GENERAL AND INTERIOR DISTRIBUTION X 



Differences between the Smaller Districts and the Illinois Basin 



Districts 



Ratios 

 of differ- 

 ence 



Illinois 



Michigan. . . 



Cairo 



Wabash 



Galena 



Saline 



Mississippi. 

 Rock River 

 Kaskaskia. , 

 Big Muddy. 



.16 



.08 



.061 



.046 



.038 



.032 



.032 



.014 



.000 



Five species were found in the Illinois system and not in any 

 other — three of them minnows of the genus Notropis (anogenus, 

 phenacobius, and pilsbryi), one of them a sunfish (Lepomis euryorus), 

 and one of them a darter (Hadropterus evermanni) . All of these spe- 

 cies have been very rare in our collections, occurring only from one to 

 three times each, and it was probable that they would be found, if at 

 all, where the largest number of collections was made. 



The Galena district is distinguished from the Illinois basin espe- 

 cially by the presence of a minnow and a darter (Hybognathus nubila 

 and Crystidlaria asprella), the latter southern in its main range, and 

 the former western, not occurring, indeed, farther east than western 

 Illinois. These two fishes appear in the Rock River basin also, to- 

 gether wit h another distinctively western darter (Hadropterus evides) . 

 In the Michigan district, besides the five lake fishes already referred 

 to — the whitefish, the lake herring, the lake trout, and two cottoids 

 or miller's thumbs, Cottus ricei and Uranidea kumlienii — are the 

 brook lamprey, the long-nosed sucker, the Great Lake catfish, and 

 one of the sticklebacks (Pygosteus pungitius). All but the lamprey 

 (which is rare in Illinois) arc northern species no1 taken by us in the 

 Illinois valley. The Mississippi distrid is distinguished from the 



