation in a field which, since the days of the illustrious Agassiz, has been comparatively little trodden.
The present communication embodies the results of my own recent investigations into these subjects, though there is room and need for much additional inquiry, as is self-evident from the nature of the remains with which we have to deal.
Amblypterus and Palæoniscus.
The definition of Amblypterus given by Agassiz in his "Tableau synoptique" is as follows:—
"Toutes les nageoires très-larges et composées de nombreux rayons, P. très-grandes; A. large; D. opposée a l'intervalle entre les V. et l'A.; point de petits rayons sur le bord des nageoires, excepté au lobe supérieur de la queue. Ecailles médiocres"[1].
Of Palæoniscus, on the other hand:—
"Toutes les nageoires médiocres, de petits rayons sur leurs bords; D. opposée à l'espace entre les V. et l'A. Ecailles médiocres; quelques espèces en ont d'assez grandes, et le corps plus large et plus court que les autres. Il y a toujours de grosses écailles impaires en avant de la D. et de l'A"[2].
Both genera are elsewhere stated to have the teeth "en brosse extrêmement fine" or "en brosse"[3]. The statement as to the absence of fulcra on the fins of Amblypterus, save on the caudal, was corrected a few pages further on, though they are here said to be "si extraordinairenient petits qu'on peut à peine les entrevoir à l'œil nu"[4]. Large azygos scales in front of the median fins are also declared to exist in Amblypterus; so that the only differences remaining between that genus and Palæoniscus are the large size of the fins and the minuteness of the fulcra in the former—differences, indeed, not of a very substantial character, as will be presently shown.
As regards the structure of the fins, their rays were believed by Agassiz to be covered with scales in some species of Palæoniscus (P. Voltzii, Blainvillei), not so in others (P. Freieslebeni), and in Amblypterus[5]—a difference which, if it did really exist, would certainly be sufficient, not to distinguish Amblypterus from Palæoniscus, but to demand the separation of the latter into two distinct genera. The scaly appearance of the fins in some so-called Palæonisci, however, is entirely deceptive, and arises solely from the form and arrangement of the minute joints of the rays themselves.
In the works of most other authors, such as Pictet, Giebel, and Quenstedt, we shall likewise fail to find any thing satisfactory as regards the discrimination of the genera in question—though Goldfuss, in 1847[6], pointed out that Amblypterus macropterus, Ag. (Bronn, sp.), possessed large conical teeth, its dentition being, therefore, not "en brosse," according to the previously received definition of the genus. A similar observation has also been more recently made by Messrs. Hancock and Atthey in the case of Palæoniscus Egertoni, Ag.[7] Agassiz himself had previously described the teeth of Amblypterus punctatus as being "en cônes obtus." The only distinction we can lay hold of at all is the large size of the fins in Amblypterus and their medium size in Palæoniscus; but in this respect the greatest differences exist in the large assemblage of species which have been referred to the latter genus. And as regards this point, the vagueness of Agassiz's own ideas is well illustrated by the arbitrary manner in which he distributed certain British Carboniferous species between the two genera; for the fins of his Palæoniscus striolatus and Robisoni are proportionally just as large, and their fulcra just as minute as those of his Amblypterus neuropterus, and one of the two species which he included under the name of Amblypterus punctatus; in fact the resemblances which those fishes bear to each other are so close that their being placed in different genera is simply inadmissible.
Only by Troschel[8] was a bold attempt made to define these genera upon strictly zoological principles, though only with partial success. He showed, however, very clearly that Agassiz's genus Amblypterus contained at least two very distinct types:—first, that of A. macropterus, in which the scales are striated, and the teeth large and conical, with an outer row of smaller ones, and for which he proposed the new generic term Rhabdolepis; second, that of A. latus, in which the scales are smooth, and the teeth minute and slender, without interspersed laniaries; and to this he limited the name Amblypterus, the character of the dentition being more in accordance with the original definition of the genus. A. Agassizii Münster, A. striatus, Ag., and A. ornatus, Giebel, he considered as probably belonging to Rhabdolepis; while, as regards A. neuropterus and punctatus, Ag., he expressed a suspicion that they might perhaps appertain to new and peculiar genera. Palatal teeth were found by him both in Rhabdolepis and Amblypterus proper; and this character he thought might possibly serve to separate Amblypterus from Padæoniscus on the supposition that they are absent in the latter. The following summaries of characters are given at the con- clusion of his paper:—
"Rhabdolepis, Troschel. Grosse conische Zähne in einer Reihe in den Kiefern; hechelförmige Gaumenzähne; Schuppen mässig und gestreift. Flossen gross.
"Amblypterus, Agass., Troschel. Zähne hechelförmige in den Kiefern; zahlreiche Gaumenzähne. Schuppen mässig und glatt. Flossen gross mil kleinen Fulcra.
"Palæoniscus, Agass. Hechelförmige Zähne in den Kiefern. Keine Gaumenzähne? Flossen mässig mit deutlichen Fulcra. Schuppen gestreift oder glatt."
The distinction here drawn between Rhabdolepis and Amblyptevus cannot be gainsaid; but as regards Palæoniscus it is simply impossible to prove the absence of palatal teeth in the large assemblage of species referred to that genus, if, indeed, in any of them, considering the state of preservation in which their heads usually occur. Other characters must then be sought whereon to found a satisfactory diagnosis, or to throw light on the question which naturally arises as to whether the Agassizian Palæoniscus may not, like his Amblypterus, include more than one generic type. Troschel, indeed, concludes his paper with the observation, "Es ist wahrscheinlich dass nach Analogie mit Amblypterus, auch die Gattung Palæoniscus in zwei Gattungen gespalten werden muss, je nachdem die Schuppen gestreift oder glatt sind."
Nevertheless, in a recent work[9], Professor J. Y. Carus has again fused together Amblypterus and Rhabdolepis, to which he also adds as synonyms Gyrolepis, Colobodus, and Tholodus. His definitions are as follows:—
"Amblyptevus, Ag. (incl. Gyrolepis, Ag., Rhabdolepis, Troschel, Colobodus, Kg., Tholodus, H. von Meyer). Schwanz kurz, Flossen gross, vielstrahlig; unterer Rand des Schwanzes mit doppelten Fulcral- reihen. Kohlenformation bis zur Trias. Arten: A. macvopterus, Ag., u. a.
"Palceoniscus, Ag. (Palæothrissum, Blainv.). Plossen nur mittelgross; Strahlen stark; Kopf gewöhnlich aufgetrieben; Fulcren wie Amblypterus. Kohle bis Trias. Arten: P. Freieslebeni, Ag., P. comptus, Ag., u. a."
Now, if by "Schwanz" is meant the caudal fin with its prolongation of the body along the upper lobe, that part is certainly no shorter in the Agassizian Amblypteri than in his Palæonisci; nor, generally speaking, is the head more "aufgetrieben" in the one than in the other. In describing the Amblypterus Agassizii of Münster, Agassiz himself states that "la mâchoire supérieure forme une saillie arrondie au-dessus de la mâchoire inférieure, saillie qui résulte probablement, comme dans les Palæoniscus, du développement considerable de l'ethmoïde. Jusqu'ici j'avais cru ce caractère exclusivement propre aux Palæoniscu, n'ayant vu que peu d'exemplaires du genre Amblypterus dont la tête fut assez bien conservée pour ne me laisser aucun doute sur sa forme"[10]. Differences of dentition being altogether ignored, we are thus thrown back on the size of the fins and the number of their rays, the unsatisfactory nature of which, as diagnostic marks, I have already alluded to; in fact, if other characters are not to be taken into account, it may become a very delicate matter to decide as to whether a given small heterocercal fish has fins large enough for an Amblypterus or small enough for a Palæoniscus!
Zoologists, however, will hardly be prepared to accept the ideas of generic comprehensiveness expressed in the reunion of Rhabdolepis with Amblypterus, any more than the location by Prof. Carus of the Palæoniscoid fishes (with the exception of Cheirolepis) among the Lepidotini as a mere "subfamily;" for if Rhabdolepis be not generically distinct from Amblypterus, neither is Palæoniscus, nor Acrolepis, nor Elonichthys, and in fact, to be consistent, nearly the whole of the Palæoniscidæ would have to be merged in one huge genus. But if, on the other hand, we are to deal (according to our information) with extinct as with living forms, then the line of investigation begun by Sir Philip Egerton and by Troschel must be continued, the generic characters of Amblypterus and Palæoniscus reinvestigated and more accurately defined, their species redistributed, and, if need be, new genera instituted for those which cannot be included in the one or the other, according to the conception of a "genus" current among modern zoologists.
The results to which I have arrived, after a careful study of a very large number of specimens of Palæoniscidæ, both British and foreign, seem to me certainly to require still further modifications of the prevalent ideas respecting the characters and limits of the genera in question, as well as those regarding the extent of their stratigraphical disibution.
Amblypterus.
The species referred to Amblypterus in the "Poissons Fossiles" certainly fall into at least five distinct types:—
I. Type of A. latus, Ag. (Genus Amblypterus, Ag., restricted). The body is rather deep; the scales smooth; the fins large and many-rayed, with minute fulcra; the dorsal placed a little further back than in the next type; the caudal powerful. The suspensorium is not so oblique as in the Palæoniscidæ in general; hence the position of the operculum is more vertical, and the gape proportionally less extensive. There is no small plate (suboperculum) intercalated between the operculum and the interoperculum. The teeth are minute and very slender; there are no large conical laniaries; hence the term "en brosse" is here more applicable than in any other genus of Palæoniscidæ.
To this type the title Amblypterus should be strictly limited as recommended by Troschel; but I must also add that I am unable to see any tangible grounds of distinction between these forms and the smooth-scaled Palæoaisci of the type of P. Duvernoyi, whose reception into the genus Amblypterus is therefore to be recommended. To this point I shall, however, return further on under Palæoniscus. A. latus and lateralis are characteristic fossils of the Lower Permian strata of Saarbrücken and Lebach; and the other species, which I propose to unite with them generically, also occur in strata of similar age in Germany, Bohemia, and France; so that Amblypterus must be deleted from the list of Carboniferous genera, in spite of the length of time during which geologists have been accustomed to look upon it as one of the characteristic forms of the Coal-period.
