GENERAL AND INTERIOR DISTRIBUTION 



XC1X 



latter part shows at once which districts are most alike and 

 which are most unlike in respect to their fish inhabitants. Thus, 

 the Rock and Illinois basins and the Mississippi are the most 

 closely related, according to these data, with affiliation ratios 

 of 68-72 per cent, and an average of 70; and the Michigan, 

 Galena, and Big Muddy districts are the least alike, with ratios 

 of 20-28 per cent, and an average of 23. The two highest 

 single ratios of ichthyological affiliation are those of the Illinois 

 and Mississippi rivers (.72) and of the Big Muddy and Saline 

 (.70). 



NUMBER OF SPECIES COMMON TO EACH PAIR OF DISTRICTS, AND RATIOS 



OF SUCH COMMON NUMBERS TO THE WHOLE NUMBER 



OF SPECIES IN EACH PAIR 



The data of this table may be generalized by bringing into 

 comparison the average of the ratios of affiliation for each district 

 with those for all the rest, as shown in the column of figures 

 farthest to the right. If the ten districts are arranged in the 

 order of the size of their average ratios, they readily fall into 



