firmly fastening the outer surface of the
peduncle with its calcareous scales and spines, to the coralline.

[51] Mr. Peach, (Transact. Brit. Assoc., 1845, p. 65,) states
that this is sometimes the case in Cornwall; and I have seen a
similar instance in a fine group from Naples.

The structure of the larval prehensile antennae will be most conveniently
described when we come to the Complemental male; and figures (10-12, Pl.
V) will be given.

_Size and Colours._--Montagu states ('Test. Brit.,' p. 18) that British
specimens rarely have a capitulum .62 of an inch in length; I have,
however, seen an Irish specimen, .7 long; and several specimens, from
the Bay of Naples, .8 long, and including the peduncle, 1.3 in length.
The valves in all the specimens are white, and the membrane connecting
them either nearly white, or dirty pale yellowish, or purplish-brown.
Within the sack the corium under the valves is tinted pale purple, and
two very faint bands of the same colour can generally be distinguished
running down the two sides of the peduncle. Body, coloured
yellowish-white, with the upper segments of the pedicels of the cirri,
tinted in front with purple.

_Body_, much flattened, the prosoma is very little developed; the mouth
placed far from the adductor muscle, and is directed in a remarkable
manner towards the ventral surface of the thorax: the first pair of
cirri stands far separated from the second pair.

_Mouth._--Labrum with the upper part highly bullate, forming an
overhanging projection equalling the longitudinal axis of the mouth;
basal margin much produced; crest with a row of bead-like teeth.

_Palpi_ rather small, with their external margin straight, and internal
margin oblique: the bristles on the two palpi just meet each other.

_Mandibles_, with five or six teeth, with the second, (or second and
third, when there are six teeth,) smaller than the others; in two
specimens, there were five teeth on one side and six on the other;
inferior angle rather broad and strongly pectinated.

_Maxillae_ with the edge nearly straight, without any notch, but with the
inferior portion very slightly projecting; there are twelve or thirteen
pairs of unequal spines, of which some of the middle ones are rather
longer than the others, and almost as long as the two upper great
spines.

_Outer Maxillae._--On the inner margin the bristles are divided into two
separate tufts; exteriorly, near the base, there is a d