movement, are all admirably adapted to secure any prey, when once entangled by the cirri. _Mouth._ The mouth, in the sub-family Chthamalinæ, cannot be distinguished from that of the Lepadidæ, which has been pretty fully described in my former volume. In the Balaninæ, however, the labrum differs considerably in not being swollen; that is, in its outer and inner fold of membrane being close together, and in having a central notch: the palpi are also larger, and the lower teeth on the mandibles, are laterally (Pl. 26, fig. 5) double, as will be more particularly stated under these two sub-families. I have given a drawing (Pl. 26, fig. 1) of the mouth, seen from above, of _Balanus perforatus_, with the right-hand palpus (_d′_) and outer maxilla (_a′_) cut off, in order that the labrum (_e_), mandibles (_c_), and inner maxilla (_b_) might be better shown; the cut-off bases (_x_, _x_) of the first cirrus on each side are also shown. In fig. 2 we have the deep supra-œsophageal cavity in _Bal. improvisus_ torn open and laid flat, with the inner surfaces of the labrum (_c_) and outer maxillæ (_a_) exhibited, the palpi, mandibles, and inner maxillæ having been removed. Figs. 3 and 4 will presently be referred to; they are parts of the mouth, with the muscles, &c. removed, of Coronula. The mouth differs extremely little in the different genera and species of the Balanidæ, much less than amongst the Lepadidæ. In the Balaninæ, the crest of the labrum is sometimes hairy, instead of having, as is usual, from two to six teeth on each side of the central notch: in _Balanus improvisus_ (Pl. 26, fig. 2) and _eburneus_, and in _Chelonobia_, the crest on each side of the central notch (_e′_) is furnished with a row of finely graduated teeth. A sub-triangular portion of the inner fold of membrane of the labrum, which overhangs the œsophagus, is always thickened and yellowish; it is also often punctured in patterns (Pl. 26, fig. 2, _f_), which, I believe, give attachment to little muscles that serve to open the upper end of the œsophagus. Opposite to this thickened, sub-triangular portion of membrane, the thin membrane forming the supra-œsophageal cavity (or the cavity surrounded by the gnathites) is strengthened by a pair of curved ribs (_h_, fig. 2) of thickened yellowish membrane, running down from the inner bases (_a′′_) of the bilobed outer maxillæ to the opening of the œsophagus (_g_): a broad branch from each of these ribs supports the sides of the orifice of the œsophagus; and this branch almost joins on to a slightly thickened rim or bar (_f′_), which branches off from the upper part of the sub-triangular (_f_) inner fold of the labrum. This structure, in _Bal. improvisus_, is represented in Pl. 26, fig. 2, as well as it could be, considering that the deep supra-œsophageal cavity has to be torn open; and then laid flat.