NO. 3668 PTERODRILUS—HOLT 11 
The spermatheca, however, does vary. The length and diameter of 
both the ectal duct and bulb may differ among the species of Ptero- 
drilus; the bulb may be thin walled as it is in P. alcicornus and many 
other branchiobdellids (Holt, 1949, p. 560, fig. 18), and an ental process 
may be present. The terms used for these parts of the spermatheca 
are defined in Holt (1960a, p. 64). 
The organ systems of P. alcicornus and its congeners, with the 
exception of those discussed above, are not noticeably different from 
those of other branchiobdellids. 
VariaTions.—The foregoing description and discussion of P. 
alcicornus is based primarily upon specimens from the New River 
drainage in Virginia. Differences in methods of killing and preserva- 
tion, that is, the use of dilute solutions of alcohol, produce some distor- 
tion of the specimens. There is little of note in the way of intrapopula- 
tional variation, except for differences in the number of prongs of the 
dorsal projections. A count of these for 10 specimens from Gules 
County, Va., gave the following results: 
segment IIL segment IV segment V segment VIII 
5 4 5 7 
a 6 6 a 
5 5 5 a 
7 5 5 a 
6 6 5 6 
8 a at 7 
7 5 5 6 
if s 5 6 
5 3 4 5 
5 5 3 i) 
Similar results were obtained from specimens from other parts of the 
range of the species. 
The “wings” of the dorsal projections of at least some specimens 
from the Watauga River system in North Carolina and Tennessee and 
the headwaters of the New River in North Carolina are of greater 
extent than those of specimens from other parts of the species’ range. 
The latter material, however, is poorly preserved, which may account 
for the apparent differences. 
The jaws of some specimens from Alleghany County, N.C., are 
much darker than usual. That this may reflect something other than 
geographical variability is indicated by the presence of dark jaws in 
at least one collection from Giles County, Va., where most specimens 
have lightly colored jaws. 
The extent of variability in the species is not enough, or at least 
it is not well enough defined geographically, to allow one to consider 
the erection of subspecies. 
ArFinities.—Pterodrilus alcicornus, in external appearance, is 
