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EOCENE MOLLUSCA. 



close-set, regular, and very slender ; over the middle and front parts of the whorls 

 they are sharp, rather distant, unequal and irregular, slender and slightly raised lines 

 alternating with other lines thicker and more prominent ; all are beautifully decus- 

 sated by the prominent lines of growth. The aperture is of a narrow, oval form ; the 

 outer lip moderately arched, thin and sharp on the edge, and smooth within; the 

 sinus, which is wide, short, and triangular, is placed in the front of the margin, the 

 apex being immediately behind the keel ; and the columella is slightly twisted, and 

 crested in front. In the specimens from Highcliff the shell is comparatively wider, 

 with a shorter spire, but the sculpture is identical. 



This Pleurotoma presents a close resemblance to P. turrella (Lamk.) from the 

 Calcaire Grossier, with which, in fact, I had formerly associated it; but a careful 

 examination of a larger series of specimens than I then possessed has induced me to 

 change that opinion. In the French species the shell is smaller, the spire much less 

 produced, the whorls more convex, the posterior margins more slanting, the body 

 whorl more conical, the keel on the shoulder not so prominent, the transverse 

 lineation more crowded and less bold and decided in character, and the sinus nar- 

 rower, deeper, and placed in the middle of the margin. The English shells present 

 altogether a character so distinct, that I am unwilling to regard them even as varieties 

 of Lamarck's species. 



Size. — Axis, 15-24ths of an inch (16 millim.) ; diameter, not quite 5-24ths 

 (5 millim.). 



Localities. — Barton and Highcliff, at both of which places it is somewhat rare, but 

 rather less so at the latter locality. 



Section II. — Shells coniform. 



No. 245. Pleurotoma prisca. Solander. Tab. XXXIII, fig. 1, a — e. 



Mukex piuscus. Sol. 1766. Brander, Foss. Hanton, p. 16, f. 25 and 44. 

 Pleurotoma clavicularis. Lamk. 1802. Ann. du Mus., vol. iii, p. 165, No. 3. 



— — Boissy, 1804. Buffon, Moll., vol. vi, p. 73. 



_ — Lamk. 1816. Tab. Encyclop. et Method., t. 440, f. 4. 



— — Lamk. 1822. Anim. sans Vert., vol. vii, p. 98. 



— priscus. Sow. 1823. Min. Con., vol. iv, p. 119, t. 386. 



— clavicularis. Brongn. 1823. Terr. tert. du Vicent., p. 73. 



— — Be. Blainv. 1826. Diet, des Sci. nat., vol. xli, p. 388. 



— prisca. De Blainv. 1826. Idem. 



— — Bronn, 1831. Ital. Tertiargeb., p. 47, No. 321. 



