208 THE ESSEX NATURALIST.
collate with them unless it may be the small Helston shells
referred to below.
Some shells kindly sent me by the Manager of the Helston
River Fishery, Falmouth, seem to be very distinct from the
ordinary run of South Coast oysters, and may belong to the
Selsey group. They have the laminae looser on the top valve,
this being sunk into the lower shell, which is strongly ribbed
for its size ; inside discoloured, margins pink to purple.
OSTREA DEVONENSIS sp. nov.
The most beautiful of the British oysters is perhaps the one
described by Montagu (Test. Britt. 1803, p. 152) as coming from
Salcombe Bay, Devon (plate xvi., fig. 20) having a very thin
shell, rather shallow, with large membranaceous plates, wrinkled
with irregular interrupted ribs. The upper valve is flat, or
rather concave on the top, with a corneous margin, half an
inch broad, extremely thin and brittle ; the lower valve convex,
clouded with pale purple, particularly round the margin. Shells
taken from different parts of the bay vary so much that they
appear like different species. The corneous imbricated lamellar
plates of the upper valve here referred to are broad, elevated and
obscurely folded, and like the lower valve more or less tinted
with violet or purplish red. The latter is traversed by radiated
folds or ribs, often vaulted, where the concentric growths are
raised (Turton, Conchylia Insularum Britannicarum, 1822).
Turton describes it as roundish oval, with scaly foliations,
the upper valve less and flattened, and the inner margin very
entire. The shell which Montagu described is apparently the
one to which Turton refers when he says "the shell is very
irregular, sometimes growing to a large size, when the beak of the
under-valve becomes much elongated and transversely striate
in the ligamentous cavity."
OSTREA MONTAGUI sp. nov.
The difference between the two forms recognized by Col.
Montagu, specimens of both of which I possess, may be briefly
stated. The one has thin walls, with finely ornamented and
foliated under-valves, and a greater development of the horny
plates ; the other is a stouter, more rugged texture, the costal
ribs are more strongly defined, and the laminae more closely