BOX- AND OYSTER-CRABS 287 



FAMILY CALAPPIDJE 

 GENUS Calappa 



C. flamma, the box-crab. This singular animal lives on sandy and 

 muddy bottoms offshore, from North Carolina southward. The cara- 

 pace is broad and straight on the posterior side, and is curved on the 

 anterior side, narrowing to the front. The posterior side has promi- 

 nent denticulations. The body is one and a half inches thick, about 

 four to five inches wide, and two to three inches long. The chelae are 

 large, broad, and flattened, and are so arranged that when flexed they 

 fit closely together across the front. When folded, and the small legs 

 are withdrawn under the carapace, the animal is shut up as if in a box, 

 and resembles a shell. When in danger it closes its doors, as it were, 

 and abandons itself to the waves, which often cany it ashore. The 

 crested claws resemble the head of a cock. (Plate LXIV.) 



FAMILY PINNOTHERIIDJE 



GENUS Pinnotheres 



JP. ostreum, the oyster-crab. The female of this species lives in the 

 gill-cavity of the oyster, and is particularly abundant in oysters from 

 the Chesapeake. The males are seldom seen, and rarely occur in the 

 oyster, but swim freely about. They 

 are smaller than the female, have a 

 firmer shell, and are dark brown above, 

 with a dorsal stripe and two conspicuous 



spots. The under side of the legs is /X\7 r>\ A~) \M\ i T i 

 whitish. The female is commensal, at /YA^ V A v X/JSV 

 least in the adult form, and its thin, 

 whitish, transparent carapace is tinged 

 with pink. The species P. maeulaiiim 



! -fw ,. 7 f T . lx j .1 _ Pinnotheres ostreum, the oyster-crab; male, 



lives in Mytihu eduhs (mussel) and in the enlarged ; onr dia y meters . 



smooth scall op , Pecten magellanicus. The 



oyster-crab is a true messmate, and its presence in the oyster may be ad- 

 vantageous in helping to provide food for its host. This crab, like the rest, 

 holds its eggs in the posterior feet until hatched, when the larvae leave the 

 parent and swim about for a while. The females, at the megalops stage, 

 enter oysters sometimes two enter the same oyster, but seldom more 

 than one ; there it remains permanently, growing to the size of an inch 

 or more in diameter, and becomes a degenerate. The eyes become 

 smaller ; the shell never hardens, like its allies which live in open water ; 

 its limbs and chelae are weak ; and it has no pugnacity, the protection 

 afforded by the oyster doing away with the need for the common protec- 

 tive features of its kind. Pinnixa cylindrica, a related species, lives in 

 the tubes of large annelid worms as a commensal. 



