BRITISH OYSTERS : OLD AND NEW. 195
Mol. Sci., vol. i., pl. vi., fig. 3), but this according to Reeve who
figures O. edulis, var. parasitica may be a species "hereditarily
distinct." His figure (op. cit. pl. xxiii., fig. 55), taken from a
specimen in Hanley's collection, is 95 mm. by 90 mm., and has
been attached to a flat surface. The O. bicolor of Hanley is
another of the same type.
Turton also figures a different species on his pl. 17, fig. 6 and
7, Bivalve Shells of the British Isles, 1822, of the same type as
that utilized by Jeffreys (B.C. v., pl. xxi., fig. 16), and Dr. Grainger
and myself have also found parasitic shells in the Irish Estuarine
Clays. Alder, alluding to the scarcity of oysters in the N.E. of
England, mentions the young as occurring on the backs of crabs
on Tyneside.
The later Ostrea parasitica of Turton is of no specific or varietal
value, the young shells taking their shape from the substances
on which the spat fell. Reeves figures it, as well as Jeffreys,
but neither McAndrew nor Forbes and Hanley notice it.
Canon Norman applies the name O. parasitica Turton to shells
derived from spat of local origin (see Coll. in Brit. Mus.)
The O. edulis var. parasitica of the Crag Mollusca suppl. 2,
p. 14, should be transferred to O. cochlear.
VAR. HIPPOPUS Lamarck.
Shell rounded, thick, upper valve flat, transverse, laminae
closely appressed, L. 120 mm. (An. s. Vert., 1836, vii., p. 219).
Jeffreys describes it as "large and extremely thick, living in
deep water, and solitary." Reeve also says it is "not gregarious,
but solitary, living in deep water, very rough and ponderous,
not at all flaky or scaly, very deep in the lower valve, and thick
in the upper." Forbes and Hanley do not refer to it, and it
does not appear to have been figured. H. and A. Adams have
included it in their lists of species.
It is by no means certain that Lamarck and Jeffreys refer
to the same shell ; indeed, if continental writers are to be fol-
lowed they can hardly be identical, but there is so much diver-
sity of opinion that Lamarck's very expressive name may very
well serve for our "solitary and deep sea shells."
The description applies especially to our North Sea forms
like the Burnham shell, and the massive valves thrown up on
Brancaster beach.