424 
indeed, been taken in company with species of other genera con- 
siderably more frequently than with each other. The sunfishes, 
consequently, are not an associate group, but tend to disperse 
themselves over a large variety of ecological situations, those least 
like each other being most likely to meet on common ground where 
their unlike capacities enable them to live together in a non-com- 
petitive way. Other striking examples of this reaction might be 
pointed out in the suckers, the minnows, the catfishes (especially 
the bullheads), and the top-minnows. 
Ninety-seven of our species have been collected in large enough 
numbers, and from a sufficient variety of locations, to give us data 
for comparison with reference to the general character and size of the 
water bodies which they prefer; 62 species furnish available data 
concerning the bottom or substratum of these water bodies; and 49 
species, data concerning current and rate of flow. The numbers of 
collections for the various species covered by these figures vary 
greatly from a minimum of 10 collections of a species to a maximum 
of 376. Unfortunately, the larger and more important fishes are 
commonly represented by the smaller numbers of collections, and 
statements made concerning these are less likely to be found fairly 
accurate and generally correct than are those concerning the smaller 
fishes, represented by larger numbers of collections. 
One available set of our data may best be presented in tabular 
form, for such use as the student may wish to make of them; and to 
this table we add, as an illustration of its use, only a few statements 
concerning the more conspicuous ecological groups of our Illinois 
fishes. . 
By assorting the species according to the size of the ratios of fre- 
quency of occurrence for each class of situations distinguished in this 
table, we may separate those strongly preferring the given situa- 
tion from those apparently avoiding it. In this way we learn that 
the species occurring in our collections with disproportionate fre- 
quency in the larger rivers of the state are the mud-cat (Leptops olt- 
varis), one of the river carp (carpio), the toothed herring (Hiodon 
tergisus), and the sheepshead (A plodinotus), among the larger fishes; 
and a small darter (Cottogaster shumardi), the trout-perch (Percopsis 
guttatus), and a minnow (Hybopsis dissimilis) among the smaller 
fishes. 
