160 BACKBONED ANIMALS. 



over its entire surface except a girdle about the throat ; it emitted a 

 light of great brilliancy. 



Dog-Fishes (Sptnacidce). The Squalus Americanus 

 is a common American variety. They have a sharp spine 

 in front of each dorsal fin, capable of inflicting a danger- 

 ous wound. The young are born alive. 



NOTE. In August, 1883, the effect of their arrival upon the Maine 

 coast was disastrous to many fishermen. Their vast numbers com- 

 pletely destroyed the fishing. They attacked oars, even biting at the 

 sails when hanging over, and several cases are known where in former 

 years they attacked swimmers and persons who had fallen overboard. 

 The fishermen gave up cod- and hake-fishing, and with wire-hooked 

 trawls captured thousands of the dog-fish, selling their livers to be 

 made into oil, while the bodies were carted upon farms and used as 

 guano. 



FIG. 197. Hammer-headed shark. 



Hammer-Head Shark (Sphyrnida). The sharks of 

 this family (Fig. 197) have the head in the shape of a 

 hammer, the eyes being placed at the ends of the curious 

 prolongations. They attain a length of twelve feet, and 



