26 
N. clypeata, Witc. (Clypeus Grit.) 
NV. Strickland, M. & Liyc. G. Oolite (Stonesfield Slate.) 
N. dubia, Wire. do. (White limestone.) 
N. striata, Buck. do. (Stonesfield Slate) 
One species, N. Cotteswoldie, Lyc., differs from group 5 in 
having only two folds on the outer wall and four on the 
columella, and differs also in its external appearance, which is 
short and more conical than that of the other species of the 
group. 
It will be seen that N. Guiser differs from all the others in 
having five internal folds, viz., two on the columella, two on 
the outer wall, and one on the posterior wall. This species 
differs likewise from the whole of the figures of D’Orsieny, 86 
in number, so that it appears to illustrate a new departure from 
preceding types, but is confined, so far as is at present known, 
to a single species. 
This classification however is only partial. Several of the 
species are so variable in their general external aspect that they 
may well be classified as sub-genera, as proposed by SHARPE. 
For instance, N. Hudesii has concave whorls, which are much 
greater in width than height; while N. altivoluta has straight 
sided whorls, which are higher than wide, the internal structure 
of both being on the same pattern with a slight variation of the 
figure owing to the difference in the height of the whorls. The 
difference in the external forms of the species in group 5 is 
much less than in the two species which I have selected for 
comparison, but still it is sufficiently marked to show that they 
are not varieties merely, and there is generally some slight 
variation of the internal character arising perhaps from the 
different form of the shell which together justifies their being 
treated as species. 
It would be interesting to ascertain how far the species of 
this genus are confined to particular zones, but unfortunately 
the exposures of the Nerinea beds are limited in number and 
extent, in fact they may be said to occur in patches, and 
frequently the beds containing several species in profusion in 
a given locality, are destitute of them altogether at the distance 
