Lamellibeanchiata. 307 



near the posterior extremity, not strongly defined ; margin gently 

 concave ; extremity produced. 



Test marked by fine concentric striae, and undulating or inter- 

 rupted filiform radiations, with wider interspaces, which have prob- 

 ably been marked by finer intermediate striae. The concentric lines 

 are obscure in the cast and appear as a few irregular concentric 

 undulations. 



The specimen is 23 mm. in length, 15 mm. in height, hinge-line 16 

 mm. 



Formation and locality. In the lower part of the Chemung group at 

 Ithaca, N. Y. 



ACTLNOPTERIA EPSILON. 



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

 tions : PI. 23, figs. 4, 8. Jan.. 1883. 



Shell of medium size, rhomboidal ; body ovate, oblique to the axis 

 at an angle of about 60° ; height about three-fourths the length ; 

 anterior margin rounded into a very abrupt sinus; base broadly 

 curved ; post-basal side abruptly rounded. Left valve moderately 

 convex. Right valve depressed-convex above, flat or concave below. 

 Hinge-line straight, length somewhat less than the height of the 

 valve. Beaks anterior, acute in the left valve ; prominent and 

 elevated above the hinge. Umbonal region gibbous, subtending an 

 angle of less than 60°. Ear short, defined by a deep, abrupt byssal 

 depression. Wing triangular, joining the body below the middle, 

 not strongly defined ; margin regularly concave ; extremity acute 

 and produced. 



Test thin, in the left valve marked by somewhat distant, elevated, 

 lamellose, concentric striae, with intermediate finer lines, and by 

 abruptly elevated rounded rays with wider interspaces ; these are 

 cancellated by the concentric striae, which are more conspicuous on 

 the wing. In the right valve the radiating striae are subdued, and 

 the concentric striae become more conspicuous. 



A specimen of the left valve is 21 mm, in length, 16 mm. in 

 height, and hinge-line 14 mm. 



This species differs from A. delta by its narrower form and greater 

 obliquity of body. 



Formation and locality. In the lower part of the Chemung group 

 at Ithaca, 1ST. Y. 



