531 



November 15, however, the oxygen ratios were precisely the same — • 

 8.9 for each. The loss of oxygen down stream in July was perhaps 

 due to a rapid hot-weather decomposition of sewage materials re- 

 ceived at Peru and La Salle. 



Our only collections at Spring Valley were made with dip-nets^ 

 dredges, and small seines October 15 to 18, 1912. The water, even 

 this far down the stream, had a noticeable sewage odor and a grayish 

 color, with no tinge of green; but it improved greatly before reach- 

 ing Hennepin, where it was odorless and of a greenish hue. The 

 bottom sludge changes more slowly, however, as one goes down 

 stream, and samples taken October 18 a quarter of a mile below 

 Spring Valley in water twelve feet deep were still swanning with 

 Tubifcx — several hundred to the plate. At Spring Valley the weeds 

 and grass at the edge of the river were free from Sphccrotilus and 

 Carchcsiuni, and these sewage organisms were not taken in the 

 plankton. No blue-green algae were found here except a small cjuan- 

 tity of Lyngbya versicolor; and the green filamentous algas were 

 mainly Cladophora crispata and Stigeodonium teniie, with some 

 Ulotlirix, Oscillaria, and Vaucheria. Sponges were found on the 

 mussel shells; leeches occurred in eight of the collections; Cyclops 

 was abundant in the algae ; and shells of five species of mussels were 

 dredged from the bottom — all dead, however, except one specimen 

 of Ouadrula pustulosa. Among the other living mollusks were many 

 Campcloina, Planorbis trivoh'is, Sphcvviuui transi'crsuin, Pisidiitm, 

 and Ancylus; and a few other species were represented by dead 

 shells. PluuiatcUa rcpcns was common on logs. 



Depue 



Similar collections were made October 17 and 18, 19 12, from 

 the Illinois River, opposite Depue Lake. The sludge at this point 

 was less offensive than above, and contained but fifty specimens of 

 Tubifex per plate. Three of the collections contained the isopod 

 crustacean Ascllus. Osfracoda were in the duckweed along shore, 

 together with the crustacean Hyalcila knickcrbockcri, the first to 

 occur in these river collections below Lockport. Here also was taken 

 the first specimen of the common river shrimp, Palcumonctes exilipcs. 

 Caddis-fiy larvae were abundant on mussel shells, and dragon-fiy 

 nymphs were taken in five collections. Six species of mussels — 

 Quadrula heros, Q. plicata, Q. pustulosa, Q, asperrinia, Anodonta 

 grandis, and Tritogonia tubercidata — were represented by living 

 specimens taken in a small dredge. Succinea, Campcloma, Planorbis, 



