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. I have already under the Family sufficiently entered on the relations of the Balaninæ to the Chthamalinæ, and of the genera, one to the other, so that I need not here add anything. I can point out no difference in habits or geographical distribution between the Balaninæ and Chthamalinæ. 1. _Genus_--BALANUS, Auct.[83] [83] The name Balanus was used, almost as at present, by Lister and Hill, before the introduction of the binomial system. Since that period the first two authors, as far as I know, who used this name, were Da Costa, in his 'Hist. Nat. Test. Brit.,' in 1778; and Bock, in the 'Naturforscher,' for the same year; Bock, however, applied it to a Chelonobia. CONOPEA (pars generis). _Say._ Journal Nat. Sc. Philadelphia, vol. ii, part ii, 1822. MESSULA (do.). _Leach._ Zoological Journal, vol. ii, 1825. CHIRONA (do.). _J. E. Gray._ Philosoph. Transacts., 1835, p. 37. _Compartments six; basis calcareous or membranous; opercular valves sub-triangular._ _Distribution._--Mundane: in the warmer seas.