14 BULLETIN 97, UNITED STATES NATIONAL MUSEUM. 



A*. Mouth field roughly square. 



B 1 . Last pair of legs abnormal, dorsal. Female openings coxal. First 

 abdominal limbs of female present. Gills usually many. 



Subtribe Dromiacca. 



B 2 . Last pair of legs normal, rarely reduced, not dorsal, except in Cymopolia 

 and Retropluma. Female openings sternal. First abdominal limbs 

 of female wanting. Gills few Subtribe BRACHYGNATHA. 



KEY TO THE SCPERFAMILIES OF THE SDBTBIBE BHACHYGNATHA. 



A 1 . Fore part of body narrow, usually forming a distinct rostrum. Body more 

 or less triangular. Orbits generally incomplete. 



SuperfarnSly OxyrJiyncha. 



A*. Fore part of body broad. Rostrum usually reduced or wanting. Body 

 oval, round, or square. Orbits nearly always well inclosed. 



Superfamily BRACHYRHYNCHA. 



KEY TO THE FAMILIES OF THE SUPEHFAMILY BttACHYRHYNCHA. 



A*. Orbits formed, but more or less incomplete. Second antennal flagella, when 

 present, long and hairy. Rostrum present. Body elongate-oval. Fore 



edge of mouth indistinct Family EunjaUdac=Corystidae. 



A". Orbits complete (though fissures may remain), except in the Mictyriuae, 

 where the eyes are almost or quite unprotected. Body rarely elongate- 

 oval. Rostrum often wanting. Second antennal flagella usually short, 

 not hairy. 



B 1 . Carpus of third maxillipeds articulates at or near antero-internal angle 

 of the merus. Body usually round or transversely oval. Male open- 

 ings nearly always coxal. In many species the right chela is always 

 larger than the left. 



C 1 . Legs more or less distinctly adapted for swimming. Usually a small lobe 

 on the inner angle of the endopodite in the first maxillipeds. The 



first antennae fold slanting or transverse Family Portunidac. 



C*. Legs not adapted for swimming, or if so modified, then the male genital 

 duct opens sternally or runs in a sternal groove. Inner lobe on the 

 endopodite in the first maxillipeds wanting. 



D 1 . Fresh-water crabs with the branchial region much developed and 

 swollen. Body often squarish, but male openings coxal. 



Family Potamonidae. 



D 1 . Marine crabs with the branchial region not greatly swollen. 

 E 1 . First antennae fold lengthwise. 



F 1 . Carapace subcircular. Second antennal flagella either long and 



hairy or wanting Family Atelecyclidae. 



F a . Carapace broadly oval or hexagonal. Second antennal flagella 



present, short, not hairy Family Cancridae. 



E*. First antennae fold slanting or transversely. 

 F 1 . Body usually transversely oval. Male openings rarely sternal. 

 Not sharply separated from the following family. 



Family Xantliidae. 



F*. Body usually square or squarish. Male ducts open on the sternum, 

 or, if coxal, pass along a groove in the sternum. Not sharply 

 separated from the foregoing family. 



Family GONEPLACIDAE, p. 15. 



