LOO PALEONTOLOGY OF NEW YORK. 



Pterine.v oonsimilis. 



PJ U'l. \\ !. FIGS. 1. J. 8, 9, II : AND PLATE LXXXIV, BIG. 23. 



Pterinen cimsimilis, Ball. Pal. N. V.. vol. v, | >t . 1. Plates and Explanations: PI. 15, figs. 1. 2, 8, 9, 11. 



Jan., 1883. 



Shell hup', sub-rhomboidal, nearly orbicular; length greater than the height; 

 margins regularly curved, moderately produced on the posterior end. 



Lel't valve convex above, depressed-convex below. Right valve convex on 

 the umbo, Hat or slightly concave below. 



Hinge-line straight, length equal to or a little greater than the length of 

 the valve. 



Beak acute, anterior, inclined slightly forward, not rising above the hinge. 

 Umbonal region prominent but not strongly limited, subtending more than a 

 right angle. 



Ear small, limited by the abrupt slope of the umbo, which becomes a dis- 

 tinct sulcus in the right valve; margin convex (except in the byssal sinus); 

 extremity rounded. Byssal sinus not distinct. Wing broad, triangular, 

 undefined, much extended ; margin concave ; extremity acute. 



Surface of left valve marked by numerous flattened, slender, filiform rays, 

 with broad, flat interspaces, which are marked by one or two, more or less dis- 

 tinct, finer rays. The radii are often undulating, and become obscure towards 

 the base. The cardinal expansions are correspondingly marked. Fine, closely 

 arranged, inconspicuous concentric striae cross the sin-face. The wings of 

 both valves are similar in surface characters. The body of the right valve 

 shows the concentric striae, with obscure indications of rays. 



Ligamental area broad, marked by fine parallel grooves the entire length. 

 Lateral teeth two, strong, converging. Cardinal teeth preserved as three short 

 plications under the beak of the left valve. Pallial line simple, originating 

 anterior to the beak, continuing nearly parallel to the margin of the valve, 

 recurving ami terminating in a large muscular scar on the post-cardinal slope 

 adjacent to the wing. 



A left valve has a length of 52 mm., height 49 mm., hinge-line about 50 



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