Pvn H,i I'UitlS

Genus I. AVI'CULA*,
AVICULA. 95
Klein. PL II. f. 3.
Body oval : palps or labial appendages large : byssus fibrous,
coarse, and thin.
Shell square or elliptical, often winged or lobed, inequivalve
: upper margin of the lower or left valve notched for
the passage of the : byssus beaks placed nearer the anterior or
narrower end, but never terminal: hinge furnished with
teeth.
This genus is distinguished by the nacreous and
iridescent lining of its shell, which in one species pro-
duces the oriental pearl, and in another is extensively
used for inlaying and button-making.
1. Avicula hirun'do f, Linne.
Mytili's hirundo, Linn. Syst. Nat. p. 1159. A. Tarentina, F. & H. ii.
p. 251, pi. slii. f. 1-3, and (animal) pi. S. f. 4.
Body suboval, yellowish-white
mottled with brown : cirri
arranged in two rows, numerous and close-set, those in the
front or outer row being longer than those in the inner row :
foot white.
Shell elliptical, resembling that of a Pinna, with the
addition of an unequal wing-like appendage on each side of
but less so in the
the beak, very inequivalve in the young,
adult state, the upper or right valve being larger than the
other, much compressed towards the margins, rather fragile,
more or less : glossy sculpture, thin concentric plates or scales,
which irregularly imbricate the surface and are sometimes
spinous towards the anterior margin, besides superficial microscopic
and close-set punctures : colour yellowish-brown, with
purplish
streaks which radiate from the beaks and are fre-
quently interrupted or zigzag : margins very thin, rounded in
front, more or less deeply incurved on the upper part of eaeh
side in consequence of the projection of the wings, straight or
nearly so behind : beaks small, sharp, and slightly projecting
over the hinge : wings triangular and bluntly pointed ; they
are of unequal size, those on the anterior side being small,
* A little bird. t Swallow.