The Lcess and its Fossils. 201 



I. The Fossils. 



The list of fossils here ijiven includes only those which the 

 writer has examined, and which, considering that they were 

 collected in at least twenty-five widely separated localities in 

 Iowa and Nebraska, certainly may be considered as repre- 

 sentative of the fauna of the Loess in these states. 



In this section of this paper the fossils are first arranged 

 systematically with brief comparative notes on form and size 

 and also on the distribution ' of recent representatives of the 

 species noted. This is followed by a grouping of the species 

 according to habitat and abundance. 



Helicina oculla. Say, Abundant. Fossils from Johnson, 

 Scott, and Polk counties, Iowa, and Cuming and Lancaster 

 counties, Nebraska w^ere compared with recent specimens 

 from Hardin and Johnson counties, low^a. On the whole the 

 fossils are a little smaller in average size than the recent shells, 

 though many of them exceed the smaller ones from Hardin 

 county. None of the fossils equal the larger Johnson county 

 specimens. 



This species has frequently been mentioned as an aquatic 

 or semi-aquatic Mollusk belonging to the Loess, though its 

 habitat (in Iowa at least) is on ver}- high, steep, cool hillsides, 

 where it is associated with mesodon profunda and Schnites 

 concava (which preys on it). This error arises from the fact 

 that Helicina belongs to the gill-bearing Prosohranchiata^ 

 though it is strictly terrestrial in its habits. Recent shells have 

 been found in Wisconsin, Virginia, and Johnson and Hardin 

 counties, Iowa. 



Zonites arborcus^ (Say) Binn. Rare in the Loess of Johnson 

 and Polk counties, Iowa. The condition and small number 

 of the specimens make it unsafe to refer definitely to the com- 

 parative development of the fossil and recent shells. Recent 



I The limits of distribution were ascertained from Binney's ^'■Terr. and 

 Air-breathing Moll, of the U. SP Vol. V, Pilsbry's ^'■Nomenclature and Check- 

 list of N. American Land Shells" Proc. Acad. Nat. Science, Phila., 1S89, and 

 the writer's private collection. 



