102 ANIMAL COMMUNITIES OF STREAMS 
places that support any amount of life. From these logs I have taken 
hundreds of specimens of small Parnidae, and with them predaceous 
diving beetles (Dytiscidae) which were found hiding in the cracks, also 
a few scattered caddis-worms (Hydropsyche). The fauna of the bottom 
is made up of burrowing and semi-burrowing forms. The little dytiscid 
(Hydroporus mellitus Lec.) (g9c) is characteristic: it has the habit of 
burying itself in the sand. The bivalved mollusks, especially mussels, 
are present. From the Deep River (upper course) we have taken 
nearly a dozen species. The only snail found is a burrowing form also. 
Animals of such a stream are subject to severe conditions. Many 
of them burrow. The substratum is very unstable and the logs and 
parts of trees to which many of them are attached are free to float down- 
stream with every flood. We know nothing of the reactions of these 
animals to various stimuli. They are distinctly subjects for investi- 
gation. 
6. THE SLUGGISH STREAM COMMUNITIES 
(Stations 19, 27, 28, and 29; Tables XVII, XVIII, XX-XXV) 
There are several phases or types of sluggish stream formations. 
The most important of these are the sluggish or base-level creek, the 
sluggish river, and the drowned river. These are all illustrated in the 
Chicago area. 
The sluggish creek type is illustrated by the west branch of the 
DuPage River and its tributaries; the upper course of the west branch 
of Hickory Creek, Dune Creek, some parts of the Little Calumet south 
of Millers, and the Kankakee and some of its tributaries. 
The sluggish rivers are the Upper Fox, the lower St. Joseph, the 
Grand Calumet, the lower Galien, the lower Black, and others. These 
constitute a group of streams representative of the sluggish type about 
the Great Lakes. 
a) Sluggish creek sub-formations (Stations 16, 18).—The west branch 
of Hickory Creek has been studied in a cursory manner. The fish are 
a strange mixture of semi-temporary stream and pond forms. The black 
bullhead (A meiurus melas) (79) is probably the most characteristic fish. 
The golden shiner (Abramis crysoleucas) and sunfish (Lepomis cyanellus) 
are also found. 
Baker (100) studied the upper portion of the east-north Chicago 
River. He recorded the same species of Mollusca as were taken in the 
upper part of Hickory Creek. He records also the black bullhead. The 
insects which he mentions are those commonly found in ponds. This 
