CRETACEOUS FOSSILS. 179 



face marked with fine oblique lines of growth, which, in well-preserved 

 specimens, are sometimes seen to be crossed on the upper volutions h\ 

 traces of minute revolving striae, scarcely visible without the aid of a mag- 

 nifier. Aperture rhombic-subcircular ; columalla rather deeply sinuous in 

 the umbilical region ; axis imperforate. 



Length of an adult shell, about 1 inch; breadth, 0.70 inch; length of 

 aperture, 0.44 inch; apical angle nearly regular, or with slightly convex 

 slopes, divergence 54°. 



The above description was made out from the typical specimens from 

 the Upper Missouri country near the mouth of the Judith Eiver. The 

 example we have figured from Wyoming is quite imperfect, though agree- 

 ing well with those from the Upper Missouri in all respects, so far as its 

 condition affords the means of comparison. Being so far as yet known . 

 apparently common to these two distantly separated localities, I have 

 thought it desirable to give a figure of it, notwithstanding the imperfect 

 condition of the specimen. The identity of the Bear River specimen with 

 the true V. Conradi cannot be regarded as positively demonstrated. 



Locality and position. — Mouth of Sulphur Creek, on Bear River, Wyom- 

 ing, at the same horizon as the last ; Museum of the Smithsonian Institu- 

 tion, Colonel Simpson's collection. 



Genus CAMPELOMA, Raf: 

 Campeloma macrospira, Meekl 



Plate 17, figs. 17 a, h. 



Melantho (Campeloma) macrospira, Meek (1872), Haydeu's Second Ann. Keport U. S. 



Geol. Survey of the Territories, 299. 

 Compare Txirho paludinceformis, Hall (1845), Fremont's Report Expl. Eocky Mts., 309, 



pi. iii, figs. 13 and 13 a. 



Shell ovate, of medium size; volutions about five or six, convex, increas- 

 ing rather gradually in size, and without revolving ridges or angularities; 

 spire moderately prominent, conical, and not eroded at the apex ; suture 

 distinct in consequence of the convexity of the volutions ; surface with fine, 

 obscure, slightly sigmoid lines of growth ; aperture ovate ; inner lip some- 

 what thickened below. 



