FROM THE CRETACEOUS FORMATION OF NEBRASKA. 389 



NATICA OBLIQUATA, n. sp. 

 PLATE III. FIG. 1, a, b. 



Shell longer than wide, very obliquely sub-ovate, spire little elevated. Volutions 

 three to three and a half, convex ; last one ventricose, prolonged in front. Suture 

 deeply impressed. Surface marked by faint, very fine, closely arranged lines of growth, 

 which are crossed by fine, nearly obsolete, revolving lines. Aperture ovate, somewhat 

 oblique. Umbilicus small, and partly closed by the deflected pillar lip. Columella 

 marked with a distinct opercular impression, which continues down to the base of the 

 aperture. Spiral angle 92. Length, .36 inch; breadth, .32 inch. Body volution, .7 

 of whole length. 



Locality and Position. Great Bend of the Missouri. From the clay beds of division 

 No. 4 of Section. 



NATICA CONCINNA, n. sp. 

 PLATE III. FIG. 2, a - d. 



Shell obliquely sub-ovate ; length and breadth nearly equal. Spire little elevated. 

 Volutions three and a half, convex ; last one ventricose. Suture sharply impressed. 

 Surface nearly smooth, or marked only with exceedingly fine, closely arranged lines of 

 growth, which are invisible to the naked eye. Aperture ovate, obtuse at both extrem- 

 ities. Umbilicus of medium size, round. Columellar lip not thickened, slightly de- 

 flected upon the body volution, but not so as to cover any part of the umbilicus. 

 Spiral angle 92. Length, .22 inch ; breadth, .23 inch. Body volution .75 of the 

 whole length. 



In form this shell bears much resemblance to the N. obliquata. The difference in 

 size, however, can hardly be due to age, as this appears to be a mature shell. 



Locality and Position. Sage Creek. Higher part of the upper clay formation, No. 

 4 of Section. 



NATICA PALUDIN^FORMIS, n. sp. 

 PLATE III. FIG. 3, a, Z>, c. 



Shell sub-rhomboidal, obliquely conical above, prolonged below ; spire extremely 

 elevated ; volutions five to five and a half, convex ; suture deeply impressed or sub- 

 canaliculate ; surface ornamented with numerous fine, closely arranged lines of growth, 



