, and in the membrane covering and connecting the valves
being spineless; but there is a greater difference in the trophi and in
the cirri. The peduncle of _S. ornatum_ presents some resemblance to
that of the singular cretaceous genus, _Loricula_.

MALE.

All the specimens, as already stated, were dry, but in an excellent
state of preservation, so that after having been soaked in spirits, they
could be minutely examined. In the four which I opened, I found, in a
transverse pouch on the under side of each scutum, a male lodged; in a
fifth dead and bleached specimen, the cavities in the shell for the
reception of the males, were present; and in a sixth young specimen,
also dead, cavities were in process of formation. As compared with
plants, the relation of the sexes in this species may be briefly given,
by saying that it belongs to the class _Diandria monogynia_. I will
first describe the males themselves, and then the cavities in the shell
of the female. The males differ in every point of detail, from the
complemental males of _S. vulgare_, but yet present so close a general
resemblance, that a comparative description will be most convenient.

The general shape of the whole animal is rather more elongated, and I
suspect flatter, but this latter point could not be positively
ascertained in dry specimens. The entire length is greater, being in the
largest specimen 13/400 (instead of at most 11/400), and the width,
7/400 of an inch. The orifice is not fimbriated; the four bristly points
over the calcareous beads are absent. The whole outer integument is much
thinner, owing evidently to its protected position, and is not covered
by little bristles, but with an extremely high power, minute points
arranged in transverse lines can be distinguished. The calcareous beads,
or rudimentary valves, are thin and regularly oval. It is remarkable
that in all the specimens, two on one side were smaller than the two on
the other side,--the smaller beads being 16/6000, and the larger,
22/6000 of an inch in diameter; therefore more than twice the size of
one of the beads in _S. vulgare_, which are only 9/6000 externally in
diameter. From the position of the eye, close to one margin, near the
upper end of the flattened animal, and from the manner in which the
little limbs and spines lay between two of the beads at the opposite
end, it was manifest that these latter, one large and one small,
corresponded with the terga of the other cirr