312 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
slopes steep. Interior with short stout brachiophores and much thickened noto- 
thyrial platform and cardinal process. Median ridge short and low. 
Measurements in mm.— 
Hinge 
Length Width width Thickness 
FUGUGEVDE few oicigaddak-s a0 ns.e ueetin pes oe 8.8 7.9 7.2 ce 
Paratype (pedicle valve 1o9842a)... 8.5 8.2 Te ? 
e Oo" “ -109840a)... 8.6 8.7 8.0 ? 
+ (brachial valve 109840j) . 9.8 10.1 9.6 ? 
iH 6 af “ — 109843b). 7.9 8.9 6.9 ry 
Types.—Holotype: 109843a; figured paratypes: 109840f-j, 109842a,b, 
109843b,c; unfigured paratypes: 109840a-e, 109843d-m. 
Horizon and locality—Athens formation (Christiania bed) in Tennessee: 600 
feet S. 40° E. of the railroad crossing 1 mile northeast of the courthouse in 
Athens, Athens (T.V.A. 125-NE) Quadrangle; roadside 24 miles south-south- 
east of Riceville; 0.2 mile southeast of Britton Church, 24 miles northeast of 
Charleston, Calhoun (T.V.A. 125-SW) Quadrangle; Cleveland-Benton road, 5 
to 54 miles east of Cleveland, near old Climer, East Cleveland (T.V.A. 120-NE) 
Quadrangle. 
Discussion—The species is characterized by the strong convexity of both 
valves, the brachial valve being unusually swollen for the genus. The distant 
costae and the elongate form are other distinctive characters. The species differs 
from O. blountensis in its elongate form and the more numerous and smaller 
costae. It differs from O. friendsvillensis in the more distant costae and the more 
convex brachial valve. It can be readily separated from O. parvicrassicostatus by 
its more inflated valves and somewhat more numerous costae. 
ORTHAMBONITES SUBCONVEXUS Cooper, new species 
Plate 34, E, figures 21-26 
Shell of about medium size for the genus, wider than long, with rounded cardi- 
nal extremities and gently rounded lateral margins. Greatest width just posterior 
to the middle. Anterior margin broadly rounded. Anterior commissure recti- 
marginate. Ornamentation consisting of about 32 strongly elevated and narrowly 
rounded costae. No finer ornamentation except concentric fila preserved. 
Pedicle valve gently convex in lateral profile and with the most convex part 
in the posterior third. Anterior profile very gently and broadly convex. Beak 
forming an angle of 140°. Umbonal and median regions gently swollen and 
descending to the anterior and lateral margins by gentle slopes, the anterior slope 
having the lesser steepness. Interarea strongly apsacline, only slightly curved. 
Pedicle interior with dental plates nearly obsolete; teeth small and with small 
fossettes. Muscle field elongate with long and straight diductor scars and long, 
narrow adductor field slightly raised and separating the diductors. Vascula media 
divergent, indistinct. 
Brachial interior with short and stout brachiophores supported by callus and 
the thickened notothyrial platform. Cardinal process simple, stout. Median ridge 
thick. Posterior adductor patches larger than the anterior ones. 
