LAMELLIBRANCHIA TA. 
37 
Aviculopecten ornatus. 
PLATE II, FIGS 7, 8; and PLATE III, FIG. 14. 
Aviculopecten ornatus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 2, fig-s. 7, 8; pi. 3, 
fig. 14. Jan., 1883. 
Shell small, longitudinally oblique-ovate, sub-rhomboidal; length and width in 
the proportion of three to four; margins regularly rounded. 
Valves depressed-convex; left valve somewhat more convex than the 
right, and a little larger. 
Hinge-line straight, slightly less than the length of the shell, central with 
regard to the body of the shell. 
B.eak obtuse-angular, directed forward, situated a little anterior to the 
middle. 
Ears sub-equal. Posterior one the larger, triangular, fiat or concave, 
defined by the abrupt post cardinal slope of the umbo; extremity acute; 
margin concave. Anterior ear defined by a deep sulcus; byssal sinus deep, 
more strongly marked in the right valve. 
Test of the left valve ornamented by about 25 strong, sharp, elevated rays, 
and wide interspaces which are marked with a smaller ray; crossed by 
undulating, concentric striae which are curved backwards between the 
stronger rays, producing arched fimbriae. The right valve shows the 
radiating striae originating near the umbo, which is smooth, and increasing 
by a double bifurcation, giving them a fasciculate appearance; they are 
crossed by undulating, concentric striae. The ears are marked by strong, 
radiating lines and fine, concentric striae. 
Internal characters not observed. 
The length of the largest specimen is 18 mm., height nearly 15 rnm., 
and hinge-line about 17 mm. 
This species, in form and general appearance, is very similar to A. bellus ; it 
differs conspicuously in the ornamentation, with proportionally shorter posterior 
