BRITISH OYSTERS : OLD AND NEW. 205
VAR. TENBIENSIS. var. novo.
(Plate xvi., fig. 17).
This is the oyster described as O. edulis by Turton (Brit.
Faun., p. 162) as "suborbicular, rugged, with undulate, imbri-
cate scales, one valve flat and entire, shell varying much in size
and bulk, generally brown with unequal valves, the upper one
flat, the lower very convex and rugged, transversely striated
and often longitudinally ribbed, pearly white inside, beak
rather oblique, with a row of small knobs running down each
side," and subsequently (Bivalve Shells of the Brit. Isl. 1848)
as a "shell roundish oval, with scaly foliations, the upper valve
less and flattened, and the inner margin very entire." The
above description corresponds very well with a large number of
specimens I have received from Tenby. The Tenby shell
as a rule does not attain very large dimensions, my largest
specimen measures 41/2 inches, breadth 31/2 inches (100 mm.
by go mm.), but Mr. Ridsdale, F.G.S., tells me that at Water-
wynd, Tenby, he finds large isolated individuals. One I have
seen from Caldy Island measures 150 mm. in length by 130 mm.
in breadth.
I have separated this as a group, partly because Turton makes
a specific note of it, and it seems peculiar to West Britain.
It is very probable that it represents a survival of the original,
long and massive Celtica group.
With much hesitation I have referred to the foregoing groups
as being varieties of the one species O. edulis. It is not a matter
of much importance whether they are so regarded or are not.
Further research will, I think, show that we are mainly dealing with
specific and not merely varietal forms. As a rule they have
nearly all dark coloured plain margins with closely appressed
laminae on the flat valve, and are characteristic of the Celtic
province, while those of the South and Atlantic coasts are more
or less coloured and have the laminations large and extending
beyond the margins of the upper or flat valve. The loss of these
usually causes great inequality in the dimensions of the two
valves, allowing the flat valve to sink into the lower one.
OSTREA ATLANTICA sp. novo.
Lamarck has utilized the name O. cristata for a Senegalese
shell referred to by Adanson (Hist. du Senegal, 1757, pl. 14,