LAMELLIBRANCHIA TA. 
123 
Test thin, in the left valve marked by somewhat distant, elevated, lamellose, 
concentric striae, with intermediate finer lines, and by abruptly elevated 
rounded rays with wider interspaces; these are cancellated by the concentric 
striae, which are more conspicuous on the wing. In the right valve the radi¬ 
ating striae are subdued, and the concentric striae become more conspicuous. 
Interior unknown. 
A specimen of the left valve is 21 mm. in length, 16 mm. in height, and 
hinge-line 14 mm. 
This species differs from A. delta by its narrower form and greater obliquity 
of body. 
Formation and locality. In the lower part of the Chemung group at Ithaca, 
N. Y. 
Actinopteria zeta. 
PLATE XXIII, FIG. 9 ; AND PLATE LXXXIV, FIGS. 1, 2. 
Actinopteria zeta. Hall. Pal. N. Y.-, vol. v, pt. 1. Plates and'Explanations : PI. 23, fig. 9. Jan., 1883. 
Shell large, rhomboid-orbicular; body broadly ovate, nearly erect; height greater 
than the length; auricular margin rounded into the byssal sinus; below the 
sinus the margin is nearly vertical and gradually joining the broad basal 
curvature; posterior end regularly rounded. 
Left valve gently convex below, moderately gibbous above. Right valve 
flat or concave below, depressed-convex above. 
Hinge-line straight, much longer than the greatest length of the valve. 
Beak in the left valve sub-anterior, elevated, curving over the hinge; in 
the right valve depressed, not rising above the hinge-line. Umbonal region 
subtending nearly a right angle. 
Ear small, rounded at the extremity, defined by a strongly marked byssal 
depression. Wing large, joining the body below the middle, not strongly 
defined; margin deeply concave in the middle; extremity produced into an 
acute extension. 
Surface marked by strong, elevated, regular, distant, lamelliform, concentric 
