130 ORTMANN— AFFINITIES OF CAMBARUS. [April 13, 



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. limosus, in more recent times 

 C. obscurus (see Ortmann, Ann. Cam. 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 a certain 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. erichsonianus, exiraneus, Jordan/', lati- 

 vianus, 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 Cambarus over the United States. But it 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., v. 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. 



