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EOCENE MOLLUSCA. 



No. 268. Neritina concava, /. Sowerby. Tab. XXXIV, fig. 14 a — c. 



Neritina concava, J. Sow. Min. Conch., tab. ccclxxxv, figs. 1 — 8, 1823. 



— — Desk. (2nd edit. Lamk.). An. s. Vert., t. viii, p. 597, 1838. 



— — Ilorris. Catal. Brit. Foss., 2nd edit., p. 264, 1854. 



— — J. Lowry. Chart Brit. Tert. Foss., pi. iii, 1866. 



— — Lyell. Students' Elemts. of Geol., p. 231, 1871. 



— — Sandberg. Land- und Siissw. -Conch., p. 267, tab. xv, fig. 13, 1872. 

 Nekita — Nyst. Coq. foss. de Belg., p. 436, pi. xxxvii, fig. 30, 1843. 



Spec. Char. N. Testa ovato-ylobosd, laevigata, apice obtuso ; Uneolis fuscis parallelis 

 vel reticulatis tenuissimis ornatd; anfractibus supra concavis ; aperturd semicirculari ; 

 columella arcaatd, in medio tenuiter denticulatd. 



Diameter, fths of an inch. 



Localities. Hempstead {Morris), Headon Hill, Muddiford (S. Wood). 

 Belgium : Kleyn-Spauwen {Nyst). 



This species is abundant at Headon Hill, and the operculum also is sometimes found, 

 a figure of which I have given. This operculum is flat on the exterior, and has not the 

 curvilinear depression possessed by that of N. Forbesii. The projecting prominent teeth 

 on the inside appear also to be different from that on the operculum of Forbesii, the 

 two bifurcations of the denticle being unequal in size, and expanding more widely. The 

 outer lip of our shell is plain and sharp, the inner moderately extended ; and the 

 columella is sharp-edged and slightly concave, and has upon its centre about half a dozen 

 fine denticles. These shells are variously ornamented on the exterior, generally having 

 fine cancellated openings, produced by lines of oblique brownish colouring matter, 

 crossed by similar oblique lines which together form small, lozenge-shaped, white spaces, 

 but the lines are sometimes confluent. 



This species is not mentioned as a fossil of the Paris Basin, but the shell from Kleyn 

 Spauwen, as given by M. Nyst, appears to be identical with it, and that author has 

 given as a synonym of it N. picta, of Dubois, from Volhynia, though with a doubt. In 

 the description of Dubois' species, however, the words " columella unidentata " occur, a 

 character which our species does not possess. 



Mr. Whitaker, in his 1 Memoir,' at p. 579, has introduced concava as from the 

 Woolwich beds at Charlton, but this I have not been able to verify, and I conclude that 

 it was inserted on the authority of the reference by J. Sowerby in 1 Min. Con./ tab. 385, 

 of that shell to Charlton, an erroneous reference, as pointed out by Mr. Prestwich in 

 ' Quart. Journ. Geol. Soc.,' vol. x, p. 121. Mr. Sowerby also in the same table represents 

 a specimen said to be from Highgate, but it does not look like our own shell, as the 

 volutions (which in that figure are sinistral) do not exhibit that concave depression on 

 their upper part which is peculiar to this species, and from which its name was, I 

 presume, given. Some specimens have a white spiral band, like that upon N. ornata. 



