340 BULLETIN 97, UNITED STATES NATIONAL MUSEUM. 



cealed, and sometimes without a flagellum. Antennular fossae nar- 

 row. Front of moderate breadth, always strong!}'' deflexed. Cara- 

 pace transversely oval, antero-lateral borders strongly arched, fronto- 

 orbital border very much less than the greatest breadth of the cara- 

 pace. Male openings sternal. 



KEY TO THE AMERICAN CJEXERA OF THE FAMILY GECAttCINIUAB. 



A\ Fronto-orbital border more than half width of carapace. Buccal cavern 

 elongate. Exognath of outer maxillipeds exposed and provided with a 

 flagellum. 

 B\ Outer maxillipeds gaping ; anterior margin of merus emarginate. Dactyli 



of legs spinous Cardisoma, p. 340. 



B*. Outer maxillipeds meeting; merus quadrangular. Dactyli of legs not 



spinous Ucides, p. 346. 



A*. Fronto-orbital border less than half width of carapace. Buccal cavern 

 liiomboidal. Exognath of outer maxillipeds concealed or nearly so and 

 without flagellum. 



B\ Palpus of outer maxillipeds hidden Gecarcinus, p. 351. 



B^ Palpus of outer maxillipeds exposed Gecarcoidca, p. 362. 



Genus CARDISOMA Latreille. 



Cardisoma Latreille, Encyc. Meth., Hist. Nat., Entom., vol, 10, 1825, p. 



68.5 ; type, C. guanhumi Latreille. 

 IHscoplax A. Milne Edwards, Ann. Soc. Entom. Prance, ser. 4, vol. 7. 1867, 



p. 284; type, D. lonfjipcs A. Milne Edwards=rof7ind«m (Quoy and 



Gaimard, 1825). 



Carapace deep, convex fore and aft, transversely oval or cordate, 

 lateral borders tumid and strongly arched owing to the vault-like 

 expansion of the gill chambers, pterygostomian regions densely 

 tomentose. 



Fronto-orbital border much more than half, and the deflexed and 

 nearly straight front about a fourth, the greatest breadth of the 

 carapace. Orbits deep, with the outer angle defined by a denticle, 

 and with the tooth at the inner angle well developed but distant 

 from the front ; eyes very loose in the orbits. 



Antennules obliquely folded, a good deal concealed by the front; 

 jnterantennular septum very broad. The antennae lie in the orbital 

 hiatus, which their broad basal joint nearly fills; flagellum very short. 



Epistome short, prominent and well defined; buccal cavern elon- 

 gate-squarish; the external maxillipeds have between them a rhora- 

 boidal gape in which the mandibles are exposed. In the external 

 maxillipeds, the merus is a longish joint, and carries the palp which 

 is large and not at all concealed, at its antero-external angle; the 

 exognath, which carries a flagellum, is exposed in much the greater 

 part of its extent. The exognaths of the other maxillipeds are 

 heavily fringed with coarse hair. 



