535 



Peoria ; but 1)cv(^ik1 that few specimens have been found, and none 

 at all in that part of the river which is noticeably polluted. 



C. lobifcnis, a dull reddish species, averaging nearly half an inch 

 in length, with only one pair of ventral blood-gills, is one of the com- 

 monest species represented in our collections, and occurs in almost 

 every collection of any size from localities on the Illinois and con- 

 nected waters up to and including De Pue and Hennepin, and also the 

 semi-isolated De Pue Lake. It was not taken from the foul bottom 

 anywhere above De Pue. 



C. modcstus, a green species found commonly in the lower river, 

 at Havana, and also in other rivers and creeks throughout the state, 

 was found in a single collection made at Ottawa. 



C. viridicollis is one of the most widely distributed species repre- 

 sented in the river collections, occurring as far north as Spring Valley 

 and Starved Rock, where the water is appreciably polluted. 



Orthocladiiis sp. E occurred in collections from Spring Valley, 

 Starved Rock, and Marseilles. 



In the part of the river beyond Ottawa (eastward) but few larvae 

 were found, but examples of Tanypus dyari occur among the collec- 

 tions made at Marseilles, above the dam, and at Morris. This species 

 has been reared from larvae found in Boneyard Creek at Urbana, 

 which is badly polluted with sewage; and it is reported to have been 

 reared from larvae found in temporary puddles on waste ground at 

 Washington, D. C. 



A species, greenish in color and measuring about 7 mm., which I 

 am unable to identify exactly — it may be C. flavus — has been found 

 in a great number of collections from different parts of the river. The 

 fact that Ottawa is among the localities from which it is listed in my 

 notes, shows that it occurs in the polluted portion of the river as well 

 as in parts that are comparatively clean — as at Havana. 



Although we have no data connected with the upper part of the 

 river prior to the opening of the canal which can be compared with 

 data obtained since that event, we have evidence that in other Illinois 

 rivers, where there are no such conditions of pollution, the insect 

 fauna does not suffer material diminution towards the sources of these 

 rivers, though at times there may be a change in its constituents. 



From the fact that out of probably one hundred species of CJiiro- 

 nohudcc that may be found in various portions of the lower Illinois 

 not over a dozen are met with in the portion between De Pue and 

 Morris, it is, to my mind, clearly evident that the influx of sewage 

 matter from the drainage canal in question very seriously reduces the 

 number of these insects normal to the river. 



