LAMELLIBRANCHIA TA. 
235 
line. Umbonal region narrow and moderately gibbous, subtending a very 
acute angle. 
The byssal depression reaches the margin just below the beak, leaving a 
very small, acute, anterior extremity. Wing large, undefined, joining the body 
at the posterior end; margin oblique, essentially straight, not recurved at the 
cardinal extremity. 
Test thin, leaving upon the cast the marks of the striae of growth which 
are more or less fasciculate upon the body, and crowded and lamellose in 
front. 
Hinge furnished with a distinct posterior tooth. Interior unknown. 
The specimen described has a length of 32 mm., height 24 mm., and 
hinge-line 22 mm. 
This species somewhat resembles L. Orodes, especially as shown in PL xxv, 
fig. 10, but the beak is more nearly anterior, the anterior end much smaller 
and more acute, the byssal sinus not extending so low on the body of the 
valve, and the body of the shell more distinctly attenuate toward the beak. 
It is especially distinguished by its narrow slender beak and small anterior 
end. 
Formation and locality. In a sandstone of the Upper Chemung group at 
Warren, Pa. 
Leptodesma mytiliforme. 
PLATE XXV, FIGS. 7, 11; AND PLATE XCI, FIGS. 22-25. 
Leptodesma my tilifor me, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 25, figs. 7, 11. 
Jan., 1883. 
Shell of medium size, elongate-ovate; body narrowly elliptical, becoming 
attenuate in front, oblique, making an angle of nearly 45° with the hinge¬ 
line ; length more than one-third greater than the height; ante-byssal margin 
oblique, gently curving into a scarcely perceptible sinus, giving a straight or 
slightly concave margin extending for two-thirds the length of the valve; 
posterior margin abruptly rounded. 
