MARINE MAMMALS, AND FISHES 99 



Of the rays, the thornback (Raja clavata) is 

 the dominant form, and the skate (Raja batis) is 

 common. Their very shape indicates their proper 

 place among the flat fishes at the sea bottom, and 

 the clumsiness of their movements condemns them 

 to such molluscan, and other diet, as they can find 

 there. Should any fish approach near enough, it is 

 speedily engulfed. The mouth of the rays being 

 entirely on the under-surface, their prey is not 

 directly seized with the jaws, but " the fish darts 

 over its victim, so as to cover and hold it down 

 with its body, when it is conveyed by some rapid 

 motion to the mouth." 



Among the sharks, the thresher produces purses 

 like the dog-fish. The still larger Greenland sharks 

 seem to differ from all the rest, in that they 

 deposit the naked eggs in the mud. 



The piked dog-fish (Acanthias vidgaris) owes 

 his common name to the pikes or spikes, standing 

 up like detached rays, in front of the dorsal fins. 

 He is a viviparous form ; and in this, as in other 

 particulars, differs from the true dog-fishes. His 

 voracity is unbounded, and the mischief he is 

 capable of doing in a short time, incalculable. He 

 comes down on the entrapped herring or pilchard 

 herring in the north, where pilchard is a rare form 



