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. loi Fig. 102 



Type: Pyrgula nevadensis 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 ; 

 Fig. 103 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. 



Fig. 104 Fig. 105 



Type: L. goudichaudii Soul. 



Example: L. monroensis (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. 



