serve as a lower lip; they are thicker than the other trophi; they have their inner surfaces clothed with spines, sometimes divided into an upper and lower group, and occasionally separated by a deep notch: there are often long bristles outside. They are furnished with at least two muscles; in sessile Cirripedes I have seen that they are capable of a rapid to and fro movement, and I have no doubt that their function is to brush any small creature, caught by the cirri, towards the maxillæ, which are well adapted to aid in securing the prey, and to hand it over to the mandibles, by them to be forced down the oesophagus. On the exterior face of the outer maxillæ, above a trace of an upper articulation, either two small orifices or two large tubular projections can always be discovered; and these, as will presently be mentioned, I believe to be olfactory organs. _Cirri._--The five posterior pair are seated close to each other and equidistant; the first pair is generally seated at a little distance, and sometimes at a considerable distance from the second pair. The first pair is the shortest; the others, proceeding backwards, increase gradually in length. The rami of each pair are either equal in length or slightly unequal: those of the first pair are oftenest unequal. The number of segments in the posterior cirri is sometimes very great; in one species of Alepas, there were above sixty segments in one ramus, the other ramus being in this unique case (Pl. X, fig. 28) small and rudimentary. The pedicels consist of two segments, a lower, longer, and upper short one (fig. 18, _c_, _d_.) In the usual arrangement of the spines on the segments of the three posterior pair of cirri, there are (figs. 26, 27) from three to six pair of long spines on the anterior face, with generally some minute spines (occasionally forming a tuft) intermediate between them: on the dorsal surface, in the uppermost part of each segment, there is a tuft of short spines generally mingled with some longer, finer ones: on the inner side of each segment, on the upper rim, there are generally a few extremely minute and short spines. From the increase of these latter and of the intermediate spines, the antero-lateral faces of the segments of the first cirrus, and of the lower segments of the anterior ramus of the second cirrus (Pl. X, fig. 25), are almost always thickly paved with brush-like masses of spines. The lower segments of the anterior ramus of the third cirrus is generally, though not always, thus paved: these paved segments are much broader than the others. The posterior rami of the second and third cirri are often in some slight degree paved, though in other cases they resemble the three posterior pair of cirri. The two segments of the pedicels have bristles on their anterior faces, essentially arranged on the same plan as on the segments of the rami: the bristles are generally not so symmetrically arranged on the pedicels of the second and third