66 NEW- YORK FAUNA — MOLLUSCA. 



Planorbis DILATATUS. 



P. lauT L«A, Am. Phil. Soc. Vol. 6, p. 68, pi. 23, fig. 83. 

 P. dUotatut. Gould, lnvertebrata 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, • 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. glabralus. (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 stria? 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. Vermont. 



