FURTHER NOTES ON HELICINA OCCULTA SAY 



B. SHIMEK 



Few American mollusks equal Helicina occulta Say in interest. 

 It is an operculate species which has been reported at times as 

 aquatic, though it is strictly terrestrial ; its living representatives are 

 distributed over widely separated areas in restricted local colonies, 

 and evidently represent a declining race ; and it is a common fossil 

 of the loess of peculiar signifiacnce, of much more general distri- 

 bution in the loess-covered portions of the upper Mississippi- 

 Missouri basin, failing to reach the region of the northernmost 

 living colonies, but extending well beyond them westward. 



The writer discussed this species quite fully in two earlier papers.^ 

 Fourteen years have passed since the publication of the later one 

 of these papers, and much additional information concerning the 

 species has been gained since both by the writer and by others. 



Some of this information is here presented, together with cor- 

 rections and modifications of certain previous statements. 



THE RECENT COLONIES 



Few localities have been added since the former reports, and 

 most of these are within counties in Iowa already represented in 

 the previous reports. 



The northeasterly range in Iowa has been slightly extended by 

 the discovery of the species in Allamakee county, along Upper Iowa 

 river, . 



The most notable discovery was that of a series of colonies in 

 Madison county, southwest of Winterset. This extends the west- 

 ward and southwestward range perceptibly. The species is here 

 found abundantly in the usual habitat, on steep wooded slopes 

 usually more or less covered with scattered fragments of limestone. 

 The specimens vary from 5.5 to 7.0 mm. in greater diameter. The 

 recent forms hitherto reported from Iowa range from 5 to 7.25 

 mm. in greater diameter, while North Carolina specimens reach a 

 size of 8 mm. 



*Helicina occulta Say: Proc. Davenport Acad, of Sciences, vol. IX, pp. 

 173-180. 1904. , ^,^^^ 



Additional Notes on Helicina occulta Say: Journal of Geology, vol. XIII, 

 pp. 232-237; 1905. 

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