Cestracion

Cestracion, a genus of sharks, the type of a family which has existed from Devonian times, and has numerous fossil genera in later formations, all far exceeding the single living genus in size. The dentition of the whole family is adapted for seizing and crushing the crustaceans and molluscs which formed their food, and the living species are similarly provided with blunt pad-like teeth. In Cestracion there is no nictitating membrane; two dorsal fins are present, each with a spine in front. The spiracles, just under the eye, are small, and the gill-slits narrow. Four species, none over five feet long, are known; from Japan, Amboyna, Australia, California, and the Galapagos. The best known is probably C. philippi, the Port Jackson shark. The egg is deposited in a pear-shaped leathery case, round which are two broad ridges or plates.