Pvn H,i I'UitlS

LEPTON. 197
shell downward, by three or four threads, which are so
fine that they cannot be seen by the naked eye ; and
even by the aid of a magnifier they can only be observed
when the light falls upon them at certain angles. When
the animal withdraws into its shell, the latter can be
completely closed; but usually the valves are kept a
little open, and the mantle protruded beyond them.
Mr. Clark kept a specimen alive for thirty-four days in
a glass of sea- water, changed daily, and it was seemingly
as vigorous all that time as when first placed in captivity.
He states that when it was in motion and had made a
step, the long tentacular filament curled inwards, like
the fore-finger of an open hand bent down to the palm,
but immediately afterwards it resumed a straight posi-
all the other filaments were
tion to await another step ;
either retractile or contractile, separately or together.
The foot can form a disk at each end. According to his
account, a glutinous red filamentous matter is copiously
poured out by the byssal gland. But I would venture
to surmise that this phenomenon may be connected
with the reproductive functions. Mr. Clark goes on to
sav, " The animal is vivacious, and allowed itself to be
examined many times daily; it marched with quick-
ness, but I only once saw it progressing in a vertical
of the shell is to rest on one
position ; the usual posture
of the disks, which is frequently changed for the other ;
the adductors did not appear to allow of a greater open-
ing of the valves than the ordinary extent. The animal,
when placed at the bottom of a glass, always crawled
up and moored itself by a filament at the side ; some-
times, however, it slipped its moorings
and floated free
on the surface of the water with the umbones down-
wards, and after an interval refixed itself by spinning a
byssal thread." He subsequently
succeeded in obtain-