PALCEONISCUS, GYROLEPIS, AND PYGOPTERUS. 551 



" Palceoniscus, Ag. (Palceothrissum, Blainv.). Plossen nur niittelgross ; 

 Strahlen stark ; Kopf gewohnlich 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 prolonga- 

 tion of the body along the upper lobe, that part is certainly no 

 shorter in the Agassizian Amblypteri than in his Palceonisci ; 

 nor, generally speaking, is the head more " aufgetrieben " in the 

 one than in the other. In describing the Amblypterus Agassizii of 

 Miinster, Agassiz himself states that " la machoire superieure forme 

 une saillie arrondie au-dessus de la machoire inferieure, saillie qui 

 resulte probablement, comme dans les Palceoniscus, du developpe- 

 ment considerable de rethmoi'de. Jusqu'ici j'avais cru ce caractere 

 exclusivement propre aux Palceoniscus, n'ayant vu que peu d'ex- 

 emplaires du genre Amblypterus dont la tete fut assez bien con- 

 served pour ne me laisser aucun doute sur sa forme" *. 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 Palceoniscus I 



Zoologists, however, will hardly be prepared to accept the ideas 

 of generic comprehensiveness expressed in the reunion of Rhabdo- 

 lepis with Amblypterus, any more than the location by Prof. Cams 

 of the Palaeoniscoid fishes (with the exception of Cheirolepis) among 

 the Lepidotini as a mere "subfamily;" for if Rhabdolep is be not 

 generically distinct from Amblypterus, neither is Palceoniscus, nor 

 Acrolepis, nor Elonichthys, and in fact, to be consistent, nearly the 

 whole of the Palaeoniscidae 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 Palceoniscus 

 reinvestigated and more accurately defined, their species redis- 

 tributed, and, if need be, new genera instituted for those which 

 cannot be included in the one or the other, according to the concep- 

 tion 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 Palaeoniscidae, 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. 



* Poissons Fossiles, vol. ii. pt. 1, pp. 105-106. 

 Q.J.G.S. No. 131. 2o 



