41 
ditch in Illinois, and was taken by us in 1912 in the worst fouled portions 
of the Illinois River between Morris and Marseilles, though not north- 
ward of those places. None of these three species was found by us 
either in 1920 or in 1913 south of Peoria; and the last one named, no- 
where at all except at Peoria. 
The list of larval midge-species that have dropped out of this section 
of the Illinois River since 1915 includes at least four, of which but one, 
Chironomus tentans F., is known definitely to do badly in the presence of 
pollution and to have been common in this section during or before 1915. 
This species was common to abundant in 1913—1915 both in the river 
and in the lakes all the way from Peoria Lake to Havana, but has now 
-apparently disappeared altogether from the lakes and from the greater 
portion of its old river-range. Species of apparently rather indifferent 
habit as indicated by their distribution in this section and above and be- 
low six or seven years ago, but that failed to appear in Peorja Lake col- 
lections in 1920, are two in number—C. lobiferus Say and C. viridicollis 
v. d. W. 
