304 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle valve moderately convex in lateral profile but more strongly convex 
in anterior profile. Greatest convexity posterior to the middle. Umbo and post- 
median region swollen; anterior half gently convex and sloping moderately 
steeply to the anterior margin. Slopes to the cardinal extremities gently con- 
cave, moderately steep. Interarea strongly curved ; beak incurved and overhang- 
ing the delthyrium. Lateral plates well developed. Interior with short receding 
dental plates, subcordate muscular area. Vascula media extending medially from 
diductors, then becoming subparallel. 
Brachial valve gently and evenly convex in lateral profile; gently concave in 
anterior profile. Sulcus shallow and wide, shallowest at the front margin. Flanks 
of shell slightly swollen; anterolateral areas depressed. Cardinal extremities 
deflected slightly dorsally. Interarea short; beak inconspicuous. Interior with 
long brachiophores, short median ridge, simple cardinal process and wide 
adductor field. 
Measurements in mm.— 
Dorsal Hinge 
Length length Width width Thickness 
Holotype oii). #225 4 10.7 9.0 11.6 10.0 5.5 
Paratype (100827c).. 8.5 7.5 9.5 75 4.6 
cy (109827g).. 11.3 0.8 11.2 9.4 5.8 
Types.—Holotype: 109827b; figured paratypes: 109827c,g,h; unfigured para- 
types: 109827a,d-f,i-p. 
Horizon and locality.—Arline formation in Tennessee: North side of wagon 
road in glade, 4 mile southeast of Friendsville; 100 yards southwest of Negro 
Cemetery, 4 mile northeast of Friendsville, Concord (T.V.A. 138-SW) Quad- 
rangle; 1,500 feet south of the mouth of Burnett Creek, Shooks Gap (T.V.A. 
147-NE) Quadrangle. 
Discussion.—This species is characterized by its subquadrate form and the fine, 
closely spaced costae. It resembles O. bellus but differs in having more finely 
costate ornamentation. 
ORTHAMBONITES MICHAELIS (Clark) 
Orthis michaelis CLARK, Journ. Paleont., vol. 9, No. 3, p. 242, pl. 24, figs. 5, 6, 1935.—ULrIcH 
and Cooper, Geol. Soc. Amer. Special Pap. 13, p. tot, pl. 14C, figs. 11, 12, 21, 23, 25-20, 
1938. 
Types.—Hypotypes: 91316a,b, 91318a,b; 91320a-d. 
Horizon and locality—Swan Peak formation in Utah; Kanosh formation in 
Utah. 
ORTHAMBONITES MINUS Cooper, new species 
Plate 34, D, figures 16-20 
Shell small, wider than long, somewhat rectangular in outline; hinge slightly 
less than the greatest shell width which is at the middle; sides gently rounded ; 
anterolateral extremities narrowly rounded; anterior margin nearly straight; 
anterior commissure sulcate ; surface marked by 35 to 36 narrowly rounded and 
elevated costae separated by spaces slightly less than the width of the costae. 
