216 THE ESSEX NATURALIST.
C. convexa Say, or an allied form, which have taken root and
flourish abundantly. The shells laid down were the medium-
sized "blue points" figured by Chemnitz, t. 73, no. 577.
Early writers extended the living range of this species to
Europe, and even to the Indian Ocean (Linne), several W.
European forms being included in it, but the true O. virginica
has not been found outside the N.E. United States and Canada.
It is the O. rostrata of early conchologists.
The Ostrea borealis described by Lamarck (An. sans. Vert.
vii., 220), is the earlier growth of the above, and Reeve (op. cit.,
plate vi., fig. 9), figures a specimen having some resemblances
to our close-pressed Ostrea edulis. Gould (Invert. Mass., p.
203), enters it in his list of shells, but doubts its specific value,
as does Dr. Dall, who says "there are certainly forms in which
the American and European forms could not be distinguished."
Jeffreys seems to have been of the same opinion.
OSTREA ANGULATA ERTHENSIS, var. nov.
Lamarck's name Gryphaea angulata (Anim. sans. Vert., vol.
vii., p. 203), has been extended by many writers to cover the
irregularly shaped oysters (the Anglo-Portuguese shell of our
markets), characterized by the strong carinated ridges extending
from the umbo to the ventral edge. The mollusc is not a British
species, nor does it occur fossil in this country, unless the shell
referred to as O. plicatula in the report on the St. Erth deposit
(Trans. R. Geol. Soc, Cornwall, 1897, vol. xii., p. 154), is, as I am
inclined to think, a member of this variable group (plate xviii.,
fig. 26). Our shell is strongly carinated and hollowed under the
cartilage pit, and the umbo is camerated within. It may be the
O. plicata of Chemnitz, and O. plicatula of Gmelin, which Lamarck
says inhabits the "seas of America and the Indies, fixed to rocks
and corals," and which Chemnitz says is American or Mediter-
ranean, varying very much in shape and size, but generally
cavernous, with a mixture of violet, sometimes white with a
bluish tint. Gmelin's name is now used for an Asiatic shell (see
Reeve, Conch. Icon). Eyton (op. cit.) says the Portuguese oyster
buries itself in muddy sand with the hinge downwards, and
was informed that the American O. virginica in the Chesapeake
River had the same habit. Brooks (The Oyster, Baltimore, 1891)
says this is due to overcrowding the hard ground so closely that