LIMNEA HUMILIS. 43 



OBSERVATIONS. 



Found upon damp ground near water, or 

 upon muddy fiats left by the receding water. 

 It is difficult to retain them in confinement, on 

 account of their dislike to living in the water; 

 and they accordingly pass over the edge of the 

 vessel in which they may be placed, and move 

 off to the distance of several feet, upon a dry 

 surface. When too much of their moisture 

 becomes abstracted, they contract, and remain 

 in an apparently torpid state, until they are 

 moistened. They are infested by a species of 

 Cercaria, a genus which appears to have been 

 first detected upon our Limneans by myself. 

 The short thick shells constitute the humilis of 

 Say, and are common on the Susquehanna. 

 (Figs. 2, 3.) These do not quite correspond 

 with the Carolina specimens, (fig. 1.) I have 

 received the slender variety modice/la, from 

 Maine, through Dr. Mighels; from Massachu- 

 setts, through Dr. Gould; and from Ohio, 

 through Mr. Anthony. 



The shells are delicate and fragile, and differ 

 considerably among themselves; but I cannot 

 regard them in any other light than as well 

 marked varieties. 



