130 Illinois State Lahoratorij of Natural History. 



pect except its smaller size, and a muddy pond near the bluff 

 at the southern limit of Quiney. 



It was from the lakes and sloughs thus briefly described 

 that the material was obtained upon which this paper is based. 

 Omitting Cedar Creek, the bay, and the river, they have much 

 in common. All were, or are now, subject to overflow by the 

 Mississippi. Since the Indian Grave levee was built, the waters 

 within it, — Bear Creek, Harkness and Ballard Sloughs, and 

 Libby Lake, — have not commonly been subject to inundation, 

 — a fact which explains certain special features of the collection 

 taken from them. The condition of the pools with reference to 

 the river was not a usual one. A late rise in the river had flooded 

 them after the spring freshets had subsided, and kept open the 

 communication with the river much longer than would other- 

 wise have been, thus helping the large fishes to escape from 

 them after spawning, and doubtless carrying away hosts of the 

 smaller organisms which had appeared in the pools. All have 

 very muddy bottoms. In most, this mud was nearly knee deep, 

 and made seining very difficult and disagreeable. In some 

 places deposits of mud were of such recent origin and were so 

 loose that it was unsafe to venture into them. Aquatic vegeta- 

 tion was almost wholly lacking. A scant growth of filamen- 

 tous algio was occasionally seen, but in nothing like the quan- 

 tities in which it occurs in ordinary stagnant or quiet water. 

 In Lily Lake alone there was a rank growth of aquatic vegeta- 

 tion. Here a permanent growth of water lilies { Nehonhimn 

 liiteum) had become established, and to the under sides of the 

 lily pads was attached a scant growth of filamentous alga?. 

 This absence of vegetation is directly traceable to the overflows, 

 since these disturb the bottoms of the pools, displacing the silt 

 in some places, depositing fresh material in others, and dislodg- 

 ing and carrying away the plants which become establislied 

 during the intervals between floods. The water was not very 

 deep at this time, but of course varied with the river. It could 

 be waded in most ])laces by the men. It was deepest in tiie 

 larger pools, such as Long and Broad Lakes, and here the tem- 

 perature was tolerably constant. In the sloughs, where the 

 water was shallow, it often became very warm, and during a 



