50 PALjEONTOLOGY of new YORK. 



mental fjrooves, diverginjj; from the rartiln^c-pit, and contimuu^ parallel to 

 tlu' hinge-line ; cartilage-pit small, triangular, placed heneatli the heak. 



Tiie 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 l)asal margin is 11 nmi. A specimen of medium size is (12 mm. in 

 height, 72 mm. in length, hinge-line 3U iiiiii. A yoimg iiulividual is 2o 

 mm. ill height, 2(1 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 teetli of the ligamental area. It differs 

 fniiu L. magnifictis, L. interradiatus, and L. cymbalon in outline; the surface of 

 the latter species is similar, but more rugose. From L. Priamus it differs in 

 fnriii and surface markings. 



lu 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, ('liemnng county; 

 and Franklin, Delaware county, N. Y. 



Lyiuopecten Polydorus. 



rr.ATK VII, FIG il. 

 Lyriipecteit P'ily:li)riu), ll\LL. I'jil. N. V., vol. \ , jit. 1 l'l;it<'s jiml Rxplanatioiis : I'l. 7, ti;;-. 2"). Jan., 1SS3. 



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

 ling 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 Hat. Right valve unknown. 



Hinge-line straight, length ei|ual to two-thirds the length of the shell, 

 extending posteriorly nearly as far as the posterior margin of the shell. 



Beak pointed, directed fnrwaiil. central to the boil\ of the shell, and 



forward ol" the middle of the liinge-line, rising a little aliove it. I'liil al 



anyle more than '.Ml°. 



