GASTEROPODA. 167 
for there is so little permanency to the characters of this group, that the 
limits of species are very uncertain. This is probably the most solid 
of all the Nerites. It is very much like what I suppose to be N. 
Guillouana, Recluz; but the spire is less elevated, without any shelv- 
ing of the lip, with twelve or fourteen sulci instead of sixteen to nine- 
teen, and has only one instead of two teeth at the posterior angle; the 
ribs are rounded and not flat. N. wndulata has an elevated spire, a 
protruding and undulating lip, fifteen to eighteen sulci, and two lip- 
teeth ; there are more rug on the transverse lip, which terminate in 
lance-shaped teeth ; the strie of growth are more delicate. 
Figures 195, 195 a, two views of the shell. 
Neriva piicata (Liv.), Syst. Nat.,779. Lamarck, An. sans Vert., 
vill. 609. 
The anrMat, as figured in the Voyage of the Astrolabe, pl. 65, figs. 
27-80, is in general correct; but the hood is protruded in a curious 
manner ; the colour of the foot should be paler, and should show longi- 
tudinal, undulating ruge of a darker shade on the sides above. 
NERITA ALBICILLA (L1w.), Syst. Nat., 778; Lamarck, An. sans Vert., 
vill. 605 ; Voy. de l’Astrol., pl. 65, f. 17, 18. 
The animat has the same abnormal hood as the preceding, as well 
as an unnatural advance of the foot; the sides are much more dis- 
tinetly lineated by dark, undulating lines; it is paler yellow, tinted 
with sky-blue and white. 
Figure 194, the animal seen from below; 194a, the animal as in 
motion. 
NeritTa unpata (Liv.), Syst. Nat., 779; Desuayes, in Lam. An. 
sans Vert., viii. 616. 
Antmat with the foot and head bright yellow above, with undula- 
ting concentric lineations of black ; tentacles short, slate-coloured ; foot 
