60 



State 



Maine. . . . 

 New York 

 Michigan. 

 Indiana. . . 

 Illinois. . . 

 Alabama . 



Catalogue 



Morse, 1864 

 Letson, 1905 

 Walker, 1906 

 Daniels, 1904 

 Baker, 1906 

 Lewis, 1876 



10 

 59 



o 



105 

 240 



52 274 

 83 ,276 

 89 332f 

 256 705 



A comparison of the figures in the table will show ( 1 ) 

 that the number 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. 



State. Land Species. Aquatic Species. 



Maine 50 55 



New York 82 158 



Michigan 78 194 



Indiana 78 198 



Illinois 91 240 



A labama 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 Illi- 

 nois 1 to 2i, and in Alabama 1 to 8. In Maine the ratios are 

 nearly equal. 



As to the great increase in certain families toward the south 

 and west, Alabama has 25 times as many species of Unionidw 

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



* This does not include the recently described Corneocyclas, which would mate- 

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



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

 t The recently described Amnicola and Somatogyrm are here included. 

 § Vide Hinkley. 



