FROM THE TERTIARY OF VIRGINIA. 273 



sides a smaller one near the superior suture. They are perfectly quadrangular, having 

 perpendicular sides and a flat top. When they cross the sulcations, they appear slightly 

 nodulous. The spaces between them are about equal to them in width. Those on the 

 base are closer and more acute. About three whorls of the apex are perfectly smooth. 



This little species can be readily distinguished from its congeners by the peculiar 

 shape of its transverse ribs. 



GENUS NASSA. 

 N. IMPRESSA, PL. 37. FIG. 101. 



N. testa elongato-ovatd; crassd, imperforatd, costatd, striatd; spird attenuatd, conicd, obtusd, prope apicem Icevi et politd: 

 suturis impj-essis, ftexuosis; anfractibus scptem, convexis, ad suturam superiorem angulatis; costis longitudinalibus, latis, ro- 

 tundatis; striis transversis, parvis, flexuosis; anfractu ultimo rotundato; basi striatd; aperturd sub-ellipticd; canale brevi, 

 olliquo; labro intus minute dentato. 



Shell elongately ovate, thick, imperforate, costate, striate; spire attenuate, conical, obtuse, smooth and polished 

 near the apex; sutures impressed, flexuose; whorls seven, convex, angular near the upper suture; costse longitudinal, 

 wide, rounded; striae transverse, flexuose, small; last whorl rounded; base striate; mouth sub-elliptical; canal short, 

 oblique; outer lip minutely dentate within. 



Length .20. Breadth .11 of an inch. 



Remarks. The transverse striae are small and abrupt; they cross the ribs. There is 

 one rather deeper than the rest on the angle of the whorls, above this is a very small one, 

 and between this and the suture the surface is smooth. The costae are very large and 

 wide, generally rounded, but occasionally somewhat angular. The three first whorls of 

 the spire are smooth. There are two or three teeth of various sizes on the inside of the 

 outer lip. 



This little shell differs in various respects from all of our other species of Nassa. It 

 is more elevated than is usual with the genus. The strias are fewer and the costaa larger 

 than in the recent N. alba, Say, to which, in sculpture, it bears some resemblance. 



FAMILY COLUMELLID.E. 



GENUS MARGINELLA. 

 M. CONTILUS, PL. 37. FIG. 102. 



M. testa obovatd, conoidali, erassd } Icevi, politd; spird cornea, obtusd; suturis sub-obsoletis; anfractibus tribus, plants; an- 

 fractu ultimo rotundato; basi Icevi; aperturd longd, arctatissimd; columelld inferne plicis tribus; labro incrassato, rotundato, 

 Icevi. 



Shell obovate, conoidal, thick, smooth, polished; spire conical, obtuse; sutures nearly obsolete; whorls three, flat; 

 last whorl rounded; base smooth; mouth long, very narrow; columella with three folds near the base; outer lip thick- 

 ened, rounded, smooth. 



Length .12. Breadth .08 of an inch. 



Remarks. The whorls of the spire are very small, and the sutures almost obliterated, 

 so that they can scarcely be seen except on a perpendicular view. The folds on the 

 columella are very near the base, and quite small. The shape of the mouth is almost 

 linear. 



This shell is more nearly allied to the M. incurva, Lea, than to any other, but differs 

 in the number of the folds on the columella, and the incrassation of the outer lip. 

 VOL. ix. 72 



