C YPRINIFORMES 



37i 



Division A. 



Although preserving the ganoine, the scales in these fish are 

 never of a rhombic ganoid character, but of the cycloid type. The 

 splenial and fulcra have disappeared, the centra are undivided. The 

 tail is scarcely yet homocercal, and there are no expanded hypurals. 



Family LEPTOLEPIDAE. The tail is still much as in the Ainioidei. 

 The scales are cycloid and thin, but ganoine covers both them and the 

 cranial dermal bones. The annular bony centra are pierced by the noto- 

 chord ; the neural arches remain separate from the centra and spines in 



Fio. 357. 



Leptolepis dubius, Blainv. ; Upper Jurassic, Bavaria; restored, without scales. 

 (Atln A. S. Woodward.) 



the abdominal region. There is no median gular. The Leptolepidae 

 .appear in the Trias and die out in the Cretaceous epoch, when the 

 modern Teleostean types begin to dominate over all others. 



Leptolepis, Ag. (Fig. 357) ; Lias to Cretaceous in Europe ; Trias in 

 N.S. Wales. Aethalion, Mu'nster ; Europe. Lycoptera, J. M. ; Jurassic, 

 Asia. Thrissops, Ag. ; Jurassic and Cretaceous, Europe. 



Division B. 



The tail is truly homocercal, with expanded hypurals, or it is 

 gephyrocercal. The ganoine has vanished, and the centra are 

 always well ossified and amphicoelous, except in degenerate forms. 

 Frequently the hinder region of the dorsal fin is differentiated as 

 an adipose fin (p. 275), in the older families. The scales are of the 

 cycloid or ctenoid type, or derived therefrom. 



Group A. 

 Sub-Order CYPRINIFORMES (Ostariophysi). 



This group is remarkable for the absence of the interorbital 

 septum, which appears to some extent only in certain Characinidae, 

 and for the presence of a superficial covering of denticles in the 

 Siluroidei. The dermal bones of the head still, for the most part, 

 lie near the surface and harbour the lateral-line canals (Fig. 327). 

 Very generally there is a fontanelle between the parietals. Usually 



