51 
. In the history of the Chironomidae of the river muds since 1915 in 
this district, after the disappearance of half a dozen of the old list of 
more sensitive species, perhaps the most important single circumstance 
is the appearance here in 1920 of the pollutional Chironomus plumosus 
Linn., which also invaded the Chillicothe—Peoria section for the first 
time in the five-year interval ending in 1920. This species was, in fact, 
quite common in September last year in the foul spongy mud taken at 
Liverpool, both in the channel and outside of it as far as the four-foot 
line, but was much rarer in the bottom samples at Hogfat Bend and just 
above Havana, its average for all the stations in the section being thus 
brought down to 20 per square yard. 
The three other commonest species of midges represented in this 
section of the river in 1920 included two species of wide range or pre- 
sumably tolerant habit, Chironomus lobiferus Say and a form near C. 
decorus Joh., and one hold-over species of more particular habit, C. 
tentans Fabr. C. lobiferus was recorded from Havana in 1913—1914 by 
Malloch, but was less common then than in 1920, when it averaged as 
high as 100 per square yard in channel collections. The decorus-like form 
had not been previously taken. Chironomus tentans F., which seems to 
have disappeared completely from its old range at and above Peoria since 
1913—1914, as also from the lakes between Liverpool and Havana, was 
still holding its own in good numbers in 1920 at the lower (but not the 
upper) river-channei stations in the section. 
Mince LarRvAE (CHIRONOMIDAE) OF Borrom Mups or ILtinois River, LIvERPOOL TO 
Havana, 1913—1914 To 1920—JuLty—Ocroser 
1. Pollutional species that has come in since 1913—14. 
Chironomus plumosus L. Common at Liverpool in 1920. 
2. Tolerant or indifferent species that has come in since 1913—1}. 
Pee sp., near decorus Joh., No. 1. Abundant, Liverpool to Havana, 
3. Tolerant or indifferent species found both 19183—14 and 1920. 
Chironomus lobiferus Say. Present, 1913—14. Common in channel only 
in 1920. 
4. Tolerant or indifferent species that have dropped out since 1913—1}. 
Chironomus viridicollis v. d. W. Common, 1913—14. 
C. decorus Joh. A few, 1913—14. 
. Cleaner-water species that have dropped out since 1913—1}. 
Tanypus monilis L. Common, 1913—14. 
T. illinoensis Mall. Present, 1913—14. 
Chironomus ferrugineovittatus Zett. Present, 1913—14. 
C. modestus Say. Present, 1913—14. 
Cricotopus trifasciatus Panz. Common, 1913—14. 
Palpomyia longipennis Lw. Common, 1913—14. 
G. Cleaner-water species still surviving in 1920. 
Chironomus tentans F. Present in 1913—14, but less common in the 
river than in the connecting lakes. Commoner in the river in 1920 
than in 1913—14, but apparently exterminated in the connecting lakes. 
a 
