LAMELLIBRANCHIATA. 41 



shorter, accessory grooves extending for a short distance from the cartilage- 

 pit, and parallel to the longer folds. 



The specimen consists of the exterior and interior impression of a right 

 valve ; it is 38 mm. in height, 43 mm. in length, and the incomplete hinge- 

 line measm'es 20 mm. from the beak to the end of the posterior ear. 



This species differs from L. orbiculatus in its comparatively greater length, 

 the convexity of the right valve, and the regular alternation of the rays. It is 

 remarkable as the only pectenoid form yet observed in the Schoharie grit, 

 while similar forms are numerous in the Upper Helderberg limestone. 



Formation and locality. In the Schoharie grit, Albany county, N. Y. 



Ltriopecten Dardanus. 



PLATE I, FIG. 5. 

 Lyriapedm Dardanus, Hall. Pal. N. Y., vol. v, jit. 1. Plates and Explanations: PI 1, fig. ,'). Jan., 18S3. 



Shell of medium size, orbicular, transverse axis not oblique ; height a little less 

 than the length ; margin regularly rounded. 



Left valve moderately convex. Right valve unknown. 



Hinge-line straight, length nearly equal to the transverse diameter of the 

 valve, extending as far as the posterior margin. 



Beak obtuse, rounded, straight, anterior to the middle of the hinge-line 

 and to the centre of the longitudinal diameter. 



Anterior ear small, narrow-triangular, flat, separated from the umbo by a 

 broad, undefined sulcus ; margin slightly convex above the sinus ; extremity 

 rectangular rounded. Posterior ear large, broad-triangular, flat; margin 

 straight or slightly concave, rectangular to the hinge-line ; extremity mucro- 

 nate. 



Test marked by about forty strong rounded continuous rays with wider 

 concave or fiat interspaces, and sometimes a smaller intermediate ray ; crossed 

 by sharp, elevated concentric striae. The rays are fine and little elevated on 

 the ears, while the concentric striae are conspicuous. 

 6 



