Lamellibranchiata. 303 



acutely rounded over the post-basal side. Valves very convex. 

 Left valve gibbous in the upper part, angular along the post-cardi- 

 nal slope. Eight valve somewhat less convex. 'Hinge-line straight, 

 about two-thirds the length of the shell. Beak anterior, acute, 

 prominent, inclined forward. Umbonal region gibbous, subtending 

 at an acute angle. Ear a small lobe, defined by a distinct sulcus 

 and shallow, elongate, byssal sinus. Wing large, triangular, limited 

 by the angular post-cardinal slope of the valves; margin moderately 

 concave, sloping forward; extremity angular. 



Test (as seen in the specimen, which is a partial cast of the in- 

 terior) marked by irregular concentric striae, which become fascicu- 

 late on the wing; the surface apparently without rays. Muscular 

 impression large, sub-quadrangular, below the middle of the post- 

 cardinal slope, from which the pallial line, curving downward below 

 the middle of the valve, extends parallel with the margin to the 

 anterior side of the umbo. 



The specimen described has a length of 37 mm., height 24 mm., 

 hinge-line 27 mm. 



This specimen occurs associated with A. Boydi and other allied 

 forms, and is known by the convexity of the valves, the sub-angular 

 character of the posterior slope of the left valve, the great obliquity, 

 the proportions of length and height, and the absence of radii in the 

 cast. 



Formation and locality. In the shales of the Hamilton group, 

 Cazenovia, Madison county, N. Y. 



ACTIKOPTERIA PUSILLA. 

 Actinopteria pusitta, Hall. Pal. N. Y., vol. v. pt. 1. Unpublished. 



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

 height nearly equal; margin for a short distance on the anterior side 

 nearly vertical, broadly rounded along the base and produced on the 

 posterior side. Eight valve convex on the umbo, becoming depressed 

 below the middle of the length. •Left valve unknown. Hinge-line 

 straight, less than the length of the shell. Beak anterior, acute, 

 moderately prominent. Umbonal region scarcely gibbous, subtend- 

 ing an acute angle. "Wing narrow, triangular, elongate, extending 

 nearly to the posterior end of the shell ; margin concave ; extremity 

 abruptly acute. 



Test thin, marked by elevated, sub-imbricating concentric bands, 

 produced by the lamellose character of the striae. Crossing these 

 bands, on the posterior half of the shell, are interrupted radiating 



