108 ORTMANN— AFFINITIES OF CAMBARUS. 105 
the distribution of the whole subgenus, with the exception that it 
is not found in the extreme west and in Mexico. (I disregard C. 
wregmant, since I do not believe that its position with this section 
is correct. ) 
Here again we have peculiar facts of distribution. The more 
primitive forms (sfzculifer-group) are restricted to the states Georgia, 
Alabama, and northwestern Florida. Thus they come into clese 
contact with the hypothetical old range of the more ancient types 
of the subgenus in the southern Appalachians, and I believe that 
they originated from an original stock of the dgwett-section, that 
immigrated into the lowlands south of the mountains, which became 
dry land by degrees during Tertiary times. Here in these low- 
lands, chiefly in Alabama and Georgia, is the center of origin of 
the d/andingt-section, which represents a secondary center for the 
subgenus. ‘The more primitive forms (sfecultfer-group) still stick 
to this center, while the more advanced forms have spread out from 
here as follows. 
The dlandingt-group invaded (C. fallax) northern Florida, and 
spread out northeastwardly along the Atlantic coast plain (C. 
blandingt-typicus), and also it migrated westward aud northward, 
up the Mississippi valley (C. ayz and dlandingt acutus). The 
clarki-group extended chiefly westward from northern Florida far 
into Texas (C. clarkz), and slightly eastward into South Carolina 
(C. troglodytes, in South Carolina and Georgia). Finally, the 
alient-group occupied Florida: C. ad/enz, the most aberrant form, 
goes farthest south here (Caloosahatchee River, Lee Co.). (The 
other species, C. evermanni and barbatus, are known from scattered 
localities in Georgia, western Florida, and Mississippi, and their 
distribution needs further investigation ; C. wzegmanni from Mexico 
possibly does not belong here. ) 
Thus the distribution of the subgenus Caméarus illustrates the 
early history of the immigration of the genus into the United 
States, and it also illustrates the later population of the southern 
parts of the United States during Tertiary times by forms of the 
blandingt-section. The latter prevail here, and hardly ever had 
any competitors, and thus the southern states are at the present 
time the center of the frequency of the whole subgenus. ‘They are, 
however, the center of origin only for the d/andingi-section, while 
the center of origin of the subgenus is to be sought in Mexico. 
