GENERAL AND INTERIOR DISTRIBUTION Ixxxiii 



If we look to the further distribution of the northern and 

 southern elements of our fish population, distinguishing north- 

 eastern from northwestern species, and southeastern from 

 southwestern, we find that the southeastern species largely 

 outnumber the southwestern in Illinois, and that the north- 

 eastern outnumber the northwestern. Thus there are 47 species 

 of the west Gulf and Rio Grande region in this state, and 58 

 species of the east Gulf and Florida districts. 



Further, there are more species known as common to Illinois 

 and the far northeast than there are to Illinois and the south- 

 western district of the west Gulf and the Rio Grande. Not- 

 withstanding the much greater distance from us of the Quebec 

 and New England district, there are 53 of the fishes of that 

 region known in Illinois to 47 of those of the west Gulf district. 

 The northeastern fishes have, however, been much more carefully 

 collected than the southwestern, and an equal knowledge of 

 both districts might change these relative numbers. 



THE INTERIOR DISTRIBUTION 



The interior distribution of the fishes of the state may best 

 be exhibited by treating each considerable stream-system as a 

 unit, and comparing the fishes of each such system with all the 

 others. The state may be convenient" y divided into ten such 

 hydrographic districts, as follows: 



1. The Galena district, including the streams of the north- 

 western unglaciated area, most of which empty into the Mis- 

 sissippi through Galena, Apple, and Plum rivers. 2. The Rock 

 River district, extending southward and westward from the 

 northern boundary of the state to the Mississippi at the mouth 

 of the Rock. 3. The Illinois district, including the entire 

 drainage of the Illinois River. 4. The Michigan district, a 

 narrow strip along the borders of Lake Michigan the Lake 

 Michigan drainage most of which centers in the Chicago and 

 the Calumet rivers. 5. The Mississippi River, and an irregular 

 strip adjacent not included in any of the more definite river 

 systems and mainly drained by small streams of the bluffs and 

 neighboring highlands. This district is divided by the lower end 

 of the Illinois basin. 6. The Kaskaskia basin. 7. The Illinois 

 drainage of the Wabash, including that stream itself so far as 

 it helps to form the boundary line between Illinois and Indiana. 

 8. The basin of the Big Muddy River, in the southwestern part 

 of the state. 9. The Saline River basin, in the southeastern 



