172 
PALAEONTOLOGY OF NEW YORK. 
Leiopteria Chemungensis. 
PLATE XXII, FIGS. 17, 18. 
Avicula Chemungensis, Vandxem. Geolog. Surv. N. Y.: .Rep. Third Dist., p. 182, fig. 49, No. 3. 1842. 
Leiopteria nitida, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 22, figs. 17, 18. 
Jan., 1883. 
Shell of medium size or larger, rhomboid-ovate; body elongate-ovate, oblique at 
an angle of about 60° with the hinge-line; length equal to more than four- 
fifths of the height; anterior margin nearly vertical for about one-half 
the height of the shell and broadly rounded on the base; post-basal margin 
abruptly rounded. 
Left valve convex, gibbous in the umbonal region. Right valve smaller, 
less gibbous. 
Hinge-line straight, a little longer than the height of the shell. 
Beaks sub-anterior, inclined forward, acute, prominent, arching over the 
hinge. Umbonal region narrow, prominent, subtending an acute angle. 
Ear of left valve small, bending slightly downward, defined by a broad 
distinct sulcus; extremity rounded. Ear of right valve flat. Byssal sinus 
shallow and broad, deeper in the right valve. Wing broad-triangular, 
joining the body below the middle of the length, limited by the abrupt 
bending of the striae; margin deeply concave in the middle; extremity 
produced and acute. 
Surface, in a partial cast, marked by fine concentric striae, which are 
crowded and lamellose on the ear, distinctly marked on the wings, and 
appearing on the body as distinct undulations: these in the perfect shell 
may have been sharp lamelliform striae. 
Interior unknown. 
A specimen of the left valve has a length of 30 mm., height 35 min., 
hinge-line 47 mm.; the body from beak to post-basal extremity measures 
43 mm. 
The specimen figured is the original of Avicula Chemungensis, Vanuxem. It 
resembles L. Dekayi of the Hamilton group, but differs in its longer hinge-line, 
larger wing, and more acute beak, while the body of the shell is narrower. 
