306 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
cardinal process a thin ridge; median ridge formed by inner swelling produced 
by sulcus ; notothyrial platform low; brachiophores short. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Paratype (pedicle valve 116883f)..... aur P 5.2 5.0 0.9 
GaAs “AMULTOSS3D ie ea ? 3.2 3.0 0.6 
3 (brachial valve 116883g).... ? 3.5 5.2 Ser 0.7 
Cinien Cn AEEBOS SE Mis tour: Dyk 2.6 3.6 3.4 0.4 
Types.—Holotype: 116883c; figured paratypes: 116883a,b,d,e; unfigured 
paratypes: 116883f-h. 
Horizon and locality—McLish formation (bed 45) in Oklahoma: On West 
Spring Creek, sec. 6, T. 2 S., R. 1 W., Murray County. 
Discussion—For differences between this species and O. minus Cooper, see 
O. minus. 
ORTHAMBONITES MOSTELLERENSIS Cooper, new species 
Plate 35, A, figures I-10 
Shell of medium size for the genus, subquadrate in outline, width slightly 
greater than length. Lateral margins nearly straight; anterolateral extremities 
broadly rounded; anterior margin truncate. Cardinal extremities a right angle. 
Anterior commissure sulcate. Surface marked by about 15 broadly angular 
costae. 
Pedicle valve moderately convex with the greatest convexity posterior to 
the middle. Median fold obscure, defined only in the anterior three-quarters. 
Lateral slopes steep, gently concave. Interarea long, strongly incurved; beak 
incurved. Teeth large; fossettes deep. Dental plates short; umbonal cavities 
filled by callus. Muscle area small, slightly thickened. 
Brachial valve slightly convex with a poorly defined median sulcus originat- 
ing at the umbo and extending to the anterior margin where it occupies slightly 
more than one-third the width. Sulcus occupied by 2 costae. Interior with short 
brachiophores partly engulfed by callus. Notothyrial platform thickened ; cardi- 
nal process stout. 
Measurements in mm.—Holotype, length 11.5, dorsal length 10.0, width 12.3, 
hinge width 10.0, thickness 5.0. 
Types.—Holotype: 1o9810b; figured paratypes: 109810a,c,e; unfigured para- 
types: 109810d,f,¢g. 
Horizon and locality.—Little Oak formation in Alabama: Cut on L. and N. 
RR., + mile northwest of Mosteller, Columbiana (15’) Quadrangle. 
Discussion.—This species is characterized by its broadly angular costae and 
its subquadrate outline. It is similar to O. rotundiformis but differs in its some- 
what larger size and the broader costae and more quadrate outline. It differs 
from O. blountensis in size and shape. It is about the same size as O. bielsteini 
but the costation is coarser. It is readily distinguishable from its associate in 
the Little Oak limestone, O. buttsi, by its more quadrate form and more distant 
and broadly angular costae. 
