358 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Horizon and locality—Lenoir formation (ss.) in Tennessee: At Sweetwater, 
Sweetwater (T.V.A. 131-SW) Quadrangle; quarry on north side U. S. High- 
way 11, 4 mile south of Philadelphia, Philadelphia (T.V.A. 131-NW) Quad- 
rangle. Shale streak in granular beds below Mosheim limestone: Behind Quaker 
Church, north corner of Friendsville, Concord (T.V.A. 138-SW) Quadrangle. 
In Virginia: Along the road on North Fork, 3 miles south-southeast of North 
Fork, Christiansburg (30’) Quadrangle. 
Discussion.—This species suggests H. australis but differs in having a nar- 
rower hinge, more convex pedicle valve, a more convex brachial valve, and more 
curved palintrope. It differs from H. longirostra in having a shorter palintrope 
and more rounded outline. 
HESPERORTHIS TRICENARIA (Conrad) 
Plate 52, C, figures 16-21; plate 54, B, figures 5-10 
Orthis tricenaria Conrad, Proc. Acad. Nat. Sci. Philadelphia, vol. 1, p. 333, 1843.—BASSLER, 
U. S. Nat. Mus. Bull. 92, p. 897, 1915. 
Hesperorthis tricenaria (Conrad) ScHUCHERT and Cooper, Mem. Peabody Mus. Nat. Hist., 
vol. 4, pt. 1, p. 86, 1932. 
Orthis disparilis CoNRAD, Proc. Acad. Nat. Sci. Philadelphia, vol. 1, p. 333, 1843. 
Large for the genus; slightly wider than long; cardinal extremities slightly 
obtuse or approximately a right angle, occasionally auriculate; sides nearly 
straight to gently rounded; anterior margin broadly rounded; anterior com- 
missure rectimarginate to faintly sulcate. Surface marked by 32 narrowly 
rounded and elevated costae; interspaces marked by a single costella in the 
trough. 
Pedicle valve strongly and evenly convex in lateral profile; anterior profile 
strongly convex with a tendency to subcarination in the median region; lateral 
slopes long and steep. Beak erect and elongated ; umbo full; fold indistinct but 
indicated by a single median costa more elevated than those surrounding it; 
median region swollen; posterolateral slopes steep. Interarea long, slightly 
curved, strongly apsacline ; pseudodeltidium small. 
Brachial valve nearly flat to gently concave in lateral profile; anterior profile 
gently concave ; umbo concave, marked by a shallow, narrow sulcus that extends 
anterior to the front margin; sulcus inconspicuous ; flanks bounding sulcus flat 
to slightly concave; cardinal extremities deflected slightly toward the pedicle 
valve. Interarea long, strongly anacline. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Hypotype (24752a).......... 19.6 15.7 21.2 20.3 9.3 
i (S4G00) 22scRHNENK Os 20.1 15.9 22.3 Zoe 9.0 
nk (:2099824:));... Haka iors 18.4 ? 21.0 20.7 6.9 
nf G200082b).... 3.04 5..'« ? 15.9 21.2 20.5 2.4 
Types—Holotype of Orthis disparilis: A.M.N.H. 911/1. Figured hypotypes 
of H. tricenaria: 24752a, 109982a; measured hypotypes: 84000, 109982b. 
