30 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 125 
ceeding % body diameter; spermiducal gland relatively long, its 
length equalling or exceeding anteroposterior dimension of seqment 
VI, narrowing at ectal end; prostate short, in diameter about % that of 
spermiducal gland, incompletely divided from latter, histologically 
undifferentiated, with ental bulb; spermatheca spatulate, its length 
subequal to body diameter, ectal duct long, ental process absent. 
Erymo.tocy.—The adjectival form of Missouri. 
Description.—The length, based on five animals, averages 1.6 
mm (range 1.5-1.8 mm). The dorsal ridges of segments I-VII are 
poorly developed and in some extended specimens might be over- 
looked. That of segment VIII, however, is well developed. The anterior 
nephridiopore is clearly visible on the dorsum of segment III. The 
teeth of the jaws appear to be longer and more sharply pointed 
than is usual. 
The male reproductive system in the totality of its primitive aspects, 
is unlike that of any other species of Pterodrilus. The spermiducal 
gland is relatively long and slender, its length more than three times 
its diameter. The prostate arises as a diverticulum of the gland rather 
far from the latter’s junction with the ejaculatory duct. There is an 
abrupt narrowing at the point of origin of the prostate, from which 
point the spermiducal gland continues to decrease in diameter until 
it passes into the ejaculatory duct. The prostate has a diameter of 
about half that of the spermiducal gland and its ental end is located 
about % of the length of the latter from its ental end: in ail, the 
prostate is about 4 the length of the spermiducal gland and lies along 
the median third of the gland. The prostate is not histologically 
differentiated, but there is an ental “bulb”, a cavity of rather small 
extent. The ejaculatory duct is prominent and noticeably expanded 
along its midlength. The bursa is large, exceeding half the body 
diameter in length. The penis is prominent and the penial sheath 
region of the bursa is larger than usual. 
The spermatheca has a long ectal duct that expands entally before 
it merges into the elongated, spatulate bulbular portion. There is no 
ental process, but in at least some specimens the entire wall of the 
bulb appears to be composed of large, granular cells with the result 
that the wall is much thicker than usual. 
VARIATION.—The prostate appears to be of variable length, but 
this is probably because of the difficulty of estimating the compara- 
tive lengths of the prostate and spermiducal gland in specimens in 
which these organs are viewed from different directions. The ental 
part of the spermathecal bulb does not always appear to be filled with 
a glandular epithelium, but this is most likely a reflection of differences 
in degree of distension of the bulb with spermatozoa. 
