he second and third pair; these two
latter are longer than either the first or three posterior pair. There
is a small interspace as usual between the first and second pair of
cirri. Internally, the cirri are occupied, even up to their tips, by
delicate striae-less muscles. The external membrane of the thorax and
limbs, when examined under a very high power, is seen to be covered with
minute toothed scales, as in most Cirripedes.

The thorax is articulated as usual: the posterior part, however, is
smaller, and tapers more suddenly than in other species, and this
corresponds with the smaller size and more rudimentary condition, of the
three posterior pair of cirri, compared with the anterior pair. The
prosoma is hardly at all developed. The orifice (Pl. IV, fig. 2 _e_) of
the acoustic (?) sack, beneath the first cirrus, is unusually large.

There are no filamentary appendages.

_Alimentary Canal._--The membrane lining the oesophagus is unusually
thin: it is furnished with the ordinary constrictor muscles, and others
radiating from them like spokes of a wheel. The stomach is lined by
unusually prominent biliary folds, which in the duodenum are transverse,
sending forth, however, short folds at right angles; and these latter,
in the proper stomach, become so much developed that the folds appear
longitudinal. The rectum extends inwards, about as far as the base of
the fourth pair of cirri, but is very short, owing to the little
development of the three posterior segments of the thorax. The anus is
seated in its usual place, at the dorsal basis of the penis, and is
hidden by loose folds of skin; but there are no distinct caudal
appendages. The stomach, in the specimen examined, was quite empty.

_Reproductive Organ._--The penis (fig. 2, _c_) is thick, short (about
twice as long as the sixth cirrus), constricted at the base, ringed,
spineless, with the terminal aperture large; internally it is well
furnished with muscles. The two vesiculae seminales, appeared to be
unusually small; and one was much smaller than the other; they do not (I
believe) become united into a common tube, till near the apex of the
penis. They were empty; and, I presume, from the state of the ova, that
their contents had lately been discharged. The whole thorax was filled
with a white, fibrous and cellular mass, consisting perhaps of the
testes in their undeveloped state. The individual dissected by me,
appeared to have been defective in its last act