PLANORBIS. 



189 



Typical Species. 



The aperture in the plane of volution and 

 not expanded. 



A. West Coast Species. 



1. PLANORBIS SUBCRENATUS, Carp. 



Plate 5, figs. 1, 2. 



Shell tumid, very thin, horn-colored ; 

 whorls six, rounded, sutures impressed, with 

 sharp radiating, somewhat crowded and occa- 

 sionally minutely crenulated ridges ; aperture 

 rounded ; parietal wall small, scarcely touch- 

 ing the penultimate whorl; labrum slightly 

 deflected, fuscous within ; umbilicus deep. 



Diameter 23, alt. 9 mill. 



Oregon. Washoe Mining District. 



In its flatness this species resembles the PI. 

 glahratus, Say, of the Atlantic States, but it 

 is larger and not nearly so smooth. 



(36) 



