Pvn H,i I'UitlS

76 PECTINID.E.
whatever they lie upon !
Shells sometimes attain an
enormous size. Dr. Landsborough says he measured
one which was 8 inches long.
I have another specimen
that is barely -g^th of an inch in length. The young are
attached by a byssus. They are quite smooth ; and in
the place of ribs a few fine white lines radiate from the
beaks, as is not unfrequently
seen in P. similis. This
might be considered by the advocates of a theory, which
was once put forward in the '
Vestiges of Creation/ a
case of arrested development as regards P. similis ; but
they ought to be aware of the fact that both these species
of every age inhabit the same spots and yet retain their
own distinctive characters. One species never grows or
merges into the other. The young of P. maximus may
be known from P. similis of the same size by the upper
valve in the former being flat, and in the other convex,
as well as by the inequality of the ears in the first-named
species. It bears a considerable resemblance to a young
Avicula, and shows the affinity which exists between
that genus and the Pectinida. The adult seem not to
have the power of spinning a byssus, nor to have any
occasion for it. Their solid shells can withstand a good
deal of buffeting by the tide ;
if they were slighter, they
would require the cable of a Pinna to hold them on their
anchorage-ground. The substance of the shells is very
durable. I have had some of the deep valves in frequent
use during the last eighteen years for scalloping oysters ;
and although they must have been baked in an oven at
least five hundred times, they are as perfect and serviceable
as ever. The prettiest specimens come from
Dublin, Cork, and the Channel Isles.
This species belongs to the genus Vola of Klein. The
young
conchologists.
is the P. Icevis of Pennant and the older British