Pvn H,i I'UitlS

134 mytilidjs.
in C. rhombea, owing to the greater thickness of the inner coat
of nacre. L. 0-15. B. 0-12.
Habitat :
Coasts of Yorkshire, Northumberland, An-
trim, and Scotland from the Clyde district and Firth of
Forth north to the Shetlands, in gravelly sand from 3
to 70 fathoms. It appears to be gregarious. Post-
glacial deposit at Elie, Fifeshire (Rev. T. Brown). It
inhabits the seas of Scandinavia, Iceland, Greenland,
and New England, occurring at various depths from
low-water to 150 fathoms.
This exquisite gem of a mollusk is hardy and active.
Not being able to examine living specimens at the time
they were taken, I picked out a few from a small heap
of dredged sand, which had been lying on a pathway for
two days, exposed to continual rain and partly trodden
underfoot. After keeping them eighteen hours in a
small glass vessel of sea-water, they revived and were
alive for many days, the water being occasionally re-
newed. While crawling about, they sometimes carried
the shell erect with the beaks in front, but more fre-
quently in a slanting position. They
seemed fond of
getting to the surface of the water, when the Crenella
would spin with its foot a single pellucid thread, which
it fixed to the side of the vessel, and it would hang (like
a Sphcerium) for hours thus suspended, the beaks of the
shell being undermost. The shell being nearly trans-
parent during the lifetime of the animal, the green liver
is distinctly seen through it, occupying the umbonal
region. The foot-stalk or pedicle is semicylindrical,
and becomes twisted if the animal is placed on the wrong
side. The creeping-disk or lobe is very flexible and in
some degree extensile. It is half as broad again as the
stalk, and proportionally thicker. A dusky line runs
down the middle of the stalk, apparently showing the