32 PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 125 
ward-flowing White River drainage system and the northward-flowing 
Gasconade River and is a part of the latter system. There is no other 
record of a species of Pterodrilus from the Missouri River basin. 
MATERIAL EXAMINED.—Five type-specimens. 
Pterodrilus species 
Poorly preserved material taken from three localities in the 
Hiwassee River drainage in Union County, Ga., and Cherokee 
County, N.C. (PCH 915, 974, 979), by Mr. Kenneth W. Simonds 
may well represent another species of Pterodrilus. These specimens 
appear to differ from those of other species of Pterodrilus in that 
there are three or four prongs of the dorsal projection on segment 
VIII, there appear to be dorsal ridges without projections on the 
other segments, and the prostate seems to be undifferentiated with a 
a thick-walled “prostatic bulb.”? The latter two points cannot be 
confirmed in my material, which raises the question as to whether 
the differences in the number of prongs of the dorsal projection may 
not be due to intraspecific variability in P. hobbsi. If the prostate 
should be differentiated and there are no dorsal ridges other than that 
bearing the projection on segment VIII, these animals could be 
distinguished from P. hobbsi only by the number of prongs of the 
dorsal projection. Better preserved material will almost surely show 
that these specimens represent a new species, but I am unwilling to 
describe a species on the basis of such poor material. 
These specimens are from the following localities in the upper 
Hiwassee drainage: Union County, Ga., 2.6 miles east of the Fannin 
County line on U.S. Highway 76, hosts Cambarus latimanus (LeConte), 
O. bartonti bartonit (Fabricius), Nov. 5, 1958, K. W. Simonds, coll. 
(PCH 915); Union County, Ga., 0.5 mile north of Vogel State 
Park on U.S. Highway 19, hosts Cambarus longulus longirostris 
Faxon, C. carolinus Erichson, Cambarus species, Nov. 5, 1958, 
K. W. Simonds, coll. (PCH 979); Cherokee County, N.C., 1.4 miles 
off Joe Brown Road, in Grape Creek, hosts Cambarus bartonii bartonia 
(Fabricius), Cambarus species, June 6, 1959, K. W. Simonds, coll. 
(PCH 974). 
Evolutionary Considerations 
The genus Pterodrilus is a group of closely related species derived 
from a primitive stock of the genus Cambarincola that specialized 
in the direction of small size and presumably a relatively narrow 
niche on the crayfish host. It would be of considerable importance if 
we knew more precisely what this niche is. Brown (1961, p. 25) has 
shown that P. alcicornus is randomly distributed over the ventral 
surface of the hosts. The other species of the genus almost surely 
