322 EOCENE MOLLUSCA. 
the P. prisca of Solander. It is true that in Lamarck’s species the shell is smaller and 
narrower, the spire more tapering, the whorls not so ventricose, and the sinus rather 
wider and shallower; but whether these differences, even when constant, are by them- 
selves of specific value may be questionable: and it must be stated that the English 
shells are variable in the length of the spire and the condition of the whorls, which, in 
some specimens, are less convex than in others, and, in fact, I have, in my collection, 
a Barton specimen which, so far as the proportions and shape of the shell may be 
relied on, cannot be regarded as specifically distinct from P. clavicularis. The only 
distinction to which, apparently, any consideration is due, lies in the condition of the 
sinus. In the shell figured by Deshayes as P. prisca, the sinus is represented as 
placed in the front of the margin with the apex almost on the shoulder, and as being 
deep and rather narrow, with nearly parallel margins ; now, this does not correspond 
with the sinus in Solander’s species, which, although similarly placed, is intermediate 
in form between the sinus in P. prisca of Deshayes and that in P. clavicularis. I 
have already suggested that the sinus may be, reasonably, expected to be liable to 
variation in its dimensions, and too much importance, therefore, must not be attri- 
buted to mere differences in size and proportion. On these grounds, I have, not- 
withstanding the array of authorities against me, considered P. clavicularis of 
Lamarck as merely a variety of Solander’s species. 
Size.—Axis, 2 inches and 11-12ths (74 millim.) ; diameter, 11-12ths of an inch 
(23 millim.) The specimen represented by fig. 1 d, is upwards of 3 inches in length ; 
but the body of the shell having been twice broken and repaired by the animal, the 
diameter cannot be accurately stated. 
Localities. —Barton, Highcliff, Bramshaw, Stubbington, Bracklesham Bay. 
French: Grignon, Parnes, Mouchy, Courtagnon, Valmondois, Acy, Tanerou (fide 
Desh.), Cuisse-Lamotte, Marquemont, Saint Félix, Gomerfontaine, Les Groux, 
Hermes, Chateaurouge, Mouy, Monneville, Neuvillebosc (fide Graves), Bos d’Arros 
(fide Rouault). falian: Palarea (Nice), (fide Bellardi), Montecchio-Maggiore on the 
Vicentin (fide Brongniart). 
No. 246. Prevroroma aMpuHiconus. Sow. Tab. XXXIII, fig. 2, a, 4. 
PLEUROTOMA AMPHICONUS. Sow. 1850. Dixon’s Geol., &c., Sussex, p. 183, t. 8, f. 7 and 8. 
P. testa glabra, angulo obtuso inequaliter bipartitd, utrinque conicd ; anfractibus pos- 
tice et antice undulato-sulcatis, ceterum levibus : aperturd angusta, marginibus sub-parallelis, 
in canalem brevem, ad extremitatem profunde emarginatum, producta ; labro arcuato, ad 
humerum late breviterque sinuato ; labio antice producto, reflexo ; columella cristaté. 
Shell nearly smooth, obtusely angulated at the shoulders, presenting the appearance 
