1905. ] ORTMANN — AFFINITIES OF CAMBARUS. 108 
this species speaks for its position here. The geographical distribu- 
tion, however, is entirely opposed to it, and I very strongly suspect 
that it belongs somewhere else. 
GEOGRAPHICAL DISTRIBUTION OF THE SUBGENUS CAMBARUS. 
Taken as a whole, the subgenus Camdarus occupies a rather con- 
tinuous area, with a possible interruption in northern Mexico: this 
gap, however, may be due only to the incompleteness of our 
knowledge. It covers Mexico, and a large part of the southern, 
central and eastern United States, but leaves unoccupied the 
mountainous region of the East; it is lacking in the larger part of 
Tennessee, in Kentucky, West Virginia, Pennsylvania, and north- 
ward. ‘The largest number of species is found in the southeastern 
states: Mississippi, Alabama, Georgia, and this region represents 
at present the center of frequency of the subgenus. From here it 
extends, gradually declining, westward into Texas, northward up 
the Mississippi valley, becoming quite scarce north of the State of 
Missouri (only two species), and further it has populated the 
Atlantic coast plain as far north as New Jersey (only one species 
north of South Carolina). 
Regarding the single sections, the distribution shows rather 
peculiar features. The digweti-section is characterized by a marked 
discontinuity : two species are found in Mexico, one in Cuba, and 
two in New Mexico, Texas and Kansas. Since I consider this 
section the most primitive of the genus, this discontinuity is highly 
interesting, and tends to confirm this view. And further, this 
peculiar distribution probably indicates the direction of the immi- 
gration into the United States. The most primitive forms (C. 
diguetti and mexicanus) are still preserved in the original home of 
the genus, in Mexico, while two other, somewhat more advanced 
species (C. semulans and gadllinas) occupy the higher plains lying 
to the east of the Rocky Mountains in the southwestern United 
States. These parts are largely formed by Cretaceous deposits, 
and represent the first land-connection between western and eastern 
North America after the Upper-Cretaceous separation. It is very 
significant, that just these parts contain the most primitive forms 
of the United States, and thus the distribution of the digueti-section 
clearly indicates this old condition prevailing at the end of the 
