THE DISTRIBUTION OF LOESS FOSSILS 129 



types of the same species, and too often the habits of one species 

 have been confused with those of another of the same genus, or 

 even family, a mistake most frequently made with the Succineas. 

 Again, the versatility of certain species — their adaptability to 

 varying conditions — has been overlooked. Zonitoides minnsculus, 

 Bifidaria pentodon, B. contracta, Stic cine aavara, S. obliqua, etc., fre- 

 quently occur in low places and then often in great numbers — 

 but they are also found scattered over comparatively dry hill- 

 sides at considerable altitudes — and some of these species in 

 such places develop the depauperate type, that is they aver- 

 age smaller in size. To show the preponderance of strictly 

 terrestrial forms in the loess, the writer calls attention to the 

 fact that in the collections made last June at Natchez and 

 Vicksburg, Miss., numbering over forty species and nearly 

 five thousand specimens, there is not a single aquatic form. 

 Furthermore, every species which was collected in the loess 

 of that region has been found by the writer, living upon the 

 high bluffs and hills in and near Natchez, or upon hillsides 

 at considerable elevations in other parts of the south, notably 

 in northern Alabama, Georgia, and Tennessee. 1 At Natchez 

 the most common living species is Sue cine a grosve?iorii, and this 

 crept upon the bare surface of the loess clay which, at the time 

 of the writer's visit, had been baked by the hot summer sun of 

 the south during a period of drouth lasting more than six weeks. 

 Moreover, several scores of specimens which had been carried 

 about in the sun all day long in a box containing loess dust, and 

 hence were subjected to extremely desiccating conditions, were 

 found, after this experience, creeping about in their prison seem- 

 ingly perfectly contented. Yet we are sometimes told that the 

 Succineas are all "semi-aquatic," or that they must have an abun- 

 dance of moisture. Another illustration, equally striking, is 

 furnished by the writer's experiences and observations at Council 



■It is also a significant fact that of all the living species found in the hills and 

 bluffs of Natchez, only two, Leucocheila fallax, and Polygyra texana, were not found 

 in the loess of that region. Only one specimen of the first and two of the second were 

 collected. The former is not uncommon in the loess of the north, while the latter is 

 not known from the loess, at least to the writer. 



