411 
above mentioned, while those most individual and peculiar—least 
closely affiliated among themselves and each with all the others— 
are the Michigan, the Galena, the Saline, and the Big Muddy dis- 
tricts, excepting only the relation of the two last mentioned, which, 
as already said, is unusually close. 
THE FISHES OF NORTHERN, CENTRAL, AND SOUTHERN ILLINOIS 
If mere difference in latitude, involving a climatic difference 
within a range of five and a half degrees, limits the distribution 
of any of our fishes, the fact should appear upon a comparison of 
the species list of the northern, central, and southern sections of the 
state, although due caution must, of course, be exercised that 
other and more local causes are not confused with climatic ones. 
The division of the state here adopted, is shown on Map I. of the 
accompanying set. 
The fishes of these three divisions number 119 species for 
northern, 123 for central, and 119 for southern Illinois, respect- 
ively. Fourteen species have been found by us only in the northern 
division, 9 only in the southern, and 5 only in the central, and 89 spe- 
cies are found in all three sections. Twelve species occur in both 
northern and central Illinois, but not in southern, 17 in both south- 
ern and central Illinois, but not in northern, and 4 in both the north- 
ern and southern divisions of the state, but not in the central. 
