PROSOBRANCHIATA. 249 
Calcaire grossier, and may be regarded by some, perhaps not unreasonably, as 
specifically distinct rather than as constituting a local variety. Thus, in the French 
shells, the posterior margins of the whorls are so feebly lined that to the naked eye 
they appear to be smooth ; the ribs are more numerous, narrower, and less prominent ; 
the concentric lines are rather more crowded and more feeble, becoming nearly 
obsolete ; and the shells themselves are thinner. It appears to me, however, that 
these variations can scarcely be regarded as of specific value; while in the relative 
proportions, the general character of the ornamentation, the condition of the outer lip, 
particularly the characteristic callus, and the shape and position of the sinus, the 
French and English shells correspond. On the whole, therefore, I am inclined to 
regard the English shells as forming merely a coarse, strongly marked variety of the 
French species. 
The shells from Dax and Bordeaux, referred to this species by Basterot and 
Grateloup, appear to be distinct, and Desmoulins has separated them under the name 
P. variabilis. According to Bronn, they correspond with certain Pleurotomoid shells 
previously separated by Millet as Defrancia variabilis. 
Size—Axis, 8-12ths of an inch (17 millim.); diameter, 3-12ths of an inch 
(63 millim.) 
Localities—Bramshaw, Brook. reach: Grignon, Parnes, Mouchy, Courtagnon 
(fide Desh.), Halaincourt (fide Graves). 
No. 170. Pxievroroma acuticosta. Wyst.? Tab. XXVIII, fig. 14, a—e. 
PievRoroma acuticosta. Nyst.? 1843. Coq., &c., foss. de Belg., p. 529, No. 454, 
tab. 42, fig. 5. 
— — Morris. 1854. Cat. Brit. Foss., 2d edit., p. 269. 
P. testé elongato-fusiformi, longitudinaliter costellatd, concentrice lineatd: spird 
elevatd, acuminata: anfractibus conveaiusculis, postice depressis, sub-canaliculatis ; ultimo 
anfractu antice coarctato, in canali brevi, indistinclo, latiusculo terminanti; costellis 
obliquis, angustis, sub-distantibus ; lineis concentricis ewilibus, numerosis: apertura ovata ; 
labro leviter arcuato acuto ; sinu lato, sub-semicirculari, in margine collocato. 
Shell oblong, fusiform, longitudinally ribbed, concentrically lined; spire pointed, 
much produced, nearly equalling three fifths of the entire length of the shell; whorls, 
eight or nine, slightly convex; the posterior margins somewhat depressed and 
furrowed ; the last whorl contracted in front and forming a wide, short, and indistinct 
canal. The longitudinal ribs are narrow, rather distant, rounded on the upper 
surface, and slightly oblique ; the concentric lines very slender, irregular, close-set, 
becoming obsolete over the posterior margins. The aperture is of an oblong-oval 
32 
