240 PALEONTOLOGY OF NEW YORK. 



PALyEOPINNA, Hall. 

 Pal^opinna flabella. 



PLATE XXV, FIG. 18; AND PLATK LXXXVII, KICJ. 4. 



Palcuyp'mna flabella, Hall. PjiI. N. Y., vol. v, pt. 1. Plates and Exi>lanations : 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 oI)lique, sub-truncate. 



Left valve depressed-convex in the posterior and ventral portions, 

 becomiuE: more convex above and moderatelv gibl)ous in the umbonal re<ri()n. 

 Right valve unknown. 



Hinge-line straight, e({ualliiig the greatest length of the shell. 



Beak antei'ior, 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, ^n 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 tlu' hinge-line of 80 nnii., 

 height 40 mm. ; measured along the axis of the body the length is about 70 

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



