INVERTEBRATE PALAEONTOLOGY. 327 



markings, but is always decidedly smaller at maturity than the adult of that 

 shell, and has a narrower spire, more flexuous costse, rather more convex 

 volutions, and a much narrower labial extension. These differences are 

 constant, and (particularly the last-mentioned one) render the separation of 

 the two species very easy. 



This shell has been referred to Drs. Evans and Shumard's species 

 on the authority of the latter, to whom we sent specimens for comparison. 

 Among foreign species, it may be compared with A. Icevisucula (—Rostellaria 

 Iceviuscula, Sowerby), from which it differs in having smaller, more numerous, 

 and more arched vertical costse, and a somewhat differently -formed labial 

 appendage. 



Locality and position. — Crow Creek, near Black Hills ; from the upper 

 beds of the Fort Pierre group of the Upper Missouri Cretaceous series; 

 also, from same horizon on Sage Creek, near the Bad Lands of White River. 



Anchura! sublevis, M. & H. 



Plate 19, figs. 3, a, b. 



Aporrhaia sullevia, Meek and Hayden (18G0), Proceed. Acad. Nat. Sci. Philad., XII, 178. 



Aporrhas sublevata (misprint), Meek and Hayden (1860), ib., 4'28. 



Andhura ? subleris, Meek (1864), Smithsonian Check-List N. Am. Cret. Fossils, It). 



Shell unequally subfusiform; spire elevated; volutions seven or more, 

 convex, and separated by a rather distinct, though not deep, suture, last one 

 convex above and abruptly contracted below, with a single small revolving 

 angle, which passes around to the suture, but is not visible on the succeeding 

 turns of the spire; surface polished, and marked by moderately distinct 

 annate lines of growth, which are crossed by rather obscure revolving lines, 

 nearly equaling the spaces between on the spire, but more distant, with some- 

 times a few indistinct, irregular, very fine, parallel stria? between on the 

 body-whorl; aperture and lip unknown. 



Length, about 0.54 inch ; breadth of body-whorl, 0.26 inch. Apical 

 angle slightly convex ; divergence, 37°. 



1 have not seen specimens of this species retaining the apex of the 

 spire or showing the aperture or lip. Its surface-markings, however, are so 

 different from those of all the other species yet known in these rocks, that it 

 may lie readily distinguished, even by comparing quite imperfect specimens. 

 It differs from all its associates with which we are acquainted, excepting 

 A. b'wmguhita, in being destitute of costse on all its whorls; and from that 



