32
THE SEAS
marine snails, of which the common limpet (Patella) and
the pewinkles (Littorina) (Plate ro) and the top—shells
(Gibbula and Calliostoma) are the commonest ; they browse
.
upon the weeds and;corallines which cover the rocks._ The
limpets (Plate 8) have ;denite “homes ”
on the rock face
to the Surface of Which their shells are exactly tted so that,
when disturbed, they_can, by pulling down the shell, x
themselves so rmly
very great force is needed to
'
_distutb them; it has been estimated that limpets with a
_
_
basal areaabout one square inch need a pull of seventy
f
pounds to remove them. - In all directions around can
occasionally .be seen radiating paths clearedof weed showing
where thempet has foraged for its food.
There are a
variety of periwinkles which live in different regi0ns of the
shore, one (L. weritoidcs) living
the. shore,
often where it is untouched by sea water for weeks together,
the common winkle -(L. littorea) lives lower on the shore
"
always on rocks,- while the smaller and less point-ed species
,
(L. obtusata) which varies
in colour from black to
‘
white, is always found on the frohds of, fucuS. ,Resembling
the winkles but rather larger and with a thicker shell is the
dog—whelk (Purpura), which inhabits the upper half of
.
the shore (Plate 13), préying upon the mussels or acorn
bamacles
Other pe’culiar
to the snails are
thechitonsof which our largest species are ab0ut an inch
long and about half as wide; they are flattened, with the
,
shell arranged in eight parts each slightly overlapping the
,
one behind, and when pi1Hed away _fromthe rocks on which
they browse, they curl up like little armadillos.‘ There is a
population growing On the weeds, notably many
‘
kinds of hydroids, sea mats and small snails.
'
Nearer low—Water mark we find the rocks'covered with
.
sponges. of
the “ crumb=of—bfead sponge
”
(H ali—
_
chondfia) is the coinmonest (Plate II), -fot1inga=dèse m‘ass
THE SEAS
marine snails, of which the common limpet (Patella) and
the pewinkles (Littorina) (Plate ro) and the top—shells
(Gibbula and Calliostoma) are the commonest ; they browse
.
upon the weeds and;corallines which cover the rocks._ The
limpets (Plate 8) have ;denite “homes ”
on the rock face
to the Surface of Which their shells are exactly tted so that,
when disturbed, they_can, by pulling down the shell, x
themselves so rmly
very great force is needed to
'
_distutb them; it has been estimated that limpets with a
_
_
basal areaabout one square inch need a pull of seventy
f
pounds to remove them. - In all directions around can
occasionally .be seen radiating paths clearedof weed showing
where thempet has foraged for its food.
There are a
variety of periwinkles which live in different regi0ns of the
shore, one (L. weritoidcs) living
the. shore,
often where it is untouched by sea water for weeks together,
the common winkle -(L. littorea) lives lower on the shore
"
always on rocks,- while the smaller and less point-ed species
,
(L. obtusata) which varies
in colour from black to
‘
white, is always found on the frohds of, fucuS. ,Resembling
the winkles but rather larger and with a thicker shell is the
dog—whelk (Purpura), which inhabits the upper half of
.
the shore (Plate 13), préying upon the mussels or acorn
bamacles
Other pe’culiar
to the snails are
thechitonsof which our largest species are ab0ut an inch
long and about half as wide; they are flattened, with the
,
shell arranged in eight parts each slightly overlapping the
,
one behind, and when pi1Hed away _fromthe rocks on which
they browse, they curl up like little armadillos.‘ There is a
population growing On the weeds, notably many
‘
kinds of hydroids, sea mats and small snails.
'
Nearer low—Water mark we find the rocks'covered with
.
sponges. of
the “ crumb=of—bfead sponge
”
(H ali—
_
chondfia) is the coinmonest (Plate II), -fot1inga=dèse m‘ass