116 
PALAEONTOLOGY OF NEW YORK. 
county, is probably from the Hamilton shales at Fultonham; and the only 
species from this locality, answering the description given, is A. Boydii, in 
a condition in which the radii and elevated concentric lamellae are more con¬ 
spicuous than in any specimens from Cazenovia, Hamilton, or any other locality 
in Central New York. 
Formation and localities. In the shales of the Hamilton group; abundant at 
numerous places in the eastern and central portions of the State. 
Actinopteria perobliqua. 
PLATE XIX, FIG. 31; PLATE LXXXIV, FIG. 14. 
Avicula 'perobliqua, Conrad. Jour. Acad. Nat. Sci., Phila., vol. viii, p. 235, pi. 12, fig-. 1. 1842. 
Actinopteria perobliqua, (Conrad) Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PL 19, fig. 31. 
Jan., 1883. 
Shell of medium size, sub-rhomboidal; body very oblique, narrow-ovate; length 
one-third greater than the height; anterior margin truncate or slightly con¬ 
cave ; basal margin regularly arched and acutely rounded over the post-basal 
side. 
Valves very convex. Left valve gibbous in the upper part, angular along 
the post-cardinal slope. Right valve somewhat less convex. 
Hinge-line straight, about two-thirds the length of the shell. 
Beak anterior, acute, prominent, inclined forward. Umbonal region 
gibbous, subtending an acute angle. 
Ear a small lobe, defined by a distinct sulcus and shallow, elongate, byssal 
sinus. Wing large, triangular, limited by the angular post-cardinal slope 
of the valves; margin moderately concave, sloping forward; extremity 
angular. 
Test (as seen in the specimen, which is a partial cast of the interior), 
marked by irregular concentric striae, which become fasciculate on the wing; 
the surface apparently without rays. 
Muscular impression large, sub-quadrangular below the middle of the post¬ 
cardinal slope, from which, the pallial line curving downward below the 
