66 
This was brought to me by Miss Benett, along with 
the last, for the purpose of being figured, that a refer- 
ence may be had to some at least of so numerous and 
obscure a tribe of shells. It is from Farley, near Salis- 
bury. The cicatrix is excavated a little like the last, 
but there does not seem to be a silicious deposit between 
the lamine. ‘The excavation in the cicatrix has been 
thought to characterize the last species ; but it is a cir- 
cumstance that may be observed, not only in other 
Oysters, but in other genera, both foreign and British: 
thus the flat valve or support of Hipponix* cornucopia of 
De France has often a deep hollow in place of the arched 
cicatrix, in consequence of the shell being more liable to 
decay in that part. 
Oysters and some other common shells are the most 
puzzling, because they admit of such extensive varia- 
tion that, although there are certainly many species 
among them, the greatest discernment meets continually 
with stumbling blocks, while attempting to distinguish 
them from one another, or the recent from those of an- 
cient times. ‘The proportions of Oysters diiler in every 
individual, more or less; the shape, placing, and even 
colour of the cicatrix also vary; and similar variations are 
to be found in both fossil and recent shells thus I have 
the placing and purplish colouring exemplified in fossil 
Oysters from Normandy, and in recent ones from Ame- 
rica; the thickness of the shell and length of the hinge 
pit are sometimes characteristic, but vary much with 
age. The fibrous shell of the inferior Oolite is proved 
by specimens I have fron: Normandy to be an Ostrea, 
and is often above two inches thick; and I have a fossil 
hinge from the Tagus above four inches long; but 
other specimens of the same species are much shorter. 
Varieties of the common recent Oyster, which are dis- 
tinguished by their localities, as Milton, Colchester, &c. 
although they are pretty well known by a general ob- 
server, yet, when compared individually, do not appear 
to possess any decided character; but after all, figures 
and a reference to a few characters must tend to assist 
us in understanding what shells are alluded to by 
Conchologists, and therefore I presume the present 
plate will be useful. 
* A new genus established by De France, containing several shells that 
were classed with Patella, but which are found te be attached bivalves. 
