uld have been great; for it is very improbable
that this singular and unparalleled position was accidental in this one
group of specimens, inasmuch as there seems to be a relation between the
naked condition of the capitulum of the parasite, and the protection
afforded to it by the capitulum of the Scalpellum. It further becomes
apparent on reflection, that these minute parasites, though having the
appearance of immaturity, can not increase in size, or but little, for
if they did grow, and acquired an ordinary size, they would either be
killed by the pressure of the scuta of the Scalpellum, or they would
destroy the latter, and in doing so soon lose their own support, and
thus necessarily perish!

The one full-grown specimen of _S. rostratum_, in Mr. Cuming's
collection, was in a good state of preservation, but dry. The three
parasites were attached, as stated, close under the labrum, between it
and the adductor muscle. They are constructed like ordinary Cirripedia,
and have a mouth, thorax and cirri, enclosed in a capitulum, supported
on a peduncle of moderate length and narrow. The entire length of the
capitulum and peduncle, as far as could be ascertained in the shrivelled
condition of the specimens, was 35/1000ths, and the greatest width of
the capitulum 11/1000ths of an inch. Both capitulum and peduncle are
hirsute with spines, nearly 1/1000th of an inch in length, mingled with
shorter hairs in little rows of three and four together. The figure (5)
in Pl. VI is merely a restoration, as accurate as could be made from the
much shrivelled specimens. There are only three valves,--namely, an oval
carina (_a_), seated rather high up on the capitulum, in a rudimentary
condition and only 1/1000th of an inch in length, and a pair of scuta;
these latter consist of a narrow, slightly curved plate, 8/1000ths in
length, broadest at the lower end, where the breadth is 2/1000ths of an
inch. The prehensile antennae, at the end of the peduncle, have pointed
hoof-like discs: I was not able to make out the other parts. It deserves
notice, that in the young specimen of the ordinary form of _S.
rostratum_, 1/10th of an inch in length, and therefore only thrice as
long as the parasites, all the valves were perfect, and seemed to have
followed the ordinary law of development.

_Mouth._--The largely bullate labrum is placed far from the adductor, in
the same manner as in the hermaphrodite. The mandibles have three large
sharp teeth, with