I9I7-] S. Kemp : Notes on Crustacea Decapoda. 271 



may or may not be upturned. The rostrum is broadly truncate 

 or triangular, never tridentate or trilobate. The epistome is long 

 sometimes very long and is separated by a ridge from the floor of 

 the buccal cavern. The external maxillipedes are broad and 

 completely close the buccal cavern; the ischium is longer, some- 

 times much longer than the raerus, and the dactylus is, as usual 

 short. The chelipedes of the male may or may not be stouter 

 than the walking legs. In the abdomen of the male the 3rd 4th 

 and 5th segments are fused and the sutures between them' ob- 

 literated. 



Judging from the Indian species, this genus, here described 

 senstt lato, differs from all other Hymenosomatidae in the absence 

 of the customary grooves on the upper surface of the carapace 

 In the character of the male abdomen it resembles Rhynchopiax 

 but differs from that genus in the form of the rostrum and ex- 

 ternal maxillipedes. Milne-Edwards' Trigonoplax is, at most, a sub- 

 genus of Elamena [v. infra, p. 274). 



Six species of Elamena, s.l. are now known from the Indian 

 coasts, all being represented in the Indian Museum with the ex- 

 ception of E. gracilis, Borradaile. I have not been able to satisfv 

 myself regarding the position of this species and have in con- 

 sequence, omitted it from the following key. It is perhaps inter- 

 mediate between Elamena^ s.s. and Trigonoplax. 



I. Margin of carapace upturned ; rostrum with a vertical 

 keel on its lower surface and in frontal view T-shaped ; 

 chelipedes of male greatly swollen, much stouter than 

 legs [dactylus of walking legs apically triunguicu- 

 late] = Elamena s.s. 



A. Carapace as broad or broader than long'; 

 rostrum broad and squarely truncate ; a small 

 post-ocular tooth present, but not visible from 

 above 



B. Carapace longer than broad ' ; rostrum prom- 

 ment, triangular; no post-ocular tooth 



II. Margin of carapace not upturned, rostrum at most 

 with a small tooth at base of lower surface, not 

 T-shaped in frontal view ; chelipedes of male slender 

 not stouter than walking legs. = subgen. Trigono- 

 plax, 



A. Rostrum parallel-sided at base ; a strong post- 



ocular tooth visible in dorsal view ; dactyli of 

 walking legs armed in their distal third with 

 a series of small teeth [carapace about as long 

 as broad] ... 



B. Rostrum strictly triangular, its sides convergent 



from base to apex ; no post-ocular tooth visible 

 in dorsal view ; dactyli of walking legs triungui- 

 culate at apex. 



I. Carapace longer than broad,' its antero- 

 lateral margins curved and not longer 

 than postero-lateral ; rostrum flat above ; 

 a post-ocular tooth visible only from 



E. truncata 

 (Stimpson). 



E. sindensis, 

 Alcock. 



E. ( T.) cimex, 

 Kemp. 



' Rostrum included. 



