LAMELLIBRANCHIATA. 55 



the exterior, is 63 mm. in height, 57 mm. in longitudinal diameter, aud 

 hinge-line about 31 mm. 



In general appearance of surface this shell is similar to L. macrodontus, but 

 the details are quite different. 



This species, though characterized from the left valve only, is distinctly 

 different from the others in form and surface ornamentation. 



Formation and locality. Associated with numerous segments of crinoidal 

 columns, and rarely with any other fossils, in the upper part of the Chemung 

 group, at Franklin, Delaware county, N. Y. 



Lyriopecten fasciatus. 



PLATE IX, FIGS. 10, 11. 



Permipeclen fasciculaUis, Hall. MS., vol. v, pt. 1. 1877. 



" " " Catalogue Amer. Palaeozoic Fossils, Miller, p. 200. 1877. 



Not Aviculiypecteu fascietilatus. Hall. 



Lyriopecten fasr-iatufi. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 9, tigs. 10, 11. 



Jan., 1883. 



Shell of medium size, very broadly ovate, erect ; length a little less than the 

 width ; margins regularly rounded. 



Right valve convex, the greatest convexity one-third the width of the 

 valve from the beak. Left valve unknown. 



Hinge-line short, straight. 



Beak acute, erect, prominent ; umbonal region distinctly defined, sub- 

 tending a right angle. 



Anterior ear small, sctircely defined, about half the length of the posterior 

 one. Posterior ear triangular, defined by a well-marked sulcus ; margin 

 nearly straight ; extremity obtuse. Byssal sinus shallow. 



Surface ornamented by strong, low, broad, rounded radii, which increase 

 by interstitial addition ; and numerous sharp, elevated, radiating striae mark 

 the surfaces of the rays, giving them a distinctly fasciculated aspect. These 

 also mark the interspaces, which are narrower than the large rays. Sharp, 

 regular, concentric striae cancellate the radii. The ears are marked only by 

 the concentric striae, which are less prominent than on the body of the valve. 



