1900.] A. Alcock — Garcinological Fauna of India. 385 



fingers : lingers slender and tapering, in the male there is an enlarged 

 tooth near the base of the dactylus. 



The legs, like the chelipeds, are rough under the lens : the edges 

 of their propodites and dactyli are finely plumed : none of their joints 

 are dilated: the first pair, which are slightly the longest, are about 

 If times the length of the carapace. 



In the Indian Museum are 5 specimens from the Andamans and 

 2 from the Nicobars. 



Family HYMENOSOMID^E, Ortm. 



Key to the Indian Genera or Sub-genera. 



I. Front conspicuously tridentate : the external maxillipeds 

 do not quite meet across the buccal cavern and their 

 exognath is not hidden in its proximal portion : chelipeds 

 muoh more massive than the legs ... ... ... ... Hymenicus. 



II. Front broadly triangular, or truncated : the external 

 maxillipeds completely close the buccal cavern and their 

 exognath is completely hidden : — 



1. The interantennular septum is a prominent plate : 

 chelipeds in the male much more massive than the 



legs Elamena. 



2. The interantennular septum is a mere ridge ; 

 chelipeds in both sexes slender, not stouter than 



the legs Trigonoplax. 



Elamena, Edw. 



Elamena t Milne Edwards, Hist. Nat. Crust. II. 33, and Ann. Sci. Nat., Zool., 

 (3) XX. 1853, p. 223 : Dana U. S. Expl. Exp. Crust, pt. I. p. 379 : A Milne Edwards, 

 Nouv. Archiv. du Mus. IX. 1873, p. 321. 



Carapace flat dorsally, thin and almost lamellar, triangular or sub- 

 circular, its edges are usually turned up to form a thin circumscribing 

 ridge and are without any teeth. Front broadly triangular, or some- 

 times truncated. There are no orbits and the eyes, though they may 

 be hidden beneath the front, are exposed aud non-retractile : a small 

 post-ocular tooth may be present or not. The antennules fold beneath 

 the front and are not visible from above when folded : the interanten- 

 nular septum is a prominent plate. Antennal peduncle slender, tho 

 nagellum of no great length. 



Epistorne well defined and remarkably long fore and aft. Buccal 

 cavern square ; the external maxillipeds, which completely close it, 

 have the merus about as large as the ischium, the palp articulating not 

 fair from the antero-external angle of the merus, and the exognath 

 slender and concealed. 



