46 PALEONTOLOGY OF NEW YORK. 



Lyriopecten macrodontus. 



PLATE IV, ETC. 9; and PLATE VIII, BIGS. », 10. 



Lyriopecten macrortontvs, Ham.. Cat. Palaeozoic Fossils. S. A. Mii.i.kk. Cincinnati. 1877. 



Pal. N. Y., vol. v. pt. 1. Plates and Explanations: PI. 4. i\g. !l ; pi. 8, 

 figs. 9, 10. Jan., 1883. 



Shell large, sub-circular ; in some large specimens becoming transversely broad- 

 ovate, from the posterior extension of the valve ; height from one-sixth to 

 one-eighth less than the length ; margins regularly rounded, more convex at 

 the posterior lateral margin, and extending in nearly a straight line to the 

 beak. 



Left valve depressed, moderately convex. Right valve unknown. 



Hinge-line straight, nearly central, varying in length with the age of the shell. 



Beak obtuse, rounded, directed slightly toward the anterior, not rising 

 above the hinge. 



Anterior ear small, about one-third the length of the posterior, triangular, 

 not well-defined ; margin straight or slightly concave ; extremity obtuse. 

 Posterior ear large, triangular, defined by the absence of the strong radii, 

 ami by a shallow, undefined depression reaching to the beak ; margin deeply 

 sinuate ; extremity acuminate. 



Surface marked by from 30 to 40 broad, rounded radii, with usually 

 smaller intermediate rays, crossed by fine stria? of growth. Some fragments 

 of shell, adhering to the internal mould, have a thickness of one millimeter. 



Muscular impression large, sub-circular, concentrically striated, situated 

 posterior to, and below the umbonal region. Cartilage-pit very small, trian- 

 gular beneath the apex of the beak, not extending to the hinge margin. 

 Ligamental area usually marked by live strong, elevated ridges, which curve 

 outward at the beak, diverging from, and partially enclosing, the cartilage- 

 pit, and continuing toward the extremities of the ears; the innermost ridges 

 disappear before reaching the extremity of the area. 



The largest specimen is 85 mm. high, 98 mm. long, and the binge-line 

 50 mm. Another specimen, somewhat different in proportions, is 68 mm. in 

 height. 7-") mm. long, with hinge-line of 40 mm. 



