322 



A COURSE ON ZOOLOGY. 



Dog-fish belong to the same class as sharks ; they grow 

 as long as three feet, and the flesh of some species is 

 eaten. The skin of the sea-dog is prepared and used as 

 " rub-skin," for polishing wood and ivory. The muzzle 



FIG. 280. 



SAW-FISH. 



of the saw-fish terminates in a strong bony plate armed 

 on the edges with sharp, pointed teeth. Rays and 

 skates have a rhomboidal body, a slender, cylindrical 

 tail, the eyes and gill-holes in the upper portion of the 

 head, the mouth below and armed with thin, obtusely- 

 pointed teeth. Some of the skates attain a large size, 

 measuring more than six feet across. They are edible, 

 and some species are much esteemed. The torpedo, or 



