124 B. SHIMEK 



species (as for example Succinea grosvenorii) seem to favor open, 

 rather grassy places, and a few others may be found among - the 

 weeds and bushes skirting prairie ponds, but as a rule rough, roll- 

 ing timber areas are favored. Here an abundance of food (for 

 nearly all are herbiverous) and more or less shade and protection 

 are furnished by the vegetation. As we recede from the timber- 

 bordered streams the number of species and specimens grows less, 

 and the writer knows from personal experience obtained in vari- 

 ous parts of the state that large prairie areas of that character 

 may be searched in vain for any trace of a land mollusc. In the 

 eastern part of the state, with its more rolling, timber-covered 

 surface, almost every locality — certainly every county — pre- 

 sents numerous favorable locations for colonies of snails, but as 

 the collector crosses the state westward he finds that in species 

 and in specimens the molluscan fauna grows poorer, the timber- 

 fringed streams or ponds and lakes alone marking the favorable 

 localities. 



If careful observations are made even in the best of these 

 collecting grounds, whether in the eastern or western parts of the 

 state, it will be found that much variation and inequality in local 

 distribution exist. One hillside may present certain species, 

 while the next, perhaps across a narrow ravine, will show a 

 wholly different series, and a third near by may have none at 

 all. A species which in one spot is the prevailing type, may, 

 only a few rods or even feet away, be wholly or in part sup- 

 planted by another. This is sometimes due to differences in the 

 abundance of trees and vegetation furnishing food, and to other 

 variations in the character of the surface, but often it seems to 

 be a mere accident. 



The number of individuals of any, or all, species in a given 

 locality is also very variable. In the most favorable spots, how- 

 ever, especially on higher grounds, one seldom finds many indi- 

 viduals together. Even such species as Zonitoides arboreus, Z. 

 minusculus, Vitrea hammonis, Coclilicopa lubrica, Succinea obliqua, S. 

 avara, etc., which may often be found in large numbers under 

 leaves or sticks and logs in comparatively low places, usually show 



