124 
PALAEONTOLOGY OF NEW YORK. 
striae, with intermediate finer lines, and by slender, filiform, undulating, 
distant rays, which are more crowded on the anterior side, becoming finer and 
more numerous at the junction of the wing with the body, and a few much 
stronger ones along "the cardinal line. Rays not present on the ear, which is 
marked only by the crowded concentric striae. The concentric striae crenu- 
late the rays and bend backward in the interspaces, producing a beautifully 
cancellated surface. 
The right valve shows two oblique lateral folds or teeth posterior to the 
beak. 
A right valve has a length of 25 mm. parallel to the hinge, height 28 mm., 
hinge-line about 34 mm. An imperfect left valve has an approximate length 
of 22 mm., height 24 mm., and hinge-line 33 mm. 
This species is distinguished by its erect, orbicular form, great extension of 
hinge-line, and marked surface characters. 
Formation and locality. In the lower part of the Chemung group at Ithaca, 
N. Y. 
Actinopteria eta, n. sp. 
PLATE LXXXIV, PIGS. 8-11. 
Shell of medium size, rhomboidal; body broad and short-ovate, oblique at an 
angle of about 45°; length about one-fourth greater than the height; anterior 
margin below the sinus nearly vertical, curving gradually into the broad 
base; posterior side regularly rounded. 
Left valve regularly convex below, moderately gibbous above. Right 
valve smaller, depressed-convex below, gently convex above. 
Hinge-line straight, length greater than the height of the shell. 
Beak in the left valve sub-anterior, prominent, arching over the hinge; in 
the right valve subdued, scarcely rising above the hinge-line. Umbonal 
region gibbous in the left valve, subtending an acute angle. 
Ear, in the left valve rounded at the extremity, slightly oblique, defined by 
a distinct byssal depression. In the right valve the ear is larger and flat, 
