EDWARDS — ON PITHARELLA RICKMANI. 
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stone of Rilley-larMontagne, and otlier estuarine forms ; and also 
masses of leaves of trees, and other vegetable remains. Associated 
with these are found, sparingly in the clay, but rather more plenti- 
fully in the sandstone band, the remains of an undescribed spiral 
shell, which were at first referred to the genus Vohita, because the 
imperfect casts, in which condition only they were then found, pre- 
sented a close resemblance to casts of the well known Bognor fossil, 
Valuta dt^mdata. Tolerably perfect specimens have been since ob- 
tained, and from these it appears that the columella is without 
the plaits characteristic of that genus, and that the base of the shell 
is rounded and entu-e, and without transverse fuiTows. The shells, 
therefore, must be referred, not to the genus Vohda, but to some 
laud or fresh-water mollusc, belonging most probably to one of the 
three families, Auriculidw, Acliatinidce, or Limneidce, 
The shells are smooth and rather thick, and in their general aspect 
present much of the character of the Auricididce, and were there any 
indication of transverse folds in the columella, they might fairly be 
considered to be an abei-rant form in the group (^Auricula, Lam., 
Geovula, Swains.), of which A. aims-Midcm forms the type. The 
prominent character by which the shells of the Am'icuHd« are dis- 
tinguished is the presence of one or more thick, well-defined, trans- 
verse folds on the columella, and this is, I believe, a constant 
character : I do not know of any genus belonging to the family in 
which it is wanting, or evanescent. 
The Acliatinidce, as a family, are characterized by the truncation 
of the columella ; and they usually have the spire much produced, so 
as to exceed the aperture in length. One group in this family — in- 
habiting the West India islands and the adjacent parts of the 
American continent, {FohjpUemus, Montf., Glandina, Schum.), in 
which the aperture and spire are nearly equal, and to which the 
Peckham shells approach more closely than to any other genus in the 
family — is represented in our Eocene faima by Achatina (Glandina) 
costellata of the upper fresh- water deposits in the Isle of Wight ; but 
in this group the body whorl is much attenuated at the base, and the 
columella is strongly truncated. 
The distinguishing characters of the Limmidce are the acute spire, 
the wide aperture rounded in front, and the obhquely twisted 
VOL. 111. 2 D 
