THE GRAPSOID CRABS OF AMERICA. 15 



B*. Carpus of third ruaxillipeds does not articulate at or near the inner angle 

 of the merus. Body usually squai'e or squarish. Male openings sternal 

 except in Rctropliirna, where the duct passes along a sternal groove to 

 the coxopodite. In no species (CymopolUdae excepted) is the right 

 chela always larger than the left. 

 C 1 . Small, usually commensal crabs, with very small eyes and orbits. Body 



usually more or less rounded Family PINNOTHERIDAE, p. 61. 



C*. Free-living crabs, with eyes not specially reduced and usually a square 



body. 



D 1 . Last pair of legs dorsally placed and weaker than the others. Inter- 

 mitennulnr soptum very thin. No distinct epistome. Exopodites of 

 third maxillipeds not hidden. 



E J . Front narrow. Female openings in normal position. Third maxilli- 

 peds subpediform, not covering the mouth. 



Family Rctroplumidae=Ptenop1acidae. 



E a . Front moderately broad. Female openings on the sternal segment 

 corresponding to the first pair of walking legs. Third maxillipeds 

 cover the mouth to a large extent and have very small meropo- 



dites Family CYMOPOLIIDAE=PaJicidae, p. 182. 



D a . Last pair of legs not dorsally placed nor markedly weaker than the 



rest. Interantennular septum not very thin. 

 E 1 . A gap of greater or less size is left between the third maxillipeds. 



Front very or moderately broad. 



F 1 . Sides of the body either straight or very slightly arched. Shape 

 squarish. Front broad. Rarely true land crabs. 



Family GRAPSIDAE, p. 224. 



F*. Sides of the body strongly arched. Shape transversely oval. 



Front narrower. Land-crabs_-Family GECARCINIDAE, p. 339. 



E*. The third maxillipeds almost or quite close the mouth. Front 



moderately or very narrow Family OCYPODIDAE, p. 365. 



B 8 . Merus of third maxillipeds small, bearing terminally a carpus of nearly 

 its own width. Iscliiuin very broad. Body somewhat oblong. First 

 antennae not retractile into sockets. Parasitic on corals. 



Family Hapalocarcinidae. 



Family GONEPLACIDAE (Dana). 



Gonoplacidae DANA, Amer. Journ. Sci., ser. 2, vol. 12, 1851, p. 285; U. S. 

 Expl. Exped., vol. 13, Crust., pt. 1, 1852, pp. 308 and 310. AT.COCK, 

 Journ. Asiat. Soc. Bengal, vol. 69, 1900, pp. 283, 286, 292, 297, and 

 synonymy. 



The palp of the external maxillipeds articulates at or near the 

 toitero-internal angle of the merus ; the exognath is of normal size and 

 if not concealed. The interantennular septum is a thin plate. The 

 division of the orbit into two fossae is usually not indicated. The 

 genital ducts of the male usually perforate the base of the last pair 

 of legs, often passing forward through a groove in the sternum. 



KEY TO THE AMERICAN SUBFAMILIES AND GENERA OP THE FAMILY GONEPLACIDAE. 



A 1 . The base of the third segment of tlie male abdomen covers the whole space 

 between the last pair of legs. 



