228 



SYSTEMATIC ZOOLOGY. 



solid pincing-claws. With increase in size the crab must 

 move into a larger shell. In other Anomura the back is 

 soft, and these 'false hermits' carry half a clam-shell 

 about with them to cover their weak point. 



Only a few of the true crabs or Brachyura live in fresh 

 water. In the tropical and semi-tropical regions are 



FIG. 55. Hermit-crab (Eupagurus bernhardus) in a snail-shell. From Emerton. 



those which live on the land; but the great majority a 

 thousand different species live in the sea. The larger 

 species have some economic value as food, but all of them 

 are important as scavengers. In America 'soft-shelled 

 crabs ' are prominent in our markets at the proper season 

 of the year. During the rest of the time this crab, known 

 as the 'blue crab ' (Neptunus hastatus), has as hard a 

 shell as any crab, but when the proper moment comes 

 the shell splits across the hinder margin, and out from 

 this opening comes the body covered only with the thin- 

 nest skin, and at this time alone it is a soft 'shell.' All 



