Lamellibranchiata. 29? 



The specimen described has a length of 20 mm., and height of 14 

 mm. 



The characters of form and surface ornamentation are very char- 

 acteristic, and the species is important as being the only one of the 

 genus yet found in the Schoharie grit. It differs from A. muricata 

 m its narrower and more oblique body and shorter wing, as measured 

 along the post-cardinal slope. 



Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 



ACTINOPTERIA MURICATA. 



Amcula muricata, Hall. Geolog. Surv. N. Y.: Rep. Fourth Dist., p. 181. 1843. 

 Pteronites muricatus, Hall. S. A. Miller. Cat. Amer. Pal. Foss, p. 202. 1877. 

 Actinopteria muricata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explana- 

 tions; PI. 17, figs. 1-3. Jan., 1883. 



Shell small, sub-rhomboidal ; body sub-ovate, very oblique; length 

 one-third greater than the height ; margin rounded below, turning 

 abruptly backward on the posterior side, and extending in a direct 

 liue to the beak. Left valve convex. Eight valve unknown. 

 Hinge-line straight from the beak to the posterior extremity, slop- 

 ing downward on the anterior side ; entire length greater than that 

 of the body of the shell. Beak acute, arching over the hinge, in- 

 clined forward, situated at the anterior third of the hinge-line. 

 Umbonal region subtending an acute angle. Ear broad-triangular, 

 separated from the body of the shell by a broad undefined sulcus 

 which is limited by a strong sub-angular fold extending from the 

 beak, and by the deep rounded byssal sinus; margin convex; ex- 

 tremity obtuse. Wing flat, triangular, defined by having more sub- 

 dued surface rays; margin deeply sinuate ; extremity mucronate. 



Test thin, marked with from eight to twelve strong filiform rays, 

 with finer intermediate ones in the broad, flat interspaces. The 

 rays on the wing are somewhat subdued. Surface crossed by fine 

 concentric lines of growth, which, at intervals, are crowded and 

 raised into lamellae, and on the rays are produced into tubular 

 spines. These spines are seen only in the better preserved speci- 

 mens, and appear in the casts as elongate elevations upon the rays. 

 The concentric striae are conspicuous in the anterior sulcus. Liga- 

 mental area grooved. 



The largest specimen has an entire length of 16 mm., height 10 

 mm., hinge-line, to the imperfect posterior extremity, 12 mm. A 

 smaller specimen has an entire length of 14 mm., height 9 mm., 



[Sen. Doc. No. 38.] 38 



