60 



A comparison of the tigures in the tal)le will show ll) 

 that the nnmber of .species increases toward the south and west; 

 (2)thatthis increase is confined mainly to the aquatic forms; 

 and (3) that the increase in certain families is very great. The 

 increase in aquatic forms is shown in the following comparisons. 



Sliiti. _ LhikI .S)«v/V.s\ Ai/iiiilir S/ii'flcs. 



Maine .50 .55 



New York .......,.,....'._........'.' 82 ].58 



Michigan 78 194 



Indiana 78 ]9,S 



Illinois 91 240 



Alabama , . , 78 627 



The ratios of land to aquatic forms increase more rapidly 

 to the south than to the west, being in New York 1 to 2. in Tlli- 

 aiqis;L to,2A, and in Alabama 1 to S. In Maine the ratios are 

 nearly equal. 



■ 5;;,-|As,to the great increase in certain families toward the south 

 and we.st, Alabama has 25 times as many species of riilonida- 

 as Maine, 3 times as many as Illinois, and nearly 4i times as 



*This does not include the recently described Conirori/rlKx, which would mate- 

 rially increase the numlier of species recorded in the older lists. 

 . . t This does not include the 56 varieties enumerated in the present list. 

 . i ... . J The, recantly deseribud Amu imiii.aMii i^jHKilogiiiiij! are here-included. 

 " S'in/c Hmkley/ ■ ■ .; ' : :;^.:"r..;- . -. . '■' . . , . . 



