NO. 3668 PTERODRILUS—HOLT 23 
process. The organ is narrower and the ectal duct is longer than is 
usual in the genus. 
VariatTion.—Observable variability is confined to the spermatheca 
and seems to depend upon the degree of distension of the bulb with 
spermatozoa. When incompletely distended, there appears to be an 
ental process and the ectal duct is long; when fully distended, the 
ental process disappears and the ectal duct is shorter; that is, the ental 
part of the duct becomes part of the bulb. A cursory inspection might 
lead to the conclusion that there are structural differences of the 
spermatheca among individuals of the same population. 
AFFINITIES.—Pterodrilus cedrus is superficially most like P. hobbsi 
but differs in having dorsal ridges on segments I-VIII, the shorter 
and finger-like dorsal projections of segment VIII instead of the 
fanlike projection with five prongs of the latter, the longer ectal duct 
of the spermatheca, and the narrower spermathecal bulb. The dorsal 
ridges of P. cedrus allies it, however, with the lineage culminating 
in P. alcicornus. Among these species (P. simondsi, P. distichus, and 
P. alcicornus), P. cedrus differs from P. distichus most markedly in 
the absence of two finger-like projections on the dorsal ridges of 
segments II-VII and the presence of four, instead of five projections 
on segment VIII. 
Hosts.—Pterodrilus cedrus has been taken with the following cray- 
fishes: Orconectes placidus (Hagen), O. rusticus subspecies, O. guvenilis 
(Hagen) and Cambarus tenebrosus Hay. 
Distripution.—Pterodrilus cedrus is known only from a small series 
of collections taken in the eastern Highland Rim and Nashville Basin 
regions of Tennessee (fig. 10). Both its anatomical features and re- 
stricted distribution impute to it the status of a phylogenetic relict. 
MATERIAL EXAMINED.—Types and 37 additional specimens. With 
the exception of three paratypes (PCH 1396) from the type-locality, 
this material is deposited in the United States National Museum 
(36465-36468). 
Pterodrilus simondsi, new species 
Fiaurss 6, 10 
TypE-SPECIMENS.—Holotype, USNM 36477, five paratypes, USNM 
36478, from Cambarus bartonii bartonii (Fabricius) taken in a tribu- 
tary to the Ocoee River, 12.2 miles south of Morganton, on State 
Highway 60, Fannin County, Ga., by Kenneth W. Simonds, Nov. 6, 
1958; four paratypes, PCH 989, from Cambarus bartonii bartonii 
taken in a tributary to the Ocoee River, 8.8 miles south of Morganton, 
Fannin County, Ga., on State Highway 60, by Kenneth W. Simonds, 
Nov. 6, 1958. 
