_S.
villosum_.

_Mouth._--Labrum bullate, with teeth on the crest. _Palpi_ blunt,
spinose.

_Mandibles_, with three teeth; inferior point rather strongly
pectinated.

_Maxillae_, with a considerable notch under the upper pair of large
spines; inferior part of the edge not prominent.

_Outer Maxillae_, with the spines on the inner edge arranged into two
groups. Olfactory orifices tubular and prominent, with some long
bristles near their bases. In the mandibles having only three teeth, in
the maxillae being notched and in the lower part not being prominent,
and, lastly, in the bristles on the inner face of the outer maxillae
being arranged in two groups, these several organs differ from those in
the hermaphrodite.

_Cirri._--First pair short, with only three or four segments in each
ramus: second cirrus, with the basal segments not very thickly clothed
with spines: sixth cirrus with seven segments, not protuberant in front,
each bearing four pairs of spines, without intermediate tufts.

_Caudal appendages_, none. This is an interesting fact, considering that
these organs are likewise absent in the hermaphrodite _S. villosum_,--an
absence highly remarkable, and confined to the genus Conchoderma and the
one species of Anelasma.

_Penis_ thick, not tapering, rather exceeding in length the pedicel of
the sixth cirrus, square at the end, and furnished with some spines. In
one specimen, I believe I distinguished the vesiculae seminales: if so,
they contained only pulpy matter, and not spermatozoa. There were no
ovarian tubes within the peduncle, which was lined by the usual muscles;
I traced the two delicate cement-ducts, running from within the antennae
close up to the animal's body. Hence in this case, as in that of _S.
Peronii_, I dare positively affirm that ovarian tubes do not occur; for
it is out of the question that I could have traced the cement-ducts,
and, at the same time, overlooked the far larger and more conspicuous
ovarian tubes, into which, moreover, the ducts, had they existed, would
have run. Consequently, these parasites are not females; but judging
from the probosciformed penis, and from the presence, as I believe, of
vesiculae seminales, they are males.

The complemental males of the present species, and of _S. Peronii_, so
closely resemble each other, that what I have stated regarding the
affinities of the latter, are here quite applicable. It is singular how
much more alike the parts of the mout