I9 o 5 .] ORTMANN — AFFINITIES OF CAMBARUS. 12"t 



primitive forms of the limosus-section (aside from C. limosus itself) 

 are found in Indiana, Kentucky and Missouri, that is to say, in the 

 same general region. 



The subgenus Bartonius has the largest number of species in 

 Tennessee (6); then follow: Georgia, North Carolina, Virginia 

 and Pennsylvania (with 4 each). The more primitive forms of the 

 extraneus-section are found in Georgia, Alabama, Tennessee and 

 Kentucky. In Tennessee is also found one of the blind cave forms 

 (C. hamulatus). Thus also here is apparently a mutual relation 

 between center of origin, location of most primitive forms, and 

 center of frequency. This rule, consequently holds good in the 

 section of C. blandingi of the subgenus Cambarus, and in the sub- 

 genera Faxoniits and Bartonius, while it is not very evident in the 

 more primitive forms of .the subgenus Cambarus, and in the sub- 

 genus Cambarellus} 



A few peculiar and striking facts ought to be mentioned especi- 

 ally. 



Discontinuity of distribution proof of antiquity. — We have found 

 this rule substantiated in the following cases: (1) In the distribu- 

 tion of the more primitive forms of the subgenus Cambarus (sec- 

 tions of C. digueti and gracilis) ; (2) in the subgenus Cambarellus ; 

 (3) in the limosus-section of the subgenus Faxonius; (4) in the 

 hamulatus-section of the subgenus Bartonius. The discontinuity 

 offered by C. wiegmanni in the alleni-group of the subgenus Cam- 

 barus needs further investigation, and cannot be regarded as estab- 

 lished before the systematic position of this species has been posi- 

 tively ascertained. 



Morphologically isolated species occupy isolated stations. — This is 

 illustrated by : (1) C. cubensis in Cuba ; (2) C. shufeldti in Louisi- 

 ana ; (3) C. limosus on the Atlantic coast plain from New Jersey 

 to Virginia; (4) C. harrisoni in Missouri; (5) C. alabamensis 

 and compressus in northern Alabama: (6) C. setosus in Missouri 

 (cave-form). 



Closely allied species occupy neighboring areas. — This is most evi- 



1 Addition to our knowledge may change this considerably. I only call atten- 

 tion to the fact, that up to very shortly ago only two species of Bartonius were 

 known from the state of Pennsylvania. Investigations during the last four years 

 have revealed the presence of two more species, thus doubling the number. This 

 may happen in any other state. 



