126 ORTMANN — AFFINITIES OF CAMBARUS. [April 13, 
subgenus Cambarus (C. blanding? acutus). The route along the 
coastal plain seems to be the least frequented, only C. dlandingz 
typicus characterizing it. But then again the Appalachian plateau 
formed a third outlet to the north; this is clearly indicated by the 
dispersal of the subgenus Barfonius. Adams says very pertinently 
(p. 129): ‘‘dispersal is both forward and backward along these 
highways,’’ and thus we see that in special cases the direction of 
the migration may become the opposite. In one case (C. clark7) 
we have a reversed current of migration from the southeastern 
United States toward the southwest, going in a direction opposite 
to the general direction of immigration of the whole genus. A 
direction downward the Mississippi valley (southward) is probable 
in the palmeri-group of Faxonius, and C. diogenes seems to repre- 
sent the identical reversed direction, descending the Ohio valley 
from the Allegheny Mountains. The same species shows indica- 
tions of a reversed migration on the Atlantic coast plain, from 
Maryland to Virginia. 
That the different centers of origin assumed above are very likely 
correct, is shown by a two-fold consideration. First, the largest 
number of species of each subgenus is generally found in or near 
these centers (Adams, /. ¢c., 1902, p. 128: first criterium), and 
then the more primitive forms of each subgenus are found there 
(third criterium of Adams). For the subgenus Camdarus, this is 
not entirely true, Mexico possessing only two species, while Kansas 
possesses three of the more primitive forms, but this may be due to 
deficiency of our knowledge, or else it is due to interruption and 
breaking up of the old southwestern range of the genus; it is ap- 
parently not so flourishing any more in these parts as it used to be. 
Of the more highly advanced forms of the subgenus Camébarus 
(dlandingt-section), the largest number of species is recorded for 
Georgia (7), Florida (6), and Alabama and Mississippi (4 each). 
The most primitive forms (sficulifer-group) are found in Georgia, 
Florida and Alabama. 
The subgenus Caméarellus also makes an exception, two species 
being found in Mexico, and only one, but this a more primitive 
one in Louisiana. 
The subgenus Faxonius possesses the largest number of species 
in Arkansas (8), and in Missouri and Indiana (7 each). Illinois 
has only 4, but this may be due to defective knowledge. The more 
