PROSOBRANCHIATA. 325 
without the pullus, are slightly convex and bluntly angulated at the shoulders ; the pos- 
terior margins are narrow, rather deeply channelled, very finely plicated round the 
suture, and ornamented with several transverse raised lines, of which the one nearest the 
edge is the most prominent ; the whorls in front of the shoulders are smooth; the last 
whorl tapers gradually towards the base, and is nearly conical, and over the front part 
presents numerous transverse furrows, which become gradually obsolete as they mount 
towards the middle of the whorl; the anterior canal is wide, indistinct, and notched 
at the extremity. The aperture is long, narrow, with straight, nearly parallel sides, 
and, like that of P. amphiconus, resembles the aperture of a Cone; the outer lip is 
much expanded, approaching nearly to a semicircle in form, and is thin and sharp- 
edged ; the columellar lip is thickened and produced in front ; the columella is nearly 
cylindrical, and presents a prominent ridge or crest at the anterior extremity; and 
the sinus, which is placed in the margin of the whorl, is wide, but very shallow, re- 
sembling in appearance that which characterises Bellardi’s section, Psewdotomate. 
I possess only one specimen of this Pleurotoma; it has attained a larger size than 
that attributed by Deshayes to the French shells, but the relative proportions are 
the same in both. The transverse furrows over the base of the English shell are 
coarser, and extend higher up the whorl than in the French shells, but in other 
respects, and particularly in the narrow, concave, posterior margins of the whorls and 
the peculiar character of the sinus, the two agree. 
Size.—Axis, | inch and 9-12ths (45 millim. nearly) ; diameter, 9-12ths of an inch 
(19 millim.) 
Localities—Bracklesham Bay, where it is very rare. Jreuch: Grignon, Parnes, 
Mouchy (fide Desh.), Chaumont, Lattainville, Gomerfontaine, Mouy, Saint-Félix, 
Ully-Saint-Georges, La Croix blanche near Chambors (fide Graves). 
Genus 27th. Borsonia. Bellardi, 1837. 
Corpisria. Rowuault, 1848. 
Among the fossil shells found in the Miocene beds of Turin, occurs one species 
possessing all the general characters of Pleurotoma, that is to say, an elevated, pointed 
spire, a lengthened straight anterior canal, and a wide semicircular sinus, placed in 
the depressed posterior margin of the whorl, but distinguished from the true Pleuro- 
toma by the presence of a single fold on the columella; and Bellardi, influenced by the 
importance generally attributed to the presence or absence of undoubted folds on the 
columella, was induced to establish the present genus for the reception of the species 
in question. It has been seen that among the English Pleurotome before described are 
