266 



stations included in this discussion number in all 643, distrib- 

 uted as follows: Illinois River 235, Spoon River 36, Quiver 

 Lake 115, Dogfish Lake 48, Flag Lake 44, Thompson's Lake 99, 

 and Phelps Lake 67. 



ILLINOIS RIVER CHANNEL, STATION E. 



(Table III.; PI. I., V., VII.— XIII.) 



DESCRIPTION OF LOCALITY OF COLLECTION. 



The collections were made two and a quarter miles above 

 the city of Havana, a short distance above the outlet of Quiver 

 Lake (PL II.), at a point where the river was about 500 feet 

 in width at low water and about 600 feet from crest to 

 crest of the banks, which are here fringed by willows (Salix 

 nigra and S. longifolia) on both sides. The eastern shore is a nar- 

 row spit, 6 to 8 feet above low water, separating the river from 

 Quiver Lake. The western bank is higher, 8 to 10 feet, and is 

 covered by bottom-land forest. This is also a spit or "towhead" 

 between the river and Seeb's Lake. At low water (PI. IV.) the 

 eastern bank is exposed as a gentle declivity of 25 to 40 feet, 

 while the western one is much wider — a belt, 50 to 75 feet in 

 width, of soft black mud with gaping cracks (PI. V.). A short 

 distance from the low-water shore-line the bank shelves some- 

 what abruptly to the bottom, which with the exception of a 

 slight ridge near the center of the channel extends in an un- 

 broken level from side to side of the stream. The depth at low 

 water for a width of over 400 feet is 8 to 9 feet. To the north- 

 ward the river deepens slightly, while towards the mouth 

 of Spoon River it shoals to 6 feet, and below it to less 

 than 5 feet. The banks are of black alluvium, hardened 

 in the upper levels by exposure at low water, but al- 

 ways soft and treacherous near the low-water line. The bot- 

 tom in the channel is firm, being a compact bed of heavy blu- 

 ish mud mingled with sand and the shells of Unionidce, which 

 form in many places continuous beds of large area. 



A slight curve in the river above our plankton station shifts 

 the current at that point towards the eastern shore, but at the 



