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 0 . virginica 
has not been found outside the N.E. United States and Canada. 
It is the 0 . 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. 
20'3), enters it in his list of shells, but doubts its specific value, 
as does Dr. Dali, 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 0 . plicatula in the report on the St. Erth deposit 
{Trdns. 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 0 . 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 0 . 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 
