Pvn H,i I'UitlS

68 PECTINID^.
which radiate from the beaks and are crossed by coarse flexuous
strise ; the edges of the ears on the lower valve project very
slightly ; byssal sinus deep : hinge-line straight, finely notched
or serrate at its edge :
cartilage rather large : ligament extremely
slight : hinge-plate very narrow, microscopically striate
across ; transverse rib slight, and not much raised on each
side of the cartilage-pit, which is proportionally more open
than in any of the foregoing species : inside slightly nacreous,
finely and closely striate lengthwise,
or furrowed when the
outside is ribbed ; margin sometimes notched or crennlated :
muscular scars indistinct except in aged specimens. L. 0*575.
B. 0-55.
Var. suborbicularis. Shell larger, with the slope much
higher than usual, and considerably narrower behind: ears
smaller. L. 0-7. B. 0-7.
Habitat: Shetland, Skye, Larne (co. Antrim), Birterbuy
Bay (co. Galway), Guernsey (J. G. J.) ; Exmouth
(Clark) ; in gravelly sand, 18-80 fathoms. It is a rare
species. The variety is remarkable. I obtained only a
single valve by dredging off the north coast of Shetland in
86 fathoms. Although of much smaller size, this
variety
resembles in shape and other respects the P. Gerardii
of Nyst, one of our Coralline Crag fossils. The foreign
range of P. Testa extends from Norway to Algeria and
the iEgean. Asbjornsen gives the depth at which it is
found in Christiania fiord as 10-20 fathoms.
This beautiful species differs from P. tigrinus, with
which it is sometimes found, in the following particulars.
The shell is broader, flatter, and thinner; the
ribs, when they occur, are scaly or prickly ; the punc-
tures are very strongly marked and arranged in squares;
the ears
the beaks are much less prominent and raised ;
are not so unequal ; and the inside margin is seldom
crenulated. Forbes and Hanley considered it to be a
variety of P. striatus-, but Malm has satisfactorily
shown some of the points of difference between these