II. Type of A. macropterus, Ag. (Genus Rhabdolepis, Troschel). The scales are moderate, finely striated; the fins large, many-rayed, with minute fulcra; the dorsal placed nearly opposite the interval between the ventrals and the anal, the base of the ventrals not specially extended; the caudal powerful. In each jaw there is a row of stout conical laniary teeth, external to which is a series of smaller ones. The dentition, thus quite conformable to that in Acrolepis or Pygopterus, would alone be sufficient to demand the separation of these forms from the true Amhlypteri; but careful examination reveals still further differences in the structure of the head. The suspensorium is very oblique, the operculum small; and between it and the square-shaped plate hitherto considered as "suboperculum," but which I have now come to look upon as interoperculum, there is another of a narrower form (suboperculum).
For fishes of this type, which have as yet only occurred in strata of Lower-Permian age, the genus Rhabdolepis of Troschel must be maintained. The presence of the subopercular plate distinguishes this genus from Elonichthys of Giebel, the form and extent of that plate as well as the shorter base of the ventral fins from Cosmoptychius (mihi).
III. Type of A. striatus, Ag. (Genus Cosmoptychius, Traquair). The body is rather deep; the scales and cranial bones striated; the fins are large, many-rayed; their fulcra small; the dorsal is nearly opposite the interval between the ventrals and the anal; the base of the ventrals is long. The operculum is narrow and pointed below; a small triangular subopercular plate, whose anterior superior angle is produced upwards in a narrow linear process lying along the anterior margin of the operculum for some distance, is intercalated between the last-named bone and the anterior part of the upper margin of the interoperculum. The laniary teeth are sharp, conical, moderate in size, and pretty closely set, with a series of smaller teeth outside.
The peculiar characters of the Amhlypterus striatus of Agassiz render necessary the institution for it of a new genus, which I propose to denominate Cosmoptychius, being in some respects intermediate between Rhabdolepis and Elonichthys, but differing from both in the extended bases of the ventral fins. In the last respect, as well as in the form of some of the bones of the head, it resembles Cheirolepis, though of course differing very widely from that genus in other respects. As yet we are only acquainted with one species of Cosmoptychius, which has been found only in the Lower Carboniferous strata (Calciferous Sandstone series) of the neighbourhood of Edinburgh.
IV. Type of A. nemopterus (Genus Elonichthys, Giebel). The scales are moderate, striated or striato-punctate; the median fins, and sometimes also the paired fins, are large and many-rayed; their fulcra small; the rays of the pectoral articulated; the base of the ventrals not extended; the dorsal situated nearly opposite the interval between the ventrals and the anal; the caudal powerful. The suspensorium is very oblique; there is no subopercular plate intercalcated between the operculum and the interoperculum. There are large conical laniary teeth intermixed with and internal to a series of smaller ones.
To this type belong the A. nemopterus of Agassiz, and one of the two species which he confounded together under the name of A. punctatus (Poiss. Foss. Atlas, vol. ii. tab. 4 c. figs. 3 and 5). Between these and at least two others referred to Palæoniscus by Agassiz, viz. P. striolatus, Ag., and P. Robisoni, Hibbert, it is, as already mentioned, simply impossible to draw any generic distinction. The same must be also said of his "Pygopterus" Bucklandi, which resembles Pygopterus in hardly anything save its large size. Palæoniscus Egertoni, Ag., agrees also very closely, save in the structure of the pectoral fin, in which the principal rays do not commence to be articulated for a little distance from their origin. Of Amhlypterus Portlockii, Egerton, I have only seen fragments; but, so far as these go, they seem to show that this species belongs to the same type with the others named above, as probably also do Palæoniscus Brownii of Jackson and P. peltigerus of Newberry.
As these fishes can be included in none of the three genera already defined, nor yet in Palæoniscus, in the sense in which that generic term must now be employed. it remains to be inquired if they constitute a new generic type or may be received into any other genus already known. If we now turn to the genus Elonichihys of Giebel[11], we shall find that that author characterized the fishes (E. Germari, crassidens, and lævis, from the Coal Measures of Weltin, near Halle) which he referred to it, as standing in the middle between Palæoniscus and Amblypterus, allied to the former by their fulcrated fins, and to the latter by the large size of these organs, as well as by the aspect of their thick striated scales, "which remind us of certain Amblypteri." From Palæoniscus, however, he considered them to differ in the want of the "scaly covering on the fins," and from both in the dentition, which consisted of an external series of minute teeth comparable to the "Bürstenzähne" of Amblypterus, between which larger ones of a slender conical shape were seen, "wie ich dieselben weder bei den Palæonisken noch Amblypteren finde." But, unfortunately for this diagnosis, the fins of Palæoniscus are no more covered with scales than those of any other genus belonging to the family, nor are the fulcra wanting in any of the species which have been classed under Amblypterus[12], and, finally, it has been shown that more than one of Agassiz's "Amblypteri" possess large laniary teeth quite similar to those of Elonichthys. But although Giebel's conceptions of its relationship to other Palæoniscoid forms were thus somewhat imperfect, I have convinced myself, by a careful examination of the type specimens in the museum of the University of Halle, that the genus Elonichthys is quite tenable, and that to it the Amblypterus nemopterus of Agassiz and the other forms referred to above as specially allied to that species are properly referable. Though closely resembling Rhabdolepis, it differs in the absence of the subopercular plate; the operculum is also usually more largely developed; while from Amblypterus, as restricted by Troschel, the dentition and the greater obliquity of the suspensorium are obvious marks of distinction. From Palæoniscus, to which some of the species were referred to by Agassiz, it is distinguished by the large size of the fins, and by the possession of more differentiated laniary teeth in the jaws. Nearly related to Acrolepis, it differs from that genus in the anterior covered area of the scales being reduced to a very narrow margin; but from Pygopterus it is widely separated by the form of the anal fin and the structure of the pectoral. In Pygopterus the dorsal is placed nearly opposite the commencement of the anal, commencing only a little in advance of the latter, which is possessed of a remarkably extensive base, being produced posteriorly in a fringe-like manner; the principal rays of the pectoral are also unarticulated till towards their terminations. It is true that in E. Egertoni and one or two other species still undescribed, these rays are not articulated to the same extent as in E. nemopterus, &c.; but I feel rather reluctant, on that ground alone, to multiply the number of genera.
V. Type of A. punctatus, pars (Genus Gonatodus, Traquair). Under the name of "Amblypterus punctatus" three imperfect specimens of fish from the shales of Wardie, near Edinburgh, were figured by Agassiz in the 'Poissons Fossiles.' One of these is a head with the anterior part of the body (Atlas, vol. ii. pi. 4 c. fig. 4); the second (ibid. fig. 5) wants the head, shoulders, and extremity of the tail; the third (ibid. fig. 3) displays the entire caudal fin, but is obliquely cut off just in front of the dorsal and anal. But a comparison of these specimens with an extensive series of entire fishes from the same beds establishes the fact that the Amblypterus punctatus of Agassiz was founded upon fragments of two distinct fishes, the specimen showing the head, but without the hinder part of the body, being not only specifically, but even generically, distinct from the other two, in which we have the hinder part of the body without the head. The latter belong to the genus Elonichthys and to a species closely allied to E. striolatus and E. nemopterus, which I propose to call E. intermedius; but for the former the peculiarity of the dentition requires the institution of a new genus, for which I propose the name Gonatodus[13], retaining for the type species the original term "punctatus." For although the enlarged representations of scales given by Agassiz (tab. cit. figs. 6–8) are taken from one of the specimens referable to Elonichthys, yet the name is indeed applicable to both species; and as the characters of the head and teeth are those which specially distinguish Amblypterus punctatus, according to Agassiz's conception, from his A. nemopterus, with which he contrasted it as occurring in the same beds, it is, I think, more appropriate to retain his specific name for the fish of which those peculiarities are characteristic.
The peculiar dentition of Gonatodus was first correctly described by Mr. R. Walker in a fish from the shales of Pitcorthie, Fifeshire, to which he gave the name of Amblypterus anconoæchmodus[14], a species which is evidently most closely allied to the G. punctatus of Wardie, and possibly identical with it. I have, however, enjoyed no opportunity of comparing with the latter any actual specimens of the Pitcorthie fish.
The teeth of G. punctatus are from 120 to 124 inch in length in specimens measuring from 5 to 6 inches: their form is cylindrical, but suddenly narrowing near the extremity to an acutely pointed apex. Each tooth is also first inclined a little inwards, then bent outwards at an obtuse angle; finally, by another curvature, the apex conies to point upwards in the mandibular teeth, downwards in those of the maxilla. The teeth are also closely set in one row of nearly uniform size: there are certainly no larger teeth inside this row; nor have I seen any trace of smaller ones outside. Mr. Walker describes the teeth of the lower jaw of the Pitcorthie fish as "placed alternately one close to the outside margin; the next to it is fully half its own thickness further in, and so on the whole length of the bone." Of this arrangement I have seen nothing more in the Wardie specimens than occasional indications. By Agassiz the teeth of G. punctatus were described as being "en cônes obtus," an appearance due to their being only seen in antero-posterior vertical section in the specimen he examined, their peculiar flexures and pointed conical apices being there invisible. Nor do I find any evidence that they were arranged "sur plusieurs rangées," at least as far as the maxilla and dentary of the mandible are concerned, though it is probable that additional teeth were present in the palate.
The dorsal fin in Gonatodus is placed rather further back than in Elonichthys, the middle of its base being opposite the commencement of the anal: both dorsal and anal are large and triangular; the base of the ventrals is short. All the fins are composed of very numerous rays, which are closely jointed, including in that respect also the principal rays of the pectoral. The suspensorium is not so oblique as in most genera of Palæoniscidæ, but more so than in Amblypterus.
A new species of this genus (G. macrolepis, Traq.), characterized by its very large and nearly smooth scales, has recently turned up in the Blackband Ironstone of Gilmerten. As yet the genus is only known from the lower division of the Carboniferous formation in Scotland.
I regret that I have had no opportunity of forming any independent opinion as to the affinities of the Triassie species Amblypterus Agassizii of Münster, A. ornatus and latimanus of Giebel, or of that from the cupriferous sandstones of Kargala in Russia, named A. orientalis by Eichwald, and can only say regarding them that, from the descriptions given, they do not seem to belong to the genus Amblypterus as restricted by Troschel. A. Olfersi has been already referred by Agassiz himself to the Teleostean genus Rhacolepis.
Palæoniscus.
The genus Palæoniscus has been made to include an immense number of species, which are, indeed, referable to more than one generic type, some of them actually not being Palæoniscidæ at all. Authors have, in point of fact, been only too apt to refer nearly every small rhombic-scaled fusiform-shaped ganoid fish from Upper Palæozoic rocks to Palæoniscus, without inquiring too narrowly into how far its structure agrees with that of the original type of the genus, and have even sometimes overlooked distinctions of more than generic importance.
