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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. Belgian: Basele, Boom, 

 and Lethen (fide JV^.). 



No. 205. Pleurotoma gentilis. Sowerbg. Tab. XXX, fig. 1, a — c. 



Pleurotoma gentilis. Sow. 1850. Dixon's Geol., &c, of Sussex, p. 183, t. 6, fig. 25. 



P. testa elongato-fusiformi, turritd, acuminata, spiraliter lineatd, longitudinaliter 

 costatd: anfraclibus antice convexis, postice concavis, ad suturam marginatis ; costis 

 numerosis, brevibus, rotundatis ; lineis spiralibus supra margines posticas fere obsoletis, 

 cateris elevatis, irregularibus : aperturd late ovali, in canali longo, angusto, sub-recto 

 exeunii ; labro arcuato, acuto ; sinu lato, sub-trigono, summum ad humerum collocato. 



Far. vetusta ; testa minori ; marginibus poslicis anfractuum 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 



