OK THE UNITED STATES. 167 



tatiou of the outer whirl, near the aperture in the 

 adult shell, forming a la*ge oval chamber. The sum- 

 mit of the outer whirl, behind the dilated portion, 

 is not, or hardly elevated above the summits of the 

 other volutions. 



Genus Lymneus. 



1. L. * elongates. Shell horn colour, tinged with 

 reddish-brown; spire elongated, tapering, acute; 

 whirls six or seven, slightly convex, wrinkled across; 

 body whirl, measured at the back, more than half the 

 total length ; suture moderately indented ; aperture 

 less than half the length of the shell; labium witk 

 calcareous deposit. 



Length, one inch and three-tenths. 



Inhabits in considerable numbers, the ponds and 

 tranquil waters of the Upper Missouri. It is very 

 distinct from L. catascopium, by the much greater 

 proportional length of the spire. 



2. Lymneus columellas. (Jour. Acad. Nat. Sci- 

 iences, vol. 1. p. 11.) Var. a. Small, black — from 

 Cold water creek of the Missouri. This is most 

 probably a distinct species, we obtained but a single, 

 specimen of it. 



3. L. *rejlexus. Shell fragile, very much elon- 

 gated, narrow, honey-yellow, tinctured with brown- 

 ish, translucent, slightly reflected from the middle; 

 volutions six, oblique, wrinkled transversely; spire 

 more than one and an half times the length of the 



