FROM THE CRETACEOUS FORMATION OF NEBRASKA. 393 



ROSTELLARIA FUSIFORMIS, n. Sp. 

 PLATE III. FIG. 10, a, Z>. 



Shell elongate, fusiform ; spire elongated ; volutions (number unknown) moderately 

 convex, marked by numerous regular rounded oblique flexuous folds, which terminate 

 abruptly above in small indistinct nodes, giving a sub-coronate aspect to the upper part 

 of the volutions ; surface unknown ; suture distinct and separated from the row of 

 nodes below it by a shallow depression ; aperture elongate, widest near the middle, and 

 narrowing anteriorly into a prolonged canal. Spiral angle 35 ; breadth, 1.1 inch. 



Our specimen is imperfect at both extremities, and so exfoliated as to preserve none 

 of the surface markings. The folds on the last volution appear to grow more irregular 

 and obscure towards the aperture. The outer lip is imperfect, and the adhesion of 

 stony matter to the columella prevents the positive determination of the generic char- 

 acters ; but the general aspect of the surface, the longitudinal folds of the volutions, 

 with the absence, as far as seen, of the characteristic features of other genera, induces 

 its reference to the genus Rostellaria. In the broken upper extremity of the shell, a 

 few faint spiral bands are visible, which, if continued, would mark the columella ; but 

 owing to the exfoliation of the specimen, they are not preserved. 



Locality and Position. Sage Creek. Upper clay or upper part of division No. 4 

 of Section. 



DENTALIUM GRACILIS, n. sp. 

 PLATE III. FIG. 11, a-c. 



Slender, terete, gradually enlarging from the apex ; section sub-oval, nearly circular ; 

 surface distinctly marked by rounded, threadlike stria?, which are irregular in size, and 

 increase in number by implantation between the larger ones, from the apex towards 

 the aperture, having about twenty-five near the apex and fifty-two at a point where 

 the diameter is twice as great, and increasing in the same ratio as far as observed ; 

 crossed obliquely by extremely fine equal striae, which ascend from the outer to the 

 inner side of the curve. Spiral angle 3 to 3i. Longest diameter of largest frag- 

 ment, .2 inch ; aperture of the same, .14 inch ; diameter of smallest fragment, near 

 the apex, .08 inch. 



This we believe is the first species of this genus described from the cretaceous for- 

 mation of this country. 



Locality and Position. Sage Creek. Upper part of division No. 4 of Section. 



VOL. V. NEW SERIES. 53 



