184 CRUSTACEANS. 



In the discussion we have already treated of three species, where the 

 hind limbs are so fashioned as to prove auxiliaries in swimming. In 

 fact, the last now remaining, is a beautiful image, in miniature, of that 

 which precedes it. This will enable us to avail ourselves of considerable 

 abbreviation, though neither that, nor subdivision, may be sufhcient. 

 Form and habits are for this the most effectual guides to assign them 

 their proper place in the Sj-stema Nat urns. 



The Cancer piisiUus is one of the smaller Crabs belonging to this 

 section of the Crustaceans. The body broadens about an inch between 

 the margins next the limbs, or across the shell, where the limbs of larger 

 specimens are about two inches asunder. 



The form of the shell is often somewhat rudely trapezoidal, the 

 breadth in front being double the breadth behind, which is the distance 

 that the hind pair of limbs stand apart. The margin, from the eyes to 

 a distance on each side, is indented by five obtuse teeth, and there are 

 three in front ; the eyes and antenna; may be compared to those of the 

 preceding species. But, it must be observed, that as the back of the 

 Common Crab is smooth, and swells regularly, here it is indented by 

 symmetrical depressions in various specimens. Also, the hind limbs are 

 broad, flattened, and finely fringed, the second articulation as if subdi- 

 vided, all as in the Portnnns livid us, to which animal it bears an intimate 

 resemblance. 



It would be difiicult to describe the great variety of colour, its in- 

 tensity and distribution, prevalent among the different specimens of 

 these pretty little animals. They are generally either light or dark, 

 plain and uniform, or mottled. A broad triangular figure, a wedge-shaped 

 belt or stripe, frequently crosses the back from the front of the margin, 

 leaving the remainder of the surface light on each side of the limbs, di- 

 viding it as if into three compartments. Whatever predominates above, 

 the limbs are always marbled. 



Neither intensity nor distribution of colour seem to be governed by 

 any obvious rule, whether uniformly dark, or beautifully variegated and 

 very light. 



This creature feeds very voraciously on fish, which facilitates its 



