33© NATURAL HISTORY BULLETIN. 



Call, who alone of this list of writers made a pretense of 

 special knowledge of conchology, reported Helicina occulta* 

 and Pomatiopsis lapidarict\ as aquatic, and Succinea as semi- 

 aquatic! 



But these forms are terrestrial, and a mere tyro who would 

 have taken the trouble to go to the field could have avoided 

 such misstatements. Yet they have been accepted with 

 others quite as unreliable and have been incorporated in geo- 

 logical papers to form the basis of important conclusions. 

 Todd and Call both reported (1. c. ) on the depauperated shells 

 of the loess, and concluded that cold was responsible, and 

 these conclusions were relied upon by McGee| who used 

 them to support the theory of the sub-glacial origin of the 

 loess. Yet the living fauna of the loess-covered regions shows 

 essentially the same depauperation. The comparisons which 

 Call makes in the paper on the Des Moines loess are based in 

 part, at least, upon measurements of eastern modern shells. § 



Had the author taken recent shells from Iowa, especially 

 from the prairie sections, he would have been left practically 

 without support for his conclusions. || 



The causes which produced a "depauperation" of some of 

 the shells are in operation today in Iowa and adjacent terri- 

 tory, for practically all of the fossil cases may be duplicated 

 in the modern fauna. 



Another source of error of a more excusable nature in the 



* As Helicina oculata: — Am. Nat. vol. xv, p. 586, 1881. This error 

 concerning habit is copied by McGee, 1. c. p. 461, in a statement at the 

 close of a list of fossils quoted from the present writer. There was no 

 warrant for such a statement in the article quoted. 



tAm. Nat.. 1. c. , Ark. Geol. Sur. , vol. ii, pp. 166, 167, 168, 1891; 

 The Loss and Associated Deposits of Des Moines, p. 16, 1882. 



% See Loss and Associated Deposits of Des Moines, p. 23, et seq. 



?The present writer, then a college student, made the drawings for 

 the plate which illustrates that paper. 



liFor discussion of depauperation of shells by the present writer see; 

 Proc. la. Acad, of Sci., vol. iii, p. 85, 1896; vol. v, pp. 43-4, 1897: 

 vol. vi, p. 101, 1899; Jour. Geol., vol. vii, pp. 126, 127, 1899. 



