92 
MOLLUSCA. 
Neritina. 
canaliculate above, and exhibiting inequidistant lines of growth, 
which are more conspicuous above, and nearly obsolete below; 
aperture transversely ovate. 
Found in the Mountain Limestone, Gloucestershire. 
7. Nerita sinuosa.—T he Sinuated Nerita, pi. XLIV. fig. 
26, 27. 
Nerita sinuosa. Sowerby, IV. p. 32, pi. 217, fig. 2. Fle¬ 
ming, p. 318. 
Subovate; 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; columellar 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. 
Nerita angulata. Sowerby, Geo. Trans. IV. N. series, p. 
347, pi. 23, fig. 2. Benetts, 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 shell. 
Found in the Portland Stone, North Wiltshire. 
Genus XLV.—PILEOLUS.— Cookson. 
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 
disk, and provided with a crenulated, internal lip; exter¬ 
nal lip furnished with a raised margin. 
1. Pileolus UEVIS —The Smooth Pileolus, pi. XLIV. 
fig. 16, 17. 
Pileolus laris. 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- 
nated. Fig. 16, natural size. 
Found in the Oolite at Hinton and Ancliffe, Somersetshire. 
2. Pileolus plicatus —The Plicated Pileolus, pi. XLIV. 
fig. 13, 14. 
Pileolus plicatus. Sowerby, V. p. 43, pi. 432, fig. 1, 2, 3, 4. 
Fleming, p. 363. 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- 
nated; centre of the base divided into a cushion-like form, and 
divided in the centre into two parts, by a slight sulcus; height 
not equal to the diameter of the base; inner lip strongly cre- 
nated. 
Found in the Oolite at Hinton and Ancliffe. 
Genus X L VI.—N E R IT IN A.— Lamarck. 
Shell thin, external surface generally smooth, and fre¬ 
quently covered with a strong, horny epidermis; spire 
usually very short, sometimes nearly concealed, and at 
others obsolete; aperture semicircular; outer lip plain, 
sharp, and destitute of teeth or crenulations internally, 
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 witli a horny epidermis, and 
provided internally at the lower end with a tooth-like 
appendage, which 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. 
Obliquely subovate; body large, 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, oblique, 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. fluviatiles , but differs in the 
aperture being smaller, and in the columella being less flattened than in 
that shell. 
Found in various strata from the London Clay to the Cra<r. 
2. Neritina unipucata— The One-plaited Neritina, pi. 
XLIV. fig. 18, 19. 
Neritina uniplieata. Sowerby, IV. p. 118, pi. 385, fin. 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, pi. XXXVII.* 
fig. 42, 43. 
Neritina littonii. Sowerby, Geo. Trans. IV. 2 nd series, p. 
346, pi. 22 , fig. 7. Mantell, 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. 
FAMILY VI.—PERISTOMIDA. 
Shell conoidal, or subdiscoidal, with the margins of 
the aperture united; aperture protected by an opercu¬ 
lum ; fluviatile, and the animals respiring in w r ater. 
