NO. 3668 PTERODRILUS—HOLT 2a 
histologically differentiated in some specimens, not in others; sper- 
matheca slightly longer than body diameter, ectal duct long, bulb 
clavate with thick muscular wall. 
Erymotoey.—I am pleased to name this species in honor of its 
discoverer, Mr. Kenneth W. Simonds. 
Description.—The dorsal ridges reach a greater height than in 
other species and more of them bear the expanded projections with 
prongs that may in turn be bifurcated or bear secondary prongs. The 
generalized description of the dorsal projections of segments III and 
VIII of P. alcicornus apply to those of segments II-IV and VIII of 
P. simondsi. The dorsal projection of segment V of P. simondsi, 
however, lacks the membranous lateral expansions of those of the 
other segments and are similar to the projections of segment VIII 
of P. distichus. Pterodrilus simondsi is composed of small worms 
about 0.9 to 1.8 mm long. 
The bursa is smaller than that of P. mezicanus, but still larger, 
or at least longer, than is usual. The ejaculatory duct is prominent 
and rather noticeably expanded along its midlength. The spermiducal 
gland is somewhat longer than the anteroposterior dimension of the 
segment in which it lies and is usually oriented diagonally in the 
segment, extending dorsally above the gut. The diameter of the 
prostate ranges from % to subequal that of the spermiducal gland 
and extends entally to the ental end of the latter. It is more nearly 
separated from the spermiducal gland than in other species of the 
genus, the separation between the two extending almost to the junc- 
tion of the spermiducal gland with the ejaculatory duct. 
The spermatheca of P. simondsi is comparable in length and general 
shape to that of such species as P. alcicornus and P. hobbsi, but it 
differs in the heavier muscular investment of the bulb that distinctly 
persists even when the bulb is distended to the maximum with 
spermatozoa. There is no ental process. 
VaRIATION.—The only detectable variations in the material I have 
studied are those involving the prostate, which is, in some specimens, 
histologically identical to the spermiducal gland; in others it is com- 
posed of large, clear cells (vacuolated cells); and in still others some 
of the cells are composed of dense cytoplasm with many granules, 
and others are filled almost entirely with a clear material. In other 
words, in this species, the distinction between differentiated and un- 
differentiated prostates breaks down. The degree of distension of the 
spermathecal bulb is also variable. There can be no doubt that these 
are individual, intrapopulational variations. 
AFFINITIES.—Pterodrilus simondsi is closest in external appear- 
ance to P. alcicornus, from which it differs most noticeably in the 
presence of an additional dorsal projection on segment II, but the 
