X. INDIAN FREvSH WATER MOLLUSCS 

 ASSIGNED TO THE GENUS BITHYNIA. 



By N, Annandale, D.Sc, F.A.S.B., Director, Zoological 

 Survey of India. 



Ill Mr. H. B, Preston's volume on the Freshwater Molluscs in 

 the Fauna of British India series, eighteen species are assigned to 

 the genus Bithynia, Leach (with the two subgenera Hydrobioides, 

 Nevill and ( ? ) Fossarulus, Neumayr) and several allied forms have 

 since been described from Burma and Assam. All of these (22 

 species) I have examined, so far at any rate as the shell and 

 operculum are concerned. I find no less than five distinct genera 

 included among jNIr. Preston's eighteen species. It is unfortunate 

 that in the official account of an important section of the fauna of 

 India no attempt seems to have been made to examine these 

 species critically. Some of them, probably the majority, must be 

 represented in English collections. 



I shall not attempt at present to revise these species, but 

 mereh^ to assign them to their proper genera and sub-genera, to 

 point out the characteristic features of these, and to describe a 

 new genus and a new subgenus that seem to be necessary. 



Of the five genera here discussed, four are closeh* related and 

 must be included in the subfamih' Bithyniinae. The fifth, how- 

 ever, which has recently been described by Col. Godwin -Austen, is 

 so distinct that it may be accepted as the type of a new subfamil}', 

 the I\l3"sorellinae. The external anatomy of the two subfamilies is 

 identical, but there are important differences in the radula as well 

 as the shell. The subfamilies may be briefly described as follows : — 



Bithyniinae. Shell never very thick, smooth to the naked 

 eye or with spiral ridges, ovate or globose, 

 with the peristome continuous and the colu- 

 mellar fold ridge-like. Operculum calcareous, 

 concentric or spiral. The central tooth of the 

 radula usualh^ bearing a series of latero-basal 

 denticulations on each side. The external male 

 organ with a well-developed lateral process. 

 Mysorei,i.inae. Shell rather thick, with strong spiral ridges, 

 turbinate, with the peristome continuous and 

 prominent. Operculum thick, calcareous, con- 

 centric. The central tooth of the radula with- 

 out latero-basal denticulations but bearing a 

 single downwardly-directed blunt process on 

 either side. The external male organ as in 

 the Bithyniinae. 



