422 
Spot-tailed minnow Red-bellied dace 
Notropis rubrifrons Notropts gilberti 
Spotted shiner Long-nosed gar 
Pike Dogfish 
Menona top-minnow Mongrel buffalo 
Trout-perch Black-head minnow 
Pumpkinseed Hybognathus nubila 
Sauger Redfin 
Yellow perch Rock bass 
Banded darter 
BOUNDARY BETWEEN NORTHERN AND SOUTHERN SPECIES 
Recurring next to the distinction made on another page be- 
tween northern and southern fishes whose areas extend into Illinois 
but not beyond, and comparing the distribution of these groups 
within the state, as given on Map CIII., we see that northern and 
southern species meet and mingle in the western part of the state 
from Meredosia to Pekin on the Illinois, and from Quincy to Dallas 
City on the Mississippi, but that in eastern Illinois they are separated 
by a wide interval extending from Cook county to the mouth of the 
Embarras, in which interval we have never taken any representative 
of either group. 
The distinctively southern species, although most abundant 
south of the line 28° 30’’, nevertheless go up the Wabash to the Em- 
barras, up the Kaskaskia to Shelby county, up the Mississippi to 
Henderson county, and up the Illinois to Pekin, also following the 
branches of the Sangamon to Logan county. The northern species, 
on the other hand, although most abundant above 40° 20’, come 
down the Illinois to Meredosia, and down the Mississippi to Quincy. 
The boundary between the northern and southern species thus 
appears as a broad belt some fifty miles in width, extending two 
thirds of the way across the state just above its center, but widening 
to a distance of one hundred and seventy-five miles on the eastern 
boundary. 
GENERAL FEATURES OF ECOLOGICAL DISTRIBUTION 
In addition to the general distribution of Illinois fishes over the 
North American continent, their general or partial distribution 
within the state, and the unevenness of their distribution over the 
different divisions of the state, hydrographic, climatic, and geolog- 
ical, there are also recognizable differences and inequalities of dis- 
tribution corresponding to the size of the water bodies in which the 
