34 BULLETIN 152, UNITED STATES NATIONAL MUSEUM 



The antennules fold transversely. The basal anteuiial article is 

 peculiarly short and has its antero-^xternal angle produced to form a 

 lobule or spine extending into the orbit; the flagellum, of moderate 

 length, stands in the orbital hiatus. Epistome short or even linear, 

 sometimes prolonged in the middle line to form a spine lying below the 

 interantennulary septum. Buccal cavity squarish, broader than long, 

 efferent branchial channels almost always well defined. Palpus of 

 outer maxillipeds subcylindrical. Chelipeds longer, usually much 

 longer than any of the legs, and massive; arm with spines; both inner 

 and outer angles of wrist spiniform; palm prismatic, costate, and 

 usually with spines, fingers usually nearly as long as the palm and 

 strongly toothed. Ambulator}^ legs compressed; in the last pair the 

 meriis and carpus are short and broad; propodus and dactylus typi- 

 cally foliaceous and paddle-like for swimming. Abdomen of male 

 triangular, five-segmented, the third, fourth, and fifth segments 

 being fused ; the first segment in both sexes is almost entirely concealed 

 beneath the carapace. 



Found in tropical and temperate seas. 



The chelipeds of the female are shorter than those of the male and 

 sometimes stouter or more swollen; the carapace may be narrower 

 than in the male. In the young the carapace is often narrower in 

 proportion to its length than in the old; the antero-lateral teeth may 

 be more unequal; usually the lateral spine is longer than in the full 

 grown but the reverse is true in some cases. The descriptions' of 

 species are based on the old so far as possible. 



KEY TO THE AMERICAN SUBGENERA AND SPECIES OF THE GENUS P0ETUNU3 



A'. Carapace wide; antero-lateral margin the arc of a circle with long radius, 

 whose center is near the posterior margin of the carapace. 



Subgenus Portunus, p. 36. 

 B^. Without stridulating apparatus. Posterior angles of carapace unarmed. 

 C. Postero-distal margin of merus of swimming feet unarmed. 



D^ Carapace convex, for the most part smooth and glossy; palms 



swollen, only one spine on upper margin sayi, p. 37. 



D^. Carapace uneven, not smooth and glossy; two spines on upper 

 margin of palm; submedian teeth of front very small. 

 E'. A spine at extremity of outer margin of arm. Subnledian 

 teeth of front much less advanced than outer teeth. 



anceps, p. 42. 



E^. No spine at extremity of outer margin of arm. Submedian 



teeth of front nearly or quite as advanced as outer teeth. 



ventralis, p. 43. 



C^. Postero-distal margin of merus of swimming feet armed with a spine 



and spinules or with spinules only. 



D'. Postero-distal margin of merus of swimming feet armed with 



spinules and with a spine at the angle. 



E'. Carapace very wide; lateral spine nearly two-thirds as long 



, as antero-lateral margin acuminatus, p. 56. 



E-. Carapace narrower; lateral spine not longer than the width 

 of four adjacent teeth. 



