AMNICOLA. O 



SHELL short or lengthened conic, thin in tex- 

 ture, composed of from 4 to 7 convex whirls, 

 separated by a distinct suture: aperture oblique, 

 peritreme simple, detached, or but slightly con- 

 nected with the body whirl, and usually by a 

 very small portion of its circumference poste- 

 riorly; base usually perforate: operculum thin, 

 corneous, composed of a few spiral volutions. 



HABITS. A. decisa and lustrica, where I have 

 observed them, live upon the inferior surface of 

 stones in running water. They are tolerably 

 active, and retract suddenly when a shadow is 

 passed over them. The ova are deposited in 

 the month of March, in small oblong detached 

 glairy masses, each of which contains appa- 

 rently but one germ, which is situated at the 

 larger end of the mass. The color of the 

 germ is orange, of the mass yellowish transpa- 

 rent, with a dark central line upon the surface 

 from end to end. The progression, at least of 

 the short species, is performed upon the foot 

 alone, with a uniform gliding motion as in 

 Physa. 



OBSERVATIONS. 



This natural genus seems at first view to be 



