LIX. Nerita. A semi-globose univalve, depressed beneath, and 
having no umbilicus : the opening entire and semicircular ; columella 
nearly transverse and flat, with an acute, and generally dentated, edge. 
The shells of this genus differ from those of Natica, in never being 
at all umbilicated. 
Nerita conoidea, Lam. Nerita ‘perversa, Gmelin, is, as well from 
its form, as from the extraordinary magnitude which it sometimes 
possesses, a very remarkable fossil. It is conical, with a very broad 
base ; the apex of the spire is inclined, and the columella is furnished 
with eight teeth. 
Chemnitz, and other naturalists, have thought that this was a re- 
versed shell ; but Lamarck has shown that its turns are in the ordi- 
nary direction, from the left to the right. It acquires, however, a 
peculiar appearance, from the top of the spire being inclined to one 
side, as if the axis of the spire had been broken or bent in its upper 
part; hence the shell is irregularly conical. The upper part is 
smooth, or only slightly striated, in a transverse direction, agreeable 
to the successive addition of new matter to the shell. The opening, 
which is nearly semicircular, possesses about one-third of the base. 
The size of some of these fossils is very considerable. Lamarck ob- 
serves that the width of the largest specimen is seven centimetres, 
(about two inches Fr. and seven lines.) One of the specimens which 
I possess is hardly more than an inch across its widest part ; whilst 
another, which I purchased from the collection of M. de Calonne, 
measures in the same direction full three inches and three quarters, 
and exceeds two inches in height. These gigantic proportions widely 
distinguish it from any recent shell of this genus. These fossils are 
from Retheuil and Courtagnon. I am not acquainted with the dis- 
covery of any shells of this genus among our English fossils. 
Plate YI. Fig. 4, is a curious fossil, being a calcedonic cast of the 
hollow of a nerite of this species, displayed by the removal of the top 
of the shell. 
