GENERAL AND INTERIOR DISTRIBUTION 



lxxvii 



Arranged according to the number of Illinois species in each, 

 these districts succeed each other in the following order. 



Next to the two Mississippi Valley districts and the Great Lake 

 basin, which average 124 Illinois species, our fishes are most largely 

 represented in the east Gulf and the Quebec and New England dis- 

 tricts, averaging 54 Illinois species — the first closely related to the 

 lower Mississippi, and the second a continuation eastward of the 

 Great Lake basin. Then follow the north and south Atlantic and 

 the west Gulf districts, with an average of 43 species ; the far North, 

 the Florida peninsula, and the Hudson River districts, with 37 to 19 

 species ; and, finally, the far Northwest, with but 4 Illinois species. 



The northern and the southern affiliations of the assemblage of 

 fishes represented in our Illinois collections may be contrasted by 

 comparing the list of Illinois species occurring; in either or both of the 

 more northerly divisions — that is, the far North and the Quebec and 

 New England districts — on the one hand, with a list of those 

 found in either or all of the three most southerly districts — that is, 

 the Florida peninsula, the east Gulf, and the west Gulf and Rio 

 Grande — on the other hand. In this northern list of Illinois fishes 

 there are 64 species, and in the southern list there are 77 ; but 25 of 

 these species are more or less common to both north and south, 

 leaving 39 Illinois fishes distinctively northern in their distribution 

 and 52 distinctively southern. Northern and southern species thus 

 mingle in our territory in unequal proportions, the southern element 

 largely preponderating. 



If we look to the further distribution of the northern and south- 

 ern elements of our fish population, distinguishing northeastern from 



