FROM THE TERTIARY OF VIRGINIA. 43 



and carina at right angles. The cariria is placed immediately below the middle of the 

 whorls, and, in some specimens, between it and the lower suture is another smaller one. 

 When this latter is not present, it is replaced by a stria. Between the carina and upper 

 suture there are generally two striaB, which vary in size. Those on the base are much 

 smaller than those on the whorls. The sutures are small and triangular. 



This shell is unusually short and thick for a Cerithium, and its effuse mouth has 

 hardly the character of the canal of that genus. 



C. DJ2DALEUM, PL. 37. FlG. 91. 



C. testa subulatd, tenui, imperforatd, coslatd, striatii; spira attenuata, sub-ovald, mamillatd, ad apicem l<evi et 

 polita; suluris llnearibus, parvis; anfraclibus septem, planulatis; costis longitudinalibus, crebris, lavibus. planulatis; 

 striis transversis, crebris, pnifundi.i; ultimo anfractu rotundato; base striatd, polita; aperturd arclatd, sub-quadratd, 

 superne angulalii, infcrnc rffusd; labro aculo. 



Shell subulate, thin, imperforate, costate, striate; spire attenuate, sub-ovate, mamillate, smooth and polished near 

 the apex; sutures small, linear; whorls seven, flattened; striae transverse, numerous, deep; costce longitudinal, nume- 

 rous, smooth, flattened; last whorl rounded; base striate, polished, mouth narrow, sub-quadrate; angulate above, effuse 

 below; outer lip acute. 



Length .15. Breadth .05 of an inch. 



Remarks. The sculpture of this shell is not unlike that of the Pasithea subula, herein 

 described. 



With this shell, as with the preceding, I feel in some doubt as to the genus to which 

 it properly belongs. 



C. MONILIFERUM, PL. 37. FIG. 92. 



C. testa subulatd, sinistrali, crassd, imperforatd, costatd; spira attenuata, cornea; suluris minimi's; anfractibus 

 decem, plants; costis tribus, transversis, noduliferis, duabus extremis magnis, und media parviore ; anfractu ultimo 

 rotundalo; basi costis tribus, l(Evibus, transversis; aperturd elongato-quadratii; columelld Itsvi, polita; canale profundo, 

 brevi. 



Shell subulate, sinistral, thick, imperforate, costate; spire attenuate, conical; sutures very small; whorls ten, flat; 

 costcc three, transverse, noduliferous, two extreme ones large, the middle one smaller; last whorl rounded; base with 

 three transverse, smooth ribs; mouth elongately quadrate; columella smooth, polished; canal deep, short. 



Length .22. Breadth .09 of an inch. 



Remarks. The middle costa is smaller than the two outer ones; it gradually decreases 

 on the upper whorls, and finally becomes obsolete near the apex. The sutures are very 

 small, and the whorls perfectly flat, so that it is difficult to determine their number. 



This shell approaches the C. nigrocinctum, Adams, a recent species from our coast, 

 but may be distinguished by its greater proportionate length, flatness of the whorls, and 

 the difference between the size of the ribs. It is also allied to the C. perversum, another 

 recent shell, but it is much smaller, and the ribs are strictly noduliferous, while in the 

 C. perversum, they intersect longitudinal sulci. The three smooth basal costa3 consti- 

 tute another character peculiar, 1 believe, to this shell. 



GENUS PLEUROTOMA. 



P. LUNATUM, PL. 37. FlG. 93. 



P. testa elongato-fusiformi, crassd, glabrd, nitente, imperforata, coslald; spira attenuata, mamillatd, ad apicem 

 l<evi; suturis Jlexuosis, minimis; anfractibus decem, media angulatis, inferne contexts et costatis, superne concavis et 

 L 



