NATURAL SCIENCES OF PHILADELPHIA. 137 



arcuate; pillar faintly sinuous below. Length about 1-04 inch; breadth -38 

 inch ; apical angle slightly concave, divergence 24". 



This species will be known from all the others we have seen in the Nebraska 

 formations, by its slender spire, and slightly concave sides. It is also propor- 

 tionally longer than any Nebraska species known to us, excepting our M. con- 

 vexa, (Proceedings of the Acad. Nat. Sci. vol. 8, p. 125,) from which it may 

 be at once distinguished by its depressed convex, instead of flat, volutions, more 

 defined suture, finer revolving lines, and more slender spire. Unfortunately 

 none of our specimens are quite perfect enough to show the number of volutions ; 

 one specimen consists of five turns of the spire, and, judging from the appear- 

 ance of the broken apex, there were probably about two more. 



Locality and position. Bad lands of Judith River, bed G. of Fresh-water and 

 Estuary formations at that place. 



Melania invendsta. 



Shell conical ovate; spire moderately elevated ; volutions about seven, very 

 slightly convex, increasing rather slowly from the apex; suture linear, not much 

 impressed ; surface marked by obscure lines of growth crossed by fine irregular 

 rather indistinct revolving lines, a few of which, just below the suture, are 

 larger than the others; aperture ovate; outer lip faintly sinuate above, rather 

 prominent below the middle inner lip reflexed upon the imperforate columella, 

 at the base of which it is broadly sinuou3. Length -90 inch ; breadth -37 inch ; 

 apical angle regular or a little convex, divergence 32°. 



This shell is nearer our M. Ncbrasccnsis, (Proceedings of Acad. Nat. Sci. vol. 

 8, p. 124,) than any of the Nebraska species known to us, but has about one 

 more volution, and is uniformly more slender, the body volution being propor- 

 tionally much smaller. From M. sublcevus of this paper and any of the varieties 

 of our 31. convexa with which it is associated, it may be known by its much less 

 elongate form, and more obscure surface markings. It appears to be about 

 intermediate between our M. convexa and M. N'ebrascensis, but quite distinct from 

 both. 



Localitij and position. Bad Lands of Judith River, bed A. of the section of 

 frtsh-water estuary strata at that place. 



Melania Warrenana. 



Shell small, somewhat acutely conical ; spire rather elevated, pointed at the 

 apex; volutions about seven and a half, depressed convex, closely wound and 

 increasing gradually from the apex, last one sub-angular round the middle ; 

 suture distinct; surface apparently smooth, or only marked by very faint lines 

 of growth ; aperture broad ovate, obtusely angular above ; outer lip very faintly 

 and broadly sinuate above; columella arcuate, rather faintly sinuate below. 

 Length -29 inch; breadth -14 inch ; apical angle convex, divergence 32®. 



This neat little shell is nearer our M. AntJwni/i, (Proceed. Acad. Nat. Sci. vol. 

 8, p. 124,) than any other species with which we are acquainted, but is larger, 

 and its spire more elevated. It has about one and a half to two more vo- 

 lutions than 3f. Anthoni/i ; also the body whorl is comparatively smaller, and 

 the apical angle nine or ten degrees less. We dedicate it to Lieut. G. K. Warren, 

 of the U. S. Top. Engs., who discovered the only specimen we have seen. 



Locality and position. Summit of Square Butte, thirty miles below Fort Clark, 

 on the Missouri, in a gray sandstone — an outlier of one of the lower strata of 

 the Lignite Tertiary basin, where it is associated with Corbula mactriformig^ 

 Melania Nebrascensis, and M, Conradi ? 



Melania tenuicarinata. 



Shell ovate conical; spire turreted, not very much elevated, pointed at the 

 apex ; volutions six, convex, obliquely flattened above ; suture well-defined, in 

 consequence of the prominence of the whirls; surface ornamented by fine 

 regular lines of growth, crossed near the middle of the volutions by from two 



1857.] 



