CRETACEOUS FOSSILS. 431 



lines. "Aperture ovate, very oblique, obtusely angular above, and rounded 

 below; outer lip sharp, joining- the whorl above nearly at right angles, slightly 

 reflexed at its junction with the columella below; axis a})})arently perfor- 

 ated by a very small umbilical opening which is not covered by the lip." 



Surface of the shell marked by very distinct, impressed, revolving 

 lines, with wider, flattened interspaces; the lines most strongly marked 

 below the middle of the outer volution, and crossed by irregular concentric 

 lines of growth, which have a decided tendency to form fascicles or transverse 

 folds on the body volution. 



Our specimen of the species is imbedded in hard limestone, so as to 

 entirely conceal the aperture side of the shell; we have therefore quoted 

 Mr. Meek's description of these parts from the Paleontology of the United 

 States Geological Survey of the Territories, p. 330. 



Formation and locality. — In limestone of the Fort Pierre Group, on the 

 Cheyenne River, Black Hills. 



Genus AMAUROPSIS Morch. 



AMAUROPSIS PALUDINiEFOEMIS. 



Plate 12, fig. 16. 



Ifatica pahidinoiformis H. & M., Mem. Am, Acad. Sci. and Arts, vol. v, p. 389, PI. iii, 



fig. 3. 

 Amatiropsis paludincefonnis (H. & M.) M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, 



p. 185. 

 Amauropsis paludinwformis (H. & M.) Meek, Smithsonian Check List Invert. Foss., 



p. 20. 

 Amaufopsis paludlnceformis (H. & M.) Meek, Pal. U. S. Geol. Surv. Terr., p. 318, PI. 



19, fig. 15. 



Shell subovate or elongate-ovate, spire moderately elevated, forming 

 a little more than one-half the entire height above the aperture; volutions 

 four and a half to five, convex, the last one ventricose and somewhat pro- 

 duced below, but not rostrate ; suture very distinct and channeled ; aper- 

 ture oblique, semi-ovate, or nearly semi-circular, the inner side being nearly 

 straight; upper angle acutely rounded, more broadly rounded below, the 

 columellar side of the base almost subrimate: outer lip thin arid sharp; 

 columellar lip scarcely thickened ; umbilicus scarcely perceptible or closed. 



