Pvn H,i I'UitlS

lucinopsis. 363
mentioned families. The microscopical striae, charac-
teristic of the shells of the Veneridce, are absent in
Lucinopsis. In its general appearance this genus agrees
with Lucina ; but the recurved beaks, sinuation of the
pallial scar, and length of the tubes offer conclusive
reasons for their separation.
Lucinopsis unda'ta *_, Pennant.
Venus undata, Penn. Brit. Zool. p. 95, pi. 55. f. 51. Z. undata, F. & II.
i. p. 435, pi. xxviii. f. 1, 2, and (animal) pi. M. f. 2.
Body milk-white, or of a pale pinkish
drabcolour : mantle
having its edges wavy, or sometimes partially jagged, but
never serrated or fringed ; ventral opening small : tubes more
or less divergent, occasionally tinged with orange, conical,
capable of being considerably extended ; incurrent tube the
smaller in diameter, but longer of the two, its orifice margined
by a circle of very short and minute dark specks, and fringed
with 16-20 white cirri of various sizes and lengths excurrent
;
tube having its orifice encircled with 12-15 white cirri, which
are uniformly short and without the marginal row of dark
gills pale drab, the upper plates being much smaller
specks :
than the lower and half overlapping them ; pectinations rather
fine, but not very distinct : palps
of the same colour as the
gills, fleshy, rather long, triangular, pointed, strongly striated
on the outside and smooth within : foot of moderate size, white,
flat, pointed, not much bent, destitute of a byssal groove, and
issuing
from the front or ventral side.
Shell almost circular, tumid, semitransparent, rather glossy :
sculpture, numerous and fine, but irregular, concentric stria?,
colour milk-white, with often
and occasional lines of growth :
a yellow or ochreous hue, especially near the beaks : epidermis
thin, like varnish and slightly iridescent, longitudinally (but
very minutely) striated or puckered: margins more or less
straight on the ventral side in the adult and rounded in the
young, regularly curved on the anterior side, excavated below
the beaks, obtusely angular at the posterior end, with an
abrupt slope or truncation on that side ; dorsal or ligamental
margin very gently curved in the adult and sloping in the
* Wavy.
R.2