ELASMOBRANCHH 



423 



The average length of most sharks commonly observed ranges be- 

 tween three and six or eight feet. Their natural food consists prin- 

 cipally of Crustacea, small fish, squids, and refuse. In the Gulf of 

 Mexico and other warm seas the so-called man-eater may occasion- 

 ally reach a length of thirty feet and is sometimes charged with 



Fig. 228. — Southern sting ray, Dasyatis americana, a common form in the Gulf of 



Mexico. 



eating human beings. The shovelnose (bonnethead) and hammer- 

 head sharks are very interesting forms. The shape of the head of 

 each is about the shape ascribed to it by the common name. The 

 former has been considered sufficiently interesting to warrant fur- 

 ther discussion of it as an example of the class. 



