104 ORTMANN — AFFINITIES OF CAMBARUS. [April . 3 , 



Cretaceous and the beginning of the Tertiary time, and also gives 

 a clue as to the direction of the migration : it did not go over the 

 lowlands of Texas, which are geologically younger, but over the 

 higher plains of the interior. (See Ortmann, 1902, pp. 282-285, 

 p. 388.) 



The gracilis-section, which is a specialized type, arising from the 

 more primitive forms of the subgenus, forms in the distribution of 

 the species C. gracilis a direct continuation of this southwestern 

 range of the digueti-section : C. gracilis is found from eastern Kansas 

 through Missouri, to Illinois, Iowa, and southern Wisconsin. This 

 is in the same line of the migration marked by the distribution of 

 the species of the digueti-section, and plainly its continuation in a 

 northeastern direction. However, the two other species of the 

 gracilis-section, C. hageniamts and advena, are entirely isolated, 

 being found only far in the east, in the lowlands of Georgia and 

 South Carolina. Here again we have discontinuity, indicating old 

 age. I have no doubt, that these separated localities once were 

 connected, namely from Kansas and northern Texas over Arkansas 

 and across the Mississippi valley into Mississippi, and the northern, 

 higher parts of Alabama and Georgia, including probably Tennessee. 



Thus I think that the most primitive forms of Cambarus occu- 

 pied, in the United States, first the Cretaceous plains of the south- 

 west, necessarily reaching in very early times the Ozark Mountains, 

 following the Ozark uplift into Illinois and beyond, and, on the 

 other hand, crossing the present Mississippi valley, and reaching 

 the southern end of the Appalachian system, and finally the sea 

 coast in Georgia and South Carolina. Representatives of the 

 primitive sections of the subgenus have now disappeared in the 

 Appalachian region, and this is very likely due to the fact, that, 

 as we shall see below, just in this region some other very vigorous 

 groups developed, which apparently suppressed those earlier forms. 

 In the southwestern extremity, where these new groups are rather 

 scarce or entirely lacking, there was a chance for the old types to 

 survive, and this may account for the presence of C. simulans and 

 gallinas in this region, while C. gracilis, which is found right in 

 the chief domain of the subgenus Faxonius, survived possibly on 

 account of its different habits. For similar reasons C. hagenianus 

 and advena may have survived at the extreme eastern seashore. 



The third section of the subgenus Cambarus represents typically 



