BRANCH CHORD AT A: CLASS MAMMALIA 



397 



and killing their prey. They are mostly fur-covered and 

 many are hunted for their skin. They have never less 

 than four toes, which are provided with strong claws that 

 are frequently more or less retractile. The canine teeth 

 are usually large, curved, and pointed. 



While most of the Ferae live on land, some are strictly 

 aquatic. The true seals, fur-seals, sea-lions, and walruses 

 comprise the aquatic forms, all being inhabitants of the 

 ocean. The true seals, of which the common harbor seal 

 (Phoca I'itulina) is our most familiar representative, have 



FIG. 156. A buffalo, Bison bison, killed for its skin and tongue, on the 

 plains of Western Kansas thirty years ago. (Photograph by J. Lee 

 Knight.) 



the limbs so thoroughly modified for swimming that they 

 are useless on land. The fur-seals, sea-lions, and walruses 

 use the hind legs to scramble about on the rocks or 



