118 
PALAEONTOLOGY OF NEW YORK. 
Right valve convex on the umbo, becoming depressed below the middle of 
the length. Left valve unknown. 
Hinge-line straight, less than the length of the shell. 
Beak anterior, acute, moderately prominent. Umbonal region scarcely 
gibbous, subtending an acute angle. 
Wing narrow, triangular, elongate, extending nearly to the posterior end 
of the shell; margin concave; extremity abruptly acute. 
Test thin, marked by elevated, sub-imbricating concentric bands, produced 
by The lamellose character of the strise. Crossing these bands, on the 
posterior half of the shell, are interrupted radiating lines, which indicate the 
presence of radii upon the original surface. The wing is marked in a 
similar manner by strong bands, which pass over the hinge-margin, and it 
also shows two or three interrupted radiating lines, like those On the poste¬ 
rior part of the body of the shell. 
Interior unknown. 
The specimen described has a length of 11 min., height 12 mm., and 
hinge-line 10 mm. 
This species is allied to A. decussata and A. Boydi, having the wing charac¬ 
teristic of the former; but it is a proportionally shorter form, and the 
surface markings are quite unlike the right valve of any of the forms at present 
known. 
Formation and locality. In shales of the Hamilton group, on the shores of 
Canandaigua lake, N. Y. 
Actinopteria perstrialis. 
P LA TE XXIII, FIGS. 2, 7; AND PLATE LXXXIV, FIG. 12. 
Actinopteria perstrialis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 23, fig’s. 2,7. 
Jan., 18S3. 
Shell small, sub-rhomboidal; body sub-ovate, axis slightly curved and oblique 
at an angle of about 45° with the hinge; height about three-fourths the 
length of the body; basal margin broadly rounded; posterior margin abruptly 
curved. 
