126 ORTMANN — AFFINITIES OF CAMBARUS. [April i 3j 



subgenus Cambarus (C blandingi acutus). The route along the 

 coastal plain seems to be the least frequented, only C. blandingi 

 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 Bartonius. 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 clarki} 

 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 Cambarus, 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 Cambarus 

 {blandingi-section) , the largest number of species is recorded for 

 Georgia (7), Florida (6), and Alabama and Mississippi (4 each). 

 The most primitive forms {spiculifer-group) are found in Georgia, 

 Florida and Alabama. 



The subgenus Cambarettus 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 



