324 SYSTEMATIC ZOOLOGY. 



feed on fish and the like have sharp cutting teeth, and 

 these are arranged in rows, one behind another, so that 

 only one row is in use at a time, the other serving as a 

 reserve supply if one of the front row be lost. In other 

 sharks, which feed on shell-fish, the teeth are flattened 

 plates, the whole forming a mill for crushing the shells. 

 Most of the species are much like the dogfish in their 

 general appearance, but there are strange forms. Thus 

 in the hammer-head sharks the sides of the front of the 

 head are drawn out like a mallet, the eyes being on the 

 outer ends of the lobes. In the sawfishes the snout is 

 drawn out in a long beak, either edge of which is armed 

 with sharp teeth. 



ORDER II. RALE (Skates, Rays). 



In the skates and rays the body is usually flattened, and 

 the gill-slits are on the under surface. In most forms the 

 body is sharply marked off from the tail, but in those saw- 

 fishes which belong to this order the body is shark-like. 

 The width of body in the true skates is partly due to 

 the fact that the pectoral fins are enclosed in it, the whole 

 making a disk, rounded or four-sided in outline. Most of 

 them are bottom feeders, living upon shell-fish, and hence 

 have flattened pavement- teeth. The torpedoes are remark- 

 able for their electrical powers. In them certain muscles 

 on the sides of the head are metamorphosed into an elec- 

 trical battery, the discharge of which is under control of 

 the will. The current is strong enough to kill small 

 animals which come into contact with the creature. The 

 largest of the skates are the huge tropical devil-fish, which 

 reach a length of twelve or more feet and a weight of 1200 

 pounds. 



