ARTICLE XV.—The Small Bottom and Shore Fauna of the Middle 
and Lower Illinois River and its Connecting Lakes, Chillicothe to Graf- 
ton: its Valuation; its Sources of Food Supply; and its Relation to the 
Fishery. By Rosert E. RicHarpson. 
INTRODUCTION 
The present paper, so far as it relates particularly to the valuation of 
the bottom and shore animals, brings together the results of three sum- 
mer-autumn seasons of dredging operations in the Illinois River and its 
connecting backwaters, July, 1913, to October, 1915. The work in the 
river proper and in the wide expansion of its waters known as Peoria 
Lake included forty cross-sections at intervals ranging from one to about 
eleven miles, covering the lower one hundred and eighty miles of the 
river, or about 80 per cent. of the total distance between the mouth and 
the head of navigation at La Salle; and embraced a total of three hundred 
and eighty-seven dredge and dipper collections. The dredging opera- 
tions in the more inclosed bottom-land lakes were mainly confined to 
those in the middle Illinois valley district of about fifty-nine miles river 
length between the Copperas Creek and Lagrange dams, in the lakes and 
other backwaters of which region three hundred and eighty-five dredge 
and dipper hauls were taken during the three working seasons. 
In addition to the collections of the bottom animals for the valua- 
tion studies, sieved samples of the mud deposits on the floor of both the 
river and the lakes were taken in 1913 and 1914 and analyzed for such 
indications as they might contain of reasons for differences in productiv- 
ity of different bottom areas. Between March, 1914, and February, 1915, 
also, standard sanitary chemical analyses of water samples from a lim- 
ited number of stations in the upper, middle, and lower river were car- 
ried on continuously at weekly intervals with a view particularly to 
obtaining data on the nitrogen load of the waters and on the rate of 
progress of its nitrification. Such comparisons as are undertaken with 
plankton production are with reference mainly to data collected in 1909 
and 1910, the most recent seasons devoted at all extensively to plankton 
operations in the region of the river covered by the present paper. Some 
principal conclusions from the plankton work of these two years in the 
river and‘lakes at Havana, as also from the sanitary chefhical analyses of 
1914-1915, have already been reported upon in papers by Prof. Forbes and 
the present writer (Forbes and Richardson, 1913; 1919). 
Apparatus—tThe collection of the bottom fauna was begun in the 
summer of 1913 with our ordinary iron dredges (modified “Blake” or 
