108 PALEONTOLOGY OF NEW YORK. 



only one of the genus \i't found in the Schoharie grit. It differs from 

 A. muricata in its aarrower and more oblique bodj and shorter wing, as 

 measured along the post-cardinal slope. 

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



Ac'TINOPTERIA MURICATA. 



PLATE XVII. FIGS. 1-3. 



AviciUa muricata, II.u.l. Geol. Surv. N. Y. : Rep. Fourth Dist.. p. 181. ls-i:l. 



Pteronites muricatus. Hall. Cat. Am. Pal- Fuss.: S. A. Miller, ]>. 202. 1*77. 



.!■'. opteria muricata, Hall. Pal. N. T., vol. v, pt 1. Plates and Explanations : PI. 17, tigs. 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 line to the beak. 



Left valve convex. Flight valve unknown. 



Binge-line straight from the beak to the posterior extremity, sloping 

 downward on the anterior side; entire length greater than that of the body 

 of the shell. 



Beak acute, arching over the hinge, inclined 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: 

 extremity obtuse. Wing flat, triangular, defined by having more subdued 

 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 pre- 

 served specimens, and appear in the casts as elongate elevations upon the 

 rays. The concentric stria' are conspicuous in the anterior sulcus. 



Interior unknown. 



