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. 
0 ST RE A DEVON ENSIS 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 MONTAGU I 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 
