110 
PALAEONTOLOGY OF NEW YORK. 
Interior unknown. 
Ligamental area with one or two longitudinal grooves. 
The specimen has a length of 18 mm., height 16 mm. 
Formation and locality. In the Marcellus shale at East Bloomfield, Ontario 
county, N. Y. 
Actinopteria subdecussata. 
PLATE XVII, FIGS. 23, 25-27, 29-31; AND PLATE XIX, FIG. 25. 
Pteronites subdecussata, Hall. MS., vol. v. 1877. 
“ “ “ S. A. Miller in Cat. Am. Pal. Foss., p. 202. 1877. 
Actinopteria subdecussata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PL 17, figs. 23, 25- 
27, 29-31 ; pi. 19, fig. 25. Jan., 1883. 
Shell large, sub-rhomboidal, very oblique; body elongate sub-ovate; height 
about one-third less than the length ; margins regularly curved, becoming 
more extended on the posterior side. 
The left valve, in old specimens, has the umbo convex above, depressed- 
convex or flat below, while in young specimens the umbo is altogether con¬ 
vex or gibbous. Right valve moderately convex near the umbo, flat or 
concave below the middle. 
Hinge-line straight, length about one-fifth less than the length of the shell, 
not extending as far as the posterior margin of the left valve, but extending 
beyond the posterior margin of the right valve. 
Beak acute, directed forward, somewhat prominent, anterior nearly 
terminal. Umbonal region (in young shells) well marked by the sulci; 
umbonal angle acute. 
Ear very small, separated by a vertical sulcus. Wing large, triangular, 
defined in young shells by the abrupt convexity of the post-cardinal slope; 
in old specimens not distinctly defined; margin concave; extremity acute. 
The .wing of the right valve is larger, and extends beyond the margin of the 
shell. 
Test comparatively thin, marked with regular, sub-angular, alternating radii, 
the stronger ones extending from the summit of the umbo; a second set interca- 
