138 Records of the Indian Museum. [Vol. XXII, 



include C. siamica, Prime, in the list of Indian species, as there 

 are specimens of this species in the Indian Museum collected at 

 Rangoon, Burma and from the Nicobar Islands. 



As to the grouping of the various species of this genus the 

 two attempts of Deshayes ' and von Martens^ have to be con- 

 sidered. The former is only an arbitrary classification of all the 

 species of the genus; von Martens' work, however, in which the 

 shape and form of the shell are utilised for the grouping of the 

 Indo-Pacific forms into four sections, is more satisfactory and is 

 followed in this paper. The Indian species fall into the following 

 groups : — 



A. Proclives .. C. bengalensis , C. siamica. C. impressa. 



B. SuBORBicULARES . . C proxima, C. tennentli. 



C. Exp.\NSAE . . C. ccvlonica. 



D. CyperinoidEAe . . C. galaiheae. 



As a result of my study of the Indian ]Museum collection the 

 geographical distribution of the various species has had to be 

 greatly e.xtended. C. bengalensis is confined to Bengal, C. ceylon- 

 ica and C. tennentii are endemic in Ceylon, C. galatheae is widely 

 distributed in the Andam.an and Nicobar Islands, C. siamica has 

 a wide range in Cochin-China, Siam, Burma and the Nicobar 

 Islands, C impressa occurs in the Philippines, Dutch East Indies, 

 Ceylon and on the West Coast of Peninsular India while C. proxi- 

 ma is found only in Siam and the Mergui Archipelago. 



Cyrena bengalensis, Lamarck. 

 Plate XX, figs. I, 2. 



iqi.=;. Cyrena bengalensis. Preston, Faun. Brit. hid. Fresliw. Moll. 

 pp. 205, 206. 



Preston in the work cited above has given a complete synon- 

 ymj' of the species but the descriptions of the shell in all pre- 

 vious memoirs are very inadequate. I, therefore, give below a 

 detailed description of the shell based on the large series of speci- 

 mens in the Indian Museum. 



Shell large, solid, subtrigonal, rather swollen but not very 

 high, very inequilateral, covered with a brownish black epidermis 

 with coarse striae, and with the regions of growth distinctly 

 marked by still coarser lines; dorsal margin very small, somewhat 

 angulate ; anterior margin rather short, concave in its upper or 

 proximal f of the length then regularly curving round to the 

 podium; posterior margin very long, high, markedly convex and 

 regularly curving down to the gonium, where it meets the ventral 

 border in a broadlj^ rounded acute angle ; ventral border nearly 

 straight except in the podial and gonial angles where it is curved 

 upwards ; umbones of fair size, situated anterior to the middle, 



1 Desha3es. Cat. Conchifera Brit. Mus. 1, pp. 241, 242 (1853)- 

 '^ Von Mattens in Max Weber's Zool.-Er^eb. Nieder. Ost.-Ind. IV, p. 9 

 (1897). 



