[91] M. Deshayes, in his descriptions of the plates, considers this figure, I have no doubt erroneously, as that of _B. perforatus_, of Bruguière. The _B. Coquimbensis_ of Sowerby, is a different species from the _B. Coquimbensis_, of Chenu, 'Illust. Conch.,' tab. 6, which latter is unknown to me. _Shell covered by brown membrane, or naked and white or pale purple; orifice small; radii very narrow. Scutum with one or two deep longitudinal furrows._ _Var._ nitidus (fig. 2): _shell not covered by membrane, white or pale purple: orifice but slightly toothed: scutum generally with two furrows_. Hab.--Chile, as far south as Concepcion; Peru; California. _Var._ Coquimbensis (fig. 2 _a_): _with the basal cup partly filled up with thin, irregular, calcareous layers, making a cancellated mass_. Fossil, and recent. _Hab._--Strait of Magellan, ten to twenty fathoms, attached to shells; often entirely surrounding pebbles, forming globular masses; associated with _Verruca lævigata_. Chile and Peru, (generally _var. nitidus_), often attached to _Balanus psittacus_. California. Very common. _Fossil_ in an ancient tertiary formation (middle bed) at Coquimbo, Chile. In a recent deposit (_var. nitidus_) at the height of 1000 feet at Valparaiso; with Human remains at San Lorenzo, Callao, Peru. I may premise that, having myself collected this species from the same locality, the Strait of Magellan, where no allied species occurs, attached to the same Mytilus and associated with the same Verruca, I feel confident that it is the _B. lævis_ described by Bruguière; and there can hardly be any doubt that it is the _B. discors_ of Ranzani. With respect to the old tertiary specimens from Coquimbo, named _B. Coquimbensis_ by Sowerby, they differ from the recent in no respect, except in being considerably larger; and therefore I cannot consider them specifically distinct. At first I was unwilling to believe that the specimens with a single very broad longitudinal furrow, and those with two rather broad, or with one narrow furrow, on their scuta, could belong to the same species; but I soon found that all these varieties occurred mingled together, and that they differed in no other respect whatever. Generally, however, all the individuals in the same cluster had the same variety of scutum,--thus adding one more to the many instances amongst cirripedes of variations common to whole groups of specimens. Still more unwilling was I to believe that _var. nitidus_ and the common variety could belong to the same species. Their general aspect is totally unlike: _var. nitidus_ has a smooth, clean, naked shell, either white or pale purple, somewhat globulo-conical, often with a nearly entire orifice; whereas the other common variety generally has a more steeply conical shell, with a toothed orifice, and is covered by a dirty brownish membrane. Moreover, though I have