I9I7'] v'^' Krmp : Notes on Crustacea Decapoda. 251 



B. The surface of the carapace is smooth, rarely 

 uneven ; its regions are never delimited by sharp- 

 cut grooves. The ischium of the external maxilli- 

 pedes is longer than the merus. [The rostrum, 

 when present, is simple. The external maxilli- 

 pcdes are broad and completely close the buccal 

 cavern. The 3rd, 4th and 5th segments of the 

 abdomen of the male are fused and the sutures 

 obliterated] ... ... ... ... Elamena, Milne- 



Edwards. 



Of these genera only the last three are found on the Indian coasts. 

 Geniis Rhynchoplax, Stimpson. 



1S5S. Rhyiiclioplax, Stimpson, Proc. Acad. Sci. PJiiladelphia, X, p. khj 



^55], 

 1900. Hynteincus, Alcock (not of Dana), 'jfoiirn. Asiat. Soc. Bengal, LXIX, 



P- 387- 

 1907. Rliynchoplax, Stimpson, Smiths. Misc. Coll., XI^IX, p. 147. 



The carapace is circular, ovate or polygonal in outline and is 

 depressed ; the upper surface is sunken with the usual grooves 

 sharply defined and the margin upturned. The rostrum is triden- 

 tate or trilobate, the lateral processes very rarely absent. The 

 epistome is of good length and the buccal cavern is bounded an- 

 teriorly by a sharp ridge. The external maxillipedes are compara- 

 tively slender and, when normally folded, gape widely in the 

 middle line ; the merus is longer than the ischium and the dactylus 

 is, as usual, short. The chelipedes in both sexes are stouter than 

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

 5th segments are fused and the sutures between them completely 

 obliterated. 



This genus is very closely related to Halicarcinus, but is dis- 

 tinguished by the more slender merus and ischium of the external 

 maxillipedes and by the fact that certain segments of the male 

 abdomen are fused. 



The six Indian species of Rhynchoplax together with the two 

 obtained by Dr. Annandale in Siam and China may be distinguished 

 in the following manner : — 



I. A large forwardly directed tooth or process on either 

 side of carapace above base of TSt walking legs [ros- 

 trum tridentate ; a sharp post-ocular tooth visible in 

 dorsal view], 

 A. Carapace subcircular, its antero-latcral border 

 armed with one or two blunt teeth ; merus of cheli- 

 pede armed with several strong teeth on its upper 

 border ; dactyli of la.st three legs armed with a series 

 of small teeth. 



1 . Two teeth on antero-lateral border of carapace ; 

 chela of adult male more than twice as long as 

 high, palm rounded below, fingers not gaping- 



and armed with regular teeth ... ... R. ivood-inasoni 



2. Only one tooth on antero-lateral border of (WIcock). 

 carapace ; chela of adult male much less than 



twice as long as high, palm keeled below, 

 fingers widely gaping and with irregularly- 

 disposed teeth ... ... ... R. alcock i, sp. 



nov. 



