Pvn H,i I'UitlS

26 craniidjE.
adapted to the angles
and extent of the basal surface.
When it has bare standing-room only, it increases in
height and becomes regularly
conical. The under valve
of specimens attached to the smooth shell of a Pinna is
usually a mere film. The brachial fringe can be protruded
slightly beyond the margin of the shell at each
side, but never in front or at the back. It may be
likened to the spokes of two wheels, each placed on its
nave within a circle ; and as the spokes are nearly equal
in length, it is evident that at the point where the wheels
approach each other, the inside spokes project into the
space between the wheels, and not outwardly. There
are no cirri at the back. The lower or flat valve con-
tains only the base of the adductor muscle, upon which
as a pivot; the upper valve turns by a semirotatory
but very confined motion. The arms and rest of the
or convex valve. The
body are enclosed in the upper
animal is by no means timid. When a camePs-hair
brush is thrust between the gaping valves, they imme-
diately close, but in a few seconds after open again;
and this teasing experiment can be repeated many times,
without alarming the Crania, or making it sulky. The
cirri are not retractile, and do not withdraw or shrink
when touched. Each arm has about sixty of them.
The fry are quite white and semitransparent, and they
have only a few tubular perforations. They adhere in
Their appearance is not
the same way as their parents.
unlike that of the very young of Anomia ephippium. The
largest specimen in my cabinet measures over four-fifths
of an inch in diameter.
Montagu called this species Patella distorta ; and it
has borne many other names, both generic and specific,
the latest being that of Criopus Orcadensis, given
by
Dr. Leach.
to it