380 BULLETIN 129, UNITED STATES NATIONAL MUSEUM 



Chelipeds long and strong, especially in male; fingers deeply 

 hollowed out at tip, gaping considerably when shut. Legs robust, 

 armed with spines and terminated by hooked dactyls which are often 

 armed with spines on lower surface. Abdomen of male formed of 

 seven free segments. 



Restricted to America and the Bermudas. 



KEY TO THE SPECIES OF THE GENUS MITHRAX 



A'. Carapace without smooth, oblique, branchial sulci. Subgenus Mithrax, p. 383. 

 B'. Manus armed above with spines or spinules. 



C. Two spines only on basal segment of antenna spinosissimus, p. 383. 



C^, Three spines on basal segment of antenna. 

 D*. Carapace not paved with flattened granules. 



E'. Carapace widest between tips of fourth antero-lateral spines (not 

 counting orbital spine). 

 F^ Three or four supraorbital spines, exclusive of preorbital and 

 exorbital spines. Propodites of legs very long and slender. 



cornutus, p. 386. 

 F^. Two supraorbital spines only, exclusive of preorbital and exor- 

 bital spines. Propodites of legs moderate. Size small. 



acuticornis (over 18 mm. long), p. 388. 



E^. Carapace as wide between tips of third antero-lateral spines as 



between tips of fourth spines. Carapace closely granulate and 



tuberculate and densely pilose pilosus, p. 394. 



D^. Carapace paved with flattened granules, concealed by short hair. 



verrucosus, young, p. 400. 

 B2. Manus not armed above with spines or spinules. 

 C. Rostral horns sharp or acute. 

 D^ Rostral horns elongate. 

 E^ A tubercle at middle of proximal end of outer surface of manus. 



orcutti, p. 397. 

 W. No tubercle on outer surface of manus. 

 F^ Carapace with a lateral angle. Size small. 



G'. Hepatic and first branchial spine bifid, or with a secondary 



spine acuticornis, small (under IS mm. long), p. 388. 



G^. Hepatic and first branchial spine simple spinipes, p. 391. 



F^. Carapace with sides rounded, without angle. 



G'. No sharp spines, only tubercles or stout, blunt spines on dorsal 



surface of carapace armatus, p. 399. 



G^. Some spines on dorsal surface of carapace __ rostratus, p. 386. 

 D*. Rostral horns very short. Carapace ovate-oblong. 

 E^ A well marked postero-lateral spine. 



F^ Four stout antero-lateral spines heraphilli, immature, p. 395. 



F^. Only two antero-lateral spines holderi, p. 392. 



E^. A small postero-lateral tubercle. Carapace densely pubescent. 



bahamensis, p. 393. 

 C^. Rostral horns blunt, either subtruncate or tuberculiform. 

 D^ Carapace paved with close-set granules or tubercles. 



E'. Carapace paved with convex tubercles each of which is gran- 

 ulate hemphilli, mature, p. 395. 



E^. Carapace paved with flat, tessellated granules. 



F'. Lateral margins of carapace spinous. Wrist nearly smooth above, 

 three tubercles on inner edge verrucosus, p. 400, 



