196 NATURAL HISTORY BULLETIN. 



more or less interruption for many years, and has gathered 

 together great numbers of both fossil and modern forms 

 which bear on this question. 



The lists representing these faunas are therefore more 

 complete than is possible where resident observers are not 

 engaged in the investigation of both branches of the 

 subject, and this fact, coupled with the comparative rich- 

 ness of both faunas, makes a comparison of them especi- 

 ally interesting and suggestive. Since all of the fossils 

 which have been found at Iowa City are molluscs, and 

 belong with few exceptions to the local modern molluscan 

 fauna, a study of the habits of the living species is of the 

 highest importance because of the light which is thus 

 thrown upon the conditions which existed during the 

 deposition of the loess. The species included in this list 

 are therefore grouped according to habit in order that 

 comparisons and conclusions may be facilitated. All notes 

 on distribution, etc. of both modern and fossil shells in 

 the following list have reference to the vicinity of Iowa 

 City only, unless otherwise specifically stated. "Western 

 loess'' means that of western Iowa and eastern Nebraska. 

 The material was abundantly collected and studied in the 

 field by the author, and is now in his private collection. 



The names of the local fossil (loess) species are pre- 

 ceded by two asterisks. Those which have been found 

 fossil in the loess in other localities, but not at Iowa City 

 though now found living here, are marked by one asterisk. 

 The latter series does not however include all the species 

 of the modern fauna of Iowa City which were reported in 

 the earlier Missouri and Nebraska lists of loess fossils, 

 as no specimens are extant and the species are not now 

 known to occur in undoubted loess. The species living 

 near Iowa City but not represented in the loess are un- 

 marked. The territory covered by this report is included 

 within a radius of six miles from Iowa City. 



