THE GRAPSOID CKABS OF AMERICA. 15 



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

 of the merus. Body usually square or squarish. Male openings sternal 

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

 the coxopodite. In no species {Cymopoliidae excepted) is the right 

 chela always larger than the left. 

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



usually more or less rounded Family PINXOTHERIDAE, p. Gl. 



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

 body. 

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

 niitennuiar sentuni very thin. No distinct epistome. Exopodites of 

 third maxlllipeds not hidden. 

 E\ Front narrow. Female openings in normal position. Third maxllli- 

 peds subpediform, not covering the mouth. 



Family RctropJumidae=PtcnopIacidae. 



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



corresponding to the first pair of walking legs. Third maxlllipeds 



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



dites Family CyMOrOLIIDAE=/'o?JC(c/«e, p. 1S2. 



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

 rest. Interantennidar septum not very thin. 

 E\ A gap of gi-eater or less size is left between the third maxlllipeds. 

 Front very or moderately broad. 

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

 squarish. Front broad. Karely true land crabs. 



Family GRAPSIDAE, p. 224. 



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



Front narrower. Land-crabs— Family GECARCINIDAE, p. 330, 



E'. The third maxlllipeds almost or quite close the mouth. Front 



moderately or very narrow Family OCYPODIDAE, p. 3G5. 



B'. Merus of third maxlllipeds small, bearing terminally a carpus of nearly 

 its own width. Ischium 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, 1S51, p. 2S5; U, S. 

 Expl, Exped,, vol, 13, Crust., pt, 1, 1852, pp. 308 and 310.— A r.cocic, 

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

 synonymy. 



The palp of the external maxlllipeds articulates at or near the 

 {tntero-internal angle o^the merus; the exognath is of normal size and 

 JF 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 GENEUA OF THE FAMILY GONEPLACID.\E. 



A\ The base of the third segment of the male abdomen covers the whole space 

 between the last pair of legs. 



