114 ORTMANN — AFFINITIES OF CAMBARUS. [April 13, 
Virginia, Maryland, Pennsylvania and New Jersey; and in the 
south, where C. sfinosus and erichsonianus cross over from the 
Tennessee River drainage into that of the gulf and the Atlantic 
Ocean in Alabama, Georgia, South and North Carolina. These 
latter cases are continuous, the same species being found in both 
drainages, while in the former case discontinuity is implied, C. 
Zimosus being cut off and isolated from the rest of the range of the 
subgenus. 
Generally speaking, this subgenus seems to belong to the 
great rivers of the interior basin, its center lying about in the 
region where the rivers Missouri, Mississippi, and Ohio come 
together, that is to say, in the states of Mississippi, Kentucky, 
southern Illinois, and southern Indiana. From this center it 
spreads out in the directions of these rivers and tributaries, chiefly 
toward the North and Northeast. However, the area remained not 
restricted to the Mississippi drainage, but crossed the divides into 
other systems in the following cases: From the Tennessee River 
two species (spémosus, ertchsonianus) have crossed over into the 
Gulf and Atlantic drainages, and from the upper Ohio drainage 
another species (/¢mosus) has crossed over into the Chesapeake and 
Delaware Bay drainage. Another species (mésszsstppiensis) is found 
in the Gulf drainage (outside of that of the Mississippi River) in 
the state of Mississippi. In the North the area largely extends 
into the drainages of the great lakes, and even into that of Hudson 
Bay (through the Red River of the North and Winnipeg Lake). 
Studying the distribution of the single sections, the following is 
to be remarked. The most primitive section (that of C. démosus) 
is marked by discontinuity: C. “mosus being found on the Atlantic 
coast plain, C. pellucidus, tndianensts, sloanet in Kentucky and 
southern Indiana, C. harrison in Missouri. ‘This discontinuity, 
chiefly the isolation of C. Zmosus, is accompanied by morpholog- 
ical isolation, the latter species possessing in its spinosity a charac- 
ter, that only recurs in the allied, but otherwise peculiar species, 
C. pellucidus. This latter species, as well as C. sloanet, indt- 
anensis and harrisoni, undoubtedly are the last remnants of 
the primitive stock of the subgenus in its original home, 7. e., 
in the central basin formed by the three great rivers. ‘Thus the 
geographical distribution of the /:mosws-section confirms the char- 
acter of antiquity: most of the species remain in the original 
