98 CALIFORNIA ACADEMY OF SCIENCES. 



Subtribe OXYSTOMATA, or LEUCO- 



SOIDEA. 



Carapace very variable in form. Epistome rudimentary. Buccal area 

 narrowed in* front. Antennules longitudinal or oblique. The afferent 

 branchial channels enter either behind the pterygostomian regions and in 

 front of the chelipeds, or at the antero-lateral angles of the palate. Verges 

 of the male in the sternum or the coxse. 



Family CALAPPID^. 



Afferent branchial channels opening behind the pterygostomian regions 

 and in front of the chelipeds. The palp of the external maxillipeds is not 

 entirely concealed by the merus. Verges of the male on the coxae of the 

 last pair of legs. 



Genus Platymera Milne-Edwards. 



Carapace convex, transversely elliptical, with a strong spine at the lat- 

 eral angles; antero-lateral margins arcuated and dentate; postero-lateral 

 margins not produced into lateral expansions. Front narrow. Orbits 

 oval, deep, of moderate size, and furnished with a prominent fissure in the 

 lower margin. The basal antennal joint is situated in the wide inner 

 orbital hiatus and does not reach the front; flagellum small. Buccal 

 cavity comparatively in front and more or less completely divided by a 

 median ridge. The external maxillipeds do not completely cover the 

 anterior portion of the buccal area; merus subequal to the ischium and 

 excavated at the antero-interual angle; palp situated at the antero-internal 

 angle of the merus and not completely covered over; the epipodite forms 

 a broad, semilunar plate which covers the opening of the afferent branchial 

 channels. Chelipeds large and, when folded, fitting closely to the body; 

 merus trigonal; hands large, compressed, distally widened, surmounted 

 by a laminate and dentate crest, and furnished with a longitudinal, granu- 

 lated ridge near the lower side of the outer surface. Ambulatory legs 

 slender, compressed, and furnished with long, styliform dactyls; first three 

 pairs subequal in length, the fourth the shortest. Sternal plastron oval. 

 The abdomen in the male is composed of five distinct joints, the third of 

 which is furnished with a prominent, transverse posterior crest. 



Type. — P. Gaudichaudii Milne-Edwards. 



