92 



MOLLUSCA. 



Neritina. 



canaliculate above, and exhibiting incquidistant lines of growth, others obsolete ; aperture semicircular ; outer lip plain, 

 which are more conspicuous above, and nearly obsolete below ; sharp, and destitute of teeth or crenulations internally, 



aperture transversely ovate. 



Found in the Mountain Limestone, Gloucestershire. 



7. Nebita sinoosa. — The Sinuated Nerita, pi. XLIV. fig. 



•26, 27. 



Nerita wiuoaa. Sowerby, IV. p. 32, pi. 217, fig. 2. Fle- 

 ming, p. 318. 



Subovale ; spire short, with three rather inflated volutions, 

 the apicial one obtuse; aperture elongated; outer lip plain, with 

 a sinuated lobe on its edge, near the base; coluniollar lip broad 

 and flat ; body with an angular, transverse sinus above the 

 middle, and bordered with an obtuse keel ; whole surface with 

 irregular, well defined lines of growth. 



Found in the Portland Oolite at Chilmarsh. 



8. Nerita angulata The Angulated Nerita, pi. 



XXXVII.* fig. 40, 41. 



Net-ita angulata. Sowerby, Geo. Trans. IV. N. series, p. 

 347, pi. 23, fig. 2. BenetU, Cat. p. 4. 



Subglobose? body large, with an elevated spiral carina some- 

 what below its centre; spire small, and obtuse; aperture 

 oblong. 



A cast of the ehell. 



Found in the Portland Stone, North Wiltshire. 



Genus XLV.— PILEOLUS— Coo/«on. 



Shell concave ; spire internal, very short ; with a sub- 

 central, erect vertex; base concave, nearly orbicular, and 

 somewhat cushion-shaped ; aperture situate in the lower that shell. 



but within the lower region of the aperture, it is pro- 

 vided with a somewhat elongated, transverse prominence, 

 which seems the fulcrum for the articulation of the oper- 

 culum; inner lip flattened, reflected on the columella, and 

 placed obliquely to the axis of the shell ; edge generally 

 short, and dentated or crenulated; as the animal enlarges 

 in dimensions, part of the columellar lip is absorbed, 

 which gives it the appearance of being devoid of a colu- 

 mella ; operculum testaceous, semicircular, closing the 

 aperture entirely, covered with a horny epidermis, and 

 provided internally at tlie lower end with a tooth-like 

 appendage, whicb fits into a hollow between the promi- 

 nence and lip. 



1. Neritina concava. — The Concave Neritina, pi. XLIV. 

 fig. 20, 21. 



Neritina concava. Sowerby, IV. p. 118, pi. 385, fig. 1 to 

 8. Fleming, p. 321. 



Obliqunly subovale; body largo, the surface ornamented with 

 deeply undulating, zigzag, fine dark-coloured lines, which nearly 

 approximate at their angles, and produce a reticulated appear- 

 ance; spire short, obhque, and somewhat prominent, with three 

 volutions, each of which is concave above ; aperture semicircu- 

 lar ; outer lip entire, smooth, and even on the edge ; pillar lip 

 broadly reflected on the columella, and narrowed above and 

 below. 



This species has much the aspect of N. fluvialilcs, but differs in the 

 aperture being smaller, and in the columella being less flattened than in 



disk, and provided with a crenulated, internal lij); exter- 

 nal lip furnished with a raised margin. 



1. PiLEOLUS L^EVis. — The Smooth Pileolus, pi. XLIV. 

 fig. 16, 17. 



Pileolus l(et3xs. Sowerby, V. p. 43, pi. 432, fig. 5, 6, 7, 8. 

 Fleming, p. 363. G. B. Sowerby, Gen. Rec. and Foss. Sh. 



Rather depressed, smooth, or with irregular, nearly obsolete, 

 divergent furrows ; margin entire ; the inner lip obscurely cre- 

 natcd. Fig. 16, natural size. 



Found in the Oolite at Hiiiton and AncIiiTe, Somersetshire. 



2. Pileolus plicatus. — The Plicated Pileolus, pi. XLIV. 

 fig. 1.3, 14. 



Pileolus plicatus. Sowerby, V. p. 43, pi. 432, (ig. 1, 2, 3, 4. 

 Fleming, p. 303. G. B. Sowerby, Gen. Rec. and Foss. Sh. 



Obtusely conical, with divergent ridges emanating at the 

 apex, and terminating on the margin, which is irregularly cre- 

 nalcd ; centre of the base divided into a cushion-like form, and 

 divided in the centre into two parts, by a slifrht sulcus ; height 

 not equal to the diameter of the base ; inner lip strongly cre- 

 natcd. 



Found in the Oolite at Hinton and AnchlTe. 



Found in various strata from the London Clay to the Crag. 



2. Neritina uniplicata. — The One-plaited Neritina, pi. 

 XLIV. fig. 18, 19. 



Nei-ilina uniplicata. Sowerby, IV. p. 118, pi. 385, fig. 9, 

 10. Fleming, p. 321. 



Smooth, subglobular ; body large ; spire concealed, and only 

 indicated by a sunk point, from which emanates a curved line, 

 terminating in the aperture, which is semilunar; outer lip sharp 

 at the edge ; inner lip extremely broad, and somewhat convex, 

 its edge somewhat curved, and provided with a single tooth-like 

 projection. 



In some specimens the remains of an olive-green epidermis is discover- 

 able. 



Found in the London Clay at Woolwich and Charlton. 



3. Neritina Fittonii Fitton's Neritina, \i\. X.XXVII.* 



fig. 42, 43. 



Neritina Fittonii. Sowerby, Geo. Trans. IV. 2nd scries, p. 

 346, pi. 22, fig. 7. Mantcll, Geo. S.E. of England, p. 248. 



Convex, much depressed above ; spire very small, consisting 

 of a single volution; body large, with three prominent, rounded, 

 transverse carina, or ribs; aperture large. 



Found in the Hastings Sand of Sussex. 



Genus XLVL— NEKITINA.— /.a;«arc/t. 

 Shell thin, external surface generally smooth, and fre- 



FAMILY VL— PERISTOMIDA. 



Shell conoidal, or subdiscoidal, with the margins of 



<iuently covered with a strong, horny epidermis; spire the aperture united; aperture protected by an opercu- 

 usually very short, sometimes nearly concealed, and at lum ; fluviatilc, and the animals respiring in water. 



