450 FISHES CHAP. 
forms the peculiarities of the adult are less marked. In the 
Bonnet Shark (S. tibwro) (Fig. 256, A), the head is crescentic or 
kidney-shaped, with prominent postero-lateral angles, and between 
this type of head and the more pronounced “hammer” of 
S. zygaena (Fig. 256, B) an almost perfect gradation is supplied 
by other species. The Hammer - heads are voracious Sharks, 
hi, 
Yi 
BLN 
NWA 
iii, > 
Fia, 256.—Ventral view of the head and trunk (A) of a young Bonnet Shark (Sphyrna 
tiburo), and (B) of a young male Hammer-head (8. zygaena). c, Clasper; cl, 
cloacal aperture ; ¢, eye; 7, nostril; 7’, nasal groove. 
usually living in deep water, and they may grow to a length of 
15 feet. As many as thirty-seven embryos have been taken from 
the oviducts of a female nearly 11 feet in length.’ 
Teeth assigned with more or less probability to Sphyrna are 
found in the Miocene of Europe and North America. 
Fam. 10. Lamnidae (Porbeagle Sharks).—Large, stout-bodied 
Sharks with two dorsal fins, the first just behind the pectoral 
fins, the second, which is small, opposite the small anal fin ; both 
1 Cantor, quoted by Giinther, op. cit. p. 318. 