The species of Palæoniscus enumerated and described by Agassiz in the 'Poissons Fossiles' are referable to at least seven different types.
I. Type of Palæoniscus Freieslebeni, Ag. (Genus Palæoniscus restricted). The body is elegantly fusiform; the scales moderate, sculptured; the fins of comparatively small size; the dorsal situated opposite the interval between the ventrals and the anal; the rays of the pectoral are articulated; the fin-fulcra are small but easily recognizable. The suspensorium is very oblique, the operculum and interoperculum broad; the mandible is slender. The teeth are small, conical, sharp, and of different sizes, the smaller ones being more externally placed, but without specially prominent laniaries. The species here included are Palæoniscus Freieslebeni, magnus, macropomus, elegans, comptus, longissimus, and macroplithalmus. Palæoniscus, if limited to the species just enumerated, becomes intelligible as a genus; otherwise it seems to me, as already stated in the preliminary part of this paper, that the conception of a Palæoniscus becomes so vague that no tangible ground of distinction can be found between it and Amblypterus and many other genera of the family. It is most closely allied to Elonichthys; but from that genus it is distinguished by the small size of the fins, and by the dentition, in which the differentiation of "laniaries" has not proceeded so far. The teeth, however, are not "en brosse," as described by Agassiz, though their small size sufficiently accounts for his use of the term; probably, also, they were not very perfectly exhibited in the specimens then at his disposal; indeed in those from the German Kupferschiefer they are rarely seen at all. Agassiz's description of them as being "en brosse," and also "si excessivement petites qu'il est très-rare de pouvoir les distinguer"[15], has been rather severely criticized by Messrs. Hancock and Atthey; it must, however, be borne in mind that the species (Egertoni) in which they correctly described the teeth as being "disposed in two distinct rows, one within the other, much in the same fashion as in Megalichthys and Rhizodopsis, but still much more like that which obtains in Pygopterus, in which the teeth are likewise arranged in two rows—one being of large laniary teeth, the other of small external ones," is not a true Palæoniscus, but is more properly referable to Elonichtliys. The passage referred to was also written by Agassiz in special reference to the species occurring in Continental Permian strata, and before he became acquainted with those Carboniferous forms with conspicuous laniaries which he somewhat incorrectly referred to the same genus.
As above restricted, the genus Palæoniscus must meanwhile be considered as limited to the Permian formation, though it has hitherto been looked upon as common also to the subjacent Carboniferous rocks. It will presently be seen that the so-called Carboniferous Palcæonisci all belong to types essentially distinct from that of P. Freieslebeni.
II. Type of Palæoniscus Duvernoyi, Ag. (Genus Amblypterus, Ag.). This includes fishes with mostly rather deep bodies arcuated in front of the dorsal fin, which is situated rather further back than in the true Palæonisci; the median fins are large; the tail large and powerful; the scales usually smooth; the suspensorium only slightly oblique; the teeth probably very minute. There must be included (besides the Agassizian species P. Duvernoyi, wratislaviensis, and lepidurus), the P. dimidiatus, elongatus, tenuicauda, gibbus, and opisthopterus of Troschel, the P. Gelberti of Goldfuss, the P. decorus, arcuatus, and Beaumonti of Egerton, and, I think, also the P. Rohanni, caudatus, obliquus, Reussii, and luridus of Heckel. P. minutus, angustus, Voltzii, and Blainvillei of Agassiz seem to be allied forms, though the latter especially may possibly be the type of still another genus.
Between these species and the smooth-scaled Amblypteri of Saarbrücken and Lebach I can, as already stated, see no tangible grounds of generic distinction, though in some (e.g. P. decorus) the fins are rather smaller and their fulcra more prominent. But the slight obliquity of the suspensorium, the general form of the body, the position of the fins, and the aspect of the squamation are similar in all. As regards the scales, they are mostly smooth, or show only slight concentric lines; in some, however (e.g. P. Gelberti, P. Beaumonti), those of the front of the flank display a certain amount of ornamentation. They are certainly not Palæonisci in the strict sense of the term: and until at least their cranial structure and dentition are more fully elucidated, they are better classed with Amblypterus than with any other genus. Giebel had, indeed, previously proposed to transfer P. Duvernoyi to Amblypterus, but, unfortunately, on the untenable ground that the fulcra were absent in it except on the upper lobe of the tail.
All these species are from strata similar in age to the beds at Saarbrücken &c., in which the typical Amblypteri occur, and which are now referred by continental geologists to the Lower Permian (unteres Rothliegendes). Even the fish-bearing schists of Autun, characterized by Palæoniscus Blainvillei, have ceased to be reckoned as appertaining to the 'Terrain houiller.'
III. Type of P. striolatus, Ag. (Genus Elonichthys, Giebel). Here are included P. striolatus, Robisoni, and Egertoni, fishes with large median fins, sculptured scales, powerful tail, very oblique suspensorium, and, as regards the dentition, possessed of a row of distinct conical laniaries internal to a series of smaller teeth. It is difficult to conceive why Agassiz placed these species in the genus Palæoniscus, while at the same time he described, as has been already shown, certain closely allied forms from the Wardie shales as Amblypteri. They are all, in my opinion, referable to the genus Elonichthys of Giebel. (See also under type of Amblypterus nemopterus, p. 553.)
IV. Type of Palæoniscus ornatissimus, Ag. (Genus Rhadinichthys, Traquair). I had long suspected that a very beautiful species from Burdiehouse was identical with the P. ornatissimus, Agassiz; and a few days ago I obtained two of the original specimens of that species, and found that one of them, at least, certainly confirmed my opinion. It is the type of a group including P. carinatus, Ag., a species described from a very imperfect specimen from the Wardie shales now in the museum of the Royal Society of Edinburgh. Examples in a much better state of preservation, however, have subsequently turned up in the same locality. The body is slender, elegantly shaped; the scales are rather large, especially on the flank; the median fins are large in proportion to the size of the fish; the dorsal is situated nearly opposite the anal; the caudal body-prolongation is delicate. I have had no satisfactory view of the dentition or of the structure of the pectoral fin in this species; but its general aspect leads me to class it along with the Palæoniscus ornatissimus, Ag., and Palæoniscus Wardii, of Prof. Young, recently briefly described by Mr. Ward, of Longton[16], as constituting a new genus, Rhadinichthys. The characters of generic importance displayed by the two last named species are as follows:—The body is comparatively slender; the suspensorium is very oblique; the jaws are armed with a row of incurved conical laniaries, outside which there is a series of smaller teeth; the principal rays of the pectoral fin are, as in Pygopterus and Oxygnathus, unarticulated till towards their terminations; the dorsal is situated rather far back, nearly opposite the anal; the caudal body-prolongation is comparatively delicate. There are, besides these, several other new species from British Carboniferous strata referable to this type, the description of which I hope soon to be able to overtake; in some of these the scales are nearly smooth, as in R. carinatus, in others elaborately ornamented.
Palæoniscus Albertii, of Jackson, seems to me to be allied to R. carinatus; but more especially so, judging from the drawings, is his P. Cairnsii, and some of the other small Palæoniscidæ from the Coal Measures of New Brunswick, figured, but not described, by the same author[17]. All the species which I propose to include under Rhadinichthys are from Carboniferous strata.
The three remaining types included by Agassiz in Palæoniscus must be altogether excluded from the family Palæoniscidaæ.
V. Type of Palæoniscus fultus, Ag. (Genus Ischypterus, Egerton). This Triassic species, in which the caudal body-prolongation is considerably more reduced than in the Palæoniscidæ, the tail consequently showing the first approach to the semiheterocercal form, and whose general structure, including the osteology of the head, betrays a strong affinity to Semionotus, has been already separated by Sir Philip Grey-Egerton under the name of Ischypterus[18]. Besides Ischypterus fultus, Ag., sp., there are here included I. Agassizii, I. macropterus, I. latus (=Eurynotus tenuiceps, Ag.), and I. ovatus of W. C. Redfield, species originally referred by that author also to Palæoniscus, though he was not unaware of their essential differences from that genus, and of the likelihood of their being eventually separated. For in alluding to the stout character of the fins and their insertions, whence the specific name fultus, given by Agassiz, he says that "this character is also found to pertain in a greater or less degree to all the American species of the genus, and would perhaps warrant their separation from the Palæonisci"[19]. He notices, further, the great strength of the fulcra, their comparatively small number, and unequal length and inclination, and, as regards the tail, that the scales of the body are prolonged into the upper lobe, "but to a more limited extent than in the European species of the genus." The small extent of the gape has also been mentioned by Sir Philip Grey-Egerton.
Ischypterus was classed by Sir Philip Grey-Egerton among the Ganoidei Heterocerci (= Lepidoidei Heterocerci, Ag.) along with Palæoniscus and Amblypterus; more recently, however, it has been, by Prof. J. V. Carus, disassociated from the Palæoniscidæ and placed among the Sauroidei as remodelled by Dr. Andreas Wagner. But as I have hitherto seen no detailed account of its structure, I may here give a few particulars concerning I. latus, which will clearly show how widely this genus deviates, not only from Palæoniscus, but from the entire group of Palæoniscidæ.
