of the peduncle in _S.
vulgare_, _S. Peronii_, and _S. villosum_, and very short ones on that
of _S. rostratum_.

_Attachment._--All the species, except _S. villosum_, are attached to
horny corallines: the singular means of attachment in _S. vulgare_ will
be described under that species, and is probably common to several of
the other species. The larva in most, or in all cases, when it proceeds
to attach itself, clings head downwards to the branch, and hence the
capitulum comes to be placed upwards, with its orifice fronting the
branch and the carina outwards. The sucking disc of the prehensile
antennae of the larva, in the five species examined, was a little
pointed, and in shape resembled the hinder hoof of a mule: this may
perhaps be accounted for by the narrowness of the branches of the
corallines, to which it has to adhere: a large circular disc, as in
Lepas, would have been worse than useless: the ultimate segment in most
or all the species, has on its inner side (the segment being supposed to
be extended straight forward) a notch or step, bearing, I believe, two
spines.

_Size and Colour._--Some of the species attain a medium size, others are
small. The valves are generally clouded red or pink, but sometimes
white.

_Mouth._--The various parts vary far more than in any genus hitherto
described. The labrum is highly bullate, with the upper part forming a
rounded overhanging projection, and with the lower part much produced,
so that the mouth is placed far from the adductor scutorum muscle, and
consequently the orifice is directed more towards the ventral surface of
the thorax than in most other Cirripedes: on the crest of the labrum
there are some very small teeth in several of the species, but not in
all. The mandibles have either three or four main teeth, generally with
either one or two small teeth intermediate between the first and second
large teeth, and in the case of _S. Peronii_, with small teeth between
all the larger ones. The maxillae have their edges furnished with many
spines, and are either straight or have the inferior part prominent and
step-formed. The outer maxillae have the spines on their inner edges
either continuous or divided into two groups, of which latter structure
we have not hitherto had any very well characterised example. The
olfactory orifices are either highly or moderately protuberant.

In most of the species the prosoma is little developed, and the first
cirrus is placed far