45 
2%. Percentages, by weight, of average total hauls 
contributed by sludge-worms 
Channel 4-7-ft. zone | 1—3-ft. zone 
1915 1920 | 1915 1920 1915 1920 
Upper lake | 0.07 42.0 | 04 22.0| 1.7 8.7 
Middle lake 0 79.0 | 0 2.0| 0 trace 
Lower lake 0.15 3.0 | 0 0 0 17.3 
Out of a miscellaneous list of insects representing five or six families 
other than Chironomidae that were present or common in the bottom 
muds between Chillicothe and the foot of Peoria Lake in 1915, we found 
none at all surviving in the summer of 1920 at the thirty-one stations 
dredged in the sluggish waters of either the channel or shore zones of 
Peoria Lake proper or in the river at Chillicothe. At these same stations 
we failed also to find any isopods, the little amphipod Hyalella, any leech- 
es or planarians, or any sponges or bryozoans. In the relatively much 
swifter water that continues for about a half mile through Peoria Nar- 
rows, however, and in the rapid portion of the river just below the lower 
outlet of the lake, large Viviparidae and Pleuroceridae were present in 
larger numbers than in the upper, middle, or lower lake, a bryozoan, 
Fredricella sp., was thriving on the shells of living snails, and the former- 
ly common sand-case-building caddis larva (Hydropsyche sp.) was still 
present in considerable numbers. As the average valuation figures of 
this group of the bottom invertebrates ran only two to eight pounds per 
acre in Peoria Lake in 1915, it will be recognized that the decline is a 
small one compared with the losses since 1915 in Mollusca, and that it 
aas been much more than made up in bulk and weight by the recent in- 
creases in the sludge-worms and the larvae of the midges. 
OrHer InsEcTs,* WorMS, CRUSTACEA, ETC. OF Bottom Mups, 
CHILLICOTHE TO Foor oF Prorta LAKE, 1915 anp 1920 
NUMBER AND WEIGHT PEK UNIT OF BOTTOM AREA 
Channel 4-7-ft. zone 1-3-ft. zone 
1915 1920 | 1915 1920 | 1915 1920 
| | 
| Upper lake 12 0 31 OL 2 0 
Average | 
No. per Middle lake 23 0 12 0 42 0 
sq. yard 
Lower lake 30 0 52 0 120 0 
Upper lake 2 0 4 0 8 0 
Average 
pounds Middle lake 4 0 4 0 7 0 
per acre 
Lower lake 5 OM 6 0 { 0 
* See foot-note p. 7. 
