2906 



SHARKS AND RAYS 



the adults are more or less pelagic. Dogfishes of smaller size from the Indian 

 Ocean constitute the genus Chiloscy Ilium, in which the first dorsal fin is either above 

 or behind the line of the pel vies; while the anal is far behind that of the second 

 dorsal, and close to the caudal; the teeth being small and triangular, with or 

 without lateral cusps. The existing species are very handsomely ornamented with 

 dark bands and spots. In a fossil state the genus has been recorded from the 

 Miocene Tertiary. Three bottom-haunting sharks from the Japanese and Australian 

 seas have been described under the name of Crossorhinus, and are remarkable for 

 the presence of leaf-like expansions of the skin on the sides of the head. As in the 

 case of other fish similarly adorned, these structures are probably for the purpose 

 of attracting prey; and in order that they may be well concealed, these sharks have 

 a coloration closely assimilating to that of a rock covered with seaweed or coral- 

 lines. 



THE PAVEMENT-TOOTHED SHARKS Family CESTRACIONTID^E 



The well-known Port Jackson shark (Cestracion philippi) and three allied 

 species are the sole existing representatives of a family which was exceedingly 

 abundant during the Secondary epoch. They differ from all the foregoing in the 

 presence of a strong spine on the front edge of each of the two dorsal fins. 

 The first dorsal fin is situated above the space between the pectoral and pelvic 



is? 



PORT JACKSON SHARK. 



(One-sixth natural size.) 



pairs; and the teeth, of which several series are in use at the same time, are more 

 or less blunt and broad, more especially in the hinder part of the jaws, although 

 those in each oblique row are never fused together into continuous plates. In 

 the existing genus there is no nictitating membrane to the eye; the body is 

 moderately elongated, with the second dorsal fin in advance of the line of the 

 anal; and the mouth is almost or quite terminal. In the dentition, the front teeth 

 are small, numerous, and sharp, while the hinder ones are broad and flattened, 



