PAVEMENT-TOOTHED SHARKS. 531 



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 



PORT JACKSON SHARK 



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, with a 

 slight longitudinal ridge and a 

 net-like ornamentation. The 

 spines of the dorsal fins are 

 smooth, covered on the sides 

 with a thick layer of ganoin ; 

 the shagreen is fine ; and the 

 head is devoid of spines. In 

 the existing species the egg- 

 capsules assume a remarkable 

 screw-like form, quite unlike 

 that of any other member of 

 the family. The living mem- 

 bers of the genus, none of 

 which exceed 5 feet in length, 

 have been recorded from the 

 seas of Japan, Amboyna, LOWER JAW OF PORT JACKSON SHARK (\ nat. size). 



Australia, the Galapagos 



Islands, and California ; while remains of extinct forms occur in the Cretaceous 

 and Upper Jurassic strata of Europe. Very little appears to be known as to their 

 habits ; but their food is stated to consist principally of molluscs, the hard shells 

 of which are crushed by the pavement-like hinder teeth. 



