548 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype (pedicle valve) ........... 8.0 ? 10.0 6.5 ? 1.8 
Paratype ( “ (on SITIO ahs ns ? 10.4 7.52 1.2 
a (brachial valve I171I0c)... ? 8.0 10.2 7.6? 3.0 
iy Ga ee TZ LION) ss. of 8.2 13.1 ? 3.0 
Types.—Holotype: 117110a; figured paratypes: 117110b,c,e; unfigured para- 
type: 117110d. 
Horizon and locality—Red Knobs formation in Tennessee: 1 mile south of 
Louisville, Louisville (T.V.A. 138-SE) Quadrangle. 
Discussion.—This is a small species so far known only from a “marble’’ facies. 
It reminds one somewhat of O. holstonensis but is more strongly costellate and 
with a wider outline. It is somewhat suggestive of O. eidsonensis in the exterior 
markings, but that species is larger and more robust with a strongly convex 
brachial valve. The costellae also suggest O. recta, but that species has a much 
flatter pedicle valve and a more strongly convex brachial valve. 
OXOPLECIA MONITORENSIS Cooper, new species 
Plate 102, D, figures 33-37 
Shell of about medium size for the genus, wider than long, with a narrow 
hinge and somewhat narrowly rounded sides. Front margin truncated. Tongue 
short and broadly rounded. From 8 to Io costae on the flanks, and 6 in the 
sulcus. 
Pedicle valve gently convex in lateral profile; broadly and gently convex in 
anterior profile; umbo somewhat swollen. Sulcus originating 2 mm. anterior to 
the beak, wide and shallow, occupying about half the width. Flanks bounding 
sulcus slightly convex and with moderately steep posterolateral slopes. Inter- 
area short, curved, apsacline; beak short. 
Brachial valve moderately convex in lateral profile but with a swollen umbo; 
anterior profile strongly arched. Fold poorly defined on the median region, be- 
coming elevated moderately at the front. Flanks moderately swollen and with 
steep slopes to the margins. 
Measurements in mm.—Holotype, length 11.6, brachial length 11.7, width 15.0, 
hinge width 9.7, thickness 8.0. 
Types.—Holotype: 117111a; unfigured paratypes: 11711Ib,c. 
Horizon and locality —Yellow limestone above the 25-foot bed of sandstone 
marking base of Eureka group, in Nevada: On the saddle just north of hill 8167, 
Martins Ridge, Monitor Range, Roberts Mountains (1°) Quadrangle. 
Discussion.—This is a small rotund type of Oxoplecia suggestive of O. hol- 
stonensis and O. parva. It is, however, slightly larger than both of these species. 
It is also more strongly costellate than O. holstonensis and has a much less con- 
vex brachial valve, a much deeper sulcus, and a somewhat wider fold. The cos- 
tellae of O. parva are somewhat stronger than those of the Nevada species, and 
its brachial valve is less strongly umbonate but is more convex. 
