GENERAL AND INTEEIOE DISTRIBUTION 



XCIX 



latter part shows at once which districts are most ahke and 

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

 the Rock and lUinois basins and the Mississippi are the most 

 closely related, according to these data, with affihation ratios 

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

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

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

 single ratios of ichthyological affihation are those of the Illinois 

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

 (.70). 



NuMBEK OF Species Common to each Pair of Districts, and Ratios 

 OF SUCH Common Numbers to the whole Number 

 OF Species in each Pair 



Districts 



03 



1 . Galena 



2. Rock River. . 



3. Illinois River. 



4. Michigan . . . . 



5. Mississippi. . . 

 6- Kaskaskia. . . 



7. Wabash 



8. Big Muddy . . 



9. Saline River. 

 10. Cairo 



Total species . 



Number of collections . 



42 

 42 

 17 

 41 

 32 

 38 

 19 

 26 

 39 



44 



13 



45 



89 

 39 



77 

 60 

 72 

 38 

 47 

 74 



92 



73 



32 

 68 



48 

 94 

 68 

 89 

 42 

 53 

 93 



128 



1115 



20 

 35 

 35 



39 

 25 

 34 



18 

 21 

 38 



57 



20 



41 

 69 

 72 

 34 



58 

 73 

 35 

 45 



79 



97 



57 



40 

 59 

 53 

 25 

 54 



66 



38 

 48 

 59 



69 



41 



38 

 63 

 66 

 29 

 61 

 66 



40 

 52 

 76 



95 



103 



28 

 40 

 33 

 22 

 34 

 52 

 41 



40 

 40 



42 



10 



36 

 47 

 41 

 23 

 42 

 63 

 53 

 70 



51 



55 



18 



37 

 62 

 68 

 32 

 66 

 53 

 63 

 39 

 49 



101 



95 



.352 



.542 



.52 



.283 



.525 



.517 



.534 



.398 



.471 



.521 



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 



