34 



Bryant Walker 



Subfamily POMATIOPSINyS Stimpson, 1865. 



Foot divided by a transverse sulcus at about its anterior third. Verge 

 simple. Rachidian tooth with one basal denticle on each side, denticles of 

 the lateral and marginal teeth fewer and proportionately larger than in the 

 other subfamihes. Only one genus. 



Genus POMATIOPSIS Tryon, 1862. 



Shell dextral, spiral, thin, smooth, long, turreted, umbilicated; aperture 

 somewhat expanded; lip simple or slightly reflected; operculum corneous, 

 subspiral. 



Fig. 120 



Fis". 121 



Fig. 119 



Animal not as long as the shell, rostrum large, longer than the tentacles, 

 which are short and subulate. Verge very large, simple, convoluted, outer 

 margin rounded and smooth, inner margin sharp and wrinkled. 

 Type: Cyclostoma lapidaria Say, fig. 119. Animal, fig. 120. Radula, fig. 121. 



Family PLEUROCERID^. 



Animal oviparous, edge of mantle smooth ; eyes on the external bases of 

 the tentacles; no verge. Rachidian tooth large, broader than long, rounded 

 below, multicuspid ; laterals subrhomboidal, multicuspid ; marginals narrow, 

 multicuspid. 



Shell dextral, spiral, thick and solid, globose or elongated ; aperture entire 

 or more or less canaliculated below, operculum corneous, subspiral. 



Key to the genera of Pleuroceridce. 



r Aperture canaliculate below 2. 



I . \ Aperture angulated below, not canaliculate . , 4. 



[ Aperture entire, rounded below Anciilosa. 



,1 



Shell fusiform, canal long lo. 



Shell conical, canal short 3, 



Spire elongated ; no callus thickening on parietal wall .... Pleurocera. 



Spire short ; parietal wall callously thickened above and be- 

 low Lithasia. 



Spire short; parietal wall callously thickened above Buryccvlon. 



Aperture entire above Goniobasis. 



Aperture with a sutural slit : . Gyrotoma. 



