LAMELLIBRANCHIATA. 51 



Posterior ear narrow-triangular, one-third longer than the anterior, 

 the limits not well-defined, and it appears as an expansion or extension of 

 the posterior side of the umbo ; margin concave ; extremity mucronate. 

 Anterior ear short-triangular ; margin convex ; extremity rounded, separated 

 from the umljo by a deep, rounded sulcus, which corresponds to the byssal 

 sinus. 



Test ornamented by about 25 irregular, strong, rounded rays, with wider 

 interspaces, marked by two or three smaller lines in each one, and crossed 

 by fine strias of growth. The surface markings extend over the ears. 



Interior not observed. 



The valve described is 28 mm. high, and of about the same length, and 

 the hinge-line 18 mm. The length of the posterior ear is 11 mm., and of 

 the anterior ear 7 mm. 



This species bears some resemblance to L. solox, but differs in the flatness of 

 the valve and less gibbous umbo. In surface character it is similar to L. 

 tricostatus, but has fewer intermediate striae between the stronger rays, which 

 in that species are more simple and rounded ; while in other characteristics 

 they are very unlike. 



Formation and locality. In argillo-arenaceous slates of the Chemung group 

 near Cassadaga, Chautauqua county, N. Y. 



Lyriopecten magnificus. 



PLATE Vni, FIG. S. 

 Lyrhipecteii magnifies, Hall. P;il. N. V., vol. v, pt. 1. Plates and Exiilaiiations: PI. 8, tig. S. Jan., 1S83. 



Shell very large, nearly circular ; height a little less than the longitudinal 

 diameter ; basal and lateral margins regularly rounded. 



Left valve nearly flat ; the greatest convexity is in the centre of the umbo- 

 nal region. Right valve unknown. 



Hinge-line short, straight, length less than one-half the transverse diameter 



