LAMELLIBRANCHIATA. 113 



This form differs from A. subdecussata in the greater and nearly equal 

 convexity of the valves, the stronger, rounded rays, and their interruption hv 

 the concentric lamellae. 



Forination and localities. In the Hamilton group, at numerous places in 

 Central and Western New York. 



ACTINOPTERIA BoYDI. 



PLATE XIX, FIGS 2-24, ■26-.30 ; AND PLATE LXXXIV, FIGS. 16, 17. 



AiHciila Boydil, Conrad. Jour. Aciul. Nat. 8'-i., Pliila., vol. viii, ji. 237, pi. 12, tig-. 4. 1S42. 



PUi-inea Boydi, Conkad. S. A. Miller in Cat. Am. Pal. Fo.ss., p. 201. 1877. 



Avicula quadrala, Conkad. Jour. Acail. Nat. Sci., Phila., vol. viii, p. 243, pi. 13, tig. 5. 1842. 



Aetlnoptena Boydi, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 19, figs. 2-24, 2(i-30 ; pi. 



23, fig-s. 5. B. Jan., 1883. 

 Compare Avinda pKrohliqiia, Conhad. Jour. Acail. Nat. Sci., I'liila., vol. viii, p. 235, pi. 12, tig-. 1. 1842. 

 " " plfumptrra. Conr.^d. " •• •■  •• p 242. pi. 13. tig-. 2. 1842. 



Shell of metHuni size, I'lioiiilioidid ; body ovtite, varying in proportions, the 

 longitudinal axis at an angle with the hinge-line of from 45° to 60° ; 

 length varying from nearly equal to one-fourth greater than the height ; 

 margins regularly rounded below, straight aixl nearly vertical for a short 

 distance in front; post-basal side extended. 



Valves convex, the right valve a little less convex tliaii the left. 



Hinge-line straight from the anterior side of the beak to the posterior 

 extremity. 



Beak anterior, acute, prominent, inclined forward, rising above the hinge 

 in the left valve. Umbonal region prominent, subtending an acute angle. 



Eiir short, oblique, limited by a deep but not sharply defined sulcus. Wing 

 large, triangular, not distinctly separated from the body of the shell ; margin 

 concave; extremity acute. In the right valve the ear is somewhat more 

 extended, the sulcus not strong, but the byssal sinus is marked ; the wing 

 is proportionally larger and usually more acute at the extremity. 



Test thick ; the left valve, in well-preserved specimens, is marked by 

 numerous strong, simple, sharp rays, which are continuous from the umbo to 

 15 



