ABSTRACT
The Balanidae may be divided into two subfamilies; namely, the Balaninae and Chthamalinae. The Balaninae differ from the Chthamalinae, as far as the shell is concerned, in the rostrum having radii but no alae, all the lateral compartments having both radii and alae; on the other hand, in the Chthamalinae, the rostrum has alae, and the rostro-lateral compartments radii on both sides, and therefore no alae. Looking to the animal's body, in the Balaninae, 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. In Chelonobia, belonging to the Balaninae, an intermediate state, with the fusion not quite effected: on the other hand, in one genus among the Chthamalinae, namely, Pachylasma, the shell at a very early age, to find the rostrum with its alae, distinct from the rostrolateral compartments.
