184 EOCENE MOLLUSCA. 



separated by a deep suture, and with the margins thickened and rather depressed, giving 

 a sub-turreted character to the spire ; the furrows are broad, round, and nearly regular ; 

 the posterior furrow is deeper than the others, and from this circumstance the margin 

 of the whorls assumes the appearance of a rim. The aperture is narrow, and of a 

 lengthened oval form ; the outer lip waved, sharp-edged, and plicated within, at a 

 short distance from the margin ; the columella is nearly straight, and presents near the 

 middle two rather prominent and nearly transverse folds, and in front of them three 

 others more oblique, and of which the anterior one is much the smallest. 



In the variety semilcevis, the whorls are nearly smooth, presenting only the deep 

 sulcus round the sutural margin, and a few obscure furrows, almost obliterated, near 

 the base ; and the spire is rather more elevated than in the type. 



In the variety pumila, the surface of the whorls presents numerous longitudinal, 

 irregular, slightly waved costellae, not much elevated, but extending almost to the 

 base, and crossed by concentric raised bands, which decussate them, and impart a 

 rough aspect to the shell. The concentric bands are irregular, more or less nume- 

 rous in different individuals, and rather flattened on the upper surface. When the 

 costellse are well defined, the concentric bands, at the points of decussation, rise into 

 little tubercles ; the marginal band, thus tuberculated, forms the crenulated edge to 

 the whorls noticed by Mr. Sowerby; but this does not appear to be a constant 

 character. 



Occasionally specimens occur (par. (3) in which the longitudinal costellse are alto- 

 gether wanting, and the whorls present only the concentric bands. 



If we look only at the extreme forms figured in c Mineral Conchology,' it need 

 not excite surprise that Mr. Sowerby, who had not any intermediate forms before 

 him, should have described the variety pumila as a distinct species. On an atten- 

 tive examination, however, it will be seen that the distinction between that 

 variety and the type lies in the character of the transverse marking, which in 

 the type consists of shallow, rounded furrows ; while in the variety it assumes 

 the form of flattened bands. This difference, however, which is attributable to the 

 greater, or less depth of the furrows, cannot be regarded as of specific value; and the 

 occurrence of ribless specimens with transverse bands, shows that the presence or 

 absence of the costellae is not a character on which reliance is to be placed. 



The apex of the shell appears to have been very susceptible of erosion, for speci- 

 mens with the embryonal whorls preserved are very rare. 



Size. — Axis, rather more than 3-12ths of an inch; diameter, 2-12ths of an inch, 

 nearly. 



Localities. — For the type, Highcliff, where it is found in profusion, Barton, Alum 

 Bay (No. 29, Prestw.), where the variety semilavis is abundant, and Brockenhurst ; 

 and for the variety pumila, Highgate, Basingstoke, Bracklesham Bay, Bramshaw (New 

 Forest), and Barton. The species appears to be confined to England. 



