i9°5-] 



ORTMANN — AFFINITIES OF CAMBARUS. 125 



here are inhabitants of smaller mountain streams and brooks. A 

 peculiar group separated from these, the section of C. diogenes, 

 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 (Bio- 

 logical Bulletin, 3, 1902, p. 115 ff. ) l 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 Cambarus 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 Cambarus. 



The different "outlets or highways of dispersal," as Adams 

 (/. c, p. 123) has characterized them, are rather well represented 

 in the distribution of Cambarus, 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 blandingi-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 Faxonius 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. 



