350 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
HESPERORTHIS ? COSTELLATA Cooper, new species 
Plate 82, A, figures 1-6 
Shell of about the usual size for the genus, length and width about equal ; sides 
gently rounded ; hinge about equal to the midwidth; anterior margin somewhat 
narrowly rounded. Surface costellate, costellae intercalated in several genera- 
tions, distinctly fasciculate in places at the front and numbering about 50. Stria 
between costellae occupied by concentric fila. 
Pedicle valve unevenly convex in lateral profile, the posterior third somewhat 
flattened, the median third moderately convex but the anterior third again flat- 
tened. Anterior profile narrowly convex in the median region but with long, steep 
lateral slopes. Beak prominent; umbo narrowly convex, the narrow convexity 
continued anteriorly to the front margin as a poorly defined fold. Interarea long, 
slightly curved, and apsacline. 
Brachial valve faintly convex in lateral profile and broadly but gently convex 
in anterior profile; sulcus shallow, indistinct, originating at the umbo and ex- 
tending to the anterior margin. Flanks bounding sulcus faintly convex ; postero- 
lateral extremities deflected and flattened in the direction of the brachial valve. 
Measurements in mm.—Holotype, length 12.0, brachial length 10.0, width 13.7, 
hinge width 14.4, thickness 5.5. 
Types.—Holotype: 116918. 
Horizon and locality.—Botetourt formation in Virginia: On Virginia High- 
way 114, 2.3 miles west of the Montgomery-Roanoke County line, 12 miles north- 
east of Blacksburg, Montgomery County. 
Discussion.—This species is characterized by its costellate surface and in this 
respect is unlike all other species of Hesperorthis described herein. The generic 
assignment is doubtful because interior details are unknown and the ornament 
is not like that of the majority of species. 
HESPERORTHIS CRINERENSIS Cooper, new species 
Plate 52, B, figures 8-15 
Small for the genus, wider than long with the hinge forming the widest part; 
cardinal extremities forming a large acute angle; sides gently oblique; front mar- 
gin strongly rounded; anterior commissure gently sulcate; surface marked by 
26 narrowly rounded elevated costae separated by striae about equal in width 
to the width of the costae. Striae occupied by several fine radial lines. 
Pedicle valve very gently convex in lateral profile; anterior profile narrowly 
rounded medianly and with long and steep lateral slopes ; umbo narrowly swollen, 
the swelling continued anteriorly nearly to the anterior margin as a poorly de- 
fined fold; interarea long, nearly catacline; delthyrium open. 
Brachial valve gently convex in lateral and anterior profiles; umbo sulcate; 
sulcus narrow, shallow, widening and deepening gradually anteriorly to the front 
margin; flanks bounding sulcus gently swollen; posterolateral extremities de- 
flected slightly toward the pedicle valve; interior with a short and stout median 
