66 NEW-YORK FAUNA— MOLLUSCA. 
PLANORBIS DILATATUS. 
P. lens? Lea, Am. Phil. Soc. Vol. 6, p. 68, pl. 23, fig. 83. 
P. dilatatus. GouLp, Invertebrata of Mass. p. 210, fig. 140. 
Description. Shell very small, minutely wrinkled. Spire flat, composed of not more than 
three whorls, separated by a well defined suture : outer whorl has a sharp margin on a level 
with the spire, diminishing near, but still modifying the aperture ; below this line the whorl 
is very convexly rounded, so as to encircle a small deep abruptly formed umbilicus: this 
whorl rapidly enlarges into a very large, not very oblique aperture, with the lip expanded 
into a trumpet-shape. Color, yellowish-green. 
Diameter, 0°15. Height, 0°05. 
This small species ranges from Massachusetts to Maryland and Ohio, occuring in pools, 
mosses, etc. ‘The previous name of Mr. Lea is predccupied by a fossil species. 
(EXTRA-LIMITAL.) 
P. glabratus. (Say, Nich. Ency. No.5; Jour. Ac. Vol. 1, p. 280.) Shell large; whorls five, 
glabrous or obsoletely rugose, polished, not carinated; spire perfectly regular, a little concave; 
umbilicus large, regularly and deeply concave, exhibiting all the volutions to the summit; aperture 
declining, remarkably oblique. Diameter, 0*9. South-Carolina. 
P. antrorsus. (Conrapv, Am. Jour. Vol. 25, p. 343.) Shell dextral, not depressed; whorls three; 
spire profoundly indented or concave, with the summit of the body-whorl angulated; umbilicus 
profound, with the margin and inner volutions angulated; body-whorl abruptly dilated near the 
aperture, which is longitudinally subovate. Alabama. 
P. virens. (Avams, Bost. Jour. Vol. 3, p. 326, pl. 3, fig. 15.) Shell small; a rough epidermis, 
and with transverse strie and revolving lines; spire not prominent, scarcely concave; last whorl 
flattened above, then abruptly curving downwards, subcarinate below; aperture nearly orbicular; 
umbilicus as broad as the last whorl, deep, and showing all the volutions. 
Color, greenish horn 
Diameter,.0+23; height, 0:09. Vermont. 
