Pvn H,i I'UitlS

62 pectinid^:.
P. opercularis may be readily known from either of
the two foregoing species by its circular form, greater
size, and nearly equal ears. The P. Audouinii of Payraudeau
can hardly be considered a variety. Its sculpture
is that of the P. lineatus of Da Costa, and only differs
from that of ordinary specimens in the scales being
more regular and continued across the ribs. The P.
subrufus of Turton is merely the young state,
straighter outline. Many other specific
with a
names have
been invented by authors for still more trifling varieties.
4. P. septemradia'tus*, Miiller.
P. septemradiatus, Mull. Zool. Dan. Prodr. p. 248, no. 2992. P. Danicus,
F. & H. ii. p. 288, pi. Hi. f. 1-2, 7-10.
Shell nearly circular and equilateral, except as in the last
species, thin, somewhat : glossy sculpture, mostly 7 rounded
but compressed ribs (the middle one being the largest), which
are much narrower than the interstices ; the surface is covered
with minute and close-set longitudinal strise, which are crossed
by equally fine but more remote transverse plates,
so as occa-
the sides
sionally to form prickles at the points of intersection ;
are marked with short and stronger strise, placed at right
angles to the longitudinal striae: colour reddish-brown, mottled
or streaked with white : margins as in P. opercularis ;
slope below the byssal sinus seldom, and never distinctly, serrate
: beaks prominent : ears nearly equal in the upper valve,
but not so in the lower valve, in which the right ear is the
from the
larger ; all of them are sculptured by ribs radiating
beak, as well as by fine and numerous striaa, which run from
the sides or shoulders and diverge outwards ; there are also
some wavy striaa in the line of growth, crossing the auricular
ribs ;
the ears of the lower valve project beyond and overlap
those of the upper valve, but much less than in any of the pre-
ceding species ; byssal notch slight : hinge-line straight
: car-
tilage small : ligament very thin : hinge-plate rather broad,
transverse rib slight and raised
microscopically striate across ;
a little on each side of the cartilage -pit : inside fluted or
* Seven-rayed.