30 



Bryant Wai.ker 



central tooth of the radula with but one basal denticle on each side; denticles 

 of the lateral teeth large and angular, those of the laterals small and slender. 



Fig. 103 



Fig. loi Fig. 102 



Type: Pyrgula ncvadcnsis Stearns, fig. loi. Radula, fig. 102. 



Genus POTAMOPYRGUS Stimpson, 1865. 



Shell ovate-conic, imperforate ; apex acute ; whorls angulated 



and usually coronated with spines ; body-whorl two-thirds the 



length of the shell; aperture ovate, lip acute. 



Animal with rostrum of moderate length ; tentacles very 



long, slender, tapering and pointed ; eyes on prominent tubercles ; 



foot rather short, strongly auriculated in front; central tooth of 

 radula trapezoidal, inferior margin nearly straight; faintly enlobate; basal 

 teeth minute and close to the lateral margin ; denticles of the intermediate 

 tooth numerous and of equal size. 

 Type : Melania corolla Gld. 

 Example: P. coronatus (Pfr.), fig. 103. 



Genus LITTORIDINA Souleyet, 1852. 



Shell narrowly perforate, subpyramidal, solid, opaque, body-whorl sub- 

 angulate at the periphery; aperture pyriform, acutely angulated above; col- 

 umella thickened, white ; peritreme not continuous, lip sharp. 



Verge very large, with five or six small, digitate appendices. Radula as 

 in Amnicola. 



.C^ 



Fig. 104 Fig. 105 



Type: L. gaiidichaiidii Soul. 



Example: L. monrocnsis (Frfld.), fig. 104. Radula, (L. hatcheri Pils.), 

 fig. 105. 



Subfamily LITHOGLYPHIN^ Fischer, 1885. 



Shell small, spiral, dextral, spire short, body-whorl large, forming most 

 of the shell; columella usually callously thickened; operculum corneous, 

 subspiral. 



Foot simple; central tooth of the radula with several basal denticles. 



