Pvn H,i I'UitlS

PECTEX. 59
number of ribs; but the shell is more solid, the ribs
sharper, and the surface resembles shagreen.
3. P. opercula'ris*, Linne.
Ostrea opercularis, Linn. Syst. ISat. p. 1147. -P. opercularis, F. & H. ii.
p. 299, pi. L. f. 3 ; li. f. o, 6 ; liii. f. 7.
Body thick, variegated with pink, cream- colour, fawn, orange,
or brown, and mottled with flake-white meandering lines, spots,
and blotches : mantle thin, except at the : fleshy margins cirri
conical, white, of unequal length and irregularly disposed in
two or three rows, the outer one of which has the longest filaments
: ocelli 35-40, nearly globose, having pearl- coloured
pupils within black circles : foot small, subcylindrical, deeply
cloven or furrowed, and scoop-shaped at its extremity, of a
yellowish-white colour.
Shell circular and equilateral, except at the back (where the
periphery is interrupted by the beak and ears), rather thin,
scarcely glossy: sculpture, about 20 rounded ribs, which are of
equal size and somewhat broader than the interstices ; the
surface is more or less covered with extremely fine and wave-
like transverse plates, which often form numerous rows of short
prickles, especially along the ribs and on their crests, making
the shell feel rough as shagreen : colour red, pink, orange,
yellow, purple, brown, or of intermediate shades,
often streaked
or marked with blotches or spots, and sometimes (but rarely)
milk-white : margins rounded in front and at the sides, notched
or indented by the ribs, sloping gradually to the beak on each
side from about three-fourths of the distance from the front
toothed or ser-
margin ; slope below the byssal sinus strongly
rate : heaJcs : prominent ears nearly equal, sculptured by ribs
which radiate from the beak; the ears of the lower valve
slightly project beyond and overlap those of the upper valve ;
byssal notch deep : hinge-line straight : cartilage rather large :
ligament narrow and slight: hinge-plate somewhat broad,
minutely striate across ; transverse rib strong and raised on
each side of the : cartilage-pit inside fluted or grooved, so as
to correspond with the folds of the outside ribs ;
each shoulder
under the ears is furnished with a thick ledge, which rests on
that in the opposite valve, thus giving additional support to the
* Like a cover or pot-lid.