Lamellibranchiata. 253 



concentric lines of growth. In the right valve the finer radiating 

 lines are conspicuous, while the others are obscure and more 

 numerous. The ears do not show the stronger rays, but usually 

 preserve the finer radiating and concentric lines, and are marked 

 by regular, concentric undulations, which are not seen on the body 

 of the valves. The thickness of the test is not known. 



The hinge-ligament in mature specimens has a width of about 2 

 mm. , and is marked with from four to seven longitudinal, raised 

 lines, or ligamental grooves, diverging from the cartilage-pit, and 

 continuing parallel to the hinge-line ; cartilage-pit small, triangular, 

 placed beneath the beak. 



The largest specimen yet seen, of the left valve, is 80 mm. in 

 height, 88 mm. in length, and the hinge-line 35 mm. ; the distance 

 between the strong rays at the basal margin is 11 mm. A specimen 

 of medium size is 62 mm. in height, 72 mm. in length, hinge-line 

 39 mm. A young individual is 23 mm. in height, 29 mm. in 

 length, and hinge-line 18 mm. 



This species somewhat resembles in outline L. macrodontus, but 

 differs in the surface markings, and the finer parallel teeth of the 

 ligamental area. It differs from L. magnificus, L. interradiatus, 

 and L. cymbalon in outline ; the surface of the latter species is similar, 

 but more rugose. From L. Priamus it differs in form and surface 

 markings. In comparing many specimens a great diversity in form 

 and ornamentation will be observed. 



Formation and localities. In the lower and middle Chemung beds 

 at Barker, Broome county ; Big Flats, Chemung Narrows, and Elmira, 

 Chemung county, and Franklin, Delaware county, N. Y. 



Lyriopecten Polydorus. 



Lyriopecten Polydorus, Hall. Pal. N". Y., vol. v, pt. 1. Plates and Explana- 

 tions : PI. 7, fig. 25. Jan., 1883. 



Shell of medium size ; transversely very broad-obovate ; height 

 nearly equalling the longitudinal diameter ; pallial margins full, 

 regularly rounded on the posterior side; and the anterior side of the 

 left valve passing in nearly a straight line to the beak. Left valve 

 depressed, nearly flat. Right valve unknown. Hinge-line straight, 

 length equal to two-thirds the length of the shell, extending pos- 

 teriorly nearly as far as the posterior margin of the shell. Beak 

 pointed, directed forward, central to the body oi the shell, and 

 forward of the middle of the hinge-line, rising a little above it. 

 Umbonal angle more than 90°. Posterior ear narrow-triangular, 



