162 J, Starhie Gardner — Cretaceous Gasteropoda. 



dilated in front, so that the extremity projects beyond the colnmella. 

 The aperture is oblique to the axis, towards which the front is in- 

 clined ; the outer lip is very much thickened, the thick edge being- 

 sinuous ; it is sometimes terminated an- 

 teriorly by a slight, narrow and shallow 

 groove, whilst in a few species the front 

 edge forms a gradual curve, the point of 

 demarcation being scarcely visible, passing 

 thus insensibly into Bissoa. The figure 

 represents the mouth of jB. Sowerhii, which Mouth of Rissoina SowerUi. 

 may be considered typical of the genus. 



H. A. Adams thus defines the genus : ^ — "■ Shell turreted, ribbed or 

 cancellated, many-whorled : spire acuminate ; aperture ovate, effuse 

 anteriorly, slightly channelled in front ; outer lip anteriorly dilated, 

 thickened internally." 



Eissoina first appears in the Jurassic rocks ; in the Cretaceous era 

 the species are few, only three being described ; of these, but one is 

 British ; a fourth is here added for the first time. 



EissoiNA iNCERTA, d'Orb. Gault, Folkestone. Plate lY.Figs. 12 and IcI. 



Shell elongated, angle of spire, exclusive of projected lip, 20° ; 

 whorls slightly rounded, smooth, without trace of ornamentation, 

 sutures distinct; mouth ovate, outer lip inflected and dilated, very 

 much thickened, slightly channelled anteriorly. The surface of the 

 shell, when highly magnified, exhibits an irregularly wavy striated 

 appearance, somewhat similar to the bark of trees (Fig. 13a). This 

 species was first described by Deshayes as Melunia incerta, 1841, 

 Mem. de la Soc. Geol., t. 4, p. 320, and again by d'Orbigny, 

 Pal. Fr. p. 62, pi. 155, fig. 11-13, and by Schwartz von Mohren- 

 stein, in his Monograph, 1860, tab. xi. f. 89. D'Orbigny's figure 

 presents a smaller angle than that of our specimen. 



It is not a very uncommon shell, being found in a beautiful state 

 of preservation in the Gault of Folkestone. The shell, when the last 

 whorl is not present, resembles and has been described as a Eulima. 



EissoiNA SowERBii, J.S.G. Gault of Folkestone. 

 Plate IV. Figs. 14 and 15. 



Shell elongated, angle of spire, exclusive of last whorl, 20°; 

 whorls ten, inflated, transversely and obliquely ribbed, the ribs, 

 extending to the sutures, without stride ; sutures distinct ; mouth 

 ovate, outer lip inflected and dilated, very much thickened, slightly 

 channelled anteriorly. Last whorl without ribs dorsally. 



Sowerby figured this shell in the Trans. Geol. Soc, vol. iv. pi. xi. 

 fig. 17, as Bostellaria huccinoides. He remarks that the shell has 

 but one varix, by which he probably intended to signify the thicken- 

 ing of the mouth, as the shell is not subject to varices. 



R. Sowerhii strongly resembles the last species in general form, 

 but is ribbed. It is abundant at Folkestone, but has hitherto been 

 1 Adams, Genera of the MoUusca, vol. i. p. 327. 



