280 EOCENE MOLLUSCA. 
produced, equalling the aperture in length. The whorls are convex, and in the young 
state, the shoulders present a series of curved and rather oblique plications ; but as 
the shell enlarges, these become gradually smaller and indistinct, and at length 
altogether disappear on the last two whorls. The posterior margins are bordered 
round the suture by a narrow, elevated band, formed of two fine, undulating, thread- 
like lines, feebly crenulated; the last whorl tapers gradually and symmetrically 
towards the front, and terminates in a moderately long and narrow canal; the 
concentric lines are very numerous, a little more crowded in the margins than over 
the rest of the whorls, where they are even and regular. The aperture is of a narrow, 
oval shape; the outer lip thin, and but slightly arched; and the sinus, which is 
on the shoulder, is wide, moderately deep, and triangular in form. 
The present Pleurotoma agrees so closely with P. Koninckii, that the identification 
can scarcely be questioned. 
Size —Of the perfect shell, axis rather more than 1 inch and 2-12ths (30 millim. 
nearly) ; diameter, nearly 4°5-12ths of an inch (10 millim.) 
Localities.—Highgate, Potter’s Bar, Hampstead Tunnel. elgian: Basele, Boom, 
and Lethen (fide Wyst.). 
No. 205. Prevuroroma centitis. Sowerby. Tab. XXX, fig. 1, a—e. 
PLEUROTOMA GENTILIS. Sow. 1850. Dixon’s Geol., &c., of Sussex, p. 183, t. 6, fig. 25. 
P. testdé elongato-fusiformi, turritd, acuminatd, spiraliter lineatd, longitudinaliter 
costatd: anfractibus antice convexis, postice concavis, ad suturam marginatis ; costis 
numerosis, brevibus, rotundatis ; lineis spiralibus supra margines posticas fere obsoletis, 
ceteris elevatis, trregularibus: apertura late ovali, in canali longo, angusto, sub-recto 
exeuntt ; labro arcuato, acuto ; sinu lato, sub-trigono, summum ad humerum collocato. 
Var. verusta; testd minori; marginibus posticis anfractium plus cavatis ; costis 
longitudinalibus crassioribus ; lineis spiralibus exilioribus. 
Shell fusiform, elongated, longitudinally ribbed, and spirally lined: the spire, 
consisting of eight or nine whorls, is pointed and moderately produced, nearly 
equalling the aperture in length: the whorls are convex at the sides, deeply concave 
round the posterior margins, and somewhat thickened along the sutural edge ; the last 
whorl is much contracted in front, and produced into a long, nearly straight, narrowish 
canal. The longitudinal ribs are numerous, rounded, and short, barely extending over 
the middle of the whorl ; the concentric lines are nearly obsolete over the hollowed 
margins, but very prominent over the other parts of the whorls, where they are rather 
thick and irregular, the lines in front of the shoulder being thicker and more 
elevated than the rest. The aperture is widely oval; the outer lip much arched, 
sharp on the edge, smooth within ; and the sinus, which is placed at the very top of 
