104 EOCENE MOLLUSCA. 
A small smooth shell, formed of three tumid rapidly-enlarging whorls, each 
embracing about one half of the preceding one ; the whorls are rounded, almost equally 
convex above and below, but a little compressed on the upper side. The apex is 
wholly concealed by the involution of the whorls. The aperture is wide, very oblique, 
and bluntly heart-shaped; sometimes, in the adult shell, the peristome is reflected. 
The upper side is slightly concave, and the under side presents a wide and moderately 
deep umbilicus. 
This species, which appears to have been first noticed by Mr. Wood, is so well 
marked that it cannot be confounded with any other. It somewhat resembles the 
young shell of P. oligyratus ; but, in the latter shell, the whorls are not so embracing, 
the upper side is more flattened, and the under side is not so regularly convex. The 
aperture, also, is narrower and much less oblique. The reflected lip, which frequently 
occurs in the present species, evidences the maturity of the shell; and the difference 
between the size of such specimens and that of the fully formed shell of P. oligyratus 
confirms the separation of the two species. In addition to these distinctions, it may 
be stated that the present species is found plentifully both in Headon Hill and at 
Hordwell; but that as yet no specimen of P. oligyratus has heen found at either of 
those localities. 
Size.—Diameter 3-10ths of an inch. 
Localities —Hordwell; Headon Hill; and Sconce. 
No. 57. PLANORBIS LENS. Brogniart. Tab. XV, fig. 8 a—d. 
PLANORBIS LENS. Brogn. 1810. Ann. du Mus., vol. xv, p. 372, t. 22, fig. 9. 
_— — Tb. 1811. Journ. de Phys., &e. vol. Ixxii, p. 421. 
— — Fér. 1814. Mém. geol., p. 61, No. 10. 
— — Sow. 1818. Min. Con., vol. ii, p. 91, t. 140, fig. 4. 
—_— — Desh. 1824—37. Desc. des coq. foss., &c., vol. ii, p. 87, t. 9, 
figs. 11—13. 
— — Bouill. 1836, Catal. des coq. foss. de ’ Auvergne, p. 115. 
— — Desh. Ency. Méth. Vers., &c., vol. iii, p. 783, No. 16. 
— — Ib. 1838. Lam. Hist. Nat., 2d edit., vol. viii, p. 396, No. 7. 
— Morris. 1843. Cat. Brit. Foss., p. 156. 
An. PLANORBE ANGULEUX? Brard. 1810. Ann. du Mus,, vol. xiv, p. 435, t. 27, figs. 23-4. 
P. testé parva, lenticulart, levi, utrinque parum, sed plus superne quam subtus, cavata; 
anfractibus quaternis, singulo fere dimidium antecedentis involventi ; supra convexiusculis, 
subtus plano-conveais, ad peripheriam acute angulatis ; aperturé parum obliqud, elongato- 
cordata. 
Mr. Sowerby, when he gave the name /. /ens to a British fossil, appears not to 
have been aware that that name had previously been dedicated by Brogniart to a 
shell from the Paris basin; but, by a singular coincidence, the shells described by 
