PROSOBRANCHIATA. 265 
exceeding the aperture in length. The whorls are slightly convex; the posterior 
margins somewhat depressed and concave. giving a turriculate aspect to the spire; a 
single row of roundish or slightly oblique, oblong granulations runs round the sutural 
margin, the space between which and the shoulder is nearly equally divided by a 
raised line granulated by the prolongation of the costellae over the margins; the 
costella, which are more or less curved in different individuals, extend a little beyond 
the middle of the whorls, and gradually attenuate as they recede from the shoulders ; 
the concentric lines are prominent, numerous, and irregular ; the two lines on the 
shoulder and on the margin being more elevated than the rest. The aperture is of an 
oblong, oval shape, and terminates in front in a short, moderately wide canal; the 
outer lip is thin, sharp on the edge, and wing-shaped; and the sinus, which is wide 
and nearly semicircular, occupies the whole breadth of the margin. 
This Pleurotoma is one of the shells figured under the superintendence of Mr. 
Charlesworth, for the British Natural History Society, and the elegant ornamentation 
which characterises it, well merits the epithet selected for a specific name. The shell, 
however, in its general form and the character of the ornamentation, so closely 
resembles P. granulata (Lamk.), that it is difficult, if not impossible, satisfactorily to 
separate the two. It will be found, on comparison, that the English shell is broader, 
the spire not so pointed, and proportionately shorter, and the aperture, consequently, 
relatively longer than in the French shell. These distinctions may fairly be attributed 
to external conditions, and I therefore regard the English shell not as a separate 
species, but merely as a strongly marked local variety of P. granulata. 
Size.—Axis, 5-12ths of an inch nearly (10 millim.); diameter, 2-12ths of an inch 
(4 millim.) 
Localities.—Barton, Alum Bay (Stratum No. 29, Prestwich); Highcliff, where it 
occurs in such profusion that it may be regarded as one of the characteristic shells of 
that deposit ; and Bracklesham Bay. French: Grignon, Parnes, Mouchy, Courtagnon 
(fide Desh.), Monneville, Varinfroy (fide Graves). 
No. 187. Pievroroma Heavonensis. F. HL. Edwards. Tab. XXVIII, fig. 17, a—c. 
Pievroroma Heaponensis. (Edw. MSS.) Morris. 1856. Forbes’s Tert. Fluv. Mar. Format., 
&c.; Mem. Geol. Surv., p. 155, t. 5, fig. 4. 
P. testé gracili, fusiformi, longitudinaliter semi-costellatd, spiraliter sulcatd: spiré 
elevatd, longitudine dimidium totius teste paulo superanti: anfractibus convexiusculis, 
postice unico sulco profundo exaratis, ad suturam marginatis ; costellis numerosis, per- 
brevibus, angustis, obliquis ; sulcis spiralibus regularibus, sub-distantibus : apertura elongato- 
ovali, in canali latiusculo, brevi, exeunti; labro leviter arcuato ; sinu sub-triangulari, lato, 
minime profundo. 
34 
