72 CONCHOLOGIA CESTRICA. 



G. parvus, SAY. 



Planorbis parvus, Say, Nich. Encyc., Amer. Ed., 1816. 



G. parvus. Shell, very small, horn color; whorls 4. 



I W C 1 B 1 



Fig, 144, ^ ne striate; flat above, with the centre im- 

 /^j\ pressed ; beneath, concave ; periphery often 

 sub-carinate ; aperture oval, oblique, longer 

 than wide. H. ft, W. 2j, mill. 



Station, with the preceding species. Chester County; 

 common. 



G. albus, MULLER. 



Planorbis albus, Mull., Hist. Vermet., II., 1773. 



G. albus. Shell, small, pale yellowish, or white; whorls 

 [w. G. B.] g-^ the outer rapidly increasing, and marked 

 by revolving lines, with stiff hair ; both sides 

 concave, the lower most so ; aperture sub-oval, 

 very oblique. H. i^, W. 5, mill. 



Station, tide marsh ditches. Delaware and 

 Schuylkill Rivers, Philadelphia. 



G. dilatatus, GOULD. 



Planorbis dilatatus, Gould, Invert. Mass., 1841. 



G. dilatatus. Shell, very small, yellowish-green; whorls 

 Fig, 146, 3 outer one carinate ; slightly convex above ; 

 closely umbilicate, beneath ; aperture large, 

 oblique, trumpet shaped. H. I, W. 3, mill. 



Stations, ponds. Pickering Creek, Chester 

 County ; common. 



Sub-genus PLANORBULA, HALDEMAN, 1842. 



Shell, with the aperture furnished with dentiform 

 plicae, not forming open partitions. 



