LAMELLIBRANCHIA TA. 
Ill 
lated on the lower part of the umbo, and a third set of smaller rays coming 
in toward the margin. The first and second series only are shown in young- 
shells. In the right valve the radii are more subdued. The rays extend 
over the cardinal expansions of both valves in nearly uniform size. Concen¬ 
tric, elevated, regularly rounded striae of growth cross the rays, and cancel- 
late the surface, and at intervals are crowded together, giving it a lamellose 
aspect. 
Interior unknown. 
Ligamental area marked by one or two parallel grooves. 
A large specimen has a length of 65 mm., height 47 mm., hinge-line 55 
mm. A specimen of medium size has a length of 51 mm., height 35 mm., 
hinge-line 41 mm. A smaller example has a length of 18 mm., height 11 
mm., hinge-line 13 mm. 
This species is similar in form to A. decussata, but differs in the convexity of 
the valves and the less strongly decussated character of the ornamentation, the 
rays being continuous and annulated by the concentric striae, while in that species 
the rays are interrupted by strong concentric lamellae, between which are the 
finer-lines of growth. 
This species is also less abundant and more restricted in geographical range. 
Formation and localities. In the shales of the Hamilton group on the shores of 
Canandaigua lake, and near Bellona, Yates county, N. Y. 
Actinopteria decussata. 
PLATE XVII, FIGS. 24, 2S ; PLATE XVIII, FIGS. 1-15 ; PLATE XX, FIG. 19 ; and PLATE LXXXIV, FIG. 4. 
Avicula decussata , Hall. Geol. Surv. N. Y.: Rep. Fourth Dist., p. 203. 1S43. 
Ptcronites decussata, Hall. S. A. Miller, Cat. Am. Pal. Foss., p 202. 1877. 
Actinopteria decussata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 17, figs. 24, 28; pi. 
18, figs. 1-15. Jan., 1883. 
Shell large, sub-rhomboidal; body sub-ovate, very oblique; length about one- 
fourth greater than the height; margins regularly curving; the anterior 
margin sometimes nearly vertical; posterior margin more abruptly rounded. 
