from the second. The _Cirri_ are generally but
little curled, and have elongated segments, with long, generally
serrated spines: the first cirrus varies in proportional length; the
second and third cirri have both their rami more thickly clothed with
spines than are the three posterior cirri, the spines being generally
arranged in three or four longitudinal rows: the cirri, however, of _S.
villosum_ in all respects resemble closely the cirri of _Pollicipes
sertus_ and _P. spinosus_.

The _Caudal Appendages_ are uniarticulate, small, and clothed with
spines: in _S. villosum_, however, differently from in all other allied
forms, there are no appendages.

The _Stomach_, in those species which I opened, is destitute of caeca.
There are no filamentary appendages.

_Generative System._ The ova are nearly spherical, and remarkably large,
as was stated to be the case in the introductory discussion, in which
the larva of _S. vulgare_, in the first stage of development, was
described: the ovigerous fraena are small. The testes are large, but the
vesiculae seminales in some of the species extraordinarily small.
_Scalpellum ornatum_, and perhaps _S. rutilum_, are unisexual; the other
species are hermaphrodite, but most or at least some of the individuals,
are furnished with Complemental Males. These latter are fully described
under each species, so I will here only remark, that _S. ornatum_, which
alone (excepting perhaps _S. rutilum_) is unisexual, has less claim than
the other species to be generically separated: we have seen also, in
Ibla, that similar sexual differences occur in two most closely allied
species. It is very singular how much more some of the Males and
Complemental Males in Scalpellum differ from each other, than do the
female and hermaphrodite forms; this seems due to the different stages
of embryonic development at which the males have been arrested. In the
males, however, of _S. rostratum_, _S. Peronii_, and _S. villosum_,
compared one with another, but not with the males of the other species,
the parts of the mouth and apparently the cirri, resemble each other
more closely, than do the same organs in the hermaphrodites. At the end
of this genus I shall give a summary on the highly remarkable sexual
relations both in Scalpellum and Ibla.

_Distribution._--The species seem distributed over the whole
world, but as far as we can trust our present scanty materials,
are most common in the warmer temp