Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/650

550 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, 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.