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EOCENE MOLLUSCA. 



5. Assiminea, Leach, 1816. 



" Operculum horny ; paucispiral nucleus on the inner side of the mouth." 

 Type. Assiminea Grayana, Leach. 



6. Hydrobia, Hartmann, 1821. 



" Operculum horny and thin, marked with flexuous and rather strong lines of 

 growth, and having a small lateral spire of three whorls." 

 Type. Turbo ulvse, Pennant. 



7. Nematura, Benson, 1836. 



" Operculum spiral, horny, of few volutions, somewhat concave externally, rather 

 larger than the aperture." 



Type. Nematura Deltse, Benson. 



? 8. Valvata, Mutter, 1874. 



" Operculum horny, circular, slightly compressed in the middle, forming a concentric 

 spire of from 10 to 12 whorls, the outer edges of which are thickened and raised so as 

 to project over and partly overlap the succeeding whorl." 



Type. Nerita piscinalis, Waller. 



Genus \Sth. — Planorbis. Geoffroy, 1767. 

 Eor generic character see ante, p. 97. 



No. 262. Planorbis l^evigatus ? Beshayes. Tab. XXXIV, fig. 1 a — b. 



Planorbis l^evigatus, Desk. Coq. foss. des Env. de Par., t. xi, p. 85, pi. x, figs. I, 2, 

 1824. 



— — Id. An. sans Vert, du Bas de Par., torn, ii, p. 746, 1858. 



— — Prestwich. Geol. Joum., vol. x, p. 1 18, 1 854. 



— — Whitaker. Geol. Surv., vol. iv, p. 5/6, 1872. 



Spec. Char. " PI. Testa discoided, laviyatissimd, tenui, symmetrica, depressd, 

 rotundatd, anfractibus quaternis, valde apparentibus ; utroque latere umbilico aquali." — 

 Desk. 



Biameter, -^ths of an i ncn - 



Locality. Brit. : Dulwich (Bott.), Counter Hill (Whitaker), Peckham (Meyer). 



France: Bernon, near Epernay (Beshayes). 

 Two or three specimens of this species have been found in our English beds, but all 

 that I have seen are in the condition of casts ; they, however, appear to correspond with 



