lxxviii FISHES OF ILLINOIS 



northwestern species, and southeastern from southwestern, we find 

 that the southeastern species largely outnumber the southwestern 

 in Illinois, and that the northeastern 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 southwestern dis- 

 trict of the west Gulf and the Rio Grande. Notwithstanding 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 southwest- 

 ern, 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 ex- 

 hibited 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 conveniently divided into ten such hydrographic 

 districts, as follows: 



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

 ern unglaciated area, most of which empty into the Mississippi 

 through Galena, Apple, and Plum rivers. 2. The Rock River dis- 

 trict, extending southward and westward from the northern bound- 

 ary 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 slate. 



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



10. The Cairo district, the driftless area of extreme southern Illi- 

 nois, drained by the Cache River and smaller tributaries of the Ohio. 

 The Ohio itself is included in this last district. 



