434 
scanty vegetation, or none at all, lying between the weedy shore zone 
and the deep open water, part of it sometimes extending within the 7- 
foot line. 
Valuations considerably better than the average were obtained in 
restricted areas with more nearly uniform bottom in four of the isolated 
lakes, the average for clay bottom overlaid with fine decayed vegetation, 
in Deep Lake being 320 Ibs.; for sand and clay, in Cedar Lake, 251 Ibs. ; 
for gravel and sand, in Deep Lake, 220 lIbs.; and for gravel and sand, 
in Lake Zurich, 212 lbs. 
In its composition the littoral bottom-fauna of these lakes differs 
most strikingly from that of the Illinois Valley bottom-land lakes in the 
relatively much lower percentages of Mollusca. Snails made up only 
Lakes, NoRTHEASTERN ILLINOIS, AUGUsT—OcrToseER, 1916, Borrom Fauna 
POUNDS PER ACRE 
LirroraL Zonr, 1—7 Feet. SOME VEGETATION 
Lake area virinaniaie Sphaeriidae | Insects | po4q, | Per cent. 
nections Bete ete. ete. Mollusca 
Deep 7 iss 39.8 169.0 208.8 19 
Cedar 24 Canes 24.2 135.6 159.8 15 
Zurich 13 9.9 10.0 49.2 69.1 23 
Crystal 6 BAe 16.0 40.4 56.4 28 
Long 6 ee 1.7 50.7 52.4 3 
Sand 10 ae ee 0.6 13.1 13.7 4 
Average 66 1.8 AGI |e Sia 105.8 |. 17.4% 
Pistakee 29 10.8 26.0 ae 79.4 46 
Fox 24 2.3 3.6 18.0 23.9 24 
Average* 53 69 | 15.8 31.4 | 54.2 41.8% 
* General (simple) average of 8 lakes (119 collections) =82.8 pounds per acre. 
