1905. ] ORTMANN—AFFINITIES OF CAMBARUS. 125 
here are inhabitants of smaller mountain streams and brooks. A 
peculiar group separated from these, the section of C. dtogenes, 
which acquired burrowing habits, and is originally also a mountain 
loving group, but began to descend into the lowlands. Finding no 
competition here, on account of its peculiar mode of life, it had 
a chance to spread over a large area. 
The centers for the more highly advanced forms of the subgenus 
Cambarus, and for the subgenera Faxonius and Bartonius, appa- 
rently form physiographically differentiated parts of one larger cen- 
ter, situated in the southeast of the United States, clearly corre- 
sponding to the southeastern center of dispersal of Adams (Azo- 
logical Bulletin, 3, 1902, p. 115 ff.)' Adams discusses this center 
chiefly with reference to the glacial and postglacial time, but it ex- 
isted, no doubt, also during the Tertiary, and the development of 
the different branches of Caméarus falls, in my opinion, chiefly 
into the preglacial time. As Adams maintains, this center is quite 
distinct from the southwestern center on the arid plateau of Mexico 
and the adjoining parts of the United States. This latter does not 
seem to be very important for, the later development of the genus, 
arid regions being generally unfavorable for crayfishes. In older 
Tertiary times, however, also the southwestern center played a part, 
in fact it is the original center of the whole genus Caméarus. 
The different ‘‘outlets or highways of dispersal,’’ as Adams 
(2. ¢., p. 123) has characterized them, are rather well represented 
in the distribution of Camdbarus, and here again I believe, that they 
were efficient in preglacial times as well as in postglacial times. 
The Mississippi valley route is represented in the dispersal of the 
subgenus Faxonius, and also by that of the d/andingi-group of the 
1 Adams’ southeastern center does not include the central basin, and he thinks 
that the Mississippi river (although it undoubtedly possessed a fauna of its own) 
was largely populated by way of the Tennessee River, which, after having cap- 
tured the upper course of the old Appalachian River, opened an outlet to its fauna 
toward the Mississippi. This is no doubt quite correct with reference to the 
freshwater shells, and, as has been pointed out already by Adams, finds some sup- 
port in the distribution of certain crayfishes (/.c., p. 849). But as we have seen 
in the above pages, the center of Aaxonzus in the central Mississippi valley is 
very marked, and apparently distinct from the other two centers. It is, however, 
easy to unite all three of them, and regard them as parts of one larger center of 
older (old Tertiary ?) age, including parts that are differentiated physiographi- 
cally, as indicated above. 
