296 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



It is referred to this genus instead of Patella, on account of its depressed 

 form, thinness, and nearly smooth surface. 



Locality and position. — The specimen first figured and described in 

 the Memoirs of the American Academy of Arts and Sciences, cited above, was 

 collected by the writer at Sage Creek, in the Upper beds of the Fort Pierre 

 group, or No. 4 of the Upper Missouri Cretaceous. That here described 

 came from the same beds on Cheyenne River near the Black Hills. 



A c in se a f |> a i- v a . M. & H. 



Plato IS, figs. 1. a,b, c, and lig. -2. 



Tectura *. parva, Meek and Haydeu ( .1860), Pivceed. Acad. Nat. Set., HX.— Meek (1864), Smithsonian Check- 

 List N. Am. Cret. Fossils, 17. 



Shell very small, thin ; summit rather elevated, located in advance of 

 the middle; aperture circular : (surface unknown). 



Breadth, 0.26 inch ; height, 0.12 inch. 



The only specimen of this little shell yet seen, is embedded in the matrix 

 in such a manner as to show only the interior. On the internal cast, the 

 muscular impression is seen to have the usual horse-shoe-form, without being 

 interrupted on the posterior side, as in the genus Anisomyon. 1 have only 

 placed it provisionally, however, in the genus Acmcea. 



Locality and position. — The specimen and label have been both mislaid, 

 and the exact locality is not remembered; no doubts, however, are enter- 

 tained in regard to its having been obtained in the Cretaceous beds either 

 on the Yellowstone, or Cheyenne River, in the upper beds of the Fort Pierre 

 group (No. 4 of the Upper Missouri Cretaceous series). 



V < in ;r a ' papillatil, M. & H. 



Plate 31, tigs. 4, a, b. 



Capulns fragiUa, Meek and Haydeu (1856), Proceed. Acad. Nat. Sci. Philad., VII, 08 (not Acmosa fragilis, 



Quoy and Gaiinard, of an earlier date). 

 Tectura Ipapillata, Meek and Haydeu (1800), it., XII, 423.— Meek (1804), Smithsonian Check -List N. Am 



Cret. Fossils, 17. 



Shell very thin, of a depressed conical form, being much elevated, with 

 the prominent summit nearly or quite central ; lateral slopes a little convex 

 near the summit, and diverging at an angle of about 80° ; anterior (?) slope 

 nearly straight, and posterior (?) moderately convex ; immediate apex, as seen 

 in the internal east, having the form of a small nipple : base circular; surface, 

 as determined from some fragments of the shell remaining about the lower 



