Pvn H,i I'UitlS

210 KELLIID^E.
in 8 fathoms, and I have taken it at Spezzia in 18
fathoms. According to Sars it is found in the post-
beds of Christiania.
glacial
Clark's account of the animal is that it is "lively,
marches with rapidity, and in its course turns from side
to side, sometimes resting the shell on the ventral range
in an upright posture." Montagu, having found it
apparently burrowing in old and thick oyster- shells, be-
lieved that it was partly the cause of the small round
holes so frequently seen on those shells. Such perfora-
tions, however, are attributable to a sponge (Cliona
celata), that fills the cylindrical
tubes of which the holes
are the outlet, and branches off in every direction— a
course never known to be taken by any mollusk. The
relative proportions of length and breadth in the shell
of M. bidentata are very variable. The young are more
triangular than the adult, and somewhat resemble in
shape the fry of Nucula nucleus. My largest specimen
is a line and a half long, and a third more in breadth.
This small shell has been bandied about by different
conchologists from one genus to another, and received
various names. Montagu referred it provisionally to
My a. Brown in 1827 placed it in the genus Anatina
of Lamarck, and Clark did the same in 1855. Gray
and Hanley called it a Petricola. It is the Erycina
faba of Nyst, E. nucleoid of Recluz, and Mesodesma
eociguum of Loven. The Montacuta elevata of Stimpson,
which Gould supposed was our shell, differs in the posi-
tion of the beaks and in other particulars.
3. M. ferrugino'sa *, Montagu.
Mya ferruginosa, Mont. Test. Brit, p. 44, tab. 26. f. 5. Montacuta ferruginosa,
F. & H. ii. p. 72, pi. xviii. f. 5, 5 a & 5 b (as M. ferruginea).
Body clear white : mantle having its margins on the ante-
* Covered with iron -rust.