ADDITIONAL NOTE ON HELICINA OCCULTA 



B. SHIMEK 

 Iowa City, Iowa 



Since the publication of the paper on Helicina occulta 1 the writer 

 visited the type locality at New Harmony, Ind., from which Say 

 obtained his fossil specimens of this species. Not only did the more 

 or less plant-covered bluff from which Say probably obtained his 

 specimens yield a number of shells, but more numerous specimens 

 were obtained from several large exposures along the roads leading 

 south from New Harmony which have been excavated since Say's 

 time. The species is not as common, however, as in many of the 

 more westerly localities. 



Two loesses also occur here, the lower being the characteristic 

 post-Kansan loess, and the upper, a light yellow loess, probably post- 

 Illinoian. Few shells of Helicina occulta were found in the upper 

 loess, and they average about 6.5 mm in diameter. 



The species is more common in the post-Kansan loess, and the 

 shells from this loess are of special interest because of their large 

 size. In the paper cited (pp. 177-79) the diameter of the largest 

 fossil shells known from the loess is given as 7.25 mm , while that of 

 the largest known recent specimens from the loess-covered region is 

 7.50 mm . 2 Several of the shells from the post-Kansan loess of New 

 Harmony measure 7.50 mm , and the average is more than 7 mm . 

 Thus the range of variation in the size of the recent shells within the 

 loess-covered territory is fully equaled by that of the fossils, and 

 differences in size cannot, therefore, be accounted for by general 

 climatic conditions. The distribution of the smallest forms of this 



1 Proceedings of the Davenport Academy of Science, Vol. IX, pp. 173-80. 



2 The largest authentically reported recent specimens were collected by Walker 

 and Pilsbry on Mount Mitchell, North Carolina, and are reported in the Proceedings 

 of the Academy of Natural Sciences, Philadelphia, in May, 1902, on p. 421, as follows: 

 "A few large specimens, diameter 7 \ to 8 mm , were found under the dead leaves 

 around the roots of the basswoods and buckeyes." This locality, however, is far 

 outside the loess-covered region. 



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