454 University of Kansas Geological Survey. 



Inoceramus umbonatus M. & H. Plate lxxxix. 



Tnoceramus umbonatus M. & H., 1858, Proc. Acad. Nat. Sci. Phil., p. 50: 

 Meek, 1876, U. S. Geol. Surv. Terr., vol. ix, p. 41. pi. in, ff. la, b, c, arjd 

 pi. iv, ff. la, b, and 2a and b ; Stanton, 1892, Bull. U. S. Geol. Surv. No. 106, 

 p. 81, pi. xviii, ff. 1 and 2. 



Stanton's revised description : " Shell attaining a rather large 

 size, vertically subovate, extremely inequivalve ; height more 

 than one-third greater than the antero-posterior diameter ; 

 base regularly rounded; hinge and interior unknown. Left 

 valve very convex ; beak greatly elevated, gibbous, strongly and 

 somewhat obliquely involute, so as to form one and a half to 

 two entire turns, the point terminating near the anterior side ; 

 surface unknown, that of internal casts sometimes showing 

 faint traces of concentric undulations. Right valve subcircular, 

 or a little oval transversely, much compressed or nearly flat, ex- 

 cepting in the central or umbonal regions, which are moderately 

 convex; beaks rather oblique, projecting little above the hinge, 

 and but slightly incurved ; surface of an internal cast orna- 

 mented with regular, rather prominent, subangular, concentric 

 undulations, separated by wider rounded depressions. Height 

 of left valve, about 7 inches; antero-posterior diameter, 5.19 

 inches ; convexity, 4.50 inches. Right valve, height, about 

 5.70 inches; antero-posterior diameter, 5.70 inches; convexity, 

 about 1.60 inches." 



This species occurs in the Fort Benton limestone group, but 

 it is not abundant. 



Inoceramus c.roguroides M. & H. Plate lxxxviii. 



Inoceramus exogyroid.es M. & H. 1S62, Proc. Acad. Nat. Sci. Phil., p. 26: 

 Meek. 1876, U. S. Geol. Surv. Terr., vol. ix, p. 46, pi. v, ff. 3a, b, c; Stan- 

 ton, 1892, Bull. U. S. Geol. Surv., p. 83, pi. xvn, ff. 1 and 2. 



Revised description : " Shell medium size, equivalve or nearly 

 so, valves suborbicular, height of the valves being greater than 

 their lengths from the anterior to the posterior side, very gib- 

 bous ; anterior and posterior sides rounded, and forming with 

 the base about three-fourths of a circle, the posterior curve being 

 broader than the other ; cardinal margin comparatively short, 

 and apparently a little arched; beaks large, elevated, gibbous, 

 distinctly incurved and directed obliquely forward, so as to 



