Lamellibranchiata. 337 



side sometimes nearly straight for a short distance below the ear. 

 Left valve convex, gibbous on the umbo. Right valve less gibbous. 

 The right valve supposed to belong to this species is convex on the 

 umbo, and of moderate convexity below; the height is considerably 

 greater than the length, and the body of the valve less distinctly 

 defined than in the left valve. Hinge-line straight ; from the 

 anterior side of the beak to the posterior extremity it is about equal 

 to the length of the shell. Beak of the left valve acute, directed 

 forward, very prominent, situated at the anterior extremity of the 

 shell. Umbonal region gibbous, subtending an acute angle. Ear 

 short, convex, obtuse, with a broad, undefined, vertical sulcus and 

 shallow byssal sinus. Wing moderately large, flat ; margin concave ; 

 extremity acute. 



Test thin, marked by regular, concentric lines of growth, which 

 are more crowded upon the cardinal expansions. The striae are 

 raised at intervals into strong, elevated lamellae, which are con- 

 spicuous on the cast, and more crowded and prominent on the an- 

 terior side. The right valve referred to this species is marked by 

 concentric wrinkles, which are well-preserved on the anterior side, 

 with distant, elevated, lamellose strias on the wing and margin of 

 the hinge. Internal characters unknown. The ligamental area ap- 

 pears to be marked by a groove along the wing parallel to the 

 hinge-line. 



Three characteristic specimens have respectively the following 

 dimensions : length, 39, 34, and 25 mm., height 41, 38, and 26 mm., 

 hinge-line 37, 39 and 26 mm. The right valve, mentioned above, is 

 23 mm. in length, 25 mm. in height, and 23 mm. along the hinge- 

 line. 



This species resembles the two preceding, but the form of body is 

 more narrowly ovate, the obliquity appears to be intermediate between 

 the two ; the ear is less strongly defined ; the wing is comparatively 

 narrower, and less extended at the extremity. 



Formation and localities. In the shales of the Hamilton group, on 

 the shores of Skaneateles lake ; at Bellona, Yates county, and Leonards- 

 ville, Madison county, N. Y. ; a single specimen from the Corniferous 

 limestone of Delaware, Ohio, has been referred to this species. 



Leiopteria Sayi. 

 Leiopteria Sayi, Hall. Pal. N. Y. vol. v, pt. 1. Unpublished. 



Shell above the medium size, sub-orbicular; body very broadly ovate, 

 scarcely oblique; height greater than the length; margin nearly 

 straight in front, thence regularly rounded. Left valve very con- 

 [Sen. Doc. No. 38.] 43 



