208 NATURAL HISTORY BULLETIN. 



exposures, and in these is usually restricted to narrow 

 bands or pockets, in which it is quite abundant. 



**Limn^Ea humilis Say. 



Very common in shallow ponds, or on mud-flats. As a 

 fossil it occurs with the preceding species, and is even 

 more common. 



**LiMNJBA desidiosa Say (?). 



Some of the smaller fossil shells of Limn tea may belong 

 to this species. It is probably found in the loess westward, 

 though in some cases at least the fossils reported under 

 this name undoubtedly belong to the preceding species. 

 Common in shallow ponds. 



**Physa gyrina Say. 



Very common in shallow ponds. Two very small speci- 

 mens, probably this species, were found in the loess at 

 Iowa City. 

 PHYSA INTEGRA Ha Id. 



Very common in ponds, etc. Hitherto reported as P. 

 heterostropha Say. In a very large series of shells from 

 Iowa and Nebraska not one specimen of the latter species 

 was found. 



Physa sayi Tap. 



Quite common locally. None fossil. 

 Planorbis campanulatus Say. 



Rare locally in ponds. None fossil. 

 * Planorbis trivolvis Say. 



Very common in shallow ponds. Reported from Mis- 

 souri, but, if occurring at all, certainly not common. 

 *Planorbis bicarinatus Say. 



Common in shallow ponds. One fossil specimen was 

 collected by Prof. Beyer at Ames, and the species has been 

 reported from the loess of Tennessee.* 



* Safford, Geology of Tenn., p. 434; 1869. 



