33 2 
CHIM/E R O IDS. 
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 chimaeras 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 Squalor a iidce, 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 Palaeozoic times, the Devonian Ptyctodus indicating a family which 
cannot at present be fully defined. 
