Loess of loiva City — Shiiiiek. 347 
Locally common on higher exposed slopes, chiefly under 
fragments of limestone. Rare in the loess of western Iowa 
and eastern Nebraska. 
**BlFIDARIA ARMIFERA (Say) StO'ki. 
Very ccmmon. Most frequent on more or less exposed 
slopes under limestone, among roots of grasses, etc. Some- 
times also in deeper shade, and occasionally on lower grounds, 
under logs, etc. Rare in the loess at Iowa City, but very com- 
mon in the western loess at Coimcil Bluffs, Iowa. 
*BlFlDARIA HOLZINGERI (Stcrkl). 
Quite common under stones, etc. on exposed hillsides. 
Rather rare in western loess. 
**BiFiDARiA PENTODON (Say) Sfci'ki. 
Quite common on rather open rocky slopes, sometimes on 
lower grounds, under stones, etc. As a fossil this species is 
widely distributed, and in this locality is very common. 
*BlFIDARIA CURVIDENS (GId.) SfCI'ki. 
Not luicommon. It is rare in the loess of the west and 
south, but has not been found fossil at Iowa City. 
*BiFiDARiA CORTICARIA (Say) Stcvki. 
Common in a few restricted localities among the roots of 
tufted grasses, etc. growing on exposed rocky slopes. Not 
found in the local loess, but reported from Des Moines by 
Keyes, from Muscatine by Witter and from Illinois by Lev- 
erett. It is not rare in the loess of Natchez, Miss. 
•"^PoLYGYRA LEAi {Ward) Pils. 
Found here under sticks, etc. on slopes near a prairie 
swamp. Also more rarely on scantily wooded slopes. Rare 
in the loess of the west, etc. 
*SucciNEA AVARA Say. 
Not rare on more or less exposed rocky slopes. This is 
the small, typical form which is now found on low grounds. 
The same form occurs abundantly as a fossil, being one of the 
most characteristic species of the loess. It occurs in all the 
fossiliferous exposures near Iowa City, l>eing the only fossil 
found in some of them. 
**VlTREA INDENTATA (Say) FUs. 
Not rare on rocky slopes. This, and the following species, 
also occur on lower grounds, but both are mpre common on 
drier slopes. Rare in the loess. 
