128 B. SHIMEK 



of the loess be used as an absolute measure of the amount of 

 moisture occurring during loess times, then we must conclude 

 that Iowa was without streams, for practically no fluviatile mol- 

 luscs occur in the loess, and that there were but few ponds in 

 which aquatic molluscs found a favorable habitat, for even 

 aquatic Pulmonates are rare in the loess, 1 the number of ter- 

 restrial forms being out of all proportion to that of the aquatic 

 forms. 



During the past summer the writer collected several thousand 

 specimens in the loess of Mississippi and western Iowa, and 

 among them all there were not a half dozen aquatic shells. A 

 list of the modern shells of Iowa shows a large number of 

 aquatic species, yet few of these occur in the loess. There is 

 also among the modern terrestrial forms a large number of those 

 which occur only in very damp places — and these, too, are 

 almost wholly missing from the loess. The writer is well aware 

 that many of the forms found in the loess are often referred to 

 as aquatic or " semi-aquatic," or at least as favoring very wet 

 situations. But evidence of this character has been furnished 

 largely by those who are familiar only with the molluscan fauna 

 of the eastern part of the country, where the amount of rainfall 

 is much greater, and where surface conditions are not the same 

 as in Iowa and Nebraska — or it has come from so-called " closet- 

 naturalists." Now, the "closet-naturalist" has done abundant 

 harm in this as in other branches of science. Too remote, often, 

 from the phenomena under discussion, or too dainty to soil his 

 fingers with the toil and the exposure of field-work, he has 

 passed judgment upon the habits of forms which he knew only 

 from material submitted by mail — or still worse, he has taken 

 the work of others and, not appreciating the significance of the 

 facts so borrowed, has distorted them to do menial service in 

 the encouragement of some pet notion. 



In the particular case in hand no distinction has been made 

 between the habits of the depauperate varieties and the larger 



1 For more detailed comparisons see writer's paper (loc. cit., pp. 43 and 44), and 

 the discussion preceding. 



