THOMPSON: SNAIL GENUS MARSTONIA


wide. The spire is relatively long, being about 1.56-1.67 times the length of the aperture. The
shell is nearly transparent and thin, light grayish-brown in color, and has a silky luster when free
of encrusting dirt. The umbilicus is narrowly perforate and is partially obscured by the reflected
columellar peristome. There are about 5.2-5.8 whorls in mature specimens (5.4 in holotype). The
first whorl protrudes above the next, and is about 0.25 mm in diameter perpendicular to the
initial suture. The whorls are broadly arched and strongly shouldered with a deeply impressed
suture. The lower whorls are sculptured with well-incised, irregularly-spaced incremental stria-
tions that are usually continuous from the shoulder to the base of the whorl. The aperture is irreg-
ularly ovate in shape, is about 0.82-0.90 times as wide as high, and the upper comer is bluntly
rounded. The peristome extends completely across the parietal wall in shells with four or more
whorls. The aperture lies at an angle of about 12-14 to the axis of the shell, and the outer lip is
slightly arched forward in lateral profile.
 Measurements in mm of specimens with 5.2 or more whorls are as follows holotypee measure-
ments in parentheses): shell length 4.0-5.1 (4.4), shell width 2.4-2.8 (2.5), aperture height 1.6-
1.8 (1.7), aperture width 1.4-1.7 (1.4).
 OPERCULUM (FIG. 25C).-Ovate, paucispiral, consisting of about two complete whorls. The
nucleus is located in the lower left third of the face. Thin, membranous, amber yellow in color,
transparent. The outer face bears several relatively strong incremental striations.
 FEMALE (FIG. 10A-B).-The lower female system contrasts with that of M. lustrica as follows.
The oviduct loop is more convoluted and oppressed flat against the posterior pallial oviduct, as
opposed to being open and transverse to it as in lustrica. The glandular wall is much thinner,
and the seminal receptacle lacks a distinct duct. The bursa copulatrix is very large, being almost
as large as the posterior pallial oviduct, and has the distal 3/4 overlapping the posterior pallial
oviduct. The bursal duct is completely exposed on the mesad surface of the posterior pallial ovi-
duct, almost to its junction with the oviduct II.
 MALE (FIG. 11A-C).-The verge is stocky and bears a broad, squarish apical lobe along its
distal left margin. The penis is short and blunt and projects from the end of the verge along the
right side. The apical gland is small and is confined to the inner surface of the tip of the apical
lobe. Other glands are absent.
 The vas deferens I is strongly convoluted above the prostate. The latter is about twice as long
as wide and is more or less kidney-shaped. The vas deferens II is only slightly convoluted within
the coelomic wall. It is nearly straight inside the verge and closely parallels the right margin of
the verge and penis.
 TYPE LOCALITY.-Owen Springs, Sequatchie, Marion Co., Tennessee. HOLOTYPE: UF
22179; collected 8 September 1973 by Fred G. Thompson. PARATYPES: UF 22180 ( 1000);
same data as holotype.
 The spring flows from a large crevice in a limestone ledge. About 100 feet
below its source it forms a narrow, clear, cold creek that broadens intermit-
tently into deeper, quieter. pools. M. ogmorhaphe was found only in quieter
pools within about 100 yards of the spring source, primarily on ooze that was
free of sand and vegetation. Colonies were sporadic and localized.
 RANGE (FIG. 8).-This species is known only from the type locality.
 ETYMOLOGY.-The specific epithet, ogmorhaphe, is derived from the Greek
ogmos, a furrow, and rhaphe, a seam, and alludes to the deeply impressed su-
ture between the whorls.

 Marstonia pachyta new species
 DIAGNOSIs.-This species of Marstonia is readily identified by characteristics of both its verge
and shell. Like other Marstonia species, the verge is stocky and has a terminal penis along the
right margin. It shares with M. castor, but not with any other species, a small raised gland on the
ventral surface of the verge. It is unique within the genus in having two small glands along the
left margin of the apical lobe. The shell is readily identified by its ovate-conical shape, its pro-
nounced thickness, and its complete peristome. Other conical-shaped Marstonia have a much


1977