﻿42 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



3. Chondrosteida. 



4. PalaoniscidcB (see p. 11). 



5. Platysomida. 



IV. Lepidosteoidei. 

 V. Amioidei. 



Though the characters assigned to the Acipenseroidei, at p. 8 of the Introduction, 

 may seem to be few and insufficient, it must be remembered that the more our know- 

 ledge of series of forms advances, the more difficult does it become to define great groups 

 sharply from each other, and to find characters which shall be invariably applicable to all 

 the members of one division, and at the same time absolutely separate them from those of 

 another. The idea of such strictly defined groups belongs in fact to that period of 

 zoological history when the evidences of evolution had not yet began to press themselves 

 on the minds of investigators. It seems to me that the recent dcipenser and Polyodon 

 are the surviving members of a series of Ganoid Fishes which in earlier days sent out the 

 families of Palaoniscida and Platysomidce, more highly developed as regards the hard 

 parts of their skeleton, but which have long since become extinct. Whether or not the 

 long array of Lepidosteoid forms owes its origin to this series is still matter for laborious 

 investigation. 



DESCRIPTION OF THE GENERA AND SPECIES OCCURRING IN 

 BRITISH CARBONIFEROUS ROCKS. 



Genus — Cosmoptychius, Traquair, 1877. 



Amblypterus (pars), Agassis. 



The body is fusiform, rather deep ; the scales are large and obliquely striated. The 

 fins are well developed ; their rays are numerous, ganoid, and finely striated, the fulcra 

 are small. The rays of the pectoral are articulated throughout, except just at the com- 

 mencement of a few of the first rays at the lateral margin of the fin. The base of the 

 ventrals is extended, as in Cheirolepis ; the dorsal is situated nearly opposite the interval 

 between the ventrals and the anal ; the caudal is powerful and inequilobate. The sus- 

 pensorium is very oblique, and the gape is consequently of very great extent ; the oper- 

 culum is narrow and pointed, a small subopercular plate being interpolated between it 



