53. 
Att SMALL Bortom-AniIMAts, ILLINoIs River, LiIveRPOoL TO 
Havana, 1915 anp 1920 
1, Average numbers per square yard 
Channel 4-7-ft. zone 
1915 1920 | 1915 1920 
| 
Viviparidae and Pleuroceridae 1294 25 121 15 
Sphaeriidae 0 34 3557 58 
Amnicolidae, Valvatidae, etc. 2 0 0.4 0 
Chironomidae 0 950 0 225 
Oligochaeta 0 89 0 4 
Other insects, worms, Crustacea, etc. 172 36 172 7 
Grand total 1468 1134 | 3850 309 
2. Average pounds per acre, 
and per cent. decrease in five years 
ea Per cent. 
Channel _n. decrease, 
1915 1920 fae av pagsn 1915—1920 
Channel | 4—7-ft. 
Viviparidae and 
Pleuroceridae 5156 50 319 26 99.2 91.8 
Sphaeriidae 0 17 1777 15 99° 
Amnicolidae, Val- | 
vatidae, etc. 0.1 0 0.2 0 
Total Mollusca 5156 67 2096 41 98.7 98.0 
Chironomidae 0 164 0 45 
Oligochaeta 0 3 0 0.1 
Other insects, worms, 
Crustacea, etc. 24 6 26 1 75.0 96.1 
Grand total | 5180 240 2122 87 95.3 95.9 
Per cent. snails | 99.5 27.9 98.7 47.1 
Per cent Chiro- 
aouidaas | 0 68.3 0 51.7 
