24 



ORTMAXX 



Ortmann, P. Amer. Philos. Soc, 44, 1905, p. 103 f.). Moreover, 

 it belongs to a rather advanced and modern group of this sub- 

 genus (alleni-gvoup), which is characteristic for the late Terti- 

 ary and Post-tertiary plains of the South Atlantic and Gulf bor- 

 der in the United States. Thus it is very probable, that this 

 species immigrated into Mexico from the United States, repre- 

 senting a direction of dispersal opposite to that generally ob- 

 served in the genus, for which, however, at least one other in- 

 stance is known (C clarki, 1. c, p. 126). The known habitat 

 of C. wicgmanni appears rather isolated, and it is much to be de- 

 sired that northern Mexico and southern Texas should be in- 

 vestigated with a view to settle this question. 



The most primitive species of the subgenus Cambarellus (C 

 shufeldti) is found in Louisiana. C. chapalanus appears slightly 

 more primitive compared with C. montezumce and its varieties, 

 and is found in western Mexico. Of the montezumce forms, 

 areolatus is the most primitive and the most northern, nearest to 

 the United States, while occidenlalis is the most advanced (shape 

 of rostrum), and is western in Mexico. Thus the evidence 

 is partly contradictory. Leaving out chapalanus, the general 

 trend of the evidence is to show that the subgenus originated in 

 the southern United States and immigrated into Mexico, first 

 into the central plateau, then into the Pacific slope. 



This would, consequently, offer a third case of reversed 

 migration in this region, and my map (1905, pi. 3) should be 

 changed accordingly (the brown color). This would also not 

 conflict with the morphological characters of Cambarellus, the 

 shape of the sexual organs inclining more toward the subgenus 

 Faxonius of the United States, than toward the Mexican sub- 

 genera. But I must confess, that the evidence for this assump- 

 tion appears at present too scanty, so that we can hardly call it 

 more than a mere theory. It is chiefly with a view to instigate 

 further research on these questions that I have ventured to ex- 

 press at all an opinion on this topic. 



