CHAPTER XXX 

 SOME COMMON FISHES OF NORTH AMERICA 



Subclass 2. Elasmobranchii 



The sharks (Fig. 161) and rays (Fig. 162) are characterized 

 by a cartilaginous skeleton, toothlike scales (Fig. 158, A), a 

 slitlike mouth on the ventral side of the head, and gill openings 

 not covered by an operculum. The sharks resemble the true 

 fish in shape, whereas the rays are very much flattened. Sharks 



A, dogfish shark ; B, sawfish. (After Goode.) 



are usually less than ten feet long and, contrary to general be- 

 lief, feed upon crustaceans, squids, and fish rather than upon 

 human beings. Occasionally the great white shark which lives 

 in the tropics and reaches a length of thirty feet may become a 

 man eater. 



The rays or skates have their bodies greatly flattened and are 

 thus adapted to a life on the bottom. The sting ray (Fig. 162) 



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