415 
ESPECIALLY NORTHERN SPECIES IN ESPECIALLY SOUTHERN SPECIES IN 
ILLINoIs (16): ILLINOIs (14): 
Whitefish Alligator-gar 
Lake herring Blue cat 
Lake trout Ictalurus anguilla 
Long-nosed sucker Freckled stonecat 
Lake carp Harelipped sucker 
Notropis anogenus Notroptis pilsbryt 
Great Lake catfish Viviparous top-minnow 
Mooneye Pigmy sunfish 
Pike Round sunfish 
Muskallunge Lepomis symmetricus 
Menona top-minnow Eupomotis heros 
Brook stickleback Hadropterus ouachite 
Nine-spined stickleback Etheostoma obeyense 
Trout-perch E. squamiceps 
Cottus ricet 
Uranidea kumlieni 
USE OF LOCALITY MAPS 
In the foregoing discussion of the sectional distribution of Illinois 
fishes no account has been taken of differences in the frequency of the 
occurrence of the species in the different sections in which they have 
been found, a single occurrence in southern Illinois, for example, 
counting for as much as fifty such occurrences in the northern part of 
the state. That highly interesting and important peculiarities of 
distribution are concealed by this gross method of comparison is 
made evident by an examination of the maps of the distribution of 
our collections of the various speciesaccompanying this report, where 
the data are presented in a way to show, not the number of collec- 
tions, it is true, in which each species was represented, but the 
number and distribution of localities from which the species has 
been obtained. From such a study of these maps it appears that 
the northern half or two thirds of this state is more favorable toa 
considerable number of species than the southern part, since these 
species have been taken there in a much larger number of localities; 
and also that a small group of species of wide general distribution 
has been found by us with surprising frequency in the Wabash drain- 
age in this state as compared with that of adjacent districts. 
The preference of certain species for the northern part of Illinois 
over the southern is clearly illustrated by the distribution maps of 
the following fifteen species: Noturus flavus, Carpiodes thompson, 
Notropis cayuga, N. hudsonius, N. rubrifrons, Hybopsis dissimults, 
H. kentuckiensis, Fundulus diaphanus, Percopsis guttatus, Eupomotts 
