194 THE ESSEX NATURALIST.
South Eastern English area, but it is not rare in the Danish
Limfiord in Jutland. The fig. 2, plate xii., is that of a very
delicate shell of this type, found in the Deben river, Suffolk.
It is a large shell 125 mm. long and 140 mm. broad.
The appellation O. edulis covers a number of forms living
outside our own coasts, as well as the varieties Jeffreys assigned
to it, i.e., O. parasitica, hippopus, deformis, rutupina, and tincta.
Messrs. Bucquoy, Dollfus, and Dautzenberg (op. cit., vol. ii.),
enumerate in addition to the type the vars. O. tarentini Issel,
O. lamellosa Broc. (including O. hippopus), O. cristata Born,
O. cyrnusi Payr., O. adriatica Earn., O. depressa Phil., O. para-
sitica Turton, O. deformis Lam., O. rutupina Jeff., with colour
forms tincta and bicolor.
Carus (Prod. Faun. Medit. 1889-93) is not so diffuse, only
admitting O. deformis and O. parasitica. Sacco in his great
work, Molluschi Terreni Terziarii del Piemonte, etc., refers to
16 or 18 different forms under the heading O. edulis.
The especial features of the shell selected as O. edulis typica
are its colour, small and closely appressed horny plates or lamellae,
and the confluent margins of the valves, the lamellae barely pass-
ing below the verge of the upper valve.
Before going any further, I propose here to examine the
varieties adopted by Dr. Jeffreys, as I am unfortunately com-
pelled to differ from his opinion in many respects.5.
VAR. PARASITICA, Turton.
Turton (Conch. Dict., 1819, p. 134, pl. I., fig. 8), describes
a shell under this name as "glossy, colour purplish to greenish
brown, with streaks of a darker hue radiating from the beaks ;
found on crab claws in Devonshire and on floating timber
in Ireland."
The shell Turton met with on floating timber in Ireland was
probably the O. parasitica Gmelin of the Atlantic tropics, a
species very partial to the Mangroves and other water-loving
trees. Thompson also records it from the coasts of Ireland.
Jeffreys, who gives its range from Galway to Carthagena and the
Mediterranean (Proc. Zool. Soc, 1879, p. 555), seems inclined to
collate Turton's shell with the O. depressa of Philippi (En.
5 For the cultivated and marketable forms Philpot's Oysters and all about them may
be consulted with advantage.