AUG 14 1905 



PROCEEDINGS 



OF THE 



AMERICAN PHILOSOPHICAL SOCIETY 



HELD AT PHILADELPHIA 

 FOR PROMOTING USEFUL KNOWLEDGE 



Vol. XLIV. April-May, 1905. No. 180. 



THE MUTUAL AFFINITIES OF THE SPECIES OF THE 



GENUS CAMBARUS, AND THEIR DISPERSAL 



OVER THE UNITED STATES. 



(Plate III.) 



BY DR. A. E. ORTMANN. 



{Read April ij, fcpoj.) 



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 Cambarus, 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 



PROC AMER. PHILOS. SOC. XLIV. l8o. G. PRINTED JULY 28, I905. 



