WHAT Is an Amblypterus ? What Is a Paheonistn~S ? How Do
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Downloaded from http://jgslegacy.lyellcollection.org/ at National University of Singapore on February 2, 2016 548 RA~ISAY tI. TRAQUAIR 01~ AMBLYPTERUS, 30. On the Agassizian Genera A~BLYPTERUS, PAI.~O~ISCUS, GYaoImPIS, and P~(}oPI~Rvs. By RamsAY H. TRAQrX~R, M.D., F.R.S.E., F.G.S., Keeper of the Natural-History Collection in the Edinburgh Museum of Science and Art. (Read May 9, 1877.) WHAT is an Amblypterus ? What is a Paheonistn~s? 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 pal~eontologists, are, it must be owned, of a somewhat unsatisfactory nature. Gyrolepis and Pyyopterus 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 Pal~eoniscid,'e 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 com- paratively 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. AMBLYPTERI~S a~d PAL~O.~ISCUS. The definition of Ambl!/])terus given by Agassiz in his "Tableau synoptique" is as follows :-- " Toutes les nageoires trbs-larges et composdes de nombreux rayons, P. trbs-grandes; A. large; D. opposge h l'intervalle entre les V. et I'A. ; point de petits rayons sur le bord des nageoires, except0 au lobe supdrieur de la queue. Ecai]les mddioeres" * Of Palceoniscus, on the other hand :-- "Toutes les nageoires mddiocres, de petits rayons sur leurs bords ; D. opposde .s l'espace entre les V. et I'A. Eeailles mgdiocres; quelques espbces en ont d'assez grandes, et le corps plus large et plus court que les autres. I1 y a toujours de grosses 6cailles impaires en avant de la D. et de I'A "r Both genera are elsewhere stated to have the teeth "en brosse extr~mement fine" or "en brosse" +% The statement as to the 9 PoissonsFossiles, vol. ii pt. 1, p. 3. t Ibid. p. 4. 9+ Ibid.p. 30, p. 42 &e. Downloaded from http://jgslegacy.lyellcollection.org/ at National University of Singapore on February 2, 2016 eAr.~oNIsc~s, ~0LEHS, AND eY~oPT~avs. 549 absence of fulcra on the fins of Amblyt)terus , save on the caudal, was corrected a few pages further on, though they are here said to be "si extraordinairement petits qu'on peut h peine les entrevoir h l'(eil nu" *. Large azygos scales in front of the median fins are also declared to exist in Amblypte~.us ; so that the only differences remaining between that genus and Pal~oniscus 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 Palceoniscus (P. Voltzii, Blainvillei), not so in others (P. Freieslebeai), and in Amblypterus ~'--a difference which, if it did really exist, would certainly be sufficient, not to distinguish Amblypter~s from Palceoaiscus, but to demand the separation of the latter into two distinct genera. The scaly appearance of the fins iu some so- called Palceoniscl, 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 ++, pointed out that Amblyivterus macrol)terus, Ag. (Bronn, sp.), possessed large conical teeth, its dentition being, there- fore, not "en brosse," according to the previously received definition of the genus. A similar observation has also been more recently made by )~essrs. Hancock and Atthey in the case of Palveoniscus Egertoni, Ag. w Agassiz himself had previously described the teeth of Amblffpterus 2unctat~s as being " en cones obtus." The only distinction we can lay hold of at all is the large size of the fins in Ambly~vterus and their medium size in Palceo~iscus; 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 Palceoniscus striolatus and t~obisoni are proportionally just as large, and their fulcra just as minute as those of his Amblypterus ~europ~erus, and one of the two species which he included under the name of Amblypterus p~nctat~s; 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 [] was a bold attempt made to define these