In Ischypterus the body is rather deep, and strongly arcuated in front of the dorsal fin; the scales are rhomboidal and smooth; but along the middle line of the back, from the occiput to the dorsal fin, there extends a row of peculiarly shaped median scales, like those in Semionotus Bergeri, Ag., and Lepidotus minor, Ag., these being somewhat spur-shaped, with posteriorly directed points, and imbricating over each other from before backwards. They were pointed out by Mr. W. C. Redfield, who says of them that they were "sometimes mistaken for an anterior comblike dorsal." The caudal fin is comparatively short and small; it is hardly cleft, being only somewhat concave behind, and is, moreover, nearly symmetrical in external form, the upper projecting point only passing a little further back than the lower. The prolongation of the body-scales along the upper margin of the fin is very narrow and rapidly attenuating, and, although it reaches nearly to the extremity of what may be called the upper lobe, is very short, owing to the shortness of the fin itself. The rays are comparatively few in number, those of the upper lobe gradually diminishing in length towards its extremity; and the fulcra, which run along the margin of the lower lobe, are nearly as strong as the V scales, usually also called fulcra, which border the upper one above. Though this form of tail cannot be called "homocercal," inasmuch as a scaled prolongation of the body does extend nearly to the point of the upper lobe, yet, from the shortness, feebleness, and attenuation of this prolongation, along with the striking reduction of the number of the fin-rays of that upper lobe, it is not heterocercal to the same extent as in Palæoniscus or Acipenser. It seems, indeed, to furnish us with the first step in the transition from the typically heterocercal tail to such semiheterocercal forms as in Lepidotus, Dapedius, Pholidophorus, &c, in which the body-prolongation is proportionally shorter still, and the rays of the upper division of the fin extend considerably beyond it. In the other fins the rays are distant compared with those of Palæoniscus, and unarticulated for the greater part of their length; the fulcra of their anterior margins are enormously large, and correspondingly few in number, being totally unlike any thing we find in the Palæoniscidæ, though much reminding us of those in some species of Semionotus and Lepidotus. Though the notochord was probably persistent, there are obvious remains of strongly developed spinous processes, interspinous bones, and ribs, the latter being apparently totally absent in the Palæoniscidæ. The bones of the head are, unfortunately, very badly preserved in all the specimens of Ischypterus which I have had the opportunity of examining; they display, however, enough to render certain the following essential points of structure. The line of the top of the head slopes very rapidly from the occiput downwards and forwards to the snout, which, in profile, appears rather sharp, and does not form the peculiar nasal prominence over the mouth seen in Palæoniscus and its allies. The opercular bones are conformed quite according to the type characteristic of the Mesozoic Ganoids and modern Teleostei. The operculum and suboperculum are rather narrow; the praeoperculum, passing first downwards, curves then gently forwards, carrying the articulation of the mandible to a point in front of the upper attachment of the suspensorium; the interoperculum is also distinctly visible as a small triangular plate with anteriorly directed apex, and placed in front of the lower part of the suboperculum and below the anterior extremity of the præ- operculum. The gape is small; the configuration of the maxilla I have not been able to determine; but the mandible is stout and short and has its dentary margin set with a row of equal-sized, small and rather bluntly conical teeth. In one specimen I have seen similar teeth, apparently in more than one row, in the upper part of the mouth; but, from defective preservation, it is hardly possible to tell on what bone they are situated. The orbit has not the remarkably anterior position characteristic of the Palæoniscidæ, but is situated nearly right above the articulation of the lower jaw. Beyond pretty distinct indications of frontals and parietals, and of a powerfully developed parasphenoid, no further details of the osteology of the head are revealed by such specimens of Ischypterus as I have had at my disposal.
The few details given above render it, however, perfectly evident that the affinities of Ischypterus are not with Palæoniscus, but that it must, on the other hand, be looked upon as the most heterocercal of that great series of Lepidosteoid Ganoids especially characteristic of Mesozoic times, and of which Lepidotus, Semionotus, Dapedius, Pholidophorus, &c. are prominent examples. To two of those, already referred to, its resemblances are especially striking, viz. to Semionotus Bergeri, Ag.[20], of the German Keuper, and Lepidotus minor of the English Purbeck.
Fishes of this genus occur in the Triassic strata of North America; it is also said to have been found in the Lower Permian schists of Autun, in France[21].
VI. Type of Palæoniscus glaphyrus, Ag. (? Genus Acentrophorus, Traquair). I have not seen the type specimen of this rare species from the English Marl Slate; but, to judge from the figures given in the 'Poissons Fossiles'[22] and in King's 'Permian Fossils'[23], the conclusion seems unavoidable that it is neither a Palæoniscus nor a member of the family of Palæoniscidæ. Certain suspicious details occur in Agassiz's description—for instance, that the mouth is "très-petite," also that the fulcra "diffèrent de ceux des autres espèces en ce qu'il sont plus allongés et moins serrés contre le bord des nageoires." This latter condition is very distinctly represented in the figure of the species, in which we also miss the prominent heterocercy characteristic of the Palæoniscidæ: in fact the entire aspect of the fish, as there delineated, is eminently suggestive of its affinity to the three little species from Fulwell Hill, Durham, described by Mr. Kirkby as Palæoniscus varians, Abbsii, and altus[24], but whose reference to that genus is certainly erroneous. Until, however, the type specimen is reexamined, it would be unsafe to pronounce as to the generic identity of P. glaphyrus with these last-mentioned forms: at least one marked distinction is found in the denticulation of the scales in the former, a difference which may possibly be only of specific importance.
But as regards the non-palæoniscoid nature of the Fulwell-Hill fishes there cannot be the smallest doubt: and although these species are not Agassizian, it may not be altogether out of place here to devote a little more attention to them than a mere passing reference. That they are not Palæonisci has been already pointed out by Dr. Lütken, of Copenhagen, in the following terms, "But already in the Dyas we find, alongside of a preponderating number of heterocercal forms, a few half-homocercal ones." And in a footnote appended to the same passage he says, "as, for example, Palæoniscus Abbsii, varians, and altus from the English Permian formation, which should be expelled from the genus Palæoniscus (like the North-American Triassic species, also previously referred to Palæoniscus, which are now called Ischypteras, Catopterus, Dictyopyge, &c), as they do not show a complete heterocercy, but only an indication or approximation to it"[25].
A glance at the beautiful plate by Mr. Dinkel, with which Mr. Kirkby's paper in the 'Quarterly Journal' is illustrated, is in itself quite sufficient to raise in one's mind the gravest doubts as to the accuracy of the position assigned by that author to the little fishes in question. However, having been, by the kindness and liberality of the Earl of Enniskillen, furnished with the loan of a beautiful series of specimens, and having also examined those in the British Museum and in the museum of the Royal Dublin Society, I am now in a position to go into the question more in detail, and with the result of finding the decision so briefly expressed by Dr. Lütken most fully substantiated.
The three species described by Mr. Kirkby are very like each other, save in the general contour of the body; so that the following observations, though principally made on specimens of Palæoniscus varians, will apply also to the other two as far as essential points of structure are concerned.
The caudal fin of P. varians so closely resembles that of Ischypterus that it would, indeed, be impossible to draw any generic distinction between them from that part alone. It is, compared with that of Palæoniscus, short and feeble, few-rayed, nearly symmetrical in external outline, and hardly cleft; the rays of the upper lobe gradually diminish in length towards its extremity. The caudal body-prolongation is, as in Ischypterus, much reduced, becoming very rapidly narrow and delicate, though its scales may be traced nearly to the extremity of the short upper lobe of the fin. The caudal fin, however, is not the only one which shows a marked deviation from the Palæoniscus type. It at once strikes the eye that the fulcra in front of the dorsal and anal fins are fewer in number, set at lower angles, and very much larger and stronger than in any of the Paæeoniscidæ—that they are, in fact, proportionally nearly as powerfully developed as in Ischypterus, though they diminish in size more gradually, from the origin to the apex of the fin, than in the latter genus. Behind the margin of strong fulcra only about ten rays are counted in the dorsal, and eight in the anal; these are rather distant save just in front, and for a considerable distance show no transverse articulations. The paired fins are very small and few-rayed; and in like manner the fulcra along their margins are strong beyond any thing met with in the Palæoniscidæ.
The osteology of the head shows a still more marked deviation from the type of structure in the Palæoniscidæ. The opercular bones are very distinctly seen in most specimens, and totally differ in form and arrangement from those in Palæoniscus, though closely resembling the corresponding bones in Lepidotus and other Mesozoic genera. The entire opercular apparatus has an evenly rounded posterior margin; the operculum and suboperculum are large, and of nearly equal area, being divided by a line running obliquely upwards and backwards. In front of the lower end of the suboperculum, a small but very distinct interoperculum is seen, of a triangular shape, with anteriorly directed apex. The præoperculum, which does not cover any portion of the cheek, shows a distinct upper and lower limb, the upper being nearly perpendicular, and curving round below into the lower, which, passing forwards, carries the articulation of the lower jaw considerably in front of the upper extremity of the suspensorium. The jaws are comparatively feeble, and the mouth very small. The mandible has quite a different shape from that in Palæoniscus, being, of. course, considerably shorter, and seems to form the immediate margin of the mouth only towards its extremity, which is bent a little downwards. The maxilla is especially feeble, extending only to about half the length of the mandible, and is absolutely unlike that in any of the Palæniscidæ, as it stops short just before the orbit, and ends with a rounded spatulate extremity, which overlaps the mandible considerably in front of the quadrate articulation of the latter. Mr. Kirkby makes no mention of teeth; nor have I discovered any; nevertheless it would be hardly safe to conclude that the jaws were edentulous. The branchiostegal rays are few in number, about seven on each side; the posterior ones are rather long, narrow, and gently curved; but they become rapidly shorter in front. In one specimen, compressed upon its back, a space is seen just behind the symphysis of the mandible, and in front of the branchiostegal rays of each side, which was probably occupied by a large median "jugular" as in Dapedius, Engnathus, &c, and in the recent Amia. The bones of the cranium proper are not well seen, owing to their delicacy, and to the crushing which they have undergone; the ethmoidal region is usually wanting or undecipherable as to its component parts. The frontals are almost always distinct as two well-marked roof-bones, broader behind than before, their outer margins being excavated in front for the orbits. Two shorter parietals succeed the frontals behind; and there are evident traces of a squamosal plate on the outer side of each parietal, above the suspensorial articulation, though the operculum is usually crushed down over this region of the skull. There are faint traces of small plates completely surrounding the orbit, which was placed nearly right over the articulation of the lower jaw instead of being considerably in front of it as in Palæoniscus. Traces also of the palatoquadrate arch are seen in many specimens; but it is hardly possible to make out its constituent bones; a well-marked quadrate, however, is distinct enough. The direction of the suspensorium is undoubtedly considerably forwards as well as downwards.
Of the elements of the shoulder-girdle, the posttemporal and supraclavicular are so generally covered and obscured by the opercular bones that a description of them is hardly possible. The clavicle, however, is usually well seen, and differs greatly from that in the Palæoniscidæ. It is a comparatively slender bone, bent forwards at a very obtuse angle about its middle; the lower extremity is pointed and comes in contact with its fellow of the opposite side; there is no trace of any infraclavicular, so constant and prominent an element in the shoulder-girdle of all the Palæoniscidæ.
The scales of the body are smooth ; and those of the flank remind us, in their form, more of the scales of Pholidophorus than of Palæoniscus.
These details render it sufficiently evident that the fishes entitled, by Mr. Kirkby, Palæoniscus varians, Abbsii, and altus belong neither to the genus Palæoniscus, nor even to the family of Palæoniscidæ. The differences of structure between them and all the other genera which may be included in the last-named family are, indeed, so strong that I am a little surprised to find him comparing Palæoniscus varians with such forms as P. Voltzii, angustus, and wratislaviensis—species which, if they cannot be included in the genus Palæoniscus as now restricted, most obviously belong to the Palæoniscidæ. Palæoniscus fultus and P. glaphyrus are also mentioned as allied, especially the latter; and here I am able most fully to agree with the author; for P. glaphyrus seems, indeed, to be closely related to, if not generically identical with, the little fishes in question. But if that be the case, then it also, as already mentioned, must cease to be regarded as having even family relations with Palæoniscus. But, as regards Palæoniscus fultus, Mr. Kirkby seems to have overlooked the fact that as far back as 1847 it was transferred by Sir Philip Grey-Egerton to a new genus, namely Ischypterus; and I have above shown how widely this genus differs from the Palæoniscidæ in most essential points of structure. It is, in fact, not the type of Palæoniscus, but that of Lepidotus and its allies, which rises before the mind on the contemplation of the structural details of these fishes along with their entire aspect. And it is precisely with this American genus Ischypterus that Mr. Kirkby's fishes display the greatest possible affinity—in the structure of the tail, of the fins, and in the osteology of the head, so far as that can be made out in the genus just named. A difference of decided generic value, however, is to be found in the absence, in the Fulwell-Hill fishes, of the median row of spur-shaped scales along the back, so prominent in Ischypterus; and in reference to this distinction, I propose the new generic term Acentrophorus for the Palæoniscus varians, Abbsii, and altus of Kirkby. Whether or not Palæoniscus glaphyrus of Agassiz is also inclusible in this genus, can only, as aforesaid, be accurately determined by a reexamination of the type specimen; but that it also is not related to the Palæonisci is meanwhile pretty clear to my mind.
VII. Type of Palæoniscus catopterus, Ag. (? Genus Dictyopyge, Egerton). This little species, from the Triassic Red Sandstone of Phone Hill, co. Tyrone, was originally named by Agassiz, but was not described by him. Sir Charles Lyell, however, in referring to it in connexion with certain American Triassic forms, says concerning it:—"The Irish Palæoniscus catopterus of Roan or Rhone Hill, referred by Col. Portlock to the Trias, is a true Palæoniscus, and not allied generically either to the Ischypterus of Egerton or the Catopterus of Redfield"[26]. And in Sir Philip Grey-Egerton's brief description of the species[27] occurs the following passage:—"The dorsal fin is placed much nearer the tail than in any other species; in this respect, but in no other, Palæoniscus catopterus resembles the genusCatopterus of Mr. Redfield. The tail is decidedly heterocerque." The eye is also said to be placed forwards, the mouth to appear small, the operculum to be nearly semicircular.
The smallness of the mouth would in itself be considerable presumptive evidence against the affinity of this species with Palæoniscus, in which the gape is enormously extensive, as it is also, more or less, in the entire family; it displays, however, another peculiarity which conclusively shows that the position hitherto assigned to it is incorrect.
However, the specimens usually seen in collections are almost always in so bad a state of preservation, from their very friable nature, that it is not astonishing that such eminent naturalists as Agassiz, Lyell, and Grey-Egerton should have fallen into error as regards its affinities; indeed they are ordinarily so rubbed and abraded that in many cases it is barely possible to determine that they are the remains of small ganoid fishes. But in the Museum of Practical Geology, Jermyn Street, there is one rather good specimen, and in the collection of the Geological Survey of Ireland there are several others, on examining which I was not a little surprised to find that the tail is not that of Palæoniscus. The fin-rays are, as in the Palæoniscidæ, closely set and articulated throughout, their fulcra being small and numerous; and the tail is deeply cleft and somewhat inequilobate. But the body-scales stop short in a little rounded "sinus," which projects only a very short distance up into the base of the upper lobe of the caudal fin, and is then followed by rays which are just as elongated as those of the lower lobe. The tail is therefore much less heterocercal than in Ischypterus or Acentrophorus, in fact not more so than in Lepidotus; so that the retention of this little fish in the family Palæoniscidæ is no longer possible.
Are we, however, to consider it as the type of a new genus, or can it be received into any previously known? This question can only be answered to complete satisfaction when fresh specimens are discovered from which the structure of the head can be more fully made out; and, unfortunately, since the first "find," none have come to light either in the original or in any other locality. Meanwhile, if we turn to the figure of Dictyopyge macrura (Catopterus macrurus, W. C. Bedf.), from the Virginian Triassic strata, given in the previously quoted memoir by Sir Charles Lyell, we shall find that there is a very obvious correspondence between it and the Rhone-Hill fish in the form of the tail, and in the structure and position of the fins—so much so that the probability of their belonging to the same genus seems to me very great. Still greater is the resemblance which it bears to the Dictyopyge socialis of Strüver, from the Keuper Sandstones of Coburg[28], for an opportunity of examining actual specimens of which I am indebted to the kindness of Prof. von Seebach, of Göttingen. Until therefore the cranial osteology and the dentition of these forms is better known, I would propose that the Palæoniscus catopterus of Agassiz be included in the genus Dictyopyge of Sir Philip Grey-Egerton. Of the closeness of the alliance there can be hardly a doubt; so that the relationship of this little fish to the American Triassic genus Catopterus is not so distant as has been supposed[29].
Gyrolepis.
In the "Tableau synoptique des genres et des espèces," given at the beginning of the second volume of the 'Poissons Fossiles,' this genus is referred to in the following terms:—
"Le genre Gyrolepis, Agass., n'étant établi que sur quelques écailles, est encore douteux. Ce qui le distingue, c'est que les stries d'accroissement forment des saillies concentriques à leur surface." Three Triassic species are here included, viz. G. maceimus, Ag., G. tenuistriatus, Ag., and G. Albertii, Ag., along with one from the Kupferschiefer, G. asper, Ag. Further on in the same volume (p. 172), in a more special description of the genus, Agassiz again owns that, having found only detached fragments, non-coherent scales, and even these rarely entire, the special characters of the genus are not satisfactorily established. Meanwhile, he says "l'aspect de ces écailles est tel, qu'il serait impossible de les rapprocher d'aucun des genres que j'ai déja décrits. La surface extérieure des écailles est ornée de grosses rides, tantôt concentriques et parallèles aux lames d'accroissement, tantôt obliques et irrégulièrement ramifiées. J'ai cru pendant quelque temps que ces rides étaient toujours concentriques; mais plus tard je me suis assuré qu'elles étaient souvent aussi disposées en peignes irrégulières." Certain dentigerous fragments found along with the scales are also, with some doubt, referred to the same genus; the teeth on them are described as being small and "en forme de cônes obtus dont l'extrémité est arrondie, et qui sont disposées comme dans la famille des Pycnodontes sur toute la surface des os qui les portent." G. asper (Palæoniscus Dunkeri, Germar) is now referred to the genus Acrolepis; but another species, G. giganteus, is added from the Old Red Sandstone of Scotland. Finally, in the general list of Ganoids from the various formations published in 1843, and appended to the beginning of the second volume, G. Rankinei, from the Coal-measures of Leeds, is named though not described, and G. giganteus is transferred to the genus Holoptychius. The latter is described in the 'Poissons fossiles du vieux Grès Rouge' (1844), p. 73.
Another species of Gyrolepis, from the German Muschelkalk, was described by Münster under the name of G. biplicatus, characterized by the possession of two strong parallel ridges on the outer surface of the scale.
But in 1848 Giebel announced that he had discovered the scales known as Gyrolepis Albertii, Ag., and G. biplicatus, Münst., in great numbers, and on the same slabs with dentigerous and other cephalic bones referable to Colobodus, a genus instituted by Agassiz for certain tooth-bearing fragments (C. Hogardii, Ag.) from the Muschelkalk, and referred by him to the family of Pycnodonts. Gyrolepis tenuistriatus, Ag., on the other hand, was referred by Giebel to Amblypterus. He therefore proposed the total abolition of the genus Gyrolepis, uniting and renaming the species G. Albertii and biplicatus as Colobodus varians, Giebel[30], and in like manner the species G. tenuistriatus and maximus as Amblypterus decipiens, Giebel[31], and in each case apparently without the smallest regard to priority of specific nomenclature. The accuracy of Giebel's reference of the two former species to Colobodus was questioned by Eck[32].
Quenstedt, in his 'Handbuch der Petrefactenkunde.' agrees with Giebel as to the reference of G. Albertii and G. maximus to Colobodus; Tholodus, v. Meyer, he also considers as belonging to the same type, but is inclined to consider these forms as related, not to the Pycnodonts nor to the heterocercal Ganoids, but to Lepidotus[33]. In the same work he expresses himself in a rather guarded manner regarding the reference of G. tenuistriatus to Amblypterus[34].
The doubtful nature of the characters of Gyrolepis is thus referred to by Sir Philip Grey-Egerton in his paper on the "Ganoidei Heterocerci:"—"The scattered and fragmentary condition in which the remains of this genus have always been found has proved hitherto an insurmountable obstacle, not only to a definition of its generic characters, but to a determination of the family in which it ought to be placed. It is not even known whether the tail was homocerque or heterocerque—a point of some importance as bearing upon the value of this character as a criterion of the age of strata, since some of the species are confined to the Triassic period"[35]. Subsequently, however, Sir Philip expressed an opinion that in Gyrolepis "we have probably a heterocerque fish"[36].
More recently Dr. Karl Martin has advocated the view that the Triassic scales known as Gyrolepis belong to Saurichthys, "because the strongly marked sculpture of their surface (like the condition of the teeth of Saurichthys) reminds us of that of the scales of Acrolepis, and because hitherto neither teeth have been found which could correspond to these scales of Gyrolepis, nor other scales which could be ascribed to the teeth of Saurichthys." Saurichthys itself is referred by Martin to the family Palæoniscidæ on account of the resemblance which the teeth and a fragment of a maxilla figured by him bear to those of Acrolepis asper[37].
Finally, as I have already mentioned (p. 550), Prof. Victor Carus has not only reunited Rhabdolepis, Troschel, to Amblypterus, Ag., but has added, as synonyms of the latter, Gyrolepis, Colobodus, and Tholodus. I need not again point out how inconsistent it is with the prevailing ideas of the limits of a genus to reckon as congeneric with such a fish as Amblypterus latus scales like those known as Gyrolepis, or teeth like those of Colobodus or Tholodus.
