270 Thirty-fifth Report ok the State Museum. 



strength, and crenulated by the concentric striae. On the right 

 valve the rays are'more equal and finer than on the opposite valve; 

 conspicuous on the posterior ears and subdued on the anterior, 



Three specimens have respectively the following dimensions: 

 length 38, 40 and 41 mm., height 30, 33 and 29 mm., hinge-line 35, 

 35 and 32 mm. 



This species resembles Pterinea reprooa, from the shales of the 

 Chemung group at Ithaca, which has straighter and more rounded 

 radii in the left valve, with sharper intermediate radii and more ele- 

 vated, undulating, concentric strias. The right valve of that species 

 is more convex with stronger and often duplicating radii ; while the 

 byssal sinus is less distinctly marked. The present species differs 

 from Pterinopecten dispandas in its greater length, proportionally 

 longer hinge-line, less strongly marked right valve, and want of dupli- 

 cation in the radii. 



Formation and locality. This species is common in the shales of the 

 Hamilton group at Bear gulf, Schoharie county, N. Y. 



Pterinopectek undosus. 



Aviculopecten undulatus, Hall. MS. 1877. 



S. A. Miller. Cat. Amer. Pal. Foss. 1877. 



Not Pecten undulatus, McCoy. Carb. Foss. of Ireland, p. 101, pi. xvii, fig. 12. 

 1844. 



Not Aviculopecten undulatus, McCoy. 1853. 



Pterinopecten undosus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explana- 

 tions: PI. 2, figs. 10-19. Jan., 1883. 



Shell larger than medium, rhomboidal or sub-orbicular ; left valve 

 moderately oblique; right valve scarcely oblique; length one-third 

 greater than the height, proportionally shorter in young shells and 

 in the right valve ; anterior and basal margins regularly rounded, 

 somewhat produced behind, and receding rapidly toward the hinge- 

 line. Valves nearly equally convex ; the right valve a little less 

 convex, more orbicular in outline, with deep byssal notch, and dif- 

 ferent surface markings. When occurring in the softer shales, the 

 valves are often depressed-convex. Hinge-line straight, length a 

 little less than the height of the shell, nearly central. Beak obtuse, 

 rounded, scarcely rising above the hinge-line, anterior to the middle 

 of the shell, inclined forward. Umbonal region ample, well-defined, 

 subtending a very obtuse angle. Ears sub-equal, triangular ; 

 margins concave. Anterior ear limited by a sulcus and shal- 



