DEC ""0 1896 



Entomology of the Illinois River. 151 



areas has partly been blown into undulating mounds 

 and ridg-es, and occasionally presents expanses of barren 

 sand. They are quite peculiar in their fauna and flora, 

 which are very different from those of the uplands. At 

 Havana the width of the sand deposit between the river 

 and the eastern upland is about fifteen miles. 



Just above Havana, Spoon River enters the Illinois 

 from the west, and the sediment brought down by it has 

 raised the bottom-lands below its mouth to a higher 

 level, narrowing the river, and forcing it for a short dis- 

 tance against the margin of the sandy plain. 



Above the mouth of Spoon River the bottom lands are 

 lower. Here wide stretches of shallow lake and marsh 

 appear, with bottoms of soft black mud, and com- 

 paratively narrow intervening wooded ridges, rarely 

 sandy, except at certain exposed and wave-washed points 

 or along the margins of the sand plain. 



THE SUBSTATIONS. 



In order to cover a variety of situations, a number 

 of typical points or substations were selected for special 

 study and periodical examination. Each of these was 

 regularly searched from the shore into deep water; but 

 as the forms here treated are essentially shallow-water 

 forms, the characteristics of the marginal surroundings 

 will receive special attention. 



Three of these stations were located in Quiver Lake. 

 This is a permanent arm of the river extending north- 

 wards along the margin of the sand plain above Havana. 

 The natural drainage of the sand escapes in large (]uan- 

 tities along its eastern side, keeping the shore con- 

 stantly saturated with cool percolating water, to a 

 greater or less width, according to the level of the river. 

 Beyond the head of the lake, this drainage forms a con- 

 siderable stream, Quiver Creek, which empties into the 

 broad shallow head of the lake through a muddy and 

 weedy flat. Near the place where the clear waters 

 of this stream cease to follow a definite channel, Station 



