BRITISH OYSTERS : OLD AND NEW. 217
they cannot lie flat, but grow vertically upwards side by side.
Hidalgo gives its habitat as Corunna and the Tagus, with a littoral
habitat. Attempts to naturalise it in British waters have not
been very successful or productive.
These may all be referred to the section Crassisostrea, Sacco,
a group which discharge their eggs into the sea water, unlike our
British shells, which retain the fry in their gills. (Dr. Dall, in
litt.)
OSTREA LUSITANICA, A. Bell.
Under this name I figured (Rept. Yorks. Phil. Soc., 1892, p.
73, pl. i., fig. 1), a shell I found occasionally in the early Pleistocene
mud deposit at Selsey in Sussex, where it occurred with 215 other
species of molluscs, all of Lusitanian types. The shell is long
and narrow in proportion, ranging up to 100 mm. by 45 mm.
On p. 197 reference is made to a small elongated shell ascribed
by Jeffreys to O. deformis Lamarck, which I showed did not agree
with the author's description in any way. Reeve's figure
(op. cit., plate v., fig. 8, d.), closely resembles this shell and both
may be assigned to the present species.
OSTREA VERTEX, sp. nov.
Sir Gardner Wilkinson (Zoologist, 1865, vol. xxiii., p. 9559),
describes finding at Tenby a small oyster with depressed end,
only 2 inches long, by five-eighths of an inch in breadth, scarcely
varying in width throughout its length. His description is that
of a young shell having the "half deck" prolonged into a tail-
like projection or spur, terminating in a sharp point corres-
ponding with the hinge area and which in my own full grown
example is much larger. This shell may be described as long,
narrow, thin ; upper valve slightly convex, lower flatly convex
to hollow or channelled longways ; beak and ligamental pit long,
narrow, and usually produced as a spur. Scar purplish, hinge
granulations indistinct. Length 70 mm., spur 15 mm., breadth
45 mm. Colour cream yellow, thin outer skin, margin plain,
surfaces smooth. One of the largest dealers in S. Wales tells
me that this form is only met with at times, and one of his men
to whom he showed my sketch at once recognized it as a local shell,
not often met with. The name vertex refers to the projecting
spur. (Plate xviii., fig. 25.)