160 BACKBONED ANIMALS. 
over its entire surface except a girdle about the throat; it emitted a 
light of great brilliancy. 
Dog-Fishes (Spinacide).—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, 
Fic. 197.—Hammer-headed shark, 
Hammer-Head Shark (Sphyrnide).—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 
