THE MUTUAL AFFINITIES OF THE SPECIES OF THE 
GENUS CAMBARUS, AND THEIR DISPERSAL 
OVER THE UNITED STATES. 
(PLATE IIT.) 
BY DR. A. E. ORTMANN. 
(Read April 13, 1905.) 
In a previous study of the geographical distribution of the cray- 
fishes of the United States (see Proc. Amer. Phil. Soc., xli, 1902, 
pp- 277-285), the present writer took it for granted that the 
division of the genus Camdarius, into five groups, as introduced by 
Faxon (Mem. Mus. Harvard, 10, 1885), and the arrangement of 
the species within each group adopted by him, would correspond, 
as far as one might expect, to the natural affinities. 
This, however, is true only to a certain degree. There is no: 
doubt that Faxon correctly recognized the chief systematic groups 
within the genus, and that he also had, in most cases, appropriate 
views as to the relationship of smaller groups of species. But accept- 
ing his system as a whole, and trying to correlate it with the peculi- 
arities shown by the geographical distribution, a number of cases 
are revealed, where such a correlation is not very apparent, and 
attempts to give a reasonable theoretical explanation prove to be 
more or less unsatisfactory. I shall mention here a few instances. 
1. The fifth group of the genus follows, in Faxon’s system, after 
Reprinted from Proceedings American Philosophical Society, Vol. xliv., 1905. 
