BRITISH OYSTERS : OLD AND NEW. 201
average breadth being about 31/2 inches (85 mm.), and are nearly
always ovate-oblong in outline, beaks but slightly projecting,
lower valve convex, upper one slightly so ; lamellae rather pro-
minent. The lower valve exhibits well defined to strong ribbing,
the costae regular and co-equal in size to the interspaces, becoming
slightly vaulted at the intersection of the yearly shoots ; margins
entire. The ligamental area is moderately broad, hinge nodules
well marked, colour inside white to purple in blotches. Scar
lunate. (plate xiii., fig. 8).
A very old shell from a deposit of some antiquity at Hillswick,
in the Shetlands, exhibits the pear-shaped interior of the shell,
and the accretionary growths seen in the Irish Estuarine types,
and the lateral expansion of the ligamental area which seems
to be characteristic of age.
Mr. Garstang, (Vict. Hist. Essex, p. 81, 1903) says "numbers
of dead shells occur where living animals are seldom if ever
found, I often think that many of these dead shells* are of a
more elongated shape than the modern living varieties."
The Manx oyster fishery is now practically extinct. I owe to
the Rev. S. N. Harrison, of Ramsey, two or three examples ob-
tained from deep water by the fishing boats, in 15-20 fathoms off
Ramsey, and dead valves may be found on the beach. They
represent a strong and large shell, length 5 inches, breadth
41/4 inches. The interior is a dull, chalky white, like most of
the other members of this series (plate xiv., fig. 9).
Prof. Forbes, in describing in the Mag. N. Hist. 1839, p.,
217, a shell bank five miles off Ballaugh, refers to the oysters he
dredged there ; they were never in great numbers, but very
large, muscular and thick shelled ; half-grown specimens were
rare, and he had never seen a very young shell. The oysters
seemed to be the aged survivors of some former colony. Most
of the examples were dead shells ; the living generally
perforated by Cliona.
Wexford shells, both raised beach and deep sea, belong to
this group. The shells from the early gravels at Blackwater
closely resemble the smaller valves I have from Cnoc-Sligeach,
Oransay. The same may be said of the shells in the limestone
drift in Ballybrack Bay, as of those found at Malahide, near
Dublin, between tide marks.
*Such as are found in the Pleistocene peat in the River Orwell.