genera upon strictly zoological principles, though only with partial * Polssons Fossiles, vol. it. pt. 1, p. 29. t Ibid. pp. 42, 43. Beitr~ige zur vorweltlichen F~una des Stelnkohlengeblrges. w Ann. & Mag. Nat. Hist. (4) vol. i. pp. 358, 359. [I "Beobachtungen fiber die Fische in den Eisennleren des Saarbriic]~er Steinkohlengebirges." Verh. naturh. Vet. preuss. Rheinl. lxiv. 1857, pp. 1-18. Downloaded from http://jgslegacy.lyellcollection.org/ at National University of Singapore on February 2, 2016 550 RAMSAY H. TRA~UAIR 0N A~IBLYPTERUS, success. He showed, however, very clearly that Agassiz's genus Amblypteru~ contained at least two very distinct types :--first, that of A. macropter~s, 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. lathes, in which the scales are smooth, and the teeth minute and slender, without interspersed laniaries ; and to this he limited the name Amblypter~ts, the character of the dentition being more in accordance with the original definition of the genus. A. Agassizii ]~[iinster, .A. striat~s, Ag., and A. ornat~es, Glebe], he considered as probably belonging to Rhabdolet)is ; while, as regards A. neuropterus and punctatus, Ag., he expressed a suspicion that they might perhaps appertain to new and peclfliar genera. Palatal teeth were found by him both in Rhabdolepis and Amblypterus proper; and this character he thought might possibly serve to separate Amblypteru~ from Palceonisc~ on the supposition that they are absent in the latter. The following summaries of characters are given at the con- clusion of his paper :-- " ltT~tbdolepis, Trosehel. Grosse conische Ziihne in ether Reihe in den Kiefern; hechelfSrmige Gaumenz~ihne; Schuppen miissig und gestreift. Flossen gross. "Amblypter~s, Agass., Trosehel. Ziihne hecheff6rmige in den Kiefern; zahlreiche Gaumenz~ihne. Schuppen miissig und glatt. Flossen gross mit kleinen Fulcra. "Palveonisct~s, Agass. HechelfSrmige Ziihne in den Kiefern. :Keine Gaumenz~ihne? Flossen miissig mit deutliehen Fulcra. Schuppen gestreift oder glatt." The distinction here drawn between Rhabdolepis and Amblypter~s cannot be gainsaid ; but as regards Palceo~isc~ts it is simply impos- sible to prove the at,sence 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 Palceo~dscus may not, like his Amblypter~s, include more than one generic type. Trosehel, indeed, concludes his paper with the observation, "Es ist wahrseheinlich dass nach Analogie mit Ambljpter~,s, auch die Gattung Pal(eoniscus in zwei Gattungen gespalten werden muss, je nachdem die Schuppen gestrelft oder glatt sind." ~'evertheless, in a recent work r Professor J. V. Carus has again fused together Amblyptert~s and Rhabdole2)is, to which he also adds as synonyms Gyrohpis , Colobodus, and Tholo&~s. His definitions are as follows :-- " Amblypterus, Ag. (incl. Gyroletffs, Ag., RhabdoleTis, Troschel, Colobod~ts, Ag., Tholodus, It. yon Meyer). Schwanz kurz,Flossen gross, vielstrahlig; unterer Rand des Schwanzes mit doppelten Fulcral- rcihen. Kohlenformation bis zur Trias. Arten: A. macropterus, Ag., u. a. Handbuch tier Zoologie, :Bd. i. 2te ttMfte, p. 591 (Leipzig, 1875). Downloaded from http://jgslegacy.lyellcollection.org/ at National University of Singapore on February 2, 2016 PALzEONISCUS, GYROLEPIS, AND PYGOPTERUS. 551 " Palo~oniscus,A g. (Pal~othriss~m, Blainv.). Flossen nur mittelgross; Strahlen stark; Kept gewShnlich aufgetrieben; Fulcren wie Amb~ypterus. Kohle his Trias. Arten: P. Freieslebeni, Ag., P. comptus, Ag., u. a." l~ow, if by "Schwanz" is meant the caudal fin with its prolonga- tion of the body along the upper lobe, that part is certainly no shorter in the Agassizian Amblypteri than in his Pal~eo~isci; nor, generally speaking, is the head more " aufgetrieben" in the one than in the other.