350 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Cannon County line, Cannon County; U. S. Highway 7oN, opposite Fairview 
Service Station, 4 mile west of Rome, Smith County. 
Lebanon formation in Georgia: Beside the road 0.1 to 0.2 mile south of the 
quarry, 13 miles south-southeast of Cove Church, 5 miles south of Chickamauga, 
Kensington (T.V.A. 106-SE) Quadrangle. 
Discussion.—This species is characterized by its parallel sides and small ears 
and the deeply sulcate anterior commissure. In the latter respect it reminds one 
of H. sulcata, but the commissure of the Lebanon form is deeper than that of the 
Oklahoma species and the outline is very different. The Lebanon species is sug- 
gestive of H. colei but has a deeper sulcus which reaches the anterior margin 
whereas this feature of H. colei does not significantly affect the margin. 
HESPERORTHIS SULCATA Cooper, new species 
Plate 52, D, figures 22-37 
Orthis tricenaria DECKER (not Conrad), Oklahoma Geol. Surv. Bull. 55, pl. 13, fig. F, 1931. 
Shell of about medium size for the genus, length and width nearly equal in 
the adult but with the width exceeding the length in the young. Hinge forming 
the greatest shell width in young specimens but equal to or slightly less than 
the greatest shell width in adults. Greatest shell width of adults variable, located 
between hinge extremity and middle. Cardinal extremities slightly auriculate in 
the young, nearly a right angle in adults. Lateral margins nearly straight or very 
gently convex ; front margin broadly rounded. Anterior commissure varying from 
strongly to gently sulcate. Valves ornamented by 28 to 30 broadly rounded to 
subangular costae separated by striae narrower than the costae. One or more 
fine radial lines occupying the striae between the costae, the line at the base of 
the stria being the larger. 
Pedicle valve moderately and evenly convex in lateral profile; broadly and 
fairly strongly convex in anterior profile. Median region somewhat swollen from 
umbo to anterior margin but well rounded and not subcarinate. Lateral slopes 
long and steep; anterior slope long but not as steep as the lateral slopes. Inter- 
area long, strongly apsacline, curved. Beak incurved; delthyrium long and nar- 
row ; pseudodeltidium short. Teeth small, dental plates short and receding. Del- 
thyrial cavity deep and narrow; muscle area small. Vascula media narrow, 
deeply impressed. 
Brachial valve gently concave in lateral profile and medially sulcate with flat- 
tened flanks in anterior profile. Beak prominent, somewhat elevated. Interarea 
moderately long, strongly anacline. Sulcus deep, originating at the beak and 
widening to the anterior margin where it occupies about one-third the width. 
Flanks bounding sulcus narrow, very gently convex; posterolateral areas flat- 
tened; cardinal extremities deflected toward the pedicle valve. Interior with 
shallow notothyrial cavity bounded by broad and long brachiophores. Median 
ridge short and low. Sockets narrow, deep. Cardinal process not strongly 
thickened. 
