nearly to crimson; others are dark chocolate and white, sharply
checkered.

Pebbles and Patella alike are half-covered with Confervae, and from
the top of the latter, fronds of Ulva are often found floating like
flags. I have one with a clump of Corallina rising from its apex, like
a coppice on the summit of a hill.

By atmospheric pressure, its union with the stone is so close that it
is not easy to pull it away without injury; but if you slip it along,
until by some slight inequality air is admitted beneath the hitherto
exhausted receiver, the little pneumatician is obliged to yield.

When turned upon its back, or resting against glass, the soft arms,
sprawling aimlessly about, and the bare, round head, give it the
appearance of an infant in a cradle, so that a tank well stocked with
them might be taken for a Liliputian foundling-hospital.

They are as innocent as they look, being vegetable-feeders, and
finding most of their sustenance in matters suspended in the water. A
friend of mine placed several upon the side of a vessel coated with
Conferva. In a few days, each industrious laborer had mowed round him
a circular space several times larger than himself.

They are not ambulatory, but remain on one spot for successive weeks,
perhaps longer.

Sometimes they raise the shell so as to allow a free circulation
beneath; but if some predatory Prawn draw near, the tent is lowered in
a twinkling, so as effectually to shut out the submarine Tartar.