44 PALAEONTOLOGY OF NEW YORK. 



Pterinopeden mborbicularis, in some of the younger specimens, resembles this 

 species in general aspect ; l)ut none of that species have shown a broad, 

 liganiental area, and tlie ears continue to increase witli the growth of the shell. 



Formation and localities. In shales of the Hamilton group at Monteith's 

 Point, Canandaigua lake, Ontario county ; Moscow, Genesee and York, Liv- 

 ingston county ; and in the shale and Encrinal limestone, along Lake Erie 

 shore, Eighteen-Mile creek, Erie county, N. Y. 



Lyriopecten intekradiatus. 



I'LATK II, FIGS. 1-4; and PLATE LXXXII, FIG. 5. 



Lyrivpiiien iiiterradiatits, Hall. Pal. N. Y.. vol. v, jit. 1. PlaU's ami Exiilanations : PI. 2, tigs. 1-4. 



Jan., 1883. 



Shell large, longitudinally very l)roadly elliptical ; transverse axis somewhat 

 oVjliqiie to the hinge-line; height about one-niuth less tliaii tlie length; 

 margins lull and regularly roumlcd. 



\ idves about equal in dimensions. Left valvi- ilepressed, moderately 

 convex. Right valve Hat, or .slightly concave below, becoming convex 

 towards the beak. 



Iliiiv;e-line straiiiht, cfutral to the body oi' the shell: leimtli less than two- 

 thirds the longitudinal diameter of the shell. 



Beak of left valve obtuse, not prominent, directed forward, situated about 

 one-thiid tlie length of the hinge-line from the extremity of the anterior ear. 

 In the right valve the umbo is often flat, and the angle subtended by its 

 sides is acute, caused liy tlie deej) liyssal sinus. 



Posterior ears narrow-triangular, distinguished from the gra<lually sloping 

 sides of the uiiilio by their flatness and finer markings ; margins concave; 

 extremities mucronate. Anterior ear <>{' the left valve .smaller, triangular; 

 margins c(mcave ; extremity rectangular. Anterior ear of the ri;:lit valve 

 convex, triangular, truncated at the extremity; separated tioiii the umbo by 

 a deep angular sulcus, and a broad longitudinal semi-elliptical byssal sinus, 

 which forms an indentation in the lateral outline of the body of the .shell. 



Test of the left valve marked by about 40 strong rounded rays with 



