Pvn H,i I'UitlS

venus. 339
They differ considerably in the comparative convexity,
and in the ribs being more or less laminar or nnmerons.
I do not regard the V. reflewa of Montagu as a dis-
tinct variety ;
for every possible gradation may be seen,
connecting it with the typical form. The dorsal margin
in this species and V. fasciata not unfrequently assumes
a serrated appearance, arising from the extremities of the
ribs projecting on that side. V. Casina may be known
from the last-mentioned species by being much larger
and broader, the ribs more laminar, delicate, and flounce-
like, the longitudinal stria? proportionally stronger, the
umbones usually not so prominent, and the colour more
sober and less diversified.
The present species is the Pectunculus membranaceus
of Da Costa, V. erycina of Pennant (but not of Linne),
and V. lactea of Donovan ; in its younger state it appears
to be the V. cancellata of Donovan, V. discina of Lamarck,
V. Rustericii of Payraudeau, and V. casinula of
Deshayes.
6. Y. verruco'sa*, Linne.
V. verrucosa, Linn. Syst. Nat. p. 1130; F. & H. i. p. 401, pi.
xxir. f. 3.
Body very thick, pale yellowish-white : mantle freely open
from the tubes to the anterior adductor muscles ;
its edges are
serrated or fringed, presenting more or less of a furbelowed
aspect: tubes short, but well separated, and of a yellowish-
white colour, with tawny specks or dark-grey spots, lines, and
small blotches ; the orifice of the branchial tube is surrounded
by a double series of cirri, the largest of which (about twenty
in number) are simple ; there are only about ten simple and
shorter filaments around the orifice of the smaller and upper
tube, which is furnished with a prominent conical valve :
gills
nearly circular, free, of a brown colour, coarsely pectinated ;
the upper pair is, as usual, smaller than the under: palps
rather small and narrow : foot white, moderately long, tongue-
shaped and pointed, when at rest axe-shaped ;
trace of a byssal groove.
* Warty.
it exhibits no
Q2