Pvn H,i I'UitlS

422 MACTRID^.
and more than three quarters of an inch thick. The
young and fry of this species
characters as the adult.
have the same constant
It is the M. stultorum of Pennant and M. lactea of
Poli (hut neither of them Linnets species of those names),
M. triangula of Renier, M. cuneata of Sowerby's ' Mi-
neral Conchology/ M, deltoides of Lamarck, M. Euxi-
nica of Krynicki (according to MiddendorfF), and the
M. obtruncata and M. triangulata of Searles Wood.
M. lateralis, Say (a common North-American shell), is
probably a variety or offset of the same species.
B. Shell longitudinally rayed ; lateral teeth and sockets
smooth.
3. M. stulto'rum *, Linne.
M. stultortm, Linn. Syst. Nat. p. 1126 ; F. & H. i. p. 362, pi. xxii. f. 4, 6,
and xxvi. f. 2.
Body white faintly tinted with blue : mantle open through-
out the ventral range, thickened at its edges, which are clothed
with a delicate fringe of short intensely white filaments : tubes
never exserted more than half an inch, covered with a slight
and pale-brown wrinkled epidermis, which appears to be in-
dependent of that on the shell ; orifices encircled by dingy palered
unequal cirri, the alimentary tube having 12-16 (which
are somewhat longer than the other set), and the excretal tube
16-20 of these appendages; the retractile valve of the last-
narrow and attached for
mentioned tube is conspicuous :
gills
two-thirds of their length, of the same proportionate size as
in other species, and (as well as the palps) similarly striated :
foot white, thick, and plastic.
Shell of the same shape as M. solida, but more evenly
convex and always ventricose, thin, although nearly opaque,
and glossy : sculpture, numerous delicate and minute irregular
concentric strice, which are apparently formed by laminar folds
of the epidermis and become somewhat coarser at the sides ;
occasional lines of growth are also observable : colour yellowish-
* Fools'.