Logan.] The Invertebrates, Benton Group. 445 



imbedded in the matrix, with the beak side down, they look 

 like short, cylindrical tubes, with one end abruptly truncated 

 and closed by the flat surface of attachment ; so that what was 

 originally the whole under surface of the valve, now appears 

 like the truncated umbo. The other valve is quite flat, or some- 

 times a little concave, and always retains the form possessed 

 by the attached valve at the time its margin became deflected 

 upward, after which it seems to have increased very little in 

 size. Its umbo is usually a little less pointed than that of the 

 other valve, and provided with a shorter area, on each side of 

 which its margins are sometimes slightly crenulated. The 

 muscular impressions of each valve are obscure, and the face 

 is nearly smooth, or only marked by fine, indistinct lines of 

 growth." 



These shells occur abundantly in the Ostrea beds of the Fort 

 Benton area. So abundant are they that the shale thrown from 

 the wells which pierce the Ostrea beds, after a short weathering, 

 is almost white with them. They may be collected from the 

 Ostrea beds exposures along the Smoky Hill, the Saline and 

 the Solomon rivers, and from numerous smaller streams in the 

 Upper Cretaceous area. 



Ostrea lugubris Conrad. Plate xci. 



Ostrea lugubris Conrad, 1857, U. S. and Mex. Bound. Rep., vol. i, p. 156, 



pi. x, ff. 5a, b; Meek, 1876, Macomb's Expl. Exped. from Santa Fe to 



Junction of Grand and Green Rivers, p. 123, pi. i, ff. la-d ; White, 1884, 



4th Ann. Rep. U. S. Geol. Surv., p. 297, pi. li, f. 3; Stanton, 1892, Bull. 



U. S. Geol. Surv., p. 58, pi. iv, ff. 1-10. 

 Ostrea belliplicata Shumard, 1816, Trans. St. Louis Acad. Sci.,vol. i, p. 608; 



White, 1879, Ann. Rep. U. S. Geol. Surv. Terr, for 1877, p. 276, pi. iv, ff. 



3a, b, and pi. vin, ff. 2a, b; White, 1884, 4th Ann. Rep. U. S. Geol. Surv. 



Terr., p. 292, pi. lxxviii, ff. 1, 2, 3. 

 Ostrea (Alectryonia) blackii White, 1880, Proc. U. S. Nat. Mus., vol. n, p. 



293, pi. iv, ff. 1, 2; Ann. Rep.'U. S. Geol. Surv. Terr, for 1878, p. 11, pi. 



xiv, ff. la, b, and pi. xvn, f. 4; 4th Ann. Rep. U. S. Geol. Surv., p. 292, pi. 



xlv, f . 1, and pi. xlvi, f . 2. 



Stanton's description : " Shell varying in size from small to 

 medium ; outline usually broad subovate, but in small speci- 

 mens often nearly circular and in large ones occasionally sub- 

 triangular ; lower valve moderately convex, the greatest 

 convexity being along the median line, which is often sub- 



