56 
Further evidence of a mixed status or condition of the bottom fauna 
in this portion of the river is furnished in the lists and figures of Chiro- 
nomidae. In the first place, we note that while midge-larvae have in- 
‘creased greatly here since 1915, in spite of the disappearance the while 
of half a dozen formerly common species of clean-bottom habit, yet no 
distinctly pollutional species has invaded this section since 1915, and only 
two forms of wide range or doubtful preference (Chironomus lobiferus 
Say and a species very close to C. decorus Joh.) are new here since the 
1918—1915 period. Further, it will be noted that more than half of the 
increase in weight-valuation of Chironomidae in the river below Havana 
in the five years preceding 1920 is not due to these two newly introduced 
tolerant forms, if indeed they are both so, but follows from the multipli- 
cation here recently of three of the large larvae of clean-bottom habit 
which were common to abundant in the Jakes above Havana in and before 
1915, but which have since been exterminated in that range, with the ex- 
ception of Quiver Lake. These three species (C. tentans F., C. ferrugi- 
neovittatus Zett., and Procladius concinnus Coq.) occurred in good num- 
bers in 1920 in this section of the river wherever there was mud, and the 
sharp reversal in their distribution, from lake and backwater above 
Havana to river below Havana, seems to lend some support to the sup- 
position that their recent appearance and rapid multiplication in their 
new range is in some manner connected with their disappearance from 
the old one. 
Mince LarvaE (CHIRONOMIDAE) oF Borrom Mups oF ILLINOIS RIVER BELOW 
Havana,* 1913—14 ro 1920—JuLty—OcrTosBER 
1. Tolerant species or species of doubtful preference that have come in since 
1913—1}. 
Chironomus lobiferus Say. Present, 1920. 
C. sp. near decorus Joh., No. 2. Abundant, 1920. 
2. Cleaner-water species that have dropped out since 1918—14. 
Palpomyia longipennis Lw. Present in 1913—14. 
Tanypus monilis L. Present in 1913—14. 
Chironomus dux Joh. Present in 1913—14. 
C. digitatus Mall. Present in 1913—14. 
Cricotopus trifasciatus Panz. Present in 1913—14. 
Cricotopus sp. Present in 1913—14. 
3. Cleaner-water species that have come in since 1913—1}4.+ 
Procladius concinnus Coq. Common, 1920, shallow zones. 
Chironomus ferrugineovittatus Zett. Present, 1920, 4—7-foot zone. 
Cc. tentans F. Common, 1920, chiefly in shallow zones. 
4. Tolerant or indifferent species that has dropped out since 19138—14. 
Chironomus decorus Joh. Present, 1913—14. 
* Occurrence in 1913—-14 principally below Beardstown; in 1920, 2.5 miles below 
Havana to 1.5 miles below head of Grand Island. * 
j All these species were present or common both in the river and the lakes 
above Havana, 1913—14, but were not found in either of those ranges last year, if 
the occurrence of C. ferrugineovittatus in Quiver’ Lake in 1920 be excepted. 
