Var. (1), Pl. [13], fig. [6 a], [6 b], [6 c], [6 d].—Hab. Java, and probably several other districts.—I will first describe a typical sub-variety, by which I mean a sub-variety not presenting any extreme character. The scutum is of a sub-triangular shape, with the basi-tergal corner much rounded off ([6 d]), and generally but not always hollowed out in a rather remarkable manner. The adductor ridge is considerably prominent, and extends high up, parallel to the articular ridge, which latter is rounded and prominent, but to a variable degree. Near the rostral angle there is sometimes a small tooth, or only a trace of one, depending beneath the basal margin; this tooth we shall hereafter see much more developed. The Tergum is about two thirds of the width of the scutum. It is often slightly beaked, but this is more conspicuous in some of the following varieties. The spur is about half the width of the valve, and its basal end is truncated, and nearly parallel to the basal margin of the valve, but the truncated form passes insensibly into a rounded outline. The shell in this variety is generally thick and is not permeated by pores; the orifice is diamond-shaped. But in another sub-variety the walls of the shell are always, or nearly always, permeated by pores, and the tergum is very much narrower, with the spur sharper, so that at first I concluded that these two sub-varieties were specifically distinct: we shall, however, soon see in var. 2 and in var. 4, that no confidence whatever can be placed in the exact breadth of the tergum, or in the porosity of the walls; hence I have been driven to consider the two varieties just mentioned as merely sub-varieties.
Var. (2), fig. [6 e], [6 f], [6 g].—Hab. China; Red Sea.—The shell is almost invariably permeated by pores, sometimes arranged in two or three very irregular rows. In some specimens the scutum exactly resembles that in var. 1, but with the tooth near the rostral angle often rather larger: in other specimens the scutum is much more elongated transversely (fig. [6 e]), with the adductor ridge more medial, and the basal margin not at all hollowed out at the basi-tergal corner of the valve. The tergum, here, is the remarkable feature, being sometimes excessively narrow, with a long sharp spur, which often, but not always, terminates in a needle-like point. In other specimens, from the same coral and certainly belonging to this same variety, the valve is not so narrow ([6 g]), and the spur not so pointed; consequently (as in several analogous cases in other cirripedes) it is impossible to draw any line of distinction between the specimens with the narrow and broad terga.
Var. (3), fig. [6 h] [Creusia gregaria of G. B. Sowerby!]—Hab. Unknown.—The scutum presents here exactly the same considerable range of variation as in var. 2. The tergum is broad, as in var. 1, but the spur is rounded, and from not being placed so immediately close to the basi-scutal angle of the valve, gives to it a rather different aspect. The breadth of the spur varies; an extreme variety is given in fig. [6 h].
Var. (4), Pl. [14], fig. [6 i], [6 k], [6 l].—Hab. Philippine Archipelago; West Indies.—The scutum here presents the same sub-varieties as heretofore, excepting that I have not seen any so much elongated transversely. The shell is covered either with slight, closely approximate ribs, as in the foregoing varieties, or with more distant and more prominent ribs. In specimens taken out of the same branch of coral the walls were either porose or solid. Sometimes the sheath is bright purplish-pink. It is the tergum, again, which presents a remarkable range of difference; for the longitudinal depression or furrow which in the former varieties was quite open, here has its edges more or less folded inwards, and is sometimes quite closed. This same variation has been commonly observed in many species of [Balanus], in which it appears to be dependent on the age of the individual; but this does not appear to be the case in the present genus. As a consequence of the greater or less folding in of the two sides of the furrow, the spur is rendered more or less narrow and pointed, and thus becomes removed to a greater or less distance from the basi-scutal angle of the valve. Further, as a consequence of this folding in, the internal surface of the valve along the line of the external furrow, is raised into a longitudinal ridge. The length of the spur varies considerably. In some very young individuals, the basal margin descends lower on the scutal than on the carinal side of the spur. In one set of specimens (fig. [6 l]), a plate extended from the carinal margin to near the central longitudinal ridge just mentioned: a similar structure was described under [Pyrgoma cancellatum].
Var. (5), Pl. [14], fig. [6 m].—Hab. Unknown.—We have seen in vars. 2 and 3 that the scutum varies considerably in shape: here it is unusually narrow, with the adductor ridge almost touching the articular ridge. There is no little tooth near the rostral angle, and the basi-scutal corner is not hollowed out. The tergum also varies; in some individuals it is truncated and like that figured of var. 1, but rather more rounded; in other specimens (from the same branch of coral) the basal margin so blends into the spur that the latter can hardly be discriminated (fig. [6 m]); in other respects the outline resembles pretty closely that of one of the sub-vars. (fig. [6 f]) of var. 2. The shell is not porose; it is thick, with strong internal ribs, and resembles that of var. 1; but it is of a pale purplish colour.
