OF THE UNITED STATES, 171 



Inhabits Lakes of Maine. 



This species was discovered by Mr. Aaron Stone. 



It is a rather larger, and considerably wider shell 

 than L. catascopium, and the emargination visible on 

 a profile view of the umbilical groove, is far more 

 profound. 



Genus Physa. 



1. P. *gyrina. Shell heterostrophe, oblong 5 

 whirls five or six, gradually acumiuating to an acute 

 apex ; suture slightly impressed ; aperture more than 

 one half, but less than two-thirds of the length of the 

 shell ; labrum a little thickened on the inner margin. 



Length rather less than one inch. 



Inhabits waters of the Missouri. 



Of this species, I found two specimens at Bowyer 

 creek, near Council Bluff. It differs from P. hete* 

 rostropha in magnitude, in having a more elon- 

 gated spire, and less deeply -impressed suture. 



2. P. *elon%ata. Shell heterostrophe, pale yel- 

 lowish, very fragile, diaphanous, oblong ; whirls six 

 or seven ; spire tapering, acute at the tip ; suture 

 slightly impressed ; aperture not dilated, attenuated 

 above, about half as long as the shell ; columella 

 much narrowed near the base, so that the view, may 

 be partially extended from the base towards the 

 apex. 



Inhabits shores of Illinois. 



Length 7-10 inch. 



Greatest breadth 3-10 nearly. 



