CONCHOLOGIA CESTRICA. 63 



R. columella, SAY. 



Lymnaea columella, Say, Jour. Acad. Phila. F. S, I., 

 1817. 



R. columella. [W. G. B.] Jaw of R. columella. [W. G. B. J 



Fig, 117, Fig, 118, 



Shell, thin, fragile, pale; whorls 4; spire acute; aper- 

 ture expanded, ovate ; columella narrowed near the base, 

 so as to exhibit the interior of the spire. H. 15, W. 8, 

 mill. 



lAngual Dentition of R. columella. [W. G. B.] 

 Fig, 119, 



Station, stagnant streams and muddy pools. Chester 

 County; common. 



R. macrostoma, SAY. 



Lymneus macrostomus, Say, Jour. Acad. Phila. F. S., 

 II, 1821. 



Shell, sub-oval, thin, and fragile, straw-yellow ; whorls 

 5, with the lines of growth crossed by R. 



minute spiral striae ; suture impressed ; t w - G - B -l 



Fig, 120, 



spire acute, one-third the length of the 

 aperture, which is large and expanded ; 

 outer peritreme slightly reflexed and 

 forming (with a thin coat of calcareous 

 matter on the columella) a slight umbili- 

 cus. H. 20, W. 12, mill. 



Station, ponds. Pickering Creek ; Chester County. 



