104 ORTMANN — AFFINITIES OF CAMBARUS. [April 13, 
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 gractlis-sectton, which is a specialized type, arising from the 
more primitive forms of the subgenus, forms in the distribution of 
the species C. graci/s a direct continuation of this southwestern 
range of the dguett-section: C. gracilis is found from eastern Kansas 
through Missouri, to Illinois, lowa, and southern Wisconsin. ‘This 
is in the same line of the migration marked by the distribution of 
the species of the dgueti-section, and plainly its continuation in a 
northeastern direction. However, the two other species of the 
gracilis-section, C. hagenianus 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 Caméarus 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. s¢mudans and 
gallinas in this region, while C. gvace/s, which is found right in 
the chief domain of the subgenus Faxonius, survived possibly on 
account of its different habits. For similar reasons C. hagentanus 
and advena may have survived at the extreme eastern seashore. 
The ¢hird section of the subgenus Cambarus represents typically 
