LAMELLIBRANCHIA TA. 
113 
This form differs from A. subdecussata in the greater and nearly equal 
convexity of the valves, the stronger, rounded rays, and their interruption by 
the concentric lamellae. 
Formation and localities. In the Hamilton group, at numerous places in 
Central and Western New York. 
Actinopteria Boydi. 
PLATE XIX, PIGS. 2-24, 26-30; AND PLATE LXXXIV, FIGS. 16, 17. 
Avicula Boydii, Conrad. Jour. Acad. Nat. Sri., Phila., vol. viii, p. 237, pi. 12, fig. 4. 1842. 
Pterinea Boydi , Conrad. S. A. Miller in Cat. Am. Pal. Foss., p. 201. 1877. 
Avicula quadrula, Conrad. Jour. Acad. Nat. Sci., Phila., vol. viii, p. 243, pi. 13, fig. 5. 1842. 
Actinopteria Boydi, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PL 19, figs. 2-24, 26-30 ; pi. 
23, figs. 5, 6. Jan., 1883. 
Compare Avicula perobliqua', Conrad. Jour. Acad. Nat. Sci., Phila., vol. viii, p. 235, pi. 12, fig. 1. 1842. 
“ “ pleuroptera, Conrad. “ “ “ “ “ p 242, pi. 13, fig. 2. 1842. 
Shell of medium size, rhomboidal; body ovate, 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 and nearly vertical for a short 
distance in front; post-basal side extended. 
Valves convex, the right valve a little less convex than 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. 
Ear 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 
