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PALAEONTOLOGY OF NEW YORK. 
P ALiEOPINN A, Hall. 
PALiEOPINNA flabella. 
PLATE XXV, FIG. 18; AND PLATE LXXXVII, FIG. 4. 
Palceopinna flabella, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 25, fig. 18. 
Jan., 1883. 
Shell large, broadly semi-ovate, gaping at the anterior extremity; axis oblique 
to the hinge at an angle of about 30°; length nearly twice the height; 
byssal margin abruptly truncate; ventral margin very broadly curving; 
posterior margin oblique, sub-truncate. 
Left valve depressed-convex in the posterior and ventral portions, 
becoming more convex above and moderately gibbous in the umbonal region. 
Eight valve unknown. 
Hinge-line straight, equalling the greatest length of the shell. 
Beak anterior, terminal, prominent, directed forward, scarcely rising above 
the cardinal line. Umbonal region subtending an acute angle. 
Anterior end abruptly truncate; margin excavate. Wing continuous with 
the body of the shell without limitation or interruption; margin directed 
backward, nearly straight, continuous with the post-basal margin of the 
body; extremity abruptly rounded. 
Test thin, marked by regular concentric striae of growth which are cancel¬ 
lated by fine sub-equal radii; in the cast the concentric and radiating striae 
are of nearly equal strength. On the anterior end the radii are obscure or 
obsolete as preserved in the cast. 
Ligamental area narrow, marked by a single longitudinal groove and a 
slight oblique furrow extending backward from the beak a little more than 
one-third the length of the hinge. 
The left valve described has a length along the hinge-line of 80 mm., 
height 40 mm.; measured along the axis of the body the length is about 70 
mm., and the anterior truncation is 25 mm. long. 
