72 CONCHOLOG TA CES ERICA: 
G. parvus, SAY. 
Planorbis parvus, Say, Nich. Encyc., Amer. Ed., 1816. 
G. parvus. Shell, very small, horn color; whorls 4, 
eee fine striate; flat above, with the centre im- 
@ pressed; beneath, concave; periphery often 
sub-carinate ; aperture oval, oblique, longer 
than wide. H. 34, W. 2%, mill. 
Station, with the preceding species. Chester County; 
common. 
G. albus, MULLER. 
Planorbis albus, Mull., Hist. Vermet., II., 1773. 
G.albus, hell, small, pale yellowish, or white; whorls 
(W.G.B.] 3-4, the outer rapidly increasing, and marked 
nee by revolving lines, with stiff hair; both sides 
Gon concave, the lower most so; aperture sub-oval, 
very oblique. H. 1%, W. 5, mill. 
(6) 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 
eae: 3, outer one carinate ; slightly convex above ; 
@) closely umbilicate, beneath; aperture large, 
cS oblique, trumpet shaped. H. 1, W. 3, mill. 
= Stations, ponds. Pickering Creek, Chester 
OS County ; common. 
Sub-genus PLANORBULA, HatLpeman, 1842. 
Shell, with the aperture furnished with dentiform 
plice, not forming open partitions. 
