554 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
OXOPLECIA PLANIVENTRA Cooper, new species 
Plate 102, C, figures 25-32 
Shell of about medium size for the genus, transversely elliptical in outline with 
narrowly rounded sides and gently rounded anterior margin. Hinge moderately 
wide. Pedicle tongue short, broadly rounded. Broadly uniplicate. Greatest width 
at or near the middle. Fold marked by 5 or 6 costellae, sulcus by 5 or 6 and the 
flanks by about 12 costellae, those of the posterolateral areas low and indistinct. 
Fila strong, about 5 to the millimeter in the middle. 
Pedicle valve slightly to gently convex in lateral profile; anterior profile 
broadly and barely convex; umbo gently inflated; sulcus originating about 2 mm. 
anterior to the beak, broad and shallow throughout. Flanks bounding sulcus flat 
to gently convex and with gentle slopes to the margins. Interarea moderately 
long, curved, apsacline. Beak moderately long. 
Brachial valve fairly evenly and strongly convex in lateral profile and with 
the maximum convexity located near the middle. Anterior profile strongly 
arched; umbonal region swollen ; fold not strongly elevated in the median region 
but only gently elevated in the anterior region. Flanks bounding fold only gently 
inflated but with steep slopes to the margins. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype: lig... iSiGr 2. 2h 10.6 9.6 14.2 8.3 6.6 
Paratype (117I2Ia) ..... nhie's'et) EO 9.2 13.1 7.7 6.8 
Types.—Holotype: 117120; figured paratype: 117121a; unfigured paratype; 
11712Ib. 
Horizon and locality —Sevier formation in Louisville (T.V.A. 138-SE) Quad- 
rangle, Tennessee: 4 mile northeast of Miser; 4 mile north of Gooseneck. 
Discussion.—This is one of the numerous small species of Oxoplecia occurring 
in the interval between the Lenoir and Benbolt. It is specially characterized by 
the flatness of the pedicle valve in both profiles. This feature distinguishes it 
from all the other small species except O. recta. That species has a more erect 
beak on the pedicle valve, a not quite so flat pedicle valve, a more umbonate 
brachial valve, and a generally rounder outline. 
OXOPLECIA PLANULATA Cooper, new species 
Plate 104, D, figures 20-24 
Shell large for the genus, subquadrate in outline; sides broadly and gently 
rounded ; anterior margin lobate; hinge narrow. Costellae broad and irregular, 
II to 13 on the flanks, 6 on the fold, and 5 in the sulcus. Fila closely crowded, 
about 8 to the millimeter at the middle of the brachial valve. 
Pedicle valve gently convex in lateral profile and with a moderate swelling in 
the umbonal region. Anterior profile broadly and gently convex; sulcus origi- 
nating 5 mm. anterior to the beak, narrow in the median region but flaring some- 
what toward the front. Sulcus occupying less than half the width at the front 
