130 ORTMANN— AFFINITIES OF CAMBARUS. [ApHlg: 
about, apparently, by extensive shifting of divides, and we know 
positively, that this has taken place in great style during and after 
glacial times. The eastern mountains (Appalachian system) have 
formed a sharper barrier, but also here certain species have been 
able to cross: in ancient times C. “mosus, in more recent times 
C. obscurus (see Ortmann, Ann. Carn. Mus., v. 3, p. 406). The 
most interesting region is at the southern extremity of the Appa- 
lachian system, as we shall presently see. 
Very important drainage changes, that have taken place in the 
southern Appalachian system, are clearly indicated by the distribution 
of crayfishes, and tend to confirm the results obtained by Simpson and 
Adams for the freshwater mollusks (see above p. 116). In the 
region of the Alabama River drainage and that of the Tennessee 
River, we had at acertain time, a large river running to the South, 
the Appalachian River, the upper course of which was deflected 
toward the Northwest, forming the present Tennessee River. The 
former unity of the drainage system is indicated by identical or 
closely allied species found now in both systems. The following 
species illustrate this: C. ertchsonianus, extraneus, jordant, lat- 
manus, and possibly others. Further investigations of the condi- 
tions present in these regions are very desirable. 
This is, I think, a rather satisfactory outline-sketch of the dis- 
tribution of the genus Caméarus over the United States. Butit is 
only a sketch, and more detailed investigations are much needed. 
We see that the migrations of the different groups are very com- 
plex, the directions of the migrations crossing at various angles, 
often being directly opposed to each other. (See map, plate III.) 
Further, we are to emphasize, that our knowledge is by no 
means complete with regard to the distributional facts. There is 
hardly a single case, where the actual boundaries of a species are 
known. We have a large number of locality-records, and by plot- 
ting them on a map, we obtained a general idea of the range of the 
different species, but rarely we know the exact limits, and nobody 
has ever tried to ascertain these, except the present writer in a 
very limited region, in western Pennsylvania (see Ann. Carnegie 
Mus., Vv. 3, 1905). But this ought to be done by all means, and 
there is no doubt, that very interesting results will be obtained. 
It may be remarked in conclusion, that I do not think that a 
number of reported localities for certain species are trustworthy. 
