Vol. 100(2)
April 30, 1986
THE NAUTILUS 71
tion of Antillean Cretaceous rudist frameworks. Verhand-
lungen Naturfor.'ichende Gesellschaft. Basel. 84:399-467.
Palmer, A. R. 198,3. The decade of North American geologT,-
1983 geologic time scale. Geology ll:.503-504.
Perkins. B. F. 1969. Rudist morphology' -Shell size ami
shape, p. N7.")l. In R. C. Moore (ed.). Trcntixc on hirci-tr-
bmte Paleontology, Part N, Vol. 2, Mollusca 6, Bivalvia.
Univ. Kansas Press, Lawrence.
Zoological Record. 1966-1981. The Zoological Society of
London.
A NEW SOMATOGYRUS FROM THE SOUTHWESTERN OZARKS WITH
A BRIEF REVIEW OF THE HYDROBHDAE FROM THE
INTERIOR HIGHLANDS (GASTROPODA: PROSOBRANCHIA)
Mark E. Gordon
Department of Zoology
University of Arkansas
Fayette vi"lle, AR 72701
ABSTRACT
A previously unknown Somatogyrus is described from the Elk River, McDoridld
County, Missouri. With this description, the number of Hydrobiidae presently
recorded from the Interior Highlands increases to 15, including 11 regional
endemics. Nine species are endemic to the Ozark Plateaus, while two
Somatogyrus are restricted to the Ouachita Mountains. Fire of the Ozark
endemics are obligate troglohites. Troglobitic Amnicola antroecetes (Hubrichf) is
considered distinct from epigean A. aldrichi (Call and Beecher).
Excepting the Unionoidea, little study has
been afforded the aquatic Mollusca of the In-
terior Highlands. Among the poorer known
groups, regional accounts of the Hydrobiidae
are rare. The primary sources of pulilished
records have been original descriptions of
several endemic species (e.g. Walker, 1915;
Hinkley, 1915; Hubricht, 1979), although the oc-
casional collection of hydrobiids has been noted
in a few species surveys (e.g. Sampson, 1913;
Wheeler, 1918; Gordon, 1981). A recent faunal
survey of drainage basins in southwestern
Missouri and northwestern Arkansas (Gordon,
1980) recovered several species of Hydrobiidae.
A previously unknown Somatogyrus. collected
from the Elk River, McDonald County,
Missouri, is here described.
Family Hydrobiidae Troschel 1857
Subfamily Lithoglyphinae Fischer 1885
Somatogyrus rosewateri new species
Shell descripfiori of holotype-SheW sub-
globose, medium size for Somatogyrus. solid,
dextral, 4.25 whorls, turbinate, subhyaline; body
whorl .90 times axial height, greatly inflated;
[penultimate whorl .34 times width of body whorl
(Fig. 1; see Table 1 for holotype measurements
and range of paratypes). Spire very short,
depressed, broadly conic; sutures moderately
impressed; protoconch flattened (Fig. 2).
Periostracum greenish (may be masked by color
of visceral mass showing through shell) with
shallow, oblique growth striae; protoconch or-
namented with fine, spiral ridges (Fig. 3). Aper-
ture broadly ovate, .74 times axial height, .80
times height and .55 times width of body whorl,
plane of aperture at 30° to shell axis. Peristome
complete across parietal wall by a callus which
continues and thickens across columella (callus
in some individuals may be slightly reflected
over columella, partially obscuring umbilicus);
lip straight along parietal wall, curving con-
cavely near the umbilicus and along columella,
parietal-columellar junction non-angular. In
lateral view (Fig. 4), periphery of parietal lip
BioStor
