484 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
about the middle; tongue short and narrowly rounded; lateral slopes steep; 
interarea moderately long, apsacline; beak incurved. 
Brachial valve moderately convex in lateral profile but with the greatest con- 
vexity at the middle; anterior profile slightly more convex and with somewhat 
steeper lateral slopes than those of the pedicle valve; umbonal region somewhat 
flattened ; median area strongly inflated; anterior region moderately convex but 
not forming a pronounced fold, the tongue of the pedicle valve inserted into a 
reentrant wave of the brachial commissure. 
Measurements in mm.—Holotype, length 20.2, brachial length 18.2, width 26.0, 
hinge width 18.9, thickness 14.4. 
Type.—Holotype: 117053. 
Horizon and locality—Benbolt formation in Virginia: On the north side of 
U. S. Highway 19, 13 miles southeast of Hansonville Post Office, Brumley 
(T.V.A. 205-SE) Quadrangle. 
Discussion.—This is a rare species; only one specimen has been found up to 
the present writing. This species suggests M. biconvexa and M. globosa. It 
differs from both of them in the somewhat narrow brachial fold of the anterior 
commissure and the small, narrow pedicle tongue. Another characteristic feature 
separating this species from the two mentioned and from most other Mimellas 
is the flattened umbo of the brachial valve. 
MIMELLA TRANSVERSA Cooper, new species 
Plate 85, D, figures 33-37 
Shell of about medium size for the genus, transversely subrectangular in out- 
line ; sides broadly rounded; greatest width anterior to the middle; anterolateral 
extremities narrowly rounded; anterior margin nearly straight ; anterior commis- 
sure broadly and faintly uniplicate. Valves subequal in depth. Surface multi- 
costellate, about 8 or 9 costellae in 5 mm. at the anterior margin; costellae nar- 
rowly rounded and separated by striae narrower than the width of the costellae. 
Pedicle valve unevenly and moderately convex in lateral profile and with the 
maximum convexity in the posterior half, anterior half flattened ; anterior profile 
broadly subtriangular with long, gently sloping sides and low, rounded apex; 
umbonal and median regions swollen ; anteromedian area flattened, posterolateral 
slopes long and moderately steep; interarea moderately long, apsacline; beak 
erect. 
Brachial valve fairly evenly convex in lateral profile with the maximum con- 
vexity in the median region; anterior profile strongly and broadly convex with 
the top gently flattened but with short, steep lateral slopes ; umbonal and median 
regions swollen. Sulcus originating on the umbo, shallow and inconspicuous, 
widening moderately anteriorly and bounded by low, narrow swellings; lateral 
slopes long and moderately steep. Beak partially overhanging pedicle interarea. 
Measurements in mm.—Holotype, length 14.5, brachial length 14.0, width 
19.4, hinge width 14.2, thickness 10.1. 
Type.—Holotype: 117052. 
