General Appearance and Structure.—Shell generally depressed; when growing crowded, sometimes cylindrical: colour dingy purplish-brown, but when much corroded, dirty gray; very young shells are very dark green, owing to the corium, which is of this colour, being seen through the valves. Surface generally rugged, from irregular slight longitudinal folds, and from the transverse overlapping tile-like lines of growth; but sometimes the surface is nearly smooth, with very slight longitudinal folds, these being gray coloured, the intermediate parts being pale dingy purple, the shell thus becoming striped. Orifice rhomboidal, passing into trigonal, owing to the great width of the carinal end. Sutures generally very distinct, rarely obliterated in the cylindrical varieties. Radii narrow, generally exposing much of the alæ, which are plainly marked by lines of growth: the radii themselves, when well developed, which is not often the case, consist of small laminæ or ridges, placed on both sides of the sutures, and interfolded or interlocked together: usually only a trace of this structure is exhibited, but occasionally, along some or along all the sutures (as in the specimen figured), the laminæ of the radii interfold, as plainly as in [C. intertextus]. The alæ differ slightly from the alæ of the other species, in not forming so much of a rectangular projection, the lower margin running with a gentle curve into the parietes. The internal surface of the parietes is either smooth, or near the basal margin is roughened with depending points: in some specimens from the Falkland Islands, both edges of each suture were inflected, forming a double ridge, with roughened edges, resting on the basal membrane, and supporting the shell. I must mention that in my notes made at these Islands, I remark that the basal membrane seemed sometimes to be surrounded by a calcareous rim; none of the specimens brought home are thus characterised; but bearing in mind the affinity of this species to [C. intertextus], no doubt we have here an indication of the shelly ledge surrounding the basis, as described under that species. The largest specimens which I have seen are a quarter of an inch in basal diameter.
