Pvn H,i I'UitlS

16 TEREBRATULID.E.
hydrographical range extends from Spitzbergen to Sicily;
and the variety is not uncommon on the coasts of Nor-
way and North America. Mr. Arthur Adams has lately
dredged the typical form in the seas of Japan, at the
depths of 26, 55, and 63 fathoms. He considers T. Ja-
ponica to be a distinct species. I have a monstrosity
which is deeply cleft in the middle, so as to form two
lobes of unequal size and height ; and other specimens
also are slightly distorted in the same way.
The brachial cirri are set on the muscular stem like
the teeth of a comb, and when in action they bend for-
ward in a most graceful manner. The pallial tentacles
are also continually moving, and sometimes curl at the
point like a crosier. When the shell is closed during
the lifetime of the animal, these tentacles are still visible
outside the edge of the shell, presenting the same
appearance as in Anomia. Sometimes the upper valve
is laden with a mass of barnacles and Serpulce. The
shells of young specimens are, of course, more strongly
and the lower
ribbed or striate than those of the adult ;
valve is eared. The fry, however, are perfectly smooth,
and much longer in proportion than the adult ; and
they have a spoon-shaped, entire, and prominent beak.
Owing to the shell being so thin and nearly transparent,
the tiny arms are distinctly perceptible on the outside.
In the early stages of growth the skeleton is not com-
plete or annular, and it then somewhat resembles the
scythe-shaped processes of T. cranium.
The Anomia retusa of Linne and A. aurita of Gual-
tieri, as well as the T. nucleus and T. pubescens
of O. F.
Muller, are synonyms of this species. The last-men-
tioned name originated in a coat of downy sponge, which
not unfrequently covers the shell, and was suspected
by the Danish zoologist to be merely a parasitic growth.