Mouth with the labrum notched in the middle, not swollen; palpi large, almost touching each other; mandibles generally with the lower teeth laterally double; third pair of cirri with their segments resembling those of the second pair.
Scutum and tergum articulated together, or overlapping each other; each branchia composed of a single plicated fold.
Genera—[Balanus]; [Acasta]; [Elminius]; [Tetraclita]; [Pyrgoma]; [Creusia]; [Chelonobia].
Scutum and tergum (when both are present) not overlapping each other; basis membranous; parietes often deeply folded, with the outer lamina, towards the basis, generally imperfect; each branchia composed of two plicated folds; shell attached to living vertebrata.
Genera—[Coronula]; [Platylepas]; [Tubicinella]; [Xenobalanus].[82]
[82] At the end of the volume a Synopsis is given, which will serve as a systematic index for the discovery of generic and specific names.
The [Balanidæ] may be divided into two sub-families; namely, the [Balaninæ] and [Chthamalinæ]; and, in the former, the genera, as we see, may be very naturally grouped into two sections. The [Balaninæ] differ from the [Chthamalinæ], as far as the shell is concerned, in the rostrum having radii but no alæ, all the lateral compartments having both radii and alæ; on the other hand, in the [Chthamalinæ], the rostrum has alæ, and the rostro-lateral compartments radii on both sides, and therefore no alæ. These differences probably arise, as already explained, from the perfect confluence, in the [Balaninæ], of the true rostrum with the rostro-lateral compartments. In [Chelonobia], belonging to the [Balaninæ], we see an intermediate state, with the fusion not quite effected: on the other hand, in one genus amongst the [Chthamalinæ], namely, [Pachylasma], we must look to the shell at a very early age, to find the rostrum with its alæ, distinct from the rostro-lateral compartments. In [Tetraclita], [Elminius], and [Creusia], the carino-lateral compartments are aborted, or possibly confluent with the lateral compartments, making altogether only four: in [Pyrgoma] all the compartments are fused together and form a solid ring. The sub-genus [Acasta] is, in one sense, very natural, as it includes species most closely allied: in another sense it is far from natural, as some of the species can hardly be distinguished from those species of [Balanus], which live attached to Gorgoniæ: I almost regret I did not merge the species of [Acasta] into [Balanus]. In the [Balaninæ] generally the parietes are either porose, or are furnished on their internal surfaces with regular ribs, representing the longitudinal parietal septa, which in other species form the tubes or pores; there are, however, many exceptions to this rule in several species of [Balanus], in [Acasta] and [Elminius], all of which have the parietes of their shells internally quite smooth, or only irregularly roughened with points.
Looking to the animal’s body, in the [Balaninæ], the labrum is always notched in the middle, and is never swollen or bullate, for the outer and inner folds of membrane of which it is composed lie close together. The palpi are large, so that their tips almost touch each other. The mandibles, generally, have their lower main teeth laterally double. Of the cirri, the third pair invariably much more closely resembles, in its whole structure, and in its action, the second than the fourth pairs; and it is also generally separated by a small interval from the fourth pair.