LAMELLIBRANCHIA TA. 
225 
Hinge-line straight; length a little more than the greatest length of the 
valve. 
Beak sub-anterior, directed forward, acute, not rising much above the 
hinge. Umbonal angle acute. 
Anterior end narrow, elongate, very acute, limited by a shallow byssal 
depression. Wing large, joining the body near the base; margin broadly and 
symmetrically concave; extremity produced into a spiniform extension reach¬ 
ing beyond the posterior extent of the shell. 
Test marked by fine concentric striae which are regular on the posterior 
part of the body and the wing, and very crowded and fasciculate on the 
anterior. 
Interior unknown. 
A large left valve has a length of 60 mm., height 37 mm., hinge-line 
62 mm. A slightly larger, imperfect specimen has been found, the body of 
which, near the posterior extremity, has a greatest width of from 25 to 28 
mm., and measures from 12 to 14 mm. in the narrow part between the beak 
and the byssal sinus. 
This species differs from L. Pelops in the longer and more erect body, more 
attenuate anterior extremity, more extended wing and deeper sinus in the 
margin. 
Formation and localities. In the middle beds of the Chemung group at 
Charleston, and near Mansfield, Tioga county, Pa. 
Section d, patulata. 
Leptodesma flaccidum, n. sp. 
PLATE XCI, FIG. 9. 
Shell of medium size, rhomboid-ovate, spatulate below; body oblique at an 
angle of about 45° to the hinge-line ; length about one-third greater than 
the height; ante-byssal margin subtruncate, oblique, a little concave below, 
curving into the broad ventral margin; posterior margin abruptly, rounded 
and recurved. 
29 
