JUEASSIC FOSSILS. . 349 



Missouri, p. 75, Figs. A-E, as the normal forms of their G. calceola var. 

 nebracensis, with which opinion we entirely agree. We have examined a 

 large number of individuals from several widely-separate localities, and 

 also masses of rock composed almost entirely of the shells, but find no 

 specimens among them having the characters of the genus Grypliaa, or 

 with the specific features ascribed to the var nebracensis. 



Formation and locality. — In rocks of Jurassic age, at a horizon of 350 

 feet above the red beds referred to the Triassic, east of the Belle Fourche 

 River ; also at an elevation of 300 feet at the same place, and at an eleva- 

 tion of 20 feet above the same horizon at the Belle Fourche; also at Sun 

 Dance Hill and near Beaver Creek, Black Hills. The localities near the 

 Belle Fourche are nearly opposite Bear Lodge Butte. 



Genus GRYPH^A Lam. 



OEYPHl^A CALCEOLA var. NEBEASCENSIS. 



Plate 3, figs. 13-16. 



Gryphcea calceola var. nebracensis M. & H., Proc. Acad. Nat. Sci. Phil., Dec. 1861, p. 437. 

 Gryphcea calceola nebracensis M. & H„ Pal. Upp. Missouri, pp. 74 and 75, figs. A-E. 



Shells of moderate size, very inequivalve, and but slightly oblique; 

 lower valve the largest, somewhat ovate in outline, strongly arcuate, and 

 showing a tendency to trilobation in the lower part of the larger individ- 

 uals; beak strong, incurved, and sometimes enrolled, but not truncated at 

 the apex by any cicatrix of attachment, its substance much thickened by 

 the solidifying or filling up of the rostral portion of the valve. Anterior 

 side of the valve rather rapidly spreading for some distance from the beak, 

 and below rounding abruptly to the narrow basal border; posterior side of 

 the valve less expanded above, but often more so below, and distinctly lobed 

 by a sulcus which marks the exterior from a little below the beak to the 

 postero-basal border, which is in consequence sometimes strongly emargi- 

 nate; ligamental area of moderate size, triangular, and concave; muscular 

 impressions not very large and rather faintly marked, elongate-paraboloid 

 or truncate-ovate, and situated behind the middle of the shell. "Upper 

 valve ovate, nearly flat on the outside, or a little convex near the beaks,' 



