Mouth: labrum with the notch wide, generally with a few little teeth; mandibles with three teeth, and some inferior knobs; maxillæ notched. Cirri, first pair with one ramus shorter by three segments than the other ramus. Second and third pairs short, of nearly equal length, thickly clothed with spines; segments very little protuberant. Posterior cirri, having elongated segments, supporting seven pairs of spines.
Var. sordidus.—This form is very common on the tidal shores of the Strait of Magellan, and of the southernmost parts of Tierra del Fuego, near Cape Horn: it lives attached to rocks, mytili, and logs of wood, and is associated with [Chthamalus scabrosus]. It almost certainly is the most antarctic form of the genus [Balanus]. If I were guided by external appearance alone, I should certainly separate this form specifically from [B. flosculus], but, as will be seen in the following description, the differences consist only in var. sordidus being much duller and rather differently coloured, in the longitudinal folds being sharper and more prominent, and in the whole shell being rather more globular, and on an average rather larger; but in the true [B. flosculus] there is considerable variation in all these respects, as there likewise is in var. sordidus; thus some of the cylindrical varieties of the latter have less prominent ridges than even [B. flosculus]. In general appearance I have seen some nearly, but not exactly, intermediate forms; therefore, I do not feel positive that these forms may not be specifically distinct, but have failed, after careful examination, to find any sufficient diagnostic characters. Moreover, in the case of [Balanus lævis], I was led to believe that there is an equal and somewhat analogous amount of variation in the specimens inhabiting Tierra del Fuego and northern Chile; and in this case I was enabled to show the existence of strictly intermediate forms in the intermediate districts.
The shell in var. sordidus is generally globulo-conical, dirty white, frequently with a green tinge, from the growth of confervoid matter. Orifice small. The exterior surface is covered with numerous prominent, narrow, sharp ribs or folds, the basal margin being serrated with projecting points where the folds terminate. When the radii are not developed, the sutures are very often obscure. Internally, the shell is faintly tinted of a port-wine purple. In all points of structure this form is identical with the true [B. flosculus]. In some few specimens the whole exterior surface was disintegrated and smooth; and this is generally the case with the upper parts of the shell. Some other specimens, which had grown crowded together on wood, had become cylindrical, and consequently the orifice was as large in diameter as the shell, namely, half an inch: in some of these cylindrical varieties the sheath was entirely soldered to the walls. The largest specimens which I have seen were .6 of an inch in diameter; and above one inch in height.
Affinities.—This species, in its opercular valves, even in such trifling characters as the strength of the opercular membrane, and in its cirri, approaches closely to [B. cariosus]. We even see on the under side of the scutum, in that species, a single little ridge, foreshadowing, as it were, the crests for the lateral scutal depressores, so remarkable in our present species. In the structure of the shell and of the basis, [B. flosculus] is much more closely related to the last species, or [B. imperator]. If it had been possible to have arranged the species in a single line, [B. flosculus] ought undoubtedly to have been placed between [B. cariosus] and [imperator].
41. [BALANUS] BISULCATUS. Pl. [8], fig. [6 a]-[6 c].
BALANUS SULCATINUS (?) Nyst, apud D’Omalius (sine descript. aut tabulâ), Geologie de Belgique, 1853.[100]
[100] I am indebted to M. Bosquet for a specimen, bearing this name and reference, found in the ‘Systeme Bolderien’ of Dumont, (miocene according to Sir C. Lyell) at Bolderberg. The specimen consists of a rostrum, with a portion of the base attached; and as these parts are in some degree characteristic, I fully believe this specimen to be the [B. bisulcatus]. I hope hereafter to give in the Palæontographical Series fuller illustrations of this and the following fossil species.
Radii with their upper margins oblique and smooth; sutural edges smooth: basis permeated by large pores. Scutum narrow, with from two to four longitudinal furrows: tergum with the spur very short, broad as half the valve.
Var. plicatus, with the walls deeply folded; radii narrow, with their upper margins very oblique.