210
THE ESSEX NATURALIST.
enlarged edition of Montagu's rock oyster, and probably repre-
sents the same form. "The upper valve is beautifully radiated
with lines and streaks of dull purplish crimson, or reddish-
chocolate, and the concentric lamellae, instead of being closely
appressed, are extremely thin, usually composed of rather large
plates, more or less elevated, overlapping each other. The
ribs or radiating folds of the lower valve are less numerous, and
mostly narrow or but moderately broad, sometimes stained with
a rich purplish red towards the margin."
Reeve also figures a handsome shell referable to this form
as O. edulis, but like Forbes and Hanley does not give any locality.
OSTREA SAXATILIS Turton.
"Shell very thin, pellucid, a little scaly, the larger valve
with strong longitudinal ribs which often end in hollow scales.
Shell two to three inches long, variously shaped but generally
suborbicular, oblong or sub-triangular, mostly with a fine purplish
tinge." (Bivalve Shells of the British Islands, 1822.) Found
adhering to rocks and stones near low-water mark at the Mumbles
near Swansea.
I have copied Turton's description, not having had the
opportunity of seeing the shell referred to as yet, as it seems to
be scarce at Swansea. The description, "very thin and pellucid,"
separates it from any form I know unless it is the one here
figured (plate xvi., fig. 19), with which I am disposed to collate it,
but with some reserve, my shell not being so pellucid as is des-
scribed by Turton. This may be only another local form (Tenby),
but sufficiently pronounced in features to make it easily separable
from other members of the same group, and it seems peculiar
to this part of the Bristol Channel. The valves are suborbicular
and unequal, more so than in others in this group, as the laminae
in none of the examples I have seen, whether 2 or 4 inches across,
old or young, seem to have these projecting beyond the edges
of the valves. Those on the upper valve are very closely flattened,
not rising above the level. The costae on the lower valve are
undulate, broad, and irregular in size and disposition, the lines of
growth hardly showing in the smaller shells, showing more as
the shell grows, where the. costae become fimbriated. In the
scaeva form these are prominent, even in the smallest stages of
growth.