Note 86 — 1. Genus—BALANUS, Auct.[83]

The following species might, owing to variation, or to the obscurity of their structure, without care, be classed in the wrong sections:—in A, Balanus Ajax, from living attached to Milleporæ, is sometimes elongated in its rostro-carinal axis, and from having its radii only finely porose, it might be classed in B: on the other hand, Bal. stultus is sometimes but little elongated, and the basis hardly boat-formed, and hence might be classed in A. The distinction between all the species in (B) and the sub-genus Acasta is artificial.

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.