386 



Small fragments of pearly nacreous shell adhere to a few points on the flatter side, 

 but they present no markings of any kind. 



We have identified this fossil as the Hipponix (Defranc), Pileopsis capulus, de- 

 scribed under the genus Cabochon by Des Hayes. Our specimen is the smaller valve, 

 very distinctly marked on its upper surface by the muscular impression which may 

 be the cast of the interior of the other valve, and on the lower surface by imbricating 

 striae, very much like those of the Hipponix (Pileopsis) patelloidea (Des Hayes, Coc. 

 Foss., Tom. II. PL III. figs. 23, 24, and 25). It may also be compared with other 

 species of this genus as figured by Des Hayes. 



Locality and Position. Sage Creek, Nebraska, from division No. 4 of the Section 

 of the cretaceous formation. 



INOCERAMUS SUBL^EVIS, n. sp. 

 PLATE II. FIG. 1, a, J. 



Shell comparatively thin, moderately convex, length about one fifth more than 

 height ; hinge line long and straight, forming an angle of about 130 with the front ; 

 anterior extremity rounded ; posterior side long and rounded at the extremity ; beaks 

 small, scarcely elevated above the hinge line ; surface with nearly obsolete concentric 

 undulations, and fine regular concentric striae, which continue almost as distinct where 

 the shell is partly exfoliated. 



The most striking feature of this shell is the almost entire absence of concentric 

 undulations, by which it will at once be distinguished from any species heretofore 

 described from that region, or even in this country. It differs from the I. sagensis 

 of Owen in the lesser obliquity of the shell, in the more extended and rounded anterior 

 extremity, and in the smaller and less elevated beaks, while the entire shell is less 

 convex. The fine equal concentric striae, and faint radiating lines with obsolete undu- 

 lations, are usually sufficient to distinguish this shell, even where the surface is much 

 exfoliated. Our specimens do not show the whole outline, but it can be inferred by 

 the direction of the concentric striae. 



Locality and Position. Great Bend of the Missouri, in division No. 4 of Section. 



INOCERAMUS CONVEXUS, n. sp. 

 PLATE II. FIG. 2, a, J. 



Shell ovate, very convex, height a little more than three fourths of length ; beaks 

 prominent ; hinge line long and straight, forming an angle with the anterior margin of 