From the preceding sketch of its history it is abundantly clear that at present all definition of Gyrolepis as a genus is impossible; and under the circumstances it does seem to me better to follow the example of Giebel in cancelling the term altogether. As regards the Triassic species which have been so named, I must necessarily leave the final determination of their position to continental palæontologists. But, as to the use of the name Gyrolepis in catalogues of British Carboniferous fossils, there can, I think, be no doubt as to the propriety of its entire abolition; for, unless the Triassic scales to which the name was originally given are really referable to Acrolepis, there is no Carboniferous fish of which we have the smallest evidence that it belongs to the same genus with them. What, then, is the real nature of the one Carboniferous species which has been definitely named Gyrolepis, but which has hitherto remained undescribed?
The name Gyrolepis Rankinei occurs in Agassiz's general list of fossil Ganoids, the formation and locality quoted being the Coal- measures of Leeds. Neither description nor figure is given; and the original specimen seems now, unfortunately, to be lost or unknown. But in Morris's 'Catalogue of British Fossils ' (p. 273) Lanarkshire is given as an additional locality for this species; and on inquiring of Dr. Rankin, of Carluke, and Mr. Grossart, of Salsburgh, in that county, I learn that Agassiz, when in Scotland, also designated as G. Rankinei a specimen in Dr. Rankin's collection. To these gentlemen I am indebted for the opportunity of examining portions of the original Lanarkshire specimen, along with others referable to the same species—and to Dr. Hunter, of Braidwood, for the loan of a magnificent slab covered with its scales, bones, and fin-rays from the shale underlying the "Main Limestone" (Lower Limestone series) of that locality. All the specimens which have as yet been found have been fragmentary, consisting only of detached scales and bones, or of masses of scales either confused or adhering together to some extent in their original rows. Dr. Hunter's slab measures 20 inches in length by 11 in breadth. It displays, in the first place, a number of bones the forms of such of which as are determinable stamp the fish at once as a member of the family Palæoniscidæ. Among these may be recognized the median superethmoidal, which in this family forms the anterior projection of the snout over the mouth: and tying near it is the impression of a bone, 4 inches in length, which displays the characteristic form of the Palæoniscid maxillary. No impressions of teeth are seen; it is therefore unfortunate that the counterpart of the specimen could not be found, as the bony substance of the maxilla has evidently remained on it, the teeth not having been exposed. The lower portions of both clavicles are also seen; and the dimensions of these are such as to lead one to suppose that the length of each, when entire, could not have been less than five or six inches. The external ornamentation of all these bones is of a tubercular nature, the tubercles sometimes finer, sometimes coarser, occasionally showing a tendency towards a linear arrangement or to coalesce into short ridges.
Besides the numerous scattered scales which occur in the slab, there are two large patches in which the scales still cohere together in rows. One of these patches evidently represents a portion of the skin of the front of the flank, the position of the other being further back towards the caudal region. These flank-scales are large; one of the largest of them is 58 inch in breadth; its exposed and ganoid area is nearly equilateral, measuring about 716 inch in breadth and in height; this area is rhomboidal, but not acutely so, and is obliquely traversed by strong subparallel ridges, which proceed in a direction from above, downwards and backwards, occasionally branching and anastomosing, or, where two diverge, another being intercalated between, there being, on an average, five such ridges in the space of 18 inch. The anterior covered area overlapped by the scale in front is extensive, being 316 inch in breadth; its lower margin is more oblique than that of the sculptured portion, with which it consequently forms an obtuse angle; above it is produced into a prominent pointed process, where it coalesces with the narrower covered area of the upper margin, overlapped by the scale next above. From the middle of the upper margin there projects, in addition, the proper articular peg of the scale, stout and triangular in form. Near these scales are scattered others which were evidently situated towards the ventral aspect of the fore part of the fish. These display a similar sculpture of the exposed area; but their form is lower, narrower, and more oblique; the articular peg of the upper margin has disappeared; but the anterior superior production of the covered areas is proportionally longer and more acute. The scales of the other coherent patch are smaller in size, and more obliquely rhomboidal in form, as regards the exposed surface ; they are further distinguished by the absence of the articular peg of the upper margin, and by the much greater narrowness of the covered areas, which are not specially produced upwards and forwards. Their thickness is also very considerable, being no less than 18 inch in one of these scales entirely detached from the matrix, and measuring about 12 inch in breadth. A difference is also observable in the sculpture of these posterior scales, viz. a tendency of the ridges to coalesce in a reticulating manner towards the posterior, superior, and interior-inferior obtuse angles of the scale, so as to interrupt the intervening furrows in these two regions, converting them more or less into pits.
The specimen also exhibits, as already mentioned, many detached and broken-up, transversely jointed fin-rays, some of which attain a breadth of 18 inch; the length of their joints is somewhat less, but varies in different rays. These rays are all seen only from their internal non-ganoid surfaces.
As already stated, it is quite evident that the fish to which these remains belonged is a member of the family Palæoniscidæ; and the form and thickness of the scales, with their very large anterior covered area, and the nature of their sculpture, along with the peculiar tubercular ornamentation of the cephalic and shoulder-bones, point out, as it seems to me, that Acrolepis is the genus to which it should be referred. The scales of the Permian A. Sedgwickii are quite similar in shape, though proportionally smaller and with fewer ridges. The tendency to reticulation of the ridges on certain parts of the posterior scales of the Lanarkshire fish reminds us also of the peculiar sculpture which is characteristic of the entire scale and over the whole body of A. exsculptus. The narrow ventral scales are, indeed, undistinguishable from the one from the Carboniferous Limestone of Derbyshire contained in the Cambridge Museum, and figured by Mc Coy as Acrolepis Hopkinsii[38]; but if that be the same, as I believe it to be, with a fish from the Millstone Grit of Hebden Bridge, of which several beautiful fragments are in the collection of Mr. John Aitken of Bacup, it is a distinct species, and differs from A. Rankinei in other respects.
In conclusion, if all definition of Gyrolepis as a genus is at pre- sent impossible, if the diagonal ridged scale-ornament, supposed to be characteristic of it, is also characteristic of the scales of many species belonging to various other genera, such as Acrolepis, Elonichthys, Rhabdolepis, Cosmoptychius, &c, and if the "Gyrolepis" Rankinei of Agassiz be referable to Acrolepis, then there is, as I have maintained above, no longer any justification for the retention of the name "Gyrolepis" in our lists of British Carboniferous fossils.
Pygopterus.
The definition of Pygopterus given by Agassiz in the "Tableau Synoptique" is as follows:—
"A. très-allongée: D. opposée a l'intervalle entre l'A. et les V. La mâchoire supérieure déborde l'inférieure. De petits rayons le long des rayons extérieurs des nageoires."
Further on in the volume the characters of the genus are indicated more in detail. The large size of the fins, especially of the heterocercal and deeply cleft caudal, is noticed, the paired fins being less developed; also the pointed conical teeth, the comparatively small size of the rhomboidal scales, and the well-developed internal skeleton. But it is on the form of the anal fin that the greatest stress is laid:—"Mais ce qui caractérise plus particulièrement les Pygopterus, c'est qu'à cette caudale inéquilobe se joint une anale fort longue qui garnit le bord inférieur du corps sur une grande étendue." The dorsal is still stated to be placed opposite the interspace between the ventrals and the anal, but "de manière à être plus rapprochée de cette dernière.' In his description of P. mandibularis, however, Agassiz states that in it the anal is more directly opposed to the dorsal than in P. Humboldtii.
The restored outline of Pygopterus given in the Atlas to the 'Poissons Possiles' (vol. i. tab. B. fig. 3) displays, however, the same faults as the accompanying restorations of Palæoniscus, Amblypterus, &c, viz. a want of acquaintance with the structure of the head, besides considerable inaccuracies as to the general form of the body and fins. Had Agassiz been acquainted with the cranial osteology of the Palæoniscidæ, it is, indeed, impossible to conceive that on the sole ground of the possession of large laniary teeth, he could have separated Pygopterus and Acrolepis, as "Sauroïdes," from their natural allies Palæoniscus and Amblypterus, a precisely similar dentition existing, as has been subsequently shown, in several of the species which he referred to the two latter genera.
By Quenstedt a peculiarity of Pygopterus, certainly of generic value, is noticed, which seems to have escaped the attention of Agassiz, viz. the non-articulation of the principal rays of the pectoral fin. As he says:—"Die grossen ungegliederten Strahlen der Brust- flossen errinern an Pachycormus." The position of the dorsal fin is also more correctly indicated by Quenstedt, according to whom it stands, "weit hinter der Bauchflosse über der vordern Hälfte der langen Afterflosse," though he might also have mentioned that it commences in front of the latter. He also gives a figure of some of the bones of the head (operculum, maxilla, mandible, branchiostegal rays), in which the essential agreement of these in form and arrangement with the corresponding bones in Palæoniscus is clearly shown[39].
The peculiar form of the anal fin is also emphasized by Germar, by whom the position of the dorsal fin is correctly stated in the following words:—"Man erkennt diesen Fisch sehr leicht an den deutlich erkennbaren Wirbelsäule, an seiner, wenn auch in verminderter Höhe sich fast bis zur Schwanzflosse fortziehenden Afterflosse, wesshalb man ihm auch die Benennung Afterflossenfisch geben kann, und an der, der Afterflosse fast gerade gegenüberstehenden Rückenflosse." Again he remarks:—"Die Afterflosse beginnt bei zwei Drittheil Länge des Bauches, dehnt sich anfangs stark in die Höhe aus, wird dann aber schnell wieder niedrig, und setzt sich nachher mit allmählig verminderter Höhe bis in die Nähe der untern Schwanzflosse fort. Die Rückenflosse steht der Afterflosse ziemlich gerade gegenüber, doch noch weiter nach vorn gerückt, so dass etwa ihre Mitte dem Anfange der Afterflosse sich gegenüber befindet, sie steigt auch anfangs schnell und hoch empor und endigt nach hinten durch eine sichel- oder halbmondförmige Ausbüchtung "[40].
The definition of Pyyopterus given by McCoy is as follows:—
"Body large, elongate ovate; fins very large, with fulcral scales, anal fin of moderate depth and very long, dorsal of moderate length, nearly opposite or a little in front of the anal fin; ventrals small, slightly in front of the middle of the body; pectorals moderately small, falcate caudal very large, deeply notched; upper jaw a little longer than the lower; endoskeleton strong, vertebræ usually wider than long; scales proportionally rather small, rhomboidal, smooth, and minutely punctured or diagonally striated, extending over the pedicles of the fins, and particularly over the thick upper lobe of the tail to the extremity, having a moderately wide articular margin, sometimes prolonged at the upper angle, and having a medial internal articular ridge which forms a prolongation from the middle of the upper margin"[41].
