542 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
OXOPLECIA FILOSA Cooper, new species 
Plate 103, A, figures 1-12 
Shell large, slightly wider than long, subcircular in outline; sides broadly 
rounded; hinge narrow; anterior margin broadly rounded; uniplicate; valves 
unequal in depth, the brachial valve usually considerably deeper ; surface costel- 
late, costellae low and rounded, separated by spaces about equal in width to the 
width of the costellae; costellae becoming broad and subdued on the anterior 
margin; 12 costellae on the flanks; fold and sulcus with variable number from 
5 to 8. 
Pedicle valve unequally convex in lateral profile the greatest convexity located 
in the posterior third ; anterior profile broadly and gently convex ; sulcus originat- 
ing 4 to 5 mm. anterior to the beak, shallow in the median region, only moder- 
ately deep at the margin where it occupies less than half the width. Sulcus 
bounded on each side by a narrow plica consisting of 2 costellae somewhat more 
elevated than those on the outside ; flanks gently convex ; slopes moderate. Inter- 
area long, curved, moderately apsacline; beak moderately protruding. Tongue 
long and narrow. 
Brachial valve gently convex in lateral profile except for the umbo which is 
inflated ; anterior profile strongly and broadly convex; fold originating about 5 
to 6 mm. anterior to the beak, very low on the middle of the valve and not be- 
coming more than moderately elevated at the front margin; flanks bounding 
fold swollen and convex and with steep lateral slopes. 
Measurements in mm.— 
a 
Brachial Hinge 
Length length Width width Thickness 
EOL PE woos vat Uae a ahs 20.5 a7, 21.6 13.1 Tr 
Paratype’ +. .!0i9 sBaveecs vets 14.0 12.8 17.9 12.6 8.9 
Types——Holotype: 1170992 ; figured paratype: 117099b. 
Horizon and locality.—Bromide formation (Mountain Lake member) in Okla- 
homa: Road cut on Oklahoma Highway 18, center NW} sec. 11, T.1S.,R.3 E,, 
1.8 miles south of Sulphur, Murray County. 
Discussion—This is one of the larger species of Oxoplecia which is orna- 
mented by slender costellae. It thus resembles O. gouldi, O. nevadensis, and 
O. multicostellata. Oxoplecia filosa differs from O. gouldi in its much rounder 
outline, the length and width being nearly equal; the interarea is longer, so that 
the beak is more elevated above the brachial umbo; the pedicle valve is less deep 
than that valve in O. gouldi; the fold originates nearer the center of the brachial 
valve than in O. gouldi, and the sulcus of the latter is deeper than that of O. filosa. 
Oxoplecia nevadensis has a stronger fold and sulcus than O. filosa and its 
valves are deeper, the outline is more transverse, and the pedicle beak is less erect. 
Oxoplecia filosa differs from O. multicostella in its less prominent fold and 
sulcus, the sulcus of the latter species originating far up on the umbo; it differs 
in its more compressed form, less exposed pedicle interarea and more inflated 
umbonal region. 
