80 PALAEONTOLOGY OF NEW YORK'. 



Formation and }ocalilie.s. In tlie shales of the Chemung group, Angelieu and 

 PliiHpshurg, Alleghany county, N. Y. 



Pterixopecten suborbicularis. 



I'LATK Vin, KlliS. 1, 2; PLATE XXIV, FIG. 10; ani> PLATE LXXXII, FIG. 6. 



PUrintn! yiiUirlniiilarix, Hall. Geolog'. Surv. N. Y. : Rep. Fourth Dist., p. 264. 1843. 

 Pttrinuptctfu sulxirhiciUarui, Hall. Pal. N. Y., vol. v, pt. 1. Plates ami Exjilanations : PI. 8, figs. 1, 2 ; 



1)1. 24, fig. 10. Jan., 18,S3. 



Shell large, rhomboid-orbicular, slightly oblique ; length a little greater than 

 the height, or sometimes equal ; pallial margins regularly curved, less con- 

 vex on the pojsterior side; post-ba.'jal margin extended. 



Left valve convex. Right valve nearly tlat ; similar in general form and 

 surface markings. 



Hinge-line straight, anterior, nearly equal ix> the length of the shell. 



Beak obtuse, broad, rounded, somewhat depressed, directed slightly 

 forward ; a little anterior to the centre of the hinge. Umbonal region 

 expanded, subtending an obtuse angle. 



Ears triangular, unequal ; extremities angular. Posterior ear tlic larger, 

 undefined ; margin concave. Anterior ear limited b}' an obscure sulcus. 

 Byssal sinus shallow in the left valve, deep and angular in the right valve. 



Surface marked by numerous regular, rounded or sub-angular radii, which 

 increase on the left valve by intercalation, and on the right valve by bifur- 

 cation ; interspaces nearly equalling the rays. On the posterior ear the 

 rays are finer, and over the body of the shell they are strongly crenulated 

 by lamellose concentric striae. 



Internal characters unknown. The ligamental area is a simple linear 

 groove. 



A large specimen measures 63 mm. in length, 55 mm. in height, the hinge- 

 line 55 mm. Another one is .SS nun. in length, .35 mm. in height, with 

 hinge-line .35 mm. 



This .species is distinguished by its sulj-orbicular form, slight obliquity, nearly 

 e<|ual length and height, ami comparativt'ly short hinge-line. 



