332 CHIM^EROIDS. 



characterised by the presence of a spine to the first dorsal fin, and also of a 

 prehensile spine-like structure on the heads of the males ; there are no superficial 

 plates on the skull, and only a single pair of lower teeth. The family, which 

 contains a number of extinct genera, mainly distinguished from one another by 

 the characters of the triturating areas on the teeth, dates from the Lias ; the 

 typical genus being, however, unknown before the latter part of the Tertiary 

 period. The living chimseras do not probably exceed 5 feet in length, and have 

 the soft muzzle devoid of an appendage. The dorsal fins occupy the greater part 

 of the back ; and the longitudinal axis of the long filamentous tail is nearly 

 continuous with that of the back, its extremity being provided above and below 

 with a long, low fin of the diphycercal type. The common species represented 

 in the annexed coloured Plate ranges from Europe and Japan to South Africa; 

 while a second occurs on the Pacific Coast of North America, and a third off 

 Portugal. The southern chimsera (Callorhynchus antarcticus), from the southern 

 temperate seas, differs from the preceding genus by the presence of a cartilaginous 

 prominence, ending in a flap of skin, on the muzzle, and likewise by the upward 

 direction of the extremity of the tail, which has no fin on its upper surface. A 

 fossil representative of this genus occurs in the Cretaceous rocks of New 

 Zealand. The third genus, Harottia, distinguished by the extreme elongation of 

 the snout, is represented by one species from the Atlantic, and a second from 

 the Pacific. As well-known extinct types of the family we may refer to the 

 Cretaceous and Tertiary genera Edaphodon and Elasmodus ; the former including 

 fishes of gigantic dimensions. The members of the extinct family Myria- 

 canthidce, of the Jurassic rocks, differ by having a few bony plates on the head, 

 and three lower teeth ; while the Squaloraiidce, as represented by Squaloraia of 

 the Lias, were somewhat ray-like forms, with a depressed trunk and elongated 

 muzzle, and no spines to the dorsal fins. The subclass appears also to be repre- 

 sented in Palasozoic times, the Devonian Ptyctodus indicating a family which 

 cannot at present be fully defined. 



