, 9 o 5 .j ORTM ANN— 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. 

 wiegmani, 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 (spiculifer-group) are restricted to the states Georgia, 

 Alabama, and northwestern Florida. Thus they come into close 

 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 digueti-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 blandingi-section, which represents a secondary center for the 

 subgenus. The more primitive forms {spiculifer-group) still stick 

 to this center, while the more advanced forms have spread out from 

 here as follows. 



The blandingi-group invaded ( C. fallax) northern Florida, and 

 spread out northeastwardly along the Atlantic coast plain ( C. 

 blandingi-typicus), and also it migrated westward aud northward, 

 up the Mississippi valley (C. hayi and blandingi acutus). The 

 clarki-group extended chiefly westward from northern Florida far 

 into Texas (C. clarki), and slightly eastward into South Carolina 

 (C. troglodytes, in South Carolina and Georgia). Finally, the 

 alleni-group occupied Florida : C. alleni, 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. wiegmanni from Mexico 

 possibly does not belong here. ) 



Thus the distribution of the subgenus Cambarus 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 

 blandingi-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 blandingi-section, while 

 the center of origin of the subgenus is to be sought in Mexico. 



