44 PALAEONTOLOGY OF NEW YORK. 



Pterinopecten suborbicalaris, in some of the younger specimens, resembles this 

 species in general aspect ; hut none of that species have shown a broad, 

 ligamental area, and the ears continue to increase with the growth of the shell. 



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

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

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

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



Lyriopecten interradiatus. 



I'LATE II, FIGS. 1-4 ; AND l'LATE I. XXXII, FIG. 5. 



Lyriopecten interradiatus, Hall. Pal. N. Y., vol. v, jit. 1. Plates and Explanations: PI. 2, fijp^. 1-1. 



Jan., 1883. 



Shell large, longitudinally very broadly elliptical ; transverse axis somewhat 

 oblique to the hinge-line; height about one-ninth less than the length; 

 margins lull and regularly rounded. 



Valves about equal in dimensions. Left valve depressed, moderately 

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

 towards the beak. 



Hinge-line straight, central to the body of the shell; length less than two- 

 thirds the longitudinal diameter of the shell. 



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

 one-third the 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 by the deep byssal sinus. 



Posterior ears narrow-triangular, distinguished from the gradually sloping- 

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

 extremities mucronate. Anterior ear of the left valve smaller, triangular; 

 margins concave; extremity rectangular. Anterior ear of the right valve 

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

 a deej) 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 



