Fauna of the Morrow Group 
207 
small portions of the shell clinging to its surface. The form was 
of medium size, transversely elongate, and moderately convex, 
with no distinct umbonal ridge. The cardinal and ventral mar- 
gins are nearly straight and parallel and the posterior portion 
of the valve is extended considerably behind the inconspicuous 
beak situated at the posterior extremity of the cardinal margin. 
The surface of the shell was apparently nearly smooth with 
faint concentric lines of growth discernible anteriorly. In gen- 
eral appearance the valve resembles that from the Moorefield 
shale described by Girty^^ as Solenomya? sp. but is much smaller. 
Horizon and locality. Kessler limestone: near Brentwood, 
Arkansas (Station 144). 
SOLENOPSID^ 
Genus SPHENOTUS Hall 
Sphenotus halensis n. sp. 
Plate XV, figure 5. 
Description. Shell small, transversely sub-trapezoidal in out- 
line, the greatest length (near the ventral margin) about twice 
the height (measuring along a line normal to the hinge-line and 
situated near the posterior margin). Left valve: hinge-line 
straight and little more than half the length of valve below, 
posterior margin obliquely truncated above and rounding into 
the ventral margin below; ventral margin nearly straight with 
a slight sinuosity immediately in front of the middle and slightly 
oblique to the hinge-line so that if produced the two would meet 
about 4 cm. in front of the beak; anterior margin slightly con- 
cave above, beneath the umbo, and rounding broadly into the 
ventral margin below; beak not prominent, situated at anterior 
end of hinge-line ; umbonal ridge ' stronger and sharper near 
beak and more rounded, though still well-defined as it nears the 
posterio- ventral angle, gently curved so that it is slightly convex 
upward; a second, fainter and less well-defined, ridge extends 
from umbo to posterior margin, bisecting the angle between the 
large umbonal ridge and the hinge-line ; a broad, shallow, unde- 
fined sinus originates on the umbo and, continuing downward, 
meets the ventral margin somewhat in front of the middle. 
Right valve unknown. 
