OUR CARCINOLOGICAL FRIENDS. 85 
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, Pl. 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 (Cullinectes hastatus) is thus the type 
of a group of swimming crabs, of which the beau- 
tiful ‘lady’s crab’ (Platyonichus ocellatus, Pl. 6, 
Fig. 5) is another representative. It is not to be 
assumed that these swimmers constantly float on 
8 
