230 EOCENE MOLLUSCA. 
pied by three or four concentric lines, broken into oblong granulations, more or less 
widely separated by smooth spaces, formed at the successive stages of growth by the 
margins of the sinus; the angulated shoulders, and somewhat depressed margins of 
the whorls, give a turreted character to the spire. The tubercles are rather numerous, 
and prominent in all stages of growth; the transverse furrows deep, but not 
wide, and separated by rounded ridges, which are narrow near the shoulders, but 
become broader over the middle and front parts of the whorls, and on the canal. 
The body-whorl is suddenly contracted near the middle, and produced anteriorly into 
a wide, moderately long canal. The aperture is of a narrow, oblong, oval shape; the 
outer lip roundedly arched, almost semicircular in form; and the sinus, which is placed 
in the middle of the margin, is deep, rather wide, and sub-trigonal. 
Specimens occur (Var. (3, fig. 2 4) in which the tubercles are compressed, and a 
little prolonged, in the direction of the axis, imparting a sub-costellated appearance 
to the earlier whorls, and becoming obsolete as the shell approaches maturity. 
This species presents a very close analogy with P. fusiformis, with which, in fact, 
it may be easily confounded. On comparing the two shells, however, it will be found 
that, in the present species, the shell is wider; the spire relatively more produced and 
tuberculated, not costated ; the body-whorl more contracted, and less conical, in front ; 
the canal wider and shorter; the outer lip more roundedly arched; and the sinus 
deeper, more trigonal, and placed nearer the middle of the margin. These distinctions, 
and the different ornamentation, which consists of deep conspicuous furrows instead of 
the rough spiral bands which characterise P. /wsiformis, appear to me to justify the 
separation. 
Size.—The dimensions of the largest specimen figured would be, if the shell were 
perfect—axis, 1 inch and 5-12ths; diameter, not quite half an inch. 
Localities.—Highgate and Potters’ Bar, at both of which localities it is rather 
scarce. 
No. 155. PLEUROTOMA ACUMINATA, Sowerby. Tab. XXVII, fig. 3 a—d. 
PLEUROTOMA ACUMINATA, Sow. 1816. Min. Con., vol. 11, p. 105, t. 146, fig. 4. 
— — D’ Orb. 1850. Index Paléont., vol. ii, p. 359, No. 420. 
— — Morris. 1854. Cat. Brit. Foss., 2d edit., p. 269. 
Nec Prevrotoma acuminata, Nyst. 1836. Rech. coq. foss. de Hoesselt et Vliermael, p. 32, 
No. 83. 
nec a — De Kon. 1837. Desc. des coq. foss. de Basele Boom, &c., p. 24, 
No. 24. 
nec — Nyst. 1843. Bull. Soc. Géol. de France, vol. xiv, p. 454, No. 27. 
nec a — Ib. 1843. Descr. des coq., &c., de la Belgique, p. 519, t. 42, 
fig. 1 a, 6. 
