48 
4. Prorta Narrows, (STRONG CURRENT) 
Channel 
4-T7-ft. zone 
1915 1920 | 1915 1920 
Viviparidae and Pleuroceridae 46.3 227. |No coll. 174 
Sphaeriidae 0.5 (0353 ees 6 
Amnicolidae, Valvatidae, ete. 0 0 ye 0 
Chironomidae 0 39.6 * 108 
Oligochaeta 0 0 0 
Other insects, worms, Crustacea, etc. 2.1 14.4 a 0 
Grand total 48.9 281.5 a 288.0 
5. Prorta AND PEKIN UNION RAILWAY BRIDGE 
(BELOW FOOT OF LAKE, IN STRONG CURRENT) 
Viviparidae and Pleuroceridae 224.6 0 60 237 
Sphaeriidae | 8.3 0 136.7 0 
Amnicolidae, Valvatidae, ete. 0 0 0 0 
Chironomidae 7.0 0 0 3.6 
Oligochaeta 0 0 0 1.2 
Other insects, worms, Crustacea, etc. 13.9 0 9.6 24 
Grand total 253.8 0 | 206.3 265.8 
The Illinois River, Liverpool to Havana 
(Mile 199.0—207.0 below Lake Michigan) 
The changes between 1915 and 1920 in the appearance and odors of 
the muds in the eight-mile section of the Illinois next above Havana, 
whose upper and lower limits are respectively about 34 and 42 miles be- 
low the foot of Peoria Lake, and 199 and 207 miles below Lake Michigan, 
are, if anything, more striking than those that have occurred in the five 
years between Chillicothe and Peoria. In this part of the river in 1915 
