[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 seen hundreds of specimens from Tierra del Fuego, I have not seen one specimen of var. nitidus, or even of an approach to it in appearance; and, on the other hand, var. nitidus is the common form in Chile and Peru; though I have seen one or two specimens of the membrane-covered variety from Valparaiso. Such facts strongly induced me to believe that these forms were specifically distinct; but upon careful examination I could find no other or more important differences than those just specified. Some specimens from northern Chile are in an intermediate condition; and from Concepcion, in the south of Chile, where the climate approaches in character to that of the more southern parts of the Continent, there are many specimens, in so intermediate a condition that I know not whether or no to rank them under var. nitidus. Thus I became convinced that these forms are only varieties. At Concepcion, some few specimens are pale purple, and yet are wholly invested by thick brown membrane, thus uniting the two extreme varieties. From California I have seen both varieties, but I do not know which is most common there. With respect to the great difference in aspect between the specimens from northern Chile and Tierra del Fuego, we shall hereafter see a strictly analogous case in [Balanus flosculus]. Finally, I may add that [B. lævis] seems to represent in the southern hemisphere and on the west coast of North America, the [B. perforatus] of Europe and Western Africa.
General Appearance.—Shell conical, sometimes slightly globular; surface smooth (that is, not folded), either naked, and in that case white or pale purple, or covered by dirty yellowish-brown membrane. Orifice small, more or less toothed, rarely exceeding one third of the basal diameter. Radii very narrow, often not developed, the six sutures forming in all cases deep and narrow clefts. The largest recent, but much depressed, specimen which I have seen (from the Strait of Magellan) was three fourths of an inch in basal diameter; specimens growing congregated are often much elongated. I have seen one with the basal cup between two and three times as deep as the height of the compartments. Of the ancient tertiary specimens, the largest had a diameter of three fourths of an inch, and a total length of actually two inches (fig. [2 a]); another of these fossils had a basal cup in depth equalling four fifths of the entire length of the shell and basis.
The scutum has either one very broad and deep longitudinal furrow ([2 b]), or two moderately broad and deep ([2 e]), or two narrow and deep, or less frequently one narrow and inconspicuous longitudinal furrow ([2 f]); rarely there is not one furrow; sometimes there are none towards the apex, whilst furrows have been formed in the lower part of the valve. In young specimens the furrows extend down to the actual basal margin, but in old specimens they often fall short of this, and, as a consequence, the furrows become crossed by one, two, or three calcareous ridges, which ridges at successive periods formed the basal margin of the valve. The external surface is covered by yellow membrane; and fragments of several successive opercular membranes are often attached to the zones of growth.
Internally the articular ridge is not very prominent, but is remarkable ([2 c], [2 d]) from its lower point being produced into a long, sharp, sub-cylindrical, free style (like the hinge of a common gate), which is generally broken off in disarticulating the valve from the tergum. The adductor ridge is either sharp and prominent or blunt: it extends up the middle of the valve nearly to the apex, and downwards it trends a little towards the occludent margin. The pit for the lateral depressor muscle is minute but deep: the basal margin is sometimes hollowed out under this pit. Sometimes there is a distinct, but blunt ridge, caused by one of the furrows outside, parallel to the adductor ridge, and placed between it and the little pit for the lateral depressor; in this case, the basal margin, as viewed internally, is rendered sinuous ([2 d]), as is best exhibited in the great fossil specimens from Coquimbo.