The Lcess and its Fossils. 213 



g-ouldif habiiudWy occur on high, cool, damp, wooded hillsides; 

 Stcnotrcma Icaii, Mcsodon miiltiJineata (the small form), Fer- 

 ttssacia stibcylindrica and Vertigo ovata prefer low and very wet 

 places; Zonilcs radiatnhts, Sticcinea avara^ Siiccinea obliqiia and 

 Patida striatcUa are habitually found under sticks, leaves, etc., 

 in low valleys of streams, or near the edges of ponds, whether 

 they are wooded or not; Zonitcs arborcns, Zoniies minuscidus^ 

 Zonitcs Juh'us, HcUcodiscus lincatns^ VaUonia pulchclla, Car- 

 ychmm cxigxmm. Pupa arniifcra and Pattda altcrnata range 

 as widely in habitat as they do in geographical distribution, 

 being found in high and low, wooded and open country, the 

 only seemingly necessary condition being the presence of a 

 little (often very little) moisture; and Siiccinea oralis, the Liin- 

 ncPiv, Phvsa, Planorbis farvtis and Pisidiitui frequent ponds 

 and sluggish streams, or their muddy shores. 



The writer was unable to get information concerning the 

 exact habitat of Zonitcs liniatiilns, Pupa decora. Pupa mits- 

 coruui and Siiccinea rcrilli. All of these are northern or 

 northerly species. 



With the exception of Hclicina occulta. Vertigo gouldii, and 

 the boreal species, all of these species have been found by the 

 writer in the vicinity of prairie ponds and streams in central 

 Iowa and eastern Nebraska, and but for the comparative 

 paucity of the Limnceidce, and the entire absence of Unionidce 

 (which however are not as a rule very abundant in the prairie 

 streams and ponds of to-day) they would closely represent 

 the recent moUuscan fauna of these regions. Indeed Siiccinea 

 lineata, the small form of IMesodon miiUilineata, the narrow 

 form of Succinea obliqua, and Stenotrema leaii are rather 

 characteristic of the region, while the remaining species extend 

 over it. 



Of the fossils listed Patula strigosa coopcri and the Linincece 

 show the most marked depauperation. Hclicina occulta^ 

 Patula altcrnata, Alesodon multilincata, Succinea obliqua, and 

 probably Vertigo ovata average somewhat smaller in size 

 than recent shells, though some of the latter approach them 



