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 0 . edulis, but like Forbes and Hanley does not give any locality. 
OSTREA SAX AT I LIS 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 
scceva form these are prominent, even in the smallest stages of 
growth. 
