Pvn H,i I'UitlS

66 PECTINID^.
the byssal sinus is finely toothed : beaJcs very prominent and
considerably raised : ears unequal ; those on the left hand of
the upper valve and right hand of the lower valve are at least
four times the size of the others;
all of them have a few
strong ribs which radiate from the beaks, and they are also
marked with coarse and numerous striae which cross the ribs
obliquely ; the ears of the lower valve project very little beyond
those of the upper valve ; byssal notch deep :
hinge-line
straight :
cartilage small : ligament very thin :
hinge-plate
narrow, microscopically striate across ; transverse rib strong
and considerably raised on each side of the : cartilage-pit inside
nacreous, finely and closely striate lengthwise and notched
on the front margin within ; the larger ears are strong grooves
which correspond with the outside ribs : muscular scars dis-
tinct, especially in aged specimens. L. 0-9. B. 0-885.
Yar. costata. Shell stronger than usual, and having either
five ribs and intermediate small ones, or else several riblets
of equal size : inside grooved and striate accordingly.
Habitat :
Not
uncommon from Shetland to the
Channel Isles in 7-82 fathoms, on a sandy bottom mixed
with gravel ; and the variety is equally diffused. This
species occurs as an upper tertiary
fossil in the Scotch
glacial deposits, and also in the Red and Coralline Crag.
It is a native of the Icelandic and Scandinavian coasts ;
and Mr. M'Andrew has taken it in Vigo Bay at a depth
of only 8 fathoms.
The shell varies greatly in size and proportions, as
well as in colour and the number of ribs. My largest
specimens are one inch and two-tenths long, and nearly
the same in breadth. Sometimes the breadth slightly
exceeds the length. Young shells are proportionally
longer than old ones. In the former the so-called "eyes"
are perceptible through the semitransparent shell many
years after the animal has ceased to exist. The fry are
not sculptured, but perfectly smooth; and the lower
valve is nearly flat and smaller than the other. Miiller
noticed the way in which he presumed this scallop pro-