550 THE OCEAN WOKLD. 
that of the Picked Dog-fish, Acanthias vulgaris (Fig. 362), which 
sometimes attains the length of between three and four feet, and is 
exceedingly voracious. It feeds upon other fish, of which it destroys 
great quantities; it does not hesitate to attack even the fishermen, 
‘and especially bathers in the sea. It places itself in ambush, like the 
‘Rays, in order to attack its prey. The flesh of the Dog-fish is hard, 
smells of musk, and is rarely eaten; but the skin becomes an article 
of commerce, and is known as shagrin, being, like the skin of the 
Fig. 362.—The Picked Dog-fish (Acanthias vulgaris).. 
shark, used for making spectacle-cases, and for other ornamental 
purposes, for which its green colour and high polish recommend it. 
There is a smaller species than the preceding, which haunts rocky 
shores, where it lies in wait for its prey. Its spots are larger and 
more scattered, and its ventral fins are nearly square. It feeds on 
molluscs, crustaceans, and small fishes. 
. The family Zygenide contains the strange Hammer-headed Shark, 
Zygena malleus (Fig. 363), which is chiefly distinguished by the 
singular conformation of its head ; it is flattened horizontally, truncate 
in front, and the sides prolonged transversely, giving it the appearance 
of the head of ahammer. The eyes of this fish are placed at the 
extremity of the lateral prolongations of the head ; they are grey, 
