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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 ll-12ths (74 millim.) ; diameter, ll-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 Felix, Gomerfontaine, Les Groux, 

 Hermes, Chateaurouge, Mouy, Monneville, Neuvillebosc (fide Graves), Bos d'Arros 

 (fide Rouault). Italian: Palarea (Nice), (fide Bellardi) ; Montecchio-Maggiore on the 

 Vicentin (fide Brongniart). 



No. 246. Pleurotoma amphiconus. Sow. Tab. XXXIII, fig. 2, a, b. 



Pleurotoma amphiconus. Sow. 1850. Dixon's Geol., &c, Sussex, p. 183, t. 8, f. 7 and 8. 



P. testa glabra, angulo obtuso inaqualiter bipartitd, utrinque conicd ; anfractibus pos- 

 tice etantice undulato-sulcatis, caterum lavibus : aperturd angustd, marginibus sub-parallelis, 

 in canalem brevem, ad extremitatem prqfunde emarginatum, productd ; labro arcuato, ad 

 humcrum late breviterque sinuato ; labio antice producto, refiexo ; columella cristatd. 



Shell nearly smooth, obtusely angulated at the shoulders, presenting the appearance 



