248 Records of the Indian Museum. [\'ol. XIII, 



The generic position of a number of other species is doubtful, 

 but I think it will eventually be found that all those from southern 

 latitudes hitherto referred to the genera Hymenicus and Hymeno- 

 sonia ' belong in reality to Halicarcinus. H. planatus, if the records 

 are to be trusted, is circumpolar in distribution and the species 

 listed above are without exception from southern latitudes. The 

 forms that can be referred to Rhynchoplax are, on the other hand, 

 all found on the Asiatic coasts, from which no representative of 

 Halicarcinus has yet been obtained. 



The genus Rhynchoplax, in my estimation, comprises Stimp- 

 son's two species, R. messor from Japan and R. setirostris from 

 Hong Kong, de Man's Elamene filholi^ from near Batavia, Alcock's 

 Hymenicus wood-masoni and H. inachoides from India and six other 

 species described below. It probably includes also Miss Rathbun's 

 R. coralicola^ from Singapore. 



A species of H3mienosomatidae found on the banks of the R. 

 Hughli, near Calcutta, does not appear to be admissible into any 

 of the genera hitherto recognized ; it is described below under the 

 name Hymenicoides carteri. In its structure this species shows a 

 high degree of specialization and generically is related to Halicar- 

 cinus and Rhynchoplax. It agrees with the former of these genera 

 in having the sutures of all the segments of the male abdomen dis- 

 tinct and with the latter in the slender form of the basal segments 

 of the third maxillipedes : it differs from both in the remarkably 

 elongate dactylus of the latter appendages and in the entire 

 absence of a rostrum (see text-fig. 16, p. 267). 



In Hymenicoides the antennule is completely exposed in dorsal 

 view. This character has frequently been used as a generic 

 criterion, but in my opinion is of specific importance only, being 

 due almost entirely to the extent to which the rostrum is reduced. 

 In Rhynchoplax the rostrum is normally trilobate and well de- 

 veloped, but in R. nasalis, sp, nov., the lateral portions are sup- 

 pressed, with the result that the antennules, just as in Hymeni- 

 coides carteri, are visible from above. 



The genus Elamena was established by Milne-Edwards in 

 1837,* the type species being Desmarest's Hymenosoma mathaei^ 

 from the lie de France. Haswell's suggestion that this species 

 is merely the young of Halicarcinus planatus'^ has been contested 

 by Stebbing and is certainly incorrect. That Riippell's identifica- 

 tion'' of Desmarest's species is correct may be assumed from the 



' Kxcepl, of course, Nviiu'iiosoiitu orbiciilnre and the synonymous //. geo»iet- 

 I'lcnm. 



2 De Man, Ai-cli.f. Natiii-gesch., LIII, i, p. ;,N6, pi. xvii, fig. 3 (1887;. 



' Hathbun, K. Danske Vid. Sehk. Skviff. i;), iiatiirviiL og'math., V. p. 316, 

 lexl-fig. 5 ( 1910). 



* Milne-Edwards. Hist. iiat. Cnisf., II, p. 3;, ( 1837J. 



6 Desmarest, Cousiif. gen. Crnsf.. Paris, p. 163 (1825I. 1 have not seen 

 this species. 



6 Haswell, Cat. Australian Crust., p. 114 (1882). 



' Riippell. Beschveih. .Ahhild. 24 Arteii Krnhheii. Frankfurt, p. .'i. pi. v, 

 fig. I (1S301. 



