435 
17.4% of the average weight of the hauls at 66 stations in the six iso- 
lated lakes; and only 41.8% in the two lakes traversed by the Fox River 
channel. The snails belonged almost entirely to the smaller-sized 
species, the larger Pleuroceridae and Viviparidae occurring only very 
rarely and in small numbers in the hauls. The most abundant families 
were the Sphaeriidae, Amnicolidae, Valvatidae, and Physidae. The most 
important insects, measured by weight, were the Trichoptera (caddis- 
flies), Chironomidae, and large Ephemeridae (May-flies). 
(A more complete report on these collections, including also the 
dredgings in deep water, is being planned for publication later.) 
2. WEED FauNA 
In August, 1916, we found the shore vegetation of the isolated glacial 
lakes so generally thin and sparse, as compared with the dense growths 
of Potamogeton and Ceratophyllum in the Illinois River bottom-land 
lakes, that it was practically impossible to employ the bucket method of 
collecting the weed animals used at Havana in 1914. Along the north 
shores of Pistakee and Nippersink lakes, however, beds of mixed 
Potamogeton, Myriophyllum, and Ceratophyllum were not uncommon 
that were fully as dense and that carried not far from as rich a fauna 
as that of such lakes as Flag and Thompson. The average for the upper 
9 inches at two stations in Pistakee and Nippersink lakes in August, 1916 
(1,665 Ibs. per acre), was only 26% less than the average of the seven 
weed-fauna stations in the vicinity of Havana in 1914 (2,118 lbs.). Both 
insects and mollusks constituted an almost insignificant part of the 
totals, 85% of the weight in one case, and 95% in the other being made 
up of a single small crustacean—the little fresh-water shrimp, Hyalella 
knickerbockert. (Table, p. 436.) 
Comparison with Outside Bottom- and 
Weed-Fauna Valuations 
1. Borrom- AND WEED-FauNA OF ONEIDA LAKE. (BAKER, 1918) 
In the Lower South Bay of Oneida Lake, New York, in 1916, Baker 
found the richest bottom-fauna within the 6-foot contour. Averaged 
by weight*, in pounds per acre,-sand bottom showed the highest valua- 
tions, 143 sixteen square-inch units examined, averaging 387 lbs. Gravel 
bottom, with 207 lbs., clay bottom, with 188 lbs., and sand and clay, 
with 210 lbs., were well under sand bottom in richness, but were all much 
richer than the mud bottom over 6 feet. The mud bottom within the 6- 
foot line averaged for 27 units 230 Ibs. per acre. These valuations much 
* Rough, approximate valuations, by present author, from Baker’s figures 
per unit of 16 square inches, on same general basis followed in valuation of Illinois 
River and lake data, 1914—1916. Average adult size of some of the snails esti- 
mated by Mr. Baker. Chironomidae and larvae of Trichoptera lumped and aver- 
aged at a round valuation about the average of those of northeastern Illinois 
glacial lakes. 
