Cxiv FISHES OF ILLINOIS 



GENERAL SUMMARY. 



The principal conclusions of this chapter may be thus sum- 

 marized : 



1 . The ISO native species of Illinois fishes here recognized, are so 

 distributed within and without the state as to indicate an unequal 

 commingling of the faunas of the surrounding territories, southeast- 

 ern species preponderating over southwestern, northeastern over 

 northwestern, eastern over western, and southern over northern. 



2. The Illinois basin may be taken as typical, in its fish popula- 

 tion, of the ichthyology of the whole state — occupying, as it does, a 

 central position, including more than half the area of the state, and 

 containing a great variety of waters and situations fit for the habita- 

 tion of fishes, and more than four fifths of the species found anywhere 

 in Illinois. The more important fishes of the state not known from 

 this basin are a few distinctively northern species, most of which are 

 peculiar to the Great Lakes, and a few southern species which do not 

 range as far north, in this state, as the mouth of the Illinois. The 

 remainder are very rare in our territory, most of them coming from 

 the west and south, and they are extremely insignificant elements of 

 our fish fauna. 



3. If the ten stream systems of the state be brought into com- 

 parison one with another, it appears that the six larger areas, con- 

 taining the largest streams and presenting the greatest variety of 

 ■situations, are much more closely affiliated ichthyologically than are 

 the four smaller areas. The least closely affiliated with each other 

 and with all the rest are the Michigan district of northeastern Illinois 

 and the Big Muddy basin in the southwest. The closest relations are 

 those between the Illinois, the Rock, and the Mississippi. 



4. In the absence, in Illinois, of geographical barriers to the dis- 

 -persal of fishes, the causes influencing their distribution are climatic, 

 geologic, and ecological. As Illinois extends through 5.5° of lati- 

 tude, differences of climate between the northern and the southern 

 sections of the state are sufficient to affect, in considerable measure, 

 the distribution of its plant and animal species — differences which, 

 !in its ichthyology, express themselves in the presence in northern 

 Illinois, but not in southern, of 17 species of general northward 

 range; and in southern Illinois, but not in northern, of 14 species of 

 general southward range. These two groups of species meet and 

 mingle in the great north and south rivers of the western half of the 

 state, in an area of common occupation about fifty miles in width, 

 from the latitude of Springfield northward; while on the eastern 



