73 
ALL SMALL BotroM-ANIMALS, STEWART LAKE, 1915 anp 1920 
MUD BOTTOM, 2 TO 5 FEET 
Number per square yard Pounds per acre 
1915 1920 1915 1920 
Viviparidae and : 
Pleuroceridae 21 0 41 0 
Sphaeriidae 32 4 13 2 
Amnicolidae, 
Valvatidae, etc. 37 0 12 0 
PRESS ILANIS rete crcds ole) v0 Gel tre alsl| 'o/3: 910 WolelersPelelatgleywie(diis afore die'e « «'- 66 2 
Chironomidae 8 74 2 28 
Oligochaeta 3 12 0.1 0.4 
Other insects, worms, 
Crustacea, etc. 43 0 6 0 
See OL Vote ct icteeterefteso eo lietniettis ekeere els eps c.2 ie eereyetga ct ace 74 30 
| 
Ercan Tarero hepiiaitsin 9 eee |eeitelets se atavalsicls © 'sic.s creole bia a's 89.1 6.5 
Estimated Reduction of Midsummer Surplus Stocks in the Com- 
bined Acreage between Chillicothe and Lagrange 
Dam (103 Miles) since 1914—1915 
While the necessarily restricted range of our bottom-and weed-fauna 
survey of 1920, compared with that of July—October, 1914 and 1915, 
leaves more gaps to be supplied by estimate in any general comparison 
than is perhaps best, it has seemed worth while, as a conclusion to the 
present paper, to make some computations of the approximate total loss 
since 1914—1915 in surplus bottom- and weed-fauna stocks*as of the 
midsummer period for the entire acreage of river and lakes in the former- 
ly enormously rich middle Illinois Valley district between the head of 
Peoria Lake and the Lagrange dam. These calculations have involved 
a partial reapportionment, by estimate largely, both of acreages and of 
acre-yields, as of 1908—1915, as published in a preceding paper,* these 
*The Small Bottom and Shore Fauna of the Illinois River and_its Connecting 
Lakes, Chillicothe to Grafton: its Valuation; its Sources of Food Supply; and its’ 
Relation to the Fishery. By R. E. Richardson. Bul. Ill. Nat. Hist. Surv., Vol. 13, 
Art. XV. 1921. 
