431. 
The Weed-Fauna of the 1—4-foot Zone of the Illinois Valley 
Lakes, and the Combined Bottom- and Weed-Fauna 
Average, August—October, 1914 
1. Weep Fauna oF THE LAKES NEAR HAVANA: 
In the autumn of 1914 a series of quantitative collections of the 
small invertebrates attached to and scattered between the leaves and 
stems of the denser growths of coarse vegetation about the margins of 
the bottom-land lakes near Havana, in depths 1 to 41% feet, were made 
at seven stations. These collections were made by inclosing the tops of 
the plants in a large bucket, lowered about them to a depth of about 9 
inches, cutting off the stems a little below the 9-inch level, shaking them 
out thoroughly in the water obtained by righting the bucket, and then 
passing the water saved through a fine sieve. Though these collections 
_ represent but a fraction of the total ‘““weed fauna’, omitting the small 
insects and other animals occurring between the bottom and the lower 
limit of the bucket hauls (a distance of 1 to 5 feet), the average valua- 
tions obtained in this way were very much above the average bottom 
valuations from the same lakes in any zone, with the single exception 
of a few hauls from the bottom of the Quiver Lake “channel” in 1914. 
The general average for the seven stations was in fact 2,118 lbs. per 
acre, or more than eight times the general average of bottom fauna for 
the five classes of lakes and backwaters between the head-of Clear Lake 
and Beardstown studied by us in 1914 and 1915 (255 Ibs.). 
The smaller snails (Amnicolidae, Physidae, and Valvatidae, prin- 
cipally) formed about 50% of the average total by weight. The ap- 
proximate half of the collections made up of insects (larvae and nymphs) 
consisted principally of immature Odonata (Agrionidae and small Libel- 
lulidae). The only large snails were a few adult Planorbis trivolvis, 
the great bulk of the material being of quite small size and easily avail- 
able, in that respect, for use as food by young to half-grown as well as 
adult fishes. 
2. COMBINED AVERAGE VALUATION OF THE BoTToM- AND WEED-FAUNA 
Stocks, AND ToTAL STOCKS IN THE ACREAGE 
For the purpose of calculating a general average, and also the total 
stocks, both of the bottom and weed animals, for the entire lake and 
other backwater acreage between Copperas Creek dam and Lagrange 
(approximately 52,700 acres at 8 feet, Havana—the average gage in 
July—October, 1910—1914), I have assigned the general bottom-fauna 
average of the twelve lakes studied (255 lbs.) to the entire acreage, as 
with no levees, and the weed-fauna average of the lakes in the imme- 
diate neighborhood of Havana (2,118 Ibs.) to the approximate 29,700 
acres with depths under 4 feet in the district. An acreage-weighted 
general average figured in this way stands at 1,447 lbs. per acre, or at 
