206 _ PLANORBIS. 
Subgenus MENETUS, Hd 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) 
