430 GEOLOGY OF THE BLACK HILLS. 



H0L0ST0MATA. 



NATICIim 



Genus LUNATIA Gray. 



LUNATIA CONCINNA. 



Plate 12, fig. 13. 



Natica concinna H. & M., Mem. Am. Acad. Sci. and Arts, vol. v, p. 384, PI. iii, fig. 2. 

 Natica moreauensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 64, and 282. 

 Natica (Lunatia) moreauensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 422. 

 Lunatia moreauensis (M. & H.) Gab. Syn. Cret. Moll., p. 58. 

 Lwnatia moreauensis (M. & H.) Meek, Smithsonian Check List Invert. Foss., p. 20. 



Shell of medium size, subglobose or very broadly rhombic-ovate; 

 erect, with strongly ventricose volutions, of which four may be counted on 

 the example figured, the last one forming the great bulk of the shell. Spire 

 low ; sutures very distinct, deep, but not channeled ; aperture obliquely ovate, 

 nearly once and a half as high as wide, obtusely pointed above and rounded 

 below; inner lip straightened, slightly callous and spreading upon the body 

 of the shell; umbilicus moderate; outer lip thin and comparatively sharp. 

 Surface marked by fine transverse lines of growth and by faint revolving 

 lines, seen only by the aid of a lens, except on the larger part of the body 

 volution, where a few may be detected with the naked eye. 



Formation and locality. — At the top of the gray shales of the Fort 

 Pierre' Group, on the Cheyenne River, near Rapid Creek, and a specimen 

 undistinguishable from it, in its condition as an internal cast, from a much 

 lower position on the east fork of Beaver Creek, Black Hills. 



Genus VANIKORA Quoy & Gaimard. 



VANIKOBA AMBIGUA. 



Plate 12, fig. 14. 



Natica? ambiguaM. & H., Proc. Acad. Nat. Sci. Phil., vol. v, p. 64. 

 Fosar ? nebracensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 423 

 Vanikora ambigua(M. & H.) Meek, Smithsonian Check List Invert. Foss., p. 18. 



Shell small, naticoid, subglobose or obliquely subglobose, spire mode- 

 rately elevated, volutions ventricose and separated by rather distinct suture 



