340 GASTEROPODA OF THE INFERIOR OOLITE. 
the operculum of Neritopsis Bajocensis (Pl. XXVII, fig. 10) shows no very obvious 
signs of the process which should fit into the notch. Hence it must be remembered 
that, so far as the Inferior Oolite of this country is concerned, one of the most 
characteristic features in the diagnosis of the genus Nevitopsis is wanting. The 
most probable explanation is that the feature has been obscured through the 
accidents of fossilisation; but the absence of this character has induced some 
conchologists of eminence, such as the late Robert Bell, to regard these forms as 
belonging to Narica (Vanikoro). 
Several species of Neritopsis are noticed by Moore as occurring in the Upper 
Lias, and he also described Neritopsis cancellata, Moore, from the Lower Lias of 
Brocastle. Seeing that specific differences, both in the Lias and Oolites, are 
mainly based on variety of ornamentation, which evidently varied according to 
locality as well as according to horizon, the precise biological value of these 
distinctions may not be very great. In the Inferior Oolite of Dorsetshire specimens 
run much larger than in other districts, but, on the whole, Neritopsis, though far 
from being abundant, is by no means confined in its distribution. 
272. Neritorsts Basocensis, d’Orbigny, 1850. Plate XXVII, figs. 9 a—e. 
Operculum, fig. 10. 
1850. Nerrropsts Basocrnsts, d’Orbigny. Prod., i, p. 264. 
5 
1852. — oo _ Terr. Jur., vol. ii, p. 223, pl. ece, 
figs. 8—10. 
1867. — a — Laube, Gast. Br. Jura von Balin, 
p- 6, pl. i, fig. 9. 
Non os — — Hudleston, Geol. Mag., dec. 3, vol. i, 
p- 300, pl. ix, fig. 11. 
Description : 
Height of a medium specimen : . 23 mm. 
Width : ; ; : . 26mm. 
The following is the author’s diagnosis :—“ Shell oval, transverse. Spire very 
short, composed of three very convex whorls, excavated near the suture, increasing 
very rapidly, of which the last, of enormous size, is furnished spirally with 
numerous small alternate unequal cost, and with radial undulations, like rounded 
furrows.” 
Relations and Distribution.—This species is especially characterised by the 
thick undulating coste on the rounded shoulder of the body-whorl. It is 
essentially a fossil of the Upper Division of the Inferior Oolite, and is almost 
