4G PALJEONTOLOGY OF NEW YORK. 



Lyriopkcten macrouontus. 



IT.ATK IV. Fit;. ;p; AXii PI.ATK VIII, FIGS. 9, 10. 



Li/rii'jiftteH viaemdiml lui. IIai.i.. Cut. Piila-ozoii: Fossils. S. A. MrLLKR. Cincinnati. 1S77. 



Pill. N. Y., vol. V, i)t. 1. Plates anil Exi.Ianatidns : I'l. 4. lifr. !l ; ].l. 8, 

 tip<. 9, 10. Jan., 1883. 



Shell liir<cc, siili-chculiii- ; in isoine large specimens becoming tran.sversely broatl- 

 ovato, t'nmi tlie posterior extension of the \alvv; height I'nuii one-sixth to 

 one-eighth less than the Icngtli ; margins regularly idiiiidcd. more convex at 

 the j)(i>tt riiir jati'ial margin, ami (■xtcnding 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, ronndetl. directed slightly toward the anterior, not rising 

 above the hinge. 



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

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

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

 and liv a shallow, nndtdined depression reaching to the beak; margin deeply 

 sinuate ; extremity acuminate. 



Surface marked l)y from 30 to 40 broad, rounded radii, with usually 

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

 of shell, nflhering 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 bene.ath the apex of the beak, not extending to the hinge margin. 

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

 outward at the beak, diverging from, and ]>artially enclosing, the cartilage- 

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

 disappear before reaching the extremity of the area. 



'file largest specimen is S-"") mm. liigh, !tS mm. long, and tlie liiuge-line 

 50 mm. Another specimen, somewhat diflerent in |ir(i|i(irtions, is liS mm. in 

 hei'_dit. 7-') mm. loni:'. with irnu:c-line of 40 mm. 



