328 INVERTEBRATA OF MASSACHUSETTS. 



This is vulgarly called the Sea-spider or Spider-crab, on ac- 

 count of its small body and long legs. It is often caught in fishing 

 for flounders from the bridges about Boston. I am not aware 

 that it is used for food. The body is somewhat heart-shaped, and 

 may be four inches in diameter, while the legs of the female will 

 span four times that extent. 



Genus PINNOTHERES, Latr. 



P. o'sTREUM. " Thorax rounded before, on each side, some- 

 ivhat truncate behind ; clypeus a little advanced, entire ; hand gib- 

 bous above, near the base of the thumb.^^ Say. 



Pinnotheres ostreum, Say ; Journ. Acad. Nat. Sc, i. G7, pi. 4, f. 5. Milne-Edw. ; 

 Hist. Xat. des Crust., ii. 33. 



This little crab is of a rounded form, about the size of a dime, 

 and is very curious in its habits. It is not protected by a hard 

 crust, and in order to supply the want of it, the crab lives among 

 the oysters, and becomes a guest within the walls of their shells ; 

 whether a bidden and a welcome one or not, we have it not in our 

 power to say. The crab, however, seems not to molest the oys- 

 ter, and is even said to act as a monitor, to inform it when to close 

 its shell, so as to entrap the food on which they may both subsist. 

 They live peaceably together, are captured together, served up 

 for the table together, and are scarcely to be distinguished from 

 each other in the eating. 



Genus HIPPA, Latr. 



H. eme'rita. Body oval, convex, minutely wrinkled; tail 

 lanceolate, more than half as long as the body ; front with three 

 teeth ; eyes minute. 



Cancer emeritus, Lin. 



Hippa enierita, Fabr. ; Siippl. E7Uom. Syst., 370. Latr.; Hist. J\~at. des Crust., 



Ml. 17G, pL 52, f. L Desm. ; Consid., <^c., 174, pi. 29, f. 2. Milne-Edw. ; Hist. 



Nat. des Crust., ii. 209. 

 Hippa talpoida. Say ; Journ. Acad. Nat. Sc, i. IGO, 444. 



This curious animal is often called the Sand-bug. I have re- 

 ceived it from Martha's Vineyard, and it seems to extend from 



