206 PLANORBIS. 



Subgenus M E N E T U S, E. & A. Adams. 



19. PLANORBIS OPERCULARIS, Gould. 



Plate 7, fig. 1, 2, 3. 



Shell small, dextral, much depressed, lenti- 

 cular, with a prominent blunted keel at the- 

 periphery defined by a marginal, compressed 

 line ; tip sunken ; beneath umbilicated for 

 about one-third the breadth of the base, show- 

 ing three volutions, convex, surface rather 

 rude and indented, marked with irregular, 

 coarse, much arcuated lines of growth, and 

 here and there a few obscure, raised, revolv- 

 ing lines ; color dark chestnut-brown, a little 

 clouded ; whorls above four, slightly convex ; 

 suture well defined, impressed ; aperture trans- 

 versely subrhombic, lip above slightly declin- 

 ing, at periphery acute-angled, beneath arched, 

 (53) 