What, therefore, the salient generic characters of Pygopterus are, is perfectly clear from the foregoing extracts, which all refer to the Permian species P. Humboldtii and P. mandibularis; for even Agassiz, though he enumerated several other species from the Carboniferous formation, made only the briefest possible reference to their distinctive characters, deferring that description to a future opportunity, which, unfortunately for fossil ichthyology, never arrived. These two species, which, indeed, resemble each other exceedingly closely, must therefore be taken as typical of the genus. It now remains for us to inquire whether the others named by Agassiz sufficiently agree with them in structure to warrant their retention under the same generic title.
The species of "Pyyopterus" enumerated by Agassiz, in his general list of Ganoids, are the following:—
|
From the "Coal-formation." 1. P. Bonnardi, Muse, near Autun. 2. P. Bucklandi, Burdiehouse. 3. P. lucius, Saarbriickcn. 4. P. Jamesoni, Burdiehouse. 5. P. Greenockii, Newhaven. |
From the Permian (Zechstein). G. P. Humboldtii. 7. P. mandibularis. 8. P. sculptus. |
Of these one must be deleted before proceeding further, viz. P. Indus, from Saarbrücken, which subsequently turned out to be a head of Archegosaurus[42]. Of two others I can give no account, viz.:—P. Bonnardi, from the Autun fish-beds (now referred to the Lower Permian), which I have never seen, nor am I aware of its having ever been described; and P. Jamesonii, from Burdiehouse, of which also no description has ever appeared; and as the specimen, a detached jaw, appears to be lost, the name must be cancelled, like too many others given by Agassiz to fish-remains to whose identification we have no longer any clue. The others fall into the three following generic types.
I. Type of P. Humboldtii (genus Pygopterus, Agassiz, restricted).—The general form is elongated; the head is rather large, the suspensorium very oblique; the jaws long, powerful, and armed with large conical laniaries, outside which is a series of smaller teeth; the operculum and interoperculum are rather small, the branchiostegal rays numerous; both the cranial and facial bones are striated. The scales of the body are small in proportion to the size of the fish, nearly equilateral over the greater part of the body, but rather higher than broad on the front of the flank; their form is rhomboidal, their anterior marginal covered area is moderate, and at the anterior superior angle of the scale is produced upwards into a prominent point; the proper articular spine of the upper margin is well marked. The pectoral fin is of considerable but not excessive size; its principal rays are, like those of Oxygnathus and Rhadinichthys, unarticulated till towards their terminations; the ventral is rather small. The anal commences rather remote from the caudal; it is high and acuminate in front; but behind the apex its contour falls rapidly away, so that posteriorly it extends in a fringe-like manner for some distance along the lower margin of the body. The dorsal commences slightly in front of the anal, and has a much shorter base, the middle of which is opposite the commencement of the last-named fin; it is acuminate and high in front, the posterior margin being concavely cut out. The caudal is of enormous size, powerfully heterocercal, deeply cleft, but not very inequilobate. The fin-rays do not seem to me to have been ganoid externally, but to have been covered with a delicate skin, as in the recent Polyodon; the fulcra are well marked. The internal skeleton is well developed, the vertebral arches, spinous processes, and interspinous bones usually showing prominently through the external scaly covering; but it seems to me very doubtful that the vertebral bodies had got beyond the stage of "Halbwirbel:" nor have I seen any trace of ribs, though these are mentioned by Germar. The snout projects over the front of the mouth, as in other Palæoniscidæ; hence, probably, the expression used by Agassiz:—"La mâchoire supérieure déborde l'inférieure."
To this type, which has as yet occurred only in rocks of Permian age, the term Pygopterus ought in future to be strictly limited. Here are embraced P. Humboldtii, Ag., P. mandibularis, Ag., and P. latus, Egerton,—P. sculptus, Ag., being pretty certainly, as suggested by Sir Philip Grey-Egerton, only a synonym of P. mandibularis[43], Agassiz not having been aware that the anterior scales of this species were sculptured with diagonal striæ. The nearest approach to Pygopterus in general form is made by some of the much smaller Carboniferous fishes which I include in the genus Rhadinichthys; but in all of these the scales are proportionally larger and thicker, the caudal body-prolongation is not so powerfully developed, and the anal fin, though considerably "échancrée," is not prolonged backwards in the same manner. In the structure of the pectoral fin it also resembles Oxygnathus and Thrissonotus, as well as Rhadinichthys: in Thrissonotus, also, the anal fin has apparently a somewhat similar form[44].
II. Type of P. Bucklandi, Ag. (genus Elonichthys, Giebel). This species has never been described; and the original type, stated by Agassiz to be in the Museum of the Royal Society of Edinburgh[45], cannot now be found. A figure of it, however, is given by Hibbert, in his celebrated memoir on the Burdiehouse Limestone[46], from which figure, along with the very brief notice of this species in the 'Poissons Fossiles,' I feel pretty confident in referring to it a number of mostly fragmentary remains of a large Palæoniscoid fish from Burdiehouse, contained in the Edinburgh Museum of Science and Art. All that Agassiz says of it is as follows:—
"Pygopterus Bucklandi, Agassiz. Espèce caractérisé par la petitesse et la forme allongée de ses écailles, et par son anale très-rapprochée de la caudale. Elle est à peu près de la taille du P. mandibularis et provient du calcaire de Burdiehouse en Ecosse"[47].
Hibbert's figure represents only the posterior half of the fish, with the dorsal, anal, and caudal fins; and the two former strike one at the first glance as having the position and shape, not of those in Pygopterus but in Elonichthys. In fact, the approximation of the anal to the caudal, mentioned by Agassiz as a specific mark, is in reality a generic one; moreover, not being prolonged backwards, the anal resembles the dorsal in size and shape, while the latter is placed relatively further forwards. A comparison of this figure with the actual specimens to which I have referred, shows that we have here to deal with a fish which is certainly not a Pygopterus, but a species closely allied to those from the North-Staffordshire Coal-field, which I have recently described as Elonichthys semistriatus, E. caudalis, and E. oblongus, as well as to the E. striolatus, which is associated with it in the same beds[48]. The only entire specimen I have seen is 1112 inches in length; it is most unfortunately crushed on its back. It displays, however, the right pectoral and ventral fins; and the former, unlike the pectoral of Pygopterus, has its principal rays articulated throughout; the ventral is of moderate size. The median fins are large; the dorsal is not shown in any of the specimens belonging to the Edinburgh Museum; but in Dr. Hibbert's figure it is seen to resemble the anal, and is evidently placed nearly opposite the interval between that fin and the ventrals, though the latter are not shown in the figure. The anal, however, is well shown in one specimen; it is large, triangular, and acuminate, and is closely followed by the caudal, which is very powerful. The fin-rays are externally ganoid and finely. striated; their transverse articulations are very close; the fulcra are closely set, and minute for the size of the fish. The scales of the body are proportionally small. Those of the front part of the body are apparently nearly equilateral; but posteriorly, and more especially towards the ventral margin, their form is low and narrow. Their anterior covered area is very narrow; the posterior margin is very finely denticulated; the exposed area is covered with a delicate yet sharply defined ornamentation, consisting of fine subparallel ridges, which pass from before backwards across the scale, in a gently sigmoid direction, tending to become intermixed with punctures posteriorly, especially above the diagonal between the two acute angles of the scale. Towards the tail the ridges become less marked on the posterior part of the scale, giving way to the thickly dotted punctures, till on the caudal body- prolongation the former, after lingering at the anterior margin, altogether disappear, and punctures alone remain.
Very little can be made out concerning the bones of the head; however, in the above-mentioned entire specimen the lower jaw is seen to be very stout, and ornamented externally with fine, sharp, closely set, wavy, branching, anastomosing, and interrupted ridges, running in a longitudinal direction. The laniary teeth are very strong, incurved and smooth, with apical enamel-cap; similar teeth are seen on the maxilla, the dental margin of which is finely tuberculated.
Imperfect as the above-described specimens are, the affinities of the fish which they represent are clear and unmistakable, and forbid its being retained any longer as a "Pygopterus." On the other hand, though attaining a larger size, the resemblances which it bears to Elonichthys striolatus, in the form, structure, and position of the fins, and in the nature of the scale-ornament, are so great that it is impossible to include them in different genera, though specifically they are at once distinguishable.
I have already stated that the original of "Pygopterus" Jamesoni seems to be lost, and that, as no figure or description of it exists, the name must consequently drop. The only statement made regarding it by Agassiz, is as follows:—
"Pygopterus Jamesoni, Agass. Sous ce nom j'ai distingué une seconde espèce de Burdiehouse, dont je ne connais encore que la mâchoire inférieure qui diffère de celle du P. mandibularis, en ce qu'elle est proportionnellement plus courte"[49]. As he does not, however, state how this jaw (the only relic found) differs from that of P. (Elonichthys) Bucklandi, I cannot help strongly suspecting that it belonged to the same fish.
The scale figured by Mr. T. P. Barkas[50], from the Northumberland coal-field, as belonging to a species of "Pygopterus" evidently appertains to the same fish as that from North Staffordshire, described by myself as Elonichthys semistriatus, as is also most probably the case with the mandible represented by him on the same plate[51].
III. Type of Pygopterus Greenockii, Agass. (genus Nematoptychius, Traquair).—Concerning "Pygopterus" Greenockii the following brief statement was made by Agassiz:—
"Espèce très-distincte sous le rapport spécifique, mais douteuse sous le rapport générique. Les fragmens connus ne sont guère que des têtes avec la partie antérieure du tronc. Les écailles qui recouvrent cette partie du corps sont plus hautes que longues, et diffèrent par-là de celles de tous les autres Pygopterus. Du terrain houiller de Newhaven. Il en existe plusieurs exemplaires dans la collection de Lord Greenock, qui sont tous contenus dans des géodes de fer hydraté carbonaté"[52].
