450 



FISHES 



CHAP. 



forms the peculiarities of the adult are less marked. In the 

 Bonnet Shark (S. tiburo) -(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, 



FIG. 256. Ventral view of the head and trunk (A) of a young Bonnet Shark (Sphyrna 

 tiburo), and (B) of a young male Hammer-head (S. zygaena). c, Clasper ; d, 

 cloacal aperture ; e, eye ; n, nostril ; n', nasal groove. 



usually living in deep water, and they may grow to a length of 

 1 5 feet. As many as thirty-seven embryos have been taken from 

 the oviducts of a female nearly 1 1 feet in length. 1 



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. 



