240 PALEONTOLOGY OF NEW YORK. 



PAL7EOPINNA, Hall. 

 Pal^opinna flabella. 



PLATE XXV, FIG. 18; am. PLATE I.XXXVII, FIG. i. 



PalcBopinna 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. 

 Right 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 striie of growth which are cancel- 

 lated by fine sub-equal radii ; in the cast the concentric and radiating striae 

 are of nearly equal strength. f)n the anterior end the radii are obscure or 

 obsolete as preserved in the cast, 



Liga mental area narrow, marked by a single longitudinal groove and a 

 slight oblique furrow extending backward from the beak a little more than 

 bne-third the length of the hinge. 



The left valve described has a length along the hinge-line of SO mm., 

 height Ml mm.: measured along the axis of the body the length is about 70 

 nun., and the anterior truncation is 25 mm. long. 



