In sections C and D, I have seen one specimen of [B. spongicola] with a solid basis, and very young specimens of [B. improvisus] are thus characterised, and therefore these species are liable to be placed in the wrong section, D: [Bal. nubilus], also, has part of its base non-porose, and therefore likewise might be placed in D: on the other hand, the circumference of the basis in [B. patellaris] is often porose, and hence this species, which belongs to D, might be placed in C.
In [Bal. glandula], in D, the parietes of the compartments, without several were examined, might be thought to be solid, and therefore this species might be wrongly placed in F; on the other hand, the fossil [B. unguiformis], in F, often has porose parietes, and such specimens would naturally be placed in D. Lastly, without care, [B. flosculus] might be thought to have a membranous basis, and so get placed in E.
The genus [Pachylasma], without an examination of the animal’s body, might easily get misplaced in the wrong genus, amongst the species in the last section (F) of Balanus, yet there can be no doubt that [Pachylasma] belongs to the [Chthamalinæ].
Section A.
1. [BALANUS] TINTINNABULUM. Pl. [1], fig. [a]-[l]; Pl. [2], fig. [1 a]-[1 o].
LEPAS TINTINNABULUM. Linn. Syst. Naturæ, 1767.
---- ------------ Ellis. Phil. Transact., vol. 50, 1758, Tab. 34, figs. 8 and 9.