CRABS. 



271 



might easily be mistaken for different species. The 

 name is derived from a supposed resemblance which 

 the carapace bears to the human face. On some 

 coasts it is very abundant, and those acquainted with 



Fig. 20Z. 



Four-horned Spider Crab (Pisa tetraodon), male. 



its habits can easily find it at low water, by slight de- 

 pressions in the sand, through which its long antennae 

 are seen protruding. As a burrowing crab, these long 

 antennas are of great service to it, inasmuch as they 

 are hollow, and thus form tubes through which the 

 water passes to the gills. The male especially has a 

 peculiar habit of occasionally sitting upright, like a 

 dog in the act of begging, and in this position its very 

 long fore-legs assist it materially. The " northern" 

 stone crab (Lithodes maid) is also a good aquanu.m 



