249 



the physiographic features of which were deteraiined in preglacial times. In the 

 upper portion of their courses, therefore, they present similar features to those of 

 the upper Wabash, but in their hiwer valleys they are quite different though alike 

 in most respects when compared with each other. The highest and roughest re- 

 gion of the State is drained by the White River and the small Wabash contribu- 

 tary basin, the Patoka. This region is the least well known conchologically. 



The Whitewater basin is very like the upper Wabash and for the most part is 

 entirely within the limit of glaciation, which reaches the Ohio in the vicinity of 

 Lawrenceburg, in Dearborn County. The lower portion of the Whitewater is pe- 

 culiarly sandy and does not seem to be suited to very great development of mol- 

 luscan life. 



The long and narrow basin of the Ohio is very rougli and the country rock, 

 chiefly limestone, everywhere appears in the bluffs and along the small tributary 

 streams. In certain of the smaller streams of this basin Strepomatid shell life 

 appears in great abundance, but the Unionid fauna is mainly confined to the (Ihio 

 itself and no species appear which are not to be found in that stream 



From these facts it is evident that a wide diversity of environmental condi- 

 tions is exhibited in the several basins as herein outlined. These differences find 

 corresponding variables in the waters of the streams ; in some they are (juite soft, 

 while in others the waters are very hard. Most of the small lakes in the northern 

 portion of the State present waters that are very hard ; in them tiie waters are 

 often so highly charged with calcium carlionate that it is deposited thickly on the 

 portions of the shells that project above the bottoms in which they are partly 

 buried. In many of the streams the same facts are to be observed ; this is especi- 

 ally noticeable in the upper Wal>ash, the shells from which are all more or less 

 heavily coated with this substance. Collections from lower down, notably from 

 Terre Haute to the mouth, are almost entirely devoid of this accretion. 



It is important to note the moUuscan facies of the various drainage areas and 

 by a. comparison of their faunas seek to correlate, if possible, the facts of distri- 

 bution with the physiographic and geologic features. The physiographic features 

 have already been noted ; to facilitate comparisons of this nature lists of the 

 mollusks have been collated, in every case based upon specimens actually col- 

 lected at one or more localities in the several basins. While these lists are incom- 

 plete in that they do not represent the full richness of the several faunas they 

 have proven instructive and may be useful in the general biologic study now un- 

 dertaken by the Academy. These lists now follow. 



