ies with all. In the
entire structure, however, of the Complemental Male, immediately to be
described, this species certainly comes nearer to _S. villosum_ than to
any other species. I may add, that in _S. villosum_ the latera are
almost rudimentary, and therefore tend to disappear, whereas in _S.
Peronii_ it is the calcareous scales on the peduncle which have actually
disappeared.

COMPLEMENTAL MALE. Pl. VI, fig. 3.

I examined, owing to the great kindness of Mr. Cunning, six dry
specimens of the hermaphrodite _S. Peronii_, from Swan River, and one in
spirits from another locality, in the British Museum. Out of these seven
specimens, only three appeared to have had parasites attached to them,
and these I infer, from reasons to be more fully given at the end of the
genus, are Complemental Males. One of the three specimens, however, had
two males close together. These parasites were firmly cemented to the
integument of the hermaphrodite, in a fold, in a central line between
the scuta, a little below (the animal being in the position in which it
is figured) the adductor scutorum muscle, and therefore some way below
the umbones of these valves. When the scuta are closed, the parasites,
from their small size, are enclosed and protected. In every detail of
structure, they are obviously pedunculated Cirripedia.

The _Capitulum_ (Pl. VI, fig. 3) has six valves; namely, a pair of scuta
and of terga, a carina, and a rostrum, all united by finely-villose
membrane, furnished near the orifice with some much longer and thicker
spines. The capitulum is truncated in a remarkable manner, the orifice
not being, as in the hermaphrodite, in the same line with the peduncle,
but almost transverse to it, and therefore almost parallel to the
surface of attachment. The largest specimen measured transversely,
through the scuta and terga, was 30/1000ths of an inch in breadth;
another was only 26/1000ths to 27/1000ths: this latter specimen,
measured longitudinally, from the base of the carina to the tips of the
terga, was 15/1000ths of an inch. A scutum of the largest specimen was
17/1000ths in length. The scuta and terga are broadly oval, with the
primordial valves very plain at their upper ends. I may here mention,
that in a central line between the scuta, I observed the _apparently_
single, minute, black eye, as in ordinary Cirripedia.

The _Carina_ is straight, triangular, and internally slightly concave;
its basal margin descends far b