Pvn H,i I'UitlS

MACTRA. 425
The fry are oval and very tumid. M. solida resembles in
form and size the variety cinerea of the present species ;
but, besides being natter and thicker, it invariably has
strong transverse grooves on each side of the beak.
I cannot think why Linne gave such an unpolite name
to this species — unless it originated in a philosopher's
joke,
like that attributed to the derivation of Assiminia.
It is the Trigonella radiata of Da Costa ; and the variety
is probably the M. coralUna of Buonanni and Linne,
and the M. siraminea of Lamarck.
4. M. glau'ca*, Born.
M. qlauca, Born, Test. Mus. C;es. Vind. p. 51, t.3. f. 11, 12. M. helvacea,
F. & H. i.
p. 366, pi.
xxiii. f. 2.
Body white, the posterior side and tubes being tinged with
with short flake-
golden yellow : mantle delicately fringed
white filaments ; edges projecting beyond
the valves : tabes
conical and rather short, extending about an inch, of equal
length and diameter, streaked lengthwise with rufous-brown ;
orifices encircled with short and unequal cirri of the same
colour.
Shell triangularly oval, convex but not ventricose, expanded
and gradually sloping from the umbones to the mar-
gins, thin for its size, and glossy under the : epidermis sculpture,
numerous delicate and minute concentric striae, as in
M. stultorum, and occasional lines of : growth colour yellowish-
white, variegated by longitudinal rays of yellowish-brown or
fawncolour, arranged as in the last species, and of a brighter
hue at the beaks, besides a large stain of chestnut on the dorsal
margins : epidermis light brown, fibrous, glistening
like fine
satin in front and on the anterior side, coarser on the posterior
side : margins scarcely (if at all) curved on the ventral side,
and obliquely sloping backwards to the anterior end, which
is rounded with a tendency to angularity, bluntly angular
and much broader on the posterior side, where there is a
considerable gape and an obscure ridge from the beak to
the angular point in each valve ; dorsal margins very gently
* Bluish-grey.