66 NEW-YORK FAUNA — MOLLUSCA. 



Planorbis DILATATUS. 



P. Um ? Lea, Am. Phil. Soc. Vol. 6, p. 68, pi. 23, fig. 83. 

 P. dilatattu. GonLD, Inrertebrata 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 preoccupied 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. (Conrad, 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. (Adams, Bost. Jour. Vol. 3, p. 326, pi. 3, fig. 15.) Shell small; a rough epidermis, 



and with transverse striae 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, • 23 ; height, • 09. Ve rmont. 



