GASTEROPODA. 57 
examples being such as usually have the most widely-separated longitudinal lines or striz. 
The surface markings vary so considerably that they may be conveniently described under 
the three following aspects :— 
a. Ribs elevated and separated ; carinee smooth and prominent. 
6’. Surface with longitudinal closely-arranged plications, but no distinct ribs; plice 
impressed with very fine longitudinal lines. 
ce’. In which the characteristics of the two former varieties are sometimes exhibited 
upon the same specimen, in which case the carine are imperfect, or, in lieu of them, there 
are slight depressions or furrows. 
The most common aspect is that of the variety a’. It is one of the most generally- 
noticed univalves of the shelly beds. Very rarely all traces of ribs and plications are 
wanting, the surface is then shining, smooth, and highly coloured. ‘The dimensions vary 
from that of a duck-shot to the largest-sized pea. 
Locality. Minchinhampton Common. In all the shelly beds of the district. 
Neriva costuata, Desh. Plate VIII, figs. 6, 6a,4,c. Plate XI, figs. 18, 18a, 4. 
Nerita costata, Sow. 1824. Min. Con., t. 463, figs. 5, 6. 
— —_ Phillips. Geol. of Yorkshire, vol. i, t. 11, fig. 32. 
— —_ Brown. Illust. Foss. Conch., p. 91, t. 44, figs. 1, 2. 
—  cosrutata, Desh. 1838. Lam. Anim. sans Vert., 2d Edit., vol. viii, p. 617. 
— — D’ Orb. 1850. Prod. Paleont., p. 299. 
N. Testé parvd; spird obliqud depressd, minutd, viv elatd; anfractu ultimo superne 
planato, costis longitudinalibus, numerosis, subundatis, et approximatis ornato. 
Shell small; spire oblique, depressed, minute, scarcely elevated; the last whorl 
flattened upon its upper portion, and covered with cost, which are longitudinal, 
numerous, closely arranged, and slightly waved; the aperture is very large, the immer lip 
very wide and flat. 
The absence of carine at once distinguishes this little shell from our Werita rugosa, for 
one variety of which it might otherwise be mistaken. It has not been found in the 
Minchinhampton Great Oolite, but occurs occasionally in the Inferior Oolite of that district. 
Axis 2 lines. 
Locality. Ancliff; Stonesfield. nf. Ool., Yorkshire. 
Secr. 2. Inner lip convex. Neridomus. 
N. Testé levigatd, ovato-globosd; spird pared, obliqud; anfractu ultimo permagno; 
apertura ovata, vel semilunari; labio externo crasso; labio interno crasso, convexo et 
levigato. 
Shell smooth, ovately globose; spire small, oblique; the last whorl very large; aperture 
ovate, or semilunar ; outer lip thick ; inner lip thick, convex, and smooth. 
