212 THE ESSEX NATURALIST.
any others I have knowledge of in Northern or British waters ;
they are mostly attached to splinters of rock, tiles, or other culch,
and vary much in shape and contour, probably arising from the
size and place of the original attachment at the place of growth.
Free examples measure on an average height 60 mm., breadth
50mm. My largest is 80 by 75 mm. (plate xvii., fig. 23). Sculpture
of lower valves strongly costate, the concentric lamellae in the free
shell rising into tubular ridges on the costae, a feature not so
well displayed in the rounder and more attached shells. The
inside has a moderate ligamental area, narrower and deeper
than in the ordinary edulis type of the East coast, and more
pointed. The margins are very marked, and deeply indented.
The upper valve is covered with broad horny plates, sometimes
extended beyond the edge, which on breaking away leaves a
broad margin to the lower valve, which is often coloured a deep
purple. Unlike most of our oysters the upper valve is convex
rather than flat. The strong ridges or ribs traverse the back
from umbo to edge, which is largely dentate, the undervalve in
all cases overlapping the upper shell.
Mr. le B. Tomlin, to whom I submitted some specimens,
suggested a reference to the figure of Ostrea stentina in the Moll.
May. du Roussillon, pl. vi., figs 1-6, and except that the dimensions
of the Scotch shells are greatly in excess of the French ones,
and also of those of a specimen I have from the Bay of Naples, I
cannot find any great divergence between the two. Lamarck's
description applies to our shell, but he gives no dimensions.
Carus says 80 mm., which agrees with the measurement of the
Scotch form. According to the Marchese di Monterosato, O. obesa
Sow. figured by Reeve op. cit. pl. xxxiii. (who does not mention
O. stentina) is the same as O. stentina Payr ; the descriptions
given by Reeve and the Roussillon authors agree with our shell.
The last named writers especially notice the flatness or slight
convexity of the upper valve, which is nearly always eroded—
a very definite feature in those from Loch Sween.
F. Buckland remarks that the Western Scottish Oysters
were quite different from those of the East English coast, the
beard being always black. Had he this group in mind ?
Like all the Mediterranean Ostreas, the synonymy of O.
stentina is very involved. Philippi and Pantanelli refer it to
the O. plicatula Brocchi. The authors of the Roussillon memoir