430 GEOLOGY OF THE BLACK HILLS. 



HOLOSTOMATA. 



NATICID^. 



Genus LUNATIA Gray. 



LUNATIA CONCINNA. 



Plate 12, fig. 13. 



Natica concinna H. & M., Mem. Am. Acad. Sci. aud Art.s, vol. v, p. 384, PI. iii, fig. 2. 

 Natica morcauensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. G4, aud 282. 

 Xaiica {Luuatia) morcauensis M. & H., Proc. Acad. Xat. Sci. Phil., vol. 12, p. 422. 

 Lunaila morcauensis (M. & H.) Gab. Syn. Cret. Moll., p. 58. 

 Lunatia morcauensis (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 Grou]), 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. 



VANIKOEA AMBIGUA. 

 Plate 12, fig. 14. 



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

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

 Vanikora ainbigua(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 



