1920.] N. AnnandaIvE : Indian Freshwater Gastropods. 113 



tendency for the outline of the body to become biangulate owing 

 to two of them assuming the form of carinae. Corresponding to 

 these bands there are on the edge of the mantle an equal number 

 of small digitiform processes. The operculum is thin, sharp round 

 the periphery and with the internal muscular scar moderately 

 developed. The radular teeth are normal. Their denticulations 

 are by no means large and the central lobular process of the free 

 edge of the central tooth is broad and quadrate or triangular. 



I believe that all described Indian forms ' of this group can be 

 comprised in the single species Vivipara hengalensis (Lamarck), of 

 which several distinct races and phases can be distinguished. 

 Major Sewell and I hope to describe it in detail shortly. It is 

 found in all parts of the plains of the Indian Empire at which 

 there is perennial still water. 



ViviPARAE OXYTROPIDKS. The shell is large or small, thin, 

 acuminate and more or less distinctly biconical. The whorls of 

 the spire are not at all swollen and the suture is less impressed 

 than in V . hengalensis. Dark spiral bands are present. They are 

 always more or less thickened, at any rate in the young, and in 

 the typical species form prominent ridges in the adult. The peri- 

 pheral band forms a prominent keel, separating the shell into two 

 regions. The region below it is obliquely flattened on the ventral 

 surface. The operculum and radula resemble those of V. hengalen- 

 sis, Ijut in the typical species the marginal processes of the mantle 

 are much larger in the adult. 



Only one species of this group has as yet received a name, 

 viz. V . oxytropis (Benson), but another, smaller and less special- 

 ized species, awaits description. The former is apparently endemic 

 in the Manipur valley, while the latter occurs in the plains of the 

 eastern part of Assam. 



ViviPARAE DissiMiLES. The shell is always small, rather high 

 and narrow, never ver}' sharply acuminate, moderately thin or thick, 

 with the whorls of the spire swollen and the suture deeply im- 

 pressed. There are no dark spiral bands or prominent spiral 

 ridges, but a minute spiral sculpture of punctured lines can often 

 be detected. There is often a broad but rather obscure pale trans- 

 verse bar on the body-whorl. The operculum is thicker than in 

 the other three sections and the muscular scar better developed. 

 Round the periphery of the operculum there is often a thickened 

 spongy ridge. The edge of the mantle is smooth in the adult. 

 The central lobe of the central tooth of the radula is rounded. 



Most of the forms that belong to this group are classified by 

 Nevill* as varieties of V. dissimilis (Miiller), but I think that he 

 has included several species, Pilsbry ^ regards the characters of 

 the operculum as subgeneric and has given the subgeneric name 



1 V. nagaensis, Preston may be distinct, but ! have not seen the species, 

 have another (undescribed) from Manipur. 



2 Nevill, Hand List Moll. Ind. Mns., II, pp. 27-30 (1885). 



3 Pilsbry, Proc. Ac. Nat. Set. Philadelphia, LIII, p. 188 (1901), 



