^^lutinosiis, Drap. which is a fra2;ile, vesicular shell, the 

 spire hardly elevated, dextral, and the mantle of the ani- 

 mal is reflected. 



These shells are abundant in most of our lakes and 

 ponds, as well as in the rivers, east of the Alleghany Moun- 

 tains. In our western streams they are less frequent and 

 even in some of them, are of rather rare occurrence. As 

 the animal can only respire air unmixed with w^ater, it is 

 imder the necessity of residing near the surface or shore, 

 to obtain it. Which, as its motions are slow, it cannot do 

 in rivers that are subject to very great, sudden and long 

 continued changes in depth, as is remarkably the case 

 Avith our western streams. In order to take in a supply 

 of air the respiratory orifice is opened at the surface with 

 an audible snapping sound, like that produced by the resi- 

 lience of the nib of a pen. 



Like the animals of some other shells it is capable of 

 sustaining itself at the surface of the water in a reversed 

 position, the shell being downward, and thus it can glide 

 along to a consideracle distance, by a slow movement. It 

 does not appear to be capable of rising from a depth to the 

 surface voluntarily : but it gradually reverses its position 

 from a supporting body that meets the surface, or that ap- 

 proaches it within reaching distance. 



Lamarck has described only twelve recent species, but 

 many more have been since made known and several fos> 

 sil species have also been described. 



