SHARKS AND SKATES. 



81 



placed, giving the animal the appearance of a hammer, or, better, a mallet. The five 

 known species are arranged in two genera, but the most common and best known 

 species is Sphryna zygcena, the Zygoena malleus, of most books. This species is 

 cosmopolitan, mostly frequenting the warmer seas of the world, but occasionally 

 appearing on the coasts of Old and New England. It reaches a length of fifteen feet, 

 is brownish gray above, and dirty white beneath. Its common food is skates, flat-fish, 

 and other bottom feeders, but it does not hesitate to attack man when the opportunity 

 offers. It is difficult to say what causes have given rise to its peculiarly shaped head. 

 Our other species, Sphryna tiburo, is smaller, and has the head regularly rounded in 





Fig. 63. — Sphryna zygtena, hammer-headed shark. 



front, whence the common names shovel-head shark and bonnet-shark. It is a smaller 

 species, reaching a length of six feet. It occurs in the Atlantic, and extends its range 

 to China. 



The Galeoehinid^ is a large family embracing over a third of the known species 

 of sharks, distributed in about twenty genera, of which eleven are represented on 

 the coasts of the United States. All agree in having an anal and two dorsal fins with- 

 out spines, a moderate caudal, the last gill-slit above the, base of the pectoral, and nicti- 

 tating membranes; the head is normal and not produced on either side, as in the last 

 family. 



The genera Mustelus and JRhinotriacis differ from the rest of the American forms 

 in having the teeth flat and pavement-like, and from many in the presence of spiracles. 



VOL. III. — 6 



