38 IOWA ACADEMY OF SCIENCES. 



possible. But it is extremely strange, if the loess was 

 deposited either in rivers or in lakes, that these remains of 

 mussel shells are not more abundant. It has been suggested 

 that the waters were too cold for the best development; of the 

 Unionidce, but species of Anodonta of this family are conimon 

 in lakes and sluggish streams far to the north, and over most 

 of the northwestern territory, and, if such conditions prevailed, 

 at least fragments of these should be found if the delicate egg- 

 shells of a small snail (see Table I) were permitted to come 

 down to us entirely uninjured. If the waters had been too cold 

 for the Unionidce, the land would likewise have been too cold 

 for the land snails. 



Moreover, the evidence of these four shells, while worthy of 

 attention, should scarcely be permitted to outweigh that of 

 the thousands of terrestrial forms so widely distributed in the 

 deposits. 



2. Terrestrial molluscs. — Of fossil terrestrial molluscs there 

 are 4,816 specimens in the collection. Some of the forms here 

 classified as terrestrial have frequently been incorrectly reported 

 as aquatic or semi-aquatic. This is especially true of Helicinn,* 

 Pomatiopsisf , and Succineol. Helicina occulta Say, though gill- 

 bearing, is strictly terrestrial. At Iowa City, where it was dis- 

 covered by the author many years ago, and in Hardin county, 

 where it is not rare, it is always found on steep hillsides high 

 above high-water mark. 



Pomatiopsis lapidaria Say is likewise wholly terrestrial. Call 

 [l. c.) repeatedly refers to it as a fresh-water form, and, when 

 we consider that a conchologist of such wide experience makes 

 this error, it is not surprising that others repeat it. At Iowa 

 City, Belle Plaine, Eldora, and other points where this species 

 is common at the present time, it is usually associated with 

 Patula striateUa and Succinea obliqua, both likewise terrestrial 

 forms, and is in no sense aquatic. 



Succinea. — Two types of this genus appear. That repre- 

 sented by S. ovalis has a very large body-whorl and a short 

 spire. These forms are mostly found in swampy places creep- 

 ing about on semi-aquatic plants, or on mud, but not living in 

 water. Of this type three specimens are in the collection. 



*.T. E. Told, Proc. Am. K. A. Sci., Vol. XXVLE, p. 6; F. M. Witter, "Notes on th^ 

 Loess;" W.,r. McGee, Rep. U. S. Geol. Sur.. Vol. XI, p. 461 



+ R. E. Call. Rpp. A.rk. Geol. Sur , Vol. If, pp. 166, 167, and 178. 



■tLyell, Prin. of Geol.. Vol. I. p. 460; J. E. Todd, Proc. Am. A. A. S., Vol. XXVJI. p 

 6, F. M. Witter, Notes on the Loes-*; R. E. Call, On the Loess and Associated Depo^it•v 

 of Des MoiLe", p. 16. 