Var. (6), an. spec.? fig. [6 n]-[6 q].—Hab. Philippine Archipelago.—This is a very remarkable variety; we have, imbedded in the same coral, and with shells absolutely identical, specimens with the scutum having three distinct but graduated forms. Firstly, a scutum transversely elongated, in all external respects like some of the varieties mentioned under vars. 2 and 3, with no rostral tooth, and not hollowed out at the basi-tergal corner, but with the adductor ridge more prominent. Secondly, a scutum of the same general shape, but with the adductor ridge so much developed (fig. [6 n]) as to descend slightly beneath the basal margin, and to be seen when the valve is viewed externally; there is a very slight tooth near the rostral angle (as in some former sub-varieties), and which can be here rather more clearly seen than hitherto, to be formed by the adductor ridge (closely united to the external surface of the valve) extending thus far, and being here produced a little downwards. Thirdly ([6 p]), we have the adductor ridge immensely developed, descending far below the basal margin of the ordinary valve; and the basal margin at the basi-tergal corner is angularly and deeply hollowed out. The appearance of the valve is widely different from that in the first sub-variety, yet it is impossible to separate the first and second sub-varieties, and it is almost equally certain that the third sub-variety is only an exaggeration of the second. The lower edge of the adductor ridge, in the third sub-variety, varies a little in outline; it is deeply sinuous, and is produced at the rostral angle into a point, of which we have heretofore seen only a feeble representation. It would appear as if the great development of the adductor plate had caused the exterior ordinary surface of the valve to shrink or be less developed. There is a striking resemblance in the structure here described with that in [Pyrgoma cancellatum] and [conjugatum]. The terga belonging to the above scuta, also, vary; the spur being sometimes square ([6 o]), and sometimes bluntly pointed: when the spur runs in the same exact line ([6 q]) with the scutal margin of the valve, a peculiar aspect is given to it, but this is by no means always the case. Both opercular valves are often partially coloured pinkish-purple. The shell is not porose; it is thin, with remarkably prominent internal plates; it is apparently always of small size, which I attribute to this variety inhabiting a hard thin plate-like coral. The sheath is bright pinkish-purple, of which we have had instances in some of the other varieties; and the shell itself is sometimes pinkish. Taking the scutum of the first sub-variety, together with the commonest accompanying variety of tergum, I find it quite impossible to assign to it a specific character; if, on the other hand, we consider the scutum of the third sub-variety by itself, nothing can appear more distinct; but I must repeat, there can be hardly a shadow of doubt that the three sub-varieties of scutum here described, graduate into each other, and are specifically identical.
Var. (7), fig. [6 r].—Hab. Probably Philippine Archipelago, associated with [Balanus quadrivittatus].—There can be hardly any question of this being specifically identical with the last variety. It inhabits a different coral. All the specimens were of small size. The walls are not so thin, and the internal ribs not so prominent as in var. 6. The sheath is either white or dull purple; I can, in short, point out no difference in the shell from the typical var. 1. The scutum is not so much elongated transversely as in var. 6, and the basi-tergal corner is more cut off,—in which respect it resembles the common varieties. The adductor ridge is largely developed, so as to be just visible when the valve is viewed from the outside, in a degree between the first and second sub-varieties of var. 6: but the most singular character is the larger development of the tooth near the rostral angle, and this was the case in the same degree in all the specimens which I examined. The tergum resembles that rather unusual sub-variety of var. 6 (fig. [6 q]), which has the scutal margin and the one side of the spur forming a straight line. It appears to me that it would be absurd to consider these slight differences, in parts unquestionably subject to much variation, as specific, when we are almost forced to admit that the much greater differences in the three sub-varieties of var. 6, are not of specific value.
Var. (8).—Hab. Unknown, Mus. Cuming.—I have seen only a single specimen of this, and refer to it on account of var. 11. The shell is rather steeply conical, with distant and prominent ribs; the radii are narrow; the walls are not permeated by pores; the colour is pale purple. Altogether its external appearance is very different from that of the foregoing varieties; but the scuta are identical with those of var. 1, excepting that the rostral tooth is rather larger, being nearly as large as in the last, var. 7. The tergum precisely resembles that in some specimens of var. 2. Hence this variety differs from the first two varieties only in the shade of colour, the external shape, and the greater prominence of the external radiating ribs of its shell. All these characters are variable in the several foregoing varieties, and they have been found, as yet, insufficient to discriminate species in any genus of sessile Cirripedes.