HELICINA OCCULTA 387 



the loess, and excepting in rare cases they should be specifically 

 designated as loess fossils rather than by the indefinite term "Post- 

 pliocene", which is used in many papers on Mollusks. The writer 

 has found but one specimen in the alluvium of western Iowa (in 

 Harrison county), but this is evidently a fossil washed out of the 

 loess in which it is frequently found in this region. 



The distribution of the fossils is almost coextensive with that of 

 the northern loess, excepting northward and westward. In a north- 

 erly direction they do not extend as far as the living colonies. The 

 writer has collected numerous loess fossils in southeastern Minne- 

 sota, southwestern Wisconsin, and northeastern Iowa, within the 

 territory over which numerous colonies of living Helicina occulta 

 are scattered, but among them were no specimens of this species. 

 This suggests that these colonies have advanced into this region 

 quite recently, or that they occupied areas over which no loess was 

 deposited. The loess of this section is patchy, and does not cover 

 the uplands generally, as was formerly supposed. It is quite 

 evident that the upland deposits, such as those between Postville 

 and Waukon, are not loess. They contain no fossils, and differ 

 from loess in physical properties. 



The northern limit of the fossils, so far as observed, is ap- 

 proximately indicated by a series of loops drawn from Ponca, 

 Nebraska, to Carroll, Des Moines, Colfax, Iowa City, Muscatine, 

 and Davenport, Iowa; Rock Island and Joy, Illinois, and Sullivan 

 county, Indiana. The fossils have been found at all the border 

 localities mentioned in this discussion, and at many points within 

 that border. 



Westward the fossils extend into eastern Nebraska (as far as 

 the writer has been able to determine) to a line drawn from Ponca 

 through West Point, Bruno and Lincoln to Peru. Numerous 

 collections of loess fossils have been made by the writer west of 

 this line, notably at Beemer, Howells, Clarkson, Milligan, Abie, 

 Atlanta, Oxford, North Platte, etc., but not a single Helicina was 

 found among them. 



The report by W. H. Russell (The American Geologist, vol. VII, 

 p. 40, 1891) of the occurrence of this species in the beds of un- 

 certain age in the southwestern part of Howard county, Nebraska, 

 is open to question. It is evident that the list of accompanying 

 species Was not accurately determined, though this species may be 

 correctly identified, as it is well marked. The deposit appears to be 

 loess, though the author himself questions it. It is well within the 



