409 
Borrom Fauna, 1—3-Froor ZonrE, LAGRANGE To GRAFTON, 1915 
POUNDS PER ACRE 
nee 5 Small 
Viviparidae Insects, 
and ! Rope Pees worms, Total 
Pkeuroceridae Sphaeriidae Crustacea 
Lagrange dam to Florence 
8 coll.’s Obed 9.2 , 0.9 10.1 
Florence to Kampsville 
8 coll.’s 2.4 0.1 5.0 7.5 
Kampsville to Grafton 
12 coll.’s 0.3 6.3 21.3 27.9 
Lagrange to Grafton 
28 coll.’s 0.8 83 10.8 16.9 
Per cent. of total | 
(by weight) 4.7% 31.3% 63.9 % 
(g) GENERAL SuMMary, Itiinois River Borrom Fauna, 
Juty—OcroseEr, 1915 
1. DISTINCTION OF MAIN REACHES 
If we have regard only to the larger average differences in weight 
of the bottom-fauna stocks of, 1915, the 180.5 mile stretch of river be- 
tween Chillicothe and Grafton separates into four principal subdivi- 
sions :—First, a section of 43.7 miles between Chillicothe and the dam at 
Copperas Creek which bears a fairly rich channel- and a similarly rich 
shore-fauna (channel average, 239 lbs. per acres ; 4—7-foot zone, 372 lbs. ; 
1—3-foot zone, 225 lbs.). Second, a short stretch between Copperas Creek 
dam and Havana which has an exceedingly rich channel fauna (3,029 
Ibs. per acre) and a shore fauna far above the average (4—7-foot zone, 
1,960 lbs. ; 1—3-foot zone, 920 lbs.). Third, 42.5 miles between Havana 
and the dam at Lagrange with very poor channel (22 Ibs. per acre) but 
with shore as rich as in the first 60 miles (4—7-foot zone, 282 lbs.: 
1—3-foot-zone, 435 lbs.). Fourth, in the lower 77.5 miles, a long 
reach that is extremely poor both in shore and channel (channel, 6 Ibs. 
per acre; both shore zones, 17 lbs.). 
Whether in the shore or the channel zones, so far as is shown by 
the data of 1915, the richest stocks of small bottom-invertebrates are 
present in the reaches with the least flood slope and velocity, these 