Although the original examples of this species, collected by Lord Greenock, and now in the Museum of the Royal Society of Edinburgh, were thus imperfect, there is hardly any Carboniferous fish concerning whose structure I have been able to acquire more complete information, my own collection being especially rich in its remains, and many other specimens being in the Edinburgh Museum of Science and Art. These specimens, some of them entire, confirm the doubts which Agassiz himself entertained regarding its generic position; and accordingly in 1875[53] I proposed for its reception the new genus Nematoptychius. The configuration of the scales is alone sufficient to demand its separation from Pygopterus. Those of the flanks are much higher than broad; their anterior covered margin is very narrow; the exposed surface is rhomboidal; but the acute angles are the anterior-inferior and posterior-superior; the articular spine is broad and triangular, and arises from the whole, or nearly the whole, of the narrow upper margin. The scales alter their form on the ventral aspect, where they become low and very small; their external ornament consists of fine, wavy, thread-like ridges. The pectorals are of moderate size, and have their principal rays unarticulated only for about 13 of their length; the dorsal and anal fins are large and triangular, the dorsal being placed far back and nearly opposite the anal. The latter is slightly larger than the dorsal, but is similar to it in shape, and is not prolonged backwards in the fringe-like manner characteristic of Pygopterus.
For further details regarding the structure of this genus I must refer to my previous papers on the subject[54]. A second species, which I have named N. gracilis, has also recently turned up in the black-band ironstone (Carboniferous Limestone series) of Gilmerton, near Edinburgh[55].
It thus follows that there is no Carboniferous species of Pygopterus as yet known, and that it must consequently be regarded as strictly a Permian genus, though in this case, as in others, negative evidence may be at any time overturned. I have also, in the preceding pages, endeavoured to show that a better understanding of the Carboniferous species hitherto ascribed to Amblypterus, Palæoniscus, and Gyrolepis excludes these genera also from the Carboniferous list, as far as our present knowledge goes. This is especially important with regard to the questions still pending as to the respective limits of the Carboniferous and Permian formations, both in England[56] and in Bohemia[57]; for it cannot be denied that an accurate determination of genera, as well as of species, of imbedded fish-remains is essential to all safe generalization as to the aspect or distinctions of particular faunas, whether they be "Carboniferous" or "Permian," and that such generalization has been seriously impeded by the vague ideas hitherto prevalent regarding the genera discussed in the present paper. I may therefore express a hope that the observations here recorded may not be without their value, in spite of the inevitable shortcomings which the nature of the subject, and the limited opportunities of any one observer, forbid them being without.
- ↑ Poissons Fossiles, vol. ii pt. 1, p. 3.
- ↑ Ibid. p. 4.
- ↑ Ibid. p. 30, p. 42 &c.
- ↑ Poissons Fossiles, vol. ii. pt. 1, p. 29.
- ↑ Ibid. pp. 42, 43.
- ↑ Beiträge zur vorweitlichen Fauna des Steinkohlengebirges.
- ↑ Ann. & Mag. Nat. Hist. (4) vol. i. pp. 358, 359.
- ↑ "Beobachtungen über die Fische in den Eisennieren des Saarbrücker Steinkohlengebirges." Verh. naturh. Ver. preuss. Rheinl. lxiv. 1857, pp. 1–18.
- ↑ Handbuch der Zoologie, Bd. i. 2te Hälfte, p. 591 (Leipzig, 1875).
- ↑ Poissons Fossiles, vol. ii. pt. 1, pp. 105–106.
- ↑ Fauna der Vorwelt, vol. i. pt. 3, pp. 249–251.
- ↑ It is remarkable that Agassiz's error in the 'Tableau Synoptique,' as to the absence of fin-fulcra in Amblypterus, "except on the upper lobe of the tail," though corrected by himself in his general description of the genus, has nevertheless been repeatedly copied into the works of subsequent writers, such as Pictet (Pal. 2nd ed. vol. ii. p. 181), Eichwald (Leth. Eossica).
Giebel, it is true, in his definition of Amblypterus (op. cit. p. 251), does not mention the absence of fulcra as a character; but nevertheless on this ground ("durch die Anwesenheit der Fulcra nur an der Schwanzflosse") he transfers Agassiz's Palæoniscus Duvernoyi to this genus. In this transference I quite agree with him, as will be seen further on, but not on that account, the fulcra being obviously present in well-preserved fins of that species. This has been vigorously pointed out by Troschel, who, referring to a specimen in the Bonn Museum, speaks of the fulcra on its anal fin as being "so schön sichtbar, wie man es nur wünschen kann " (op. cit. p. 17).
- ↑ γόνυ, knee, and ὀδούς, tooth.
- ↑ Trans. Edinb. Geol. Soc. vol. ii. pt. 1 (1872), pp. 118–124.
- ↑ Poissons Fossiles, vol. ii. pl. 1.
- ↑ North Staffordshire Naturalists' Field Club, Addresses and Papers (Hanley, 1875), pp. 239–240.
- ↑ Report on the Albert Coal Mine, New Brunswick.
- ↑ Quart. Journ. Geol. Soc. iii. 1847, p. 279; ibid. vi. 1850. p. 8.
- ↑ Am. J. Sc. xli. 1841, p. 25.
- ↑ Poissons Fossiles, vol. ii. pt. 1, p. 224–227. Strüver in Zeitschr. der deutschen geol. Gesellsch. xvi. 1864, pp. 303–330, pl. xiii.
- ↑ The statement that "at Autun, in France, we find the genus Ischypterus accompanying the true Palæonisci" is made by Sir Charles Lyell (Quart. Journ. Geol. Soc. iii. 1847, p. 278); but Sir Philip Grey-Egerton, three years later, states that he is not cognizant of any species of the genus being found there (ibid. vi. 1850, p. 8).
- ↑ Atlas, vol. ii. tab. 10 c. figs. 1 and 2.
- ↑ Pl. xxii. fig. 3.
- ↑ Ann. & Mag. Nat. Hist. (3) ix. 1862, pp. 267–269, also in Quart. Journ. Geol. Soc. xxi. 1865. pp. 345–358.
- ↑ "Ueber die Begrenzung und Eintheilung der Granoiden," Palæontographica, vol. xxii. 1873, p. 26.
- ↑ Quart. Journ. Geol. Soc. iii. (1847), p. 278.
- ↑ Quart. Journ. Geol. Soc. vi. (1850), p. 4
- ↑ Zeitschr. der deutschen geol. Gesellsch. xvi. 1864, pp. 303–330, pl. xiii.
- ↑ The genus Dictyopyge was separated from Catopterus of J. H. Redfield by Sir Philip Grey-Egerton on account of the supposed heterocercal nature of the tail in the latter. I hope, however, that I shall not be deemed wanting in respect to the high authority of our greatest English writer on fossil ichthyology in pointing out that not only is the semiheterocercal nature of the tail in Catopterus distinctly asserted in Mr. J. H. Redfield's original description and borne out by his figure (Ann. Lyc. Nat. Hist. N. York, iv. 1848, pp. 35–40, pl. i.), but also reaffirmed by Mr. W. C. Redfield, who therefore proposed to cancel Dictyopyge, recalling D. macrura as a Catopterus (Proc. Am. Assoc. Albany, 1856, pp. 180–188). But, as in the typical Catopterus gracilis, J. H. Redf., the dorsal fin is situated still further back than in the species macrurus, W. C. Redf., socialis, Strüver, or in the little catopterus of Agassiz, the genus Dictyopyge may, I think, be advantageously retained for these last-named forms.
- ↑ Fauna der Vorwelt, i. 3, pp. 181, 182.
- ↑ Ibid. p. 255.
- ↑ 'Ueber die Fauna des bunten Sandsteins and des Muschelkalks in Oberschlesien,' p. 67. I have not myself seen this work, which I therefore quote on the authority of Dr. Martin.
- ↑ Handbuch der Petrefactenkunde, 2nd ed. (1867), pp. 248–250.
- ↑ Ibid. p. 268, 269.
- ↑ Quart. Journ. Geol. Soc. vol. vi. 1850, pp. 8, 9.
- ↑ Dec. Geol. Survey, viii. 1855, text accompanying pl. ix. p. 3.
- ↑ Zeitschrift der deutschen geol. Gesellsch. xxv. (1873).
- ↑ 'British Palæozoic Rocks and Fossils,' p. 609, pl. 3g. fig. 10.
- ↑ 'Handbuch der Petrefactenkunde,' 2nd ed. (1867). p. 269, pl. 21. fig. 4.
- ↑ 'Die Versteinerungen des Mansfelder Kupferschiefers' (Halle, 1840), pp. 22–24.
- ↑ 'Palæozoic Fossils.'
- ↑ Dr. G. Jäger, "Ueber die Uebereinstimmung des Pygopterus lucius, Ag., mit dem Archegosaurus Dechenii, Goldf.," Abh. der k.-bayerisch. Ak. der Wiss. v. pp. 877–886. See also a notice by Prof. Ferd. Römer, in Verh, preuss. Rheinl. u. Westphal. 1850. pp. 155–157.
- ↑ In King's 'Permian Fossils,' p. 233.
- ↑ Dec. Geol. Surv. ix. 1858, pl. 2.
- ↑ It is possible that this is a mistake, and that the specimen may have been in the private collection of Dr. Hibbert, as all the other type specimens mentioned by Agassiz as belonging to the Royal Society of Edinburgh are in their places.
- ↑ Trans. Roy. Soc. Edinb. vol. xiii. pl. 7. fig. 2.
- ↑ 'Poissons Fossiles,' vol. ii. pt. 2, p. 77.
- ↑ These species are described in the first part of my monograph on the British Carboniferous Ganoids, in the Memoirs of the Paleontographical Society for 1877, plates 3–7.
- ↑ 'Poissons Fossiles,' vol. ii. pt. 2, p. 78.
- ↑ 'Manual of Coal-measure Palæontology,' pl. 4. fig. 130
- ↑ Ibid. fig. 131.
- ↑ 'Poissons Fossiles,' vol. ii. pt. 2. p. 78.
- ↑ Ann. & Mag. Nat. Hist. (4) vol. xv. pp. 258–262.
- ↑ Trans. Royal Soc. Edin. vol. xiv. 1867, pp. 701–713. Also paper in Ann. & Mag. Nat. Hist., quoted already.
- ↑ Proc. Roy. Soc. Edin. 1876–77, pp. 262–265.
- ↑ "On the Relation of the Upper Carboniferous Strata of Shropshire and Denbighshire to Beds usually described as Permian," by D. C. Davies, F.G.S. (Quart. Journ. Geol. Soc. vol. xxxiii. 1877, pp. 10–28).
- ↑ "A Permian Flora associated with a Carboniferous Flora in the uppermost portion of the Coal-formation of Bohemia," by Dr. O. Feistmantel (Geol. Mag. (2) vol. iv. 1877, pp. 105–120).