Records of the Indian Museum. [Vol. XXII. 



callus flattened and plate-like, occluding the umbilicus. 

 Central tooth of radula with basal denticulalions. 



A. Lip of shell thickened. Operculum thick, calcare- 

 ous, concentric. Male organ with a lateral process 



B. Lip of shell not or slightly thickened. Operculum 

 horny, spiral 



I IL Shell more or less elongate, thick or moderately so, with the 

 main axis of the spire and the bod3--whorl in the same 

 straight line, and the mouth comparatively narrow. 

 Operculum thick, calcareous. Male organ with a lateral 

 process. 



A. Shell turbinate, conspicuously perforate, ornament- 

 ed with prominent spiral ridges. Operculum con- 

 centric externally. Central tooth of radula with a 

 vertical lateral process on each side, but without basal 

 denticulations 



B. Shell not turbinate, without (in Indian species) pro- 

 minent sculpture. Central tooth of radula with basal 

 denticulations. 



1. Shell almost trochiform, shallowly but openly 

 umbilicate, ornamented with spiral incised lines. 

 Operculum concentric externally 



2. Shell ovate, narrowly umbilicate or imperforate, 

 with sculpture microscopic, except for a varix in 

 some species. 



a. Lip of shell distinctly thickened. Opercu- 

 lum concentric externally. 



a. Columellar callus more or less flattened 

 and plate-like ; no channel proceeding 

 downwards from the umbilicus ; inner 

 lower extremity of lip rounded 



;8. Columellar callus ridge-like; a dis- 

 tinct channel proceeding downwards 

 from the umbilicus ; inner lower extre- 

 mity of lip angulate and produced 



b. Lip of shell not distinctly thickened. 



a. Operculum concentric 

 0. Operculum spiral 

 /. Operculum horn\' 



/(. Operculum calcareous ... 



Paraiieyita. 

 Lithoglvphiis. 



Mysorella. 



Sat aria. 



Hydrobiuides 



Digoniostoma. 



Bitliyiiia. 

 Amnicola. 

 subgenus Am- 



tticola (s.s.) 

 subsfenus Alo- 



We divide these genera into four subfamilies, viz. Hydrobiinae 

 (or Paludestrinae), Bithyniinae, Mysorellinae and Lithoglyphinae. 



Subfamily HYDROBIINAE. 



The representatives of this subfamily are small or minute. 

 They may be recognized by their horny, paucispiral operculum, 

 undivided foot, unbranched male organ ' and by the absence of 

 denticulations at the base of the central tooth of the radula. 

 Their shells are never thick or inflated. 



' In the European Hydrobia or Paludestrina jenkinsi males are seldom or 

 never produced and the females are parthenogenetic. See Robson, Ann. Mag. 

 Nat. Nist.{g), V, pp. 425 — 431, pi. x\- (1920). 



