LAMELLIBRANCHIA TA. 
197 
Test moderately thick, marked by elevated lamellose striae, with finer 
intermediate lines. 
Interior unknown. 
The specimen described has a length of 42 mm., height 24 mm., hinge¬ 
line, to base of spine, 30 mm. The spine is probably extended from 5 to 
10 mm. beyond. 
This species resembles L. lepidum, but differs in its more gibbous form, larger 
and more obtuse anterior extremity. 
Formation and locality. In sandstones of the Upper Chemung group, McKean 
county, Pa., on the road from Bradford to Farmers’ Valley, Cattaraugus 
county, N. Y. 
Section b, umbonata. 
i 
Leptodesma Medon, n. sp. 
PLATE XC, FIGS. 1-4. 
Shell of medium size, sub-rhomboidal; body broad-ovate, oblique at an angle 
of about 60° with the hinge-line; length nearly one-third greater than the 
height; ante-byssal margin curving slightly outward, concave at the sinus; 
basal and posterior margins broadly rounded, passing directly into the wing. 
Left valve gibbous above, depressed-convex below. Bight valve some¬ 
what less convex than the left. The right valve appears to have been 
somewhat smaller and the base more extended than in the left valve. 
Hinge-line straight; length a little greater than the height of the shell. 
Beaks at about the anterior third of the hinge, acute, prominent, arching 
over the hinge-line. Umbonal region gibbous, descending almost vertically 
oil the posterior, and sloping abruptly on the anterior side. Umbonal angle 
acute. 
Anterior end short, separated from the body by a marked sinus; extremity 
angular, gently rounded below. Wing not defined, broad-triangular, teaching 
nearly to the posterior end of the body ; margin slightly concave ; extremity 
acute. 
