12 PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 125 
most like P. simondsi and P. distichus. It differs from both in the 
absence of dorsal projections on segment II and from P. distichus in 
the fanlike instead of finger-like nature of the projections. The re- 
productive systems of P. alcicornus differ in only minor details, 
mostly in length and shape of the spermatheca, from those of P. hobbst 
and P. distichus and in the fully differentiated prostate and thin- 
walled spermathecal bulb from P. simondsi. 
Hosts.—Pterodrilus alcicornus was found with the following cray- 
fishes: Cambarus sciotensis Rhoades, C. bartonii bartonit (Fabricius), 
C. robustus Girard, C. bartonii subspecies, C. longulus longirostris 
Faxon, C. longulus chasmodactylus James, Cambarus species, Or- 
conectes juvenilis Hagen, Cambarus parvoculus Hobbs and Shoup, C. 
bartonit cavatus Hay, C. veteranus Faxon, C. acuminatus Faxon, C. 
longulus longulus Girard, Orconectes sanborni sanborni (Faxon). The 
most frequent hosts are C. sciotensis and C. bartonit bartoni. 
DistripuTion.—Pterodrilus alcicornus is widespread in the streams 
of the Tennessee and New Rivers in Tennessee, North Carolina, 
and Virginia. In addition, it has moved—apparently recently since it 
is not common there—into other adjacent drainages: the Savannah 
River in Transylvania County, N.C., the James River drainage in 
Craig County, Va., the Roanoke River drainage in Franklin and 
Patrick Counties, Va., the Big Sandy River drainage in Buchanan 
and Dickenson Counties, Va., and Wyoming County, W. Va. (fig. 10). 
Most of my collections of P. alcicornus are from Virginia, and the greater 
number of known localities for the species in the New River drainage 
in Virginia may be, but probably is not, a peculiarity of collecting. 
The range as given here may not be complete for it is possible that 
P. alcicornus occurs in other adjoining drainages. 
MATERIAL EXAMINED.—Several hundred specimens from 122 
collections were studied. The bulk of this materia! is deposited in the 
U.S. National Museum (USNM 36184-36250). 
Pterodrilus distichus Moore 
Ficurss 2, 10 
Pterodrilus distichus Moore, 1895a, pp. 453-454.—Pierantoni, 1912, p. 25.—Hall, 
1914, pp. 190, 193.—Ellis, 1919, p. 254.—Goodnight, 1940, pp. 60-61; 1943, 
p. 100. 
TYPE-SPECIMENS.—The material from western New York, upon 
which Moore based this species, has not been found. The species is 
distinctive, subsequent identifications are not disputed, and no 
neotype has been designated. 
Diacnosis.—Low, somewhat indistinct ridges on segments I-VIII, 
those of segments II-VII each with two bluntly pointed cylindrical 
