PAL^ONISCTJS, GYEOLEPIS, AND PYGOPTEETTS. 549 



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 a peine les entrevoir a 

 Toeil nu " *. 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 Palceoniscus 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. Freieslebeni), and in 

 Amblypterus f — a difference which, if it did really exist, would 

 certainly be sufficient, not to distinguish Amblypterus from 

 Palceoniscus, but to demand the separation of the latter into two 

 distinct genera. The scaly appearance of the fins in some so- 

 called Palceonisci, 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 

 Qlienstedt, we shall likewise fail to find any thing satisfactory as 

 regards the discrimination of the genera in question — though 

 Goldfuss, in 1847 t, pointed out that Amblypterus macropterus, 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 Messrs. Hancock and Atthey in the case of Palceoniscus 

 Egertoni, Ag. § Agassiz himself had previously described the teeth 

 of Amblypterus punctatus as being " en cones 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 Palceoniscus ; 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 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 |j was a bold attempt made to define these 

 genera upon strictly zoological principles, though only with partial 



* Poissons Fossiles, vol. ii. pt. 1, p. 29. 

 t Ibid. pp. 42, 43. 



I Beitrage zur vorweltiicken Fauna des Steinkohlengebirges. 

 § Ann. & Mag. Nat. Hist. (4) vol. i. pp. 358, 359. 



|| " Beobachtungen iiber die Fische in den Eisennieren des Saarbriicker 

 Steiixkohlengebirges." Verh. naturh. Ver. preuss. Eheinl. lxiv. 1857, pp. 1-18. 



