GENERAL AND INTERIOR DISTRIBUTION < V 



Spot-tailed minnow Red-bellied dace 



Notropis rubrifrons Notropis gilberti 



Spotted shiner Long-nosed gar 



Pike Dogfish 



Menona top-minnow Mongrel buffalo 



Trout-perch Black-head minnow 



Pumpkinseed Hybognathns nubila 



Sauger Redrin 



Yellow perch Rock bass 

 Banded darter 



BOUNDARY BETWEEN NORTHERN AND SOUTHERN SPECIES 



Recurring next to the distinction made on another page (xciv) 1 >e- 

 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 

 species are found, to the nature of the bottom and the consequent 

 clearness and purity of the waters, and to the existence and rate of 

 current or flow in the waters inhabited by them. In this class of 



