234 BULLETIN 152, UNITED STATES NATIONAL MUSEUM 



transversely. Antennal flagella short, slender. Anterior margin 

 of buccal cavity well defined, not overlapped by the outer maxillipeds. 

 Legs ambulatory. 



KEY TO THE AMERICAN GENERA OF THE FAMILY XANTHIDAE 30 



A'. Tlie ridges that define the efferent branchial channels, if present, are low 

 and are confined to the posterior part of the endostome, never reaching 

 to the anterior boundary of the buccal cavity. 

 B'. Fronto-orbital border less than half the greatest width of carapace. 



C. Antero-lateral border of carapace thin, cristif orm ; upper border at 

 least of arms and of merus, carpus and propodus of legs sharp, 



cristif orm Platypodia, p. 246. 



C^. Antero-lateral border of carapace and upper border of legs not 

 cristiform. 

 D'. Antero-lateral border entire up to a strong lateral epibranchial 

 tooth. Carapace perfectly smooth without trace of regions. 

 Chelipeds unequal, fingers pointed. Front three-lobed. 



Carpilius, p. 239. 

 D^. Antero-lateral border cut into teeth or lobes. 



E'. Anterior half of buccal frame nearly vertical. Fronto- 

 orbital width about one-third width of carapace. Orbits 

 largely dorsal in position. Male abdomen with segments 



3-5 fused Paraxanthus, p. 286. 



E*. Buccal frame horizontal. Orbits forward looking. 



F'. Fronto-orbital border less than a third width of cara- 

 pace. Regions indistinctly marked. Antero-lateral 



border obscurely lobed Homalaspis, p. 287. 



F2. Fronto-orbital border more than a third width of 

 carapace. 

 G'. Carapace narrow, lateral teeth about nine, front 

 strongly produced. Male abdomen with seg- 

 ments 3-5 fused Cycloxanthops, p. 289. 



G^. Carapace wider, lateral teeth or lobes not more 

 than five. 

 H'. Carapace more or less octagonal, the first 

 two antero-lateral teeth obsolete or nearly 

 so, the last three laterally prominent. 

 J'. Fronto-orbital distance nearly half width 

 of carapace. Orbits long. 



Lophopanopeus, p. 319. 

 P. Fronto-orbital distance less than two- 

 fifths of width of carapace. Orbits 

 subcircular. Front four-toothed. 



Gaudichaudia, p. 278. 

 H^. Carapace with antero-lateral margins foiming 

 a regular arch. 

 J'. Carapace usually conspicuously lobulate, 

 granulate, or eroded. 

 Ri. Carapace lobulate or granulate, che» 

 lipeds and legs also granulate, 

 often hairy. Small species. 



Actaea, p. 250. 



M Subfamilies are omitted as no satisfactory arrangement to include all genera has yet been made. 



