1905 | ORTMANN— AFFINITIES OF CAMBARUS. ig 
zmmunis inhabits the (often temporary) shallow, stagnant ponds 
and roadside ditches of the western prairies, and is a burrower, 
while C. wiri’s prefers rocky places in running streams. (See 
Harris, Americ. Natural., 35, 1901, f. 187 ff., and Kansas Univ. 
Quart., 9, 1900, pp. 268 and 270). 
Of the other two groups of the third section, that of C. alaéda- 
mensts contains only two species, which are very local, being found 
only in northern Alabama. Both are rather primitive, and appar- 
ently are the last remnants in the Tennessee drainage of a once 
more widely distributed stock. The dfficzlis-group seems to rep- 
resent a southern extension of the subgenus Faxonius: the species 
are found in western Tennessee, Missouri, Arkansas, Indian Ter- 
ritory, northeastern Texas and Mississippi, all in the drainage of 
the lower Mississippi (below Cairo), only C. mass¢ssippiensis be- 
longs to the Tombigbee river drainage. 
C. lancifer would agree in its range (Mississippi and Arkansas) 
with this latter group. 
The species of this subgenus, generally, are river-species, and 
prefer the large rivers of the great central basin. Some species 
have become lake-forms (C. propinguus, for instance), and others 
ascend the rivers into the smaller streams (chiefly so in the Tennes- 
see and upper Ohio drainages), but they rarely inhabit true moun- 
tain streams. 
Further investigation of the distribution of this subgenus should 
pay particular attention to the ways by which several species have 
crossed the divides of the Hudson Bay, Great Lakes, and Atlantic 
coast plain drainage systems. It is very likely that wandering of 
the divides has played here an important part. 
Subgenus: Bartonius (Type: C. dartont). 
This subgenus, which corresponds to the third group of Faxon, 
is a very natural one, and, in my opinion, contains the most mod- 
ern and most highly specialized forms in those that have acquired 
burrowing habits (dogenes-section). There are, however, other 
species, which are rather primitive, as indicated by certain char- 
acters. 
The length of the areola, in this subgenus, is rather variable: in 
the extraneus-section it is shortest, about half as long as the anterior 
section of the carapace, and it is even shorter than that in C. acu- 
minatus. In all other species it is considerably longer. The an- 
