Affinities.—[C. intertextus] is the most distinct species of the genus, as shown by the peculiar radii and alæ, by the scuta and terga being calcified together, by the character of the third pair of cirri, and by the inflected parietes forming a ledge round the membranous basis; but in this latter respect [C. intertextus] resembles [C. Hembeli]. [C. Hembeli], in its serrated radii, is closely related to [C. dentatus]; and this latter species differs in the structure of its radii only in degree from certain varieties of [C. stellatus]. Lastly, [C. intertextus], in its peculiar radii, closely resembles [C. scabrosus], and this latter species does not differ much from the other species. Hence the genus [Chthamalus] has no claims to be subdivided into smaller genera.
Range.—The species are found all round the world, from (as far as I have seen) 54°-55° north, to Cape Horn, in 55°-56° south. All the species, of the habits of which I know anything, are littoral; and in many parts of the world are excessively numerous, quite covering large spaces of the coast-rocks, and often coating the coast-shells. [Chthamalus dentatus] is littoral, like the other species; but it often lives attached on [Balanus tintinnabulum] and [amphitrite], on the bottoms of ships arriving in British ports from the west coast of Africa. I do not know of any instance of more than two species occurring in the same region. Some of the species have large ranges: [C. scabrosus] extends from the Falkland Islands and Tierra del Fuego to Peru; and [C. stellatus] has an enormous extension over almost the whole world, excepting the west coast of South America and Australia. I do not believe any species of the genus, owing probably to their littoral habits, have hitherto been found fossil.
1. [CHTHAMALUS] STELLATUS. Pl. [18], fig. [1 a]-[1 h].
LEPAS STELLATA. Poli. Testacea Utriusque Siciliæ (1795), Tab. 5, fig. 18-20.
---- DEPRESSA (var.) Ib., Tab. 5, fig. 12-16.
CHTHAMALUS STELLATUS. Ranzani. Memoire di Storia Naturale (1820), Tab. 3, fig. 21-24.
-------- GLABER (var.) Ranzani. Ib.
-------- STELLATUS. Philippi (!). Enumeratio Mollusc. Siciliæ.