BULLETIN FLORIDA STATE MUSEUM


thinner, almost transparent shell, and the peristome is seldom complete across the parietal margin
of the aperture.
 SHELL (Fig. 3A; 12A-E).-The shell is ovate-conical in shape, and is about 1.43-1.70 times
as long as wide. The spire is conical in outline, and exceeds the height of the aperture. The height
of the aperture is about 0.39-0.46 times the length of the shell. The shell is very thick and opaque.
The periostracum is light yellowish-gray in color and has a dull luster. The shell is sculptured
with a few very fine, irregularly-spaced, incremental striations, which become stronger on the
base of the last whorl and occasionally form low wrinkles behind the baso-columellar margin of
the peristome. The umbilicus is imperforate or only narrowly rimate. There are 4.9-5.2 whorls
in mature shells (5.2 in holotype). The whorls have a moderately impressed suture and are moder-
ately arched. There is no tendency for the whorls to be shouldered. The initial whorl protrudes
above the succeeding whorl and is about 0.25 mm in diameter perpendicular to the initial su-
ture. The peristome is complete across the parietal margin of the aperture and may be slightly
solute from the body whorl in some specimens. The outer lip is nearly straight in lateral profile.
The aperture is broadly elliptical in outline, is about 0.80-0.88 times as wide as high, and is
angulate both above and below. The upper corner of the aperture is considerably thickened, as
are the outer and basal walls, whereas the columellar and parietal margins are thinner and nearly
uniform in thickness.
 Measurements in mm of mature specimens are as follows holotypee measurements in paren-
theses): shell length 3.3-4.0 (3.9), shell width 2.2-2.5 (2.3), aperture height 1.5-1.7 (1.5), aperture
width 1.2-1.4 (1.3).
 OPERCULUM (FIG. 25D).-Relatively elongate, irregularly ovate; thin, transparent, mem-
branous, light amber colored. Paucispiral, consisting of about two rapidly expanding whorls.
The nucleus is located just to the left of midline and is in the lower third of the face. The outer
surface is almost devoid of sculpture and bears only a few incremental striations.
 VERGE (FIG. 13A-D).-The verge is moderately stocky and bears a stout penis that projects
from the right distal margin. The region of the apical lobe is not as enlarged as in other Marstonia,
and it usually bears two small apical glands along the left margin and facing toward the snail's
body (Fig. 13, B); however, in one of six specimens examined only a single well developed apical
gland is present, with the second gland being indicated only by a few glandular cells (Fig. 13, D).
In addition, the ventral (inner) surface of the verge bears a small gland raised on a very low pedi-
cel about a fourth of the distance from the base to the apex and to the right of the midline. The
penis and adjacent parts of the verge are dark gray. The remainder of the verge is white.
 TYPE LOCALITY.-Limestone Creek, 0.7 mi. E Mooresville, Limestone Co., Alabama. HOLO-
TYPE: UF 22222; collected 1 October 1969 by Fred G. Thompson. PARATYPE: UF 22228 (45);
same data as the holotype.
 The creek at the type locality is shallow and consists of alternating
shallow, quiet pools and riffles over broken limestone. Snails were found on
dead leaves and tree rootlets in still shallow water at the edge of a pool.
 OTHER SPECIMENS EXAMINED.-Piney Creek, Mooresville, Limestone Co., Alabama (UMMZ
160735).
 RANGE (FIG. 8).-This snail is known to occur only in Limestone Creek
and Piney Creek, Limestone County, Alabama.
 ETYMOLOGY.-The name pachyta is derived from the Greek pachytes,
meaning thickness, and refers to the characteristically thick shell of this
species.

 Marstonia olivacea (PILSBRY)
Amnicola olivacea Pilsbry 1895:115. Walker 1918:135.
 DIAGNOSIs.-A thin-shelled Marstonia of dubious systematic status. It is similar to M. lustrica
in its elongate conical shape and its wide umbilicus. It differs by having a relatively inflated
penultimate whorl, a broader operculum, and a darker periostracum.
 SHELL (FIGs. 1D, 14A-D).-The shell is elongate-conical, or in some obese specimens ovate-
conical, and is 1.43-1.61 times as long as wide. The periostracum is very thin and grayish-brown.


Vol. 21, No. 3