OUR CARCINOLOGICAL FRIENDS. g5 



and ornamentation. This is, however, a false con- 

 ception, for they differ among themselves not only 

 in important structural characters, but largely also 

 in habit. Some are habitually walkers of the sand, 

 others burrowers in the mud, a few parasitic on dif- 

 ferent animals, and others, again, good swimmers. 

 A number use the floating sea- weed for their home, 

 drifting far into mid-ocean. The famous Sargasso 

 Sea is a carcinological world of itself. Down to 

 a depth of several thousand feet in the sea the 

 lonely crab lurks about in the darkness, finding 

 companionship with the mollusks whose shells it 

 frequently robs. Again, On mountain heights, of 

 4000 feet elevation or more the land-crab (Birgo) is 

 not uncommonly met with on its travels. 



Look at the extremities of the last pair of legs 

 of the soft-shell crab (PL 6, Fig. 4) — the crab par 

 excellence of the Atlantic coast — and compare them 

 with the similar parts of the spotted or sand-crab 

 ( Cancer irroratus, PI. 6, Fig. 1), the common trans- 

 verse species, whose empty 'boxes' are to be found 

 at almost all times on the beach. In this species, 

 which can be readily recognized by the nine blunt 

 teeth projecting from each side of the anterior edge 

 of the carapace, they are merely pointed blades, but 

 in the soft-shell, the edible form, they are flattened 

 out into paddles, forming efficient swimming organs. 

 The soft-shell (Gallinecies kastatus) is thus the type 

 of a group of swimming crabs, of which the beau- 

 tiful ' lady's crab' (Plaiyonichus ocellaius, PI. 6, 

 Fig. 5) is another representative. It is not to be 

 assumed that these swimmers constantly float on 



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