IOWA ACADEMY OF SCIENCES. 39 



The other type with smaller body-whorl, more exserted spire, 

 and more convex whorls, is represented by S. avara, S. lineota, 

 and S. obliqua These are not only not semi-aquatic, but are 

 often found in high, very dry situations. This is especially 

 true of the small form of S. avara, and of S. lineata, both of 

 which are very common in the loess. Of this type there were 

 1,714 fossil specimens in the collection, and even if the three 

 specimens of S. ovalis be accepted as "semi-aquatic," their 

 importance is far outweighed by these strictly terrestrial forms. 



Remaining forms. — Of all the remaining forms in the list it 

 may be said that they are wholly terrestrial in habit. While 

 they require a certain amount of moisture, tha" which is 

 retained under a stick or leaf is suflicient. Most of the species 

 are abundmt to-day in both Iowa and eastern Nebraska, and 

 several prefer a decidedly dry region.* 



Their presence, therefore, does not prove a moist climate, 

 but rather suggests less moisture f 



In all discussions of loess conditions it should be borne in 

 mind that the forms of mollus s which are every where present, 

 and which are truly characteristic of the oess, are all terres- 

 trial and none require much moisture. 



So far as evidences of a glacial climate are concerned, this 

 much may be briefly said: The climate was of necessity such 

 as to permit the development of abundant plant- food for the 

 terrestrial molluscs, for they are almost without exception 

 herbivorous The fresh water pulmonate fauna of the loess, 

 instead of being of the large, comparatively thin- shelled type 

 which prevails northward, is more nearly like that of our com- 

 paratively dry prairies to-day, as has been stated 



Great stress has been placed upon the depauperate condition 

 of the shells of the loess \ 



With the exception of the extremely variable Patula strigosa 

 cooperi the author has found every species occurring in the loess 

 exhibiting modern mature forms which do not exceed, and in 

 many cases are smaller than the fossils The conditions which 

 produce the depauperation exist to-day in the loess covered 



*Tbis is especially true of Patula strigosa eooperi, Pttpi altie ila and SiKcin^a lineata. 



+It may be added, parenthetically, thtt ttie larger shells, such as JfeiSjdjn mutti- 

 lineata, M. profunda and Patula alternita, often h \.ve their apices broken in exactly the 

 sanae manner which may often be observed ia fresh shells from which birds (blue j lys, 

 etc.) have extracted the animals. 



$J. E. Todd, Proc. Am. A. A. S., Vol. XX VI[, p. 6; McGjs and Call, On the Loess and 

 Associated Deposits of Des Moines, pp. 31-2, and plate; Chas. R. Keyes, Bull. Essex 

 Ins., Vol. XX, p. 5; W.J. McGee, Rep. U. S Geol. Sur., Vol. XI, pp SOO-1, 435 and 448. 

 See also author's paper in Bull. Lab. Nat. Hist. State Univ. of Iowa, Vol. II, pp. 9-3-4. 



