BULLETIN FLORIDA STATE MUSEUM


 Even though the shells of M. olivacea and M. lustrica are very similar,
other distinguishing features, such as the soft anatomy, must be considered.
There are no available preserved anatomical specimens of M. olivacea. I at-
tempted to extract and relax dried bodies from paratypes (ANSP 65466) but
had unsatisfactory results. Because other species (i.e., M. pachyta, M. castor)
differ from M. lustrica in the structure of the verge, it cannot be assumed that
M. olivacea does not.
 There is a tendency to conclude that if two forms cannot be distinguished
on the basis of available evidence, they must be identical. In the case of M.
olivacea, I hesitate to draw this conclusion for the reasons mentioned above.
This species' status remains uncertain.

 Marstonia lustrica (PILSBRY)
Amnicola lustrica Pilsbry 1890:53.
Amnicola (Marstonia) lustrica Pilsbry; Baker 1926:195; Berry 1943:29-32.
Amnicola winkleyi Pilsbry 1912:1, pl. 1, figs. 9-10.
Amnicola oneida Pilsbry 1917:46: Baker 1928:111-113, pl. 6, figs. 24, 25, 28-31.
Amnicola lustrica gelida Baker 1921:22.
Amnicola gelida Baker 1928:110-111, pl. 6, figs. 19-23.
Amnicola lustrica decepta Baker 1928:108-109, text-fig. 45.
Amnicola lustrica perlustrica Baker 1928:109-110, pl. 6, fig. 15, text-fig. 45.
Marstonia decepta (Baker); Taylor 1960:51, pl. 2, fig. 9; Clarke 1974:244-247, pl. 21, fig. 16.
Marstonia gelida (Baker); Clarke 1974:247, pl. 21, figs. 7-8.
 DIAGNOSIS.-The verge is relatively simple in structure and similar to that of M. arga and
M. ogmorhaphe. It has a single apical gland on the apical lobe and a relatively short and stocky
penis. Anatomically the species is unique because of the following features: (1) prostate consoli-
dated and ovate in shape, being only slightly longer than wide; (2) glandular wall of oviduct
loop relatively thick; (3) seminal receptacle borne on a short duct; (4) bursa copulatrix relatively
small, projecting beyond posterior pallial oviduct for about half its length; and (5) bursal duct
completely imbedded in posterior pallial oviduct.
 The shell of M. lustrica is distinguished from other Marstonia by the combination of a mod-
erately open umbilicus, conical spire, striate sculpture, and complete peristome that is nearly
straight in lateral profile. The inside of the aperture never bears a thick callus, such as occurs
in M. arga.
 SHELL (FIGs. 2A-D; 16A-N).-The shell is dull olivaceous-gray in color, moderately thin, and
weakly translucent or opaque. Occasional specimens may be thick-shelled, but they do not have
heavy calluses deposited inside the aperture. The shell is ovate-conical to elliptical-conical in
shape and generally about 0.55-0.75 times as wide as high. Some extremely narrow specimens
from marshy lakes along the southern edge of the range may be terete. The spire is straightsided
or weakly convex in outline. The aperture is about 0.30-0.45 times the height of the shell. The
base is openly umbilicate. The surface of the shell is sculptured with fine, rather widely-spaced
incremental striatioris that are nearly continuous across the whorls. The suture is deeply im-
pressed. There are about 4.5-6.0 whorls in mature shells. Large terete specimens may have six
or more whorls. The whorls are arched and moderately shouldered. The apical whorl protrudes
and is about 0.25 mm in diameter perpendicular to the initial suture. The remaining whorls in-
crease rather regularly in size. The aperture is broadly elliptical or ovate in shape and is higher
than wide, the posterior corner is weakly angulate or rounded, and the plane of the aperture
lies at an angle of about 150 to the axis of the shell. The peristome generally is complete at ma-
turity. The columellar margin is thin and slightly reflected. The outer lip is nearly straight in
lateral profile.
 Measurements in mm for selected specimens representing riverine, lacustrine, and marsh
habitats are shown in Table 1.


Vol. 21, No. 3