15 
by the above name. When a well-known species is removed 
to a new genus, it is very desirable that the specific name 
should be retained; but mstances occur, where it can be 
changed with much advantage. Under this view of the 
subject, perhaps, Mr. Dillwyn was justified in changing the 
name of Helix perversa of Linneus, to Helix aurea. See 
“ool, Ill. vol. i. pl. 46. 
PHASIANELLA VENTRICOSA. 
(Lot 285, 967.) 
P, testd ventricosd ; spire anfractibus convexis, apice acuto ; aper= 
ture viv effuse sprreque longitudine eddem. 
Shell ventricose; spiral whorls convex, the tip acute; aperture 
nearly effuse, as long as the spire. 
Tue varieties of this species present as great a diversity in 
their colouring, as the P. varia of Lamarck. De Montfort 
was the first writer who, with much accuracy, pointed out 
what he terms the internal plait, existing on the inner side 
of the columella, and which is constant in all the species 
which I have examined; he does not, however, appear to 
have been aware of its use, or of the connexion it bears 
with the structure of the animal: when viewed in this light, 
it assumes an important character. The opercula of all 
Phasianelle are thick and shelly, and that part of the 
columella which is seen at the aperture, is very convex and 
highly polished; there would be danger, therefore, when the 
animal suddenly drew itself into the shell, either that the 
operculum would slip within, beyond its due limits, or that 
its sudden contact with the shell might produce injury: to 
guard against this, Nature has wisely furnished the columella 
with a little groove, just at that part where the confines of 
the mouth are fixed. This groove receives the rim of the 
operculum, while the projecting margin thus left inside 
