302 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
from the Upper Pogonip of Nevada but differs in having wider valves with 
narrower and less distantly spaced costae. 
ORTHAMBONITES DIVARICATUS Cooper, new species 
Plate 33, A, figures 1-3 
Shell of about the usual size for the genus, valves unequally convex, length 
equal to four-fifths of the width; hinge slightly narrower than the greatest shell 
width which is located slightly anterior to the middle. Cardinal extremities 
slightly obtuse. Anterolateral margins somewhat narrowly rounded, anterior 
margin broadly rounded. Anterior commissure slightly sulcate. Surface marked 
by strong subangular costae on the center and flanks, a generation of finer costae 
intercalated between the larger ones on the flanks and posterolateral extremities. 
Spaces between the costae ornamented by low, rounded fila, about 5 to the milli- 
meter near the middle. 
Pedicle valve moderately convex with the maximum convexity near the mid- 
dle; anterior profile broadly convex. Beak small, incurved, protruding beyond 
the posterior margin. Median portion of valve forming an ill-defined fold and 
bearing the 3 largest costae. Flanks gently convex in anterior profile; antero- 
lateral slopes gentle but the posterolateral slopes moderately steep. Interarea 
only slightly curved, apsacline. Delthyrium open. Dental plates short, reced- 
ing ; adductor field with small ridge extending anteriorly from thickened anterior 
end. 
Brachial valve gently convex in both profiles; sulcus originating less than a 
millimeter anterior to the beak, shallow, widening anteriorly but occupying only 
about one-quarter of the width. Flanks gently convex with short gentle slopes 
to the cardinal extremities. Posterolateral extremities slightly flattened. Noto- 
thyrial cavity shallow, median ridge short, cardinal process not developed. 
Measurements in mm.— 
Hinge 
Length Width width Thickness 
Holotype (pedicle valve) ............. 12.7 15.3 12.8 4.2 
Paratype (brachial valve 109838b) ... 7.8 11.4 8.9 " 
- (Gbeegtt se ppALOOESEC) tka iaye, MEO 12.4 9.9 ? 
Types.—Holotype: 109838a ; figured paratype: 109838b ; unfigured paratypes: 
109838c-e. 
Horizon and locality —Effna-Rich Valley formations, in Virginia: Porter- 
field Quarry, 5 miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle. 
Discussion.—This species is characterized by the strong intercalation of costae 
between the primary ones and in this respect is unlike any other member of the 
genus from Virginia described in this paper. Some resemblance exists between 
this species and O. mycale Billings, but in the latter the muscular area of the 
pedicle valve is smaller and the fold of the brachial valve and sulcus of the pedicle 
valve are pronounced. 
