272 PNEUMONOBRANCHIATA. 



In stagnant waters, on aquatic plants. 



Shell hardly a quarter of an inch in diameter, 

 highly polished and smooth, of a chestnut or reddish- 

 brown colour, flattish and semitransparent ; volutions 

 four, the outer one very large in pro- 

 portion, and marked with two or three 

 whitish transverse lines exhibiting the internal par- 

 titions ; the upper surface very convex, with a deep 

 umbilicus in the centre, the under side nearly flat, and 

 umbilicate in the centre; the circumference slightly 

 carinate ; aperture oval, inclining to triangular, with 

 the peristome interrupted. 



Except for its internal semiconcamerated par- 

 tition, this shell exactly resembles the Planorbis fon- 

 tanus, but is larger. 



