118 PALEONTOLOGY OF NEW YORK. 



Right 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, subtending 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 hands, produced 

 li\ the lamellose character of the striae. Grossing these hands, on the 

 posterior half of the shell, are interrupted radiating lines, which indicate the 

 presence of radii upon the original surface. The wing is marked in a 

 similar manner by strong hands, which pass over the hinge-margin, and it 

 also shows two or three interrupted radiating lines, like those on the poste- 

 rior part of the body of the shell. 



Interior unknown. 



The specimen described has a length of 11 mm., height 12 mm., and 

 hinge-line Hi mm. 



This species is allied to A. decussata and A. Bnydi, having the wing charac- 

 teristic of the former; but it is a proportionally shorter form, and the 

 surface markings are quite unlike the right valve of any of the forms at present 

 known. 



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

 Canandaigua lake, N. Y. 



- 



A.CTIN0PTERL4 PERSTRIALI8. 

 PLATE .Will, FIGS. -'. 7: AND PLATE I.XXXIV, FIG. 12. 



Actinopteria pertttrialis, Hall. Pal. N. V.. vol. v, pt. 1. Plates ami Explanations: PI. 23, figs. -.'. 



Jan., iss:{. 



Shell small, sub-rhomboidal ; body sub-ovate, axis slightly curved and oblique 



at an angle of about 45° with the hinge; height about three-fourths the 

 length of the body : basal margin broadly rounded; posterior margin abruptly 

 curved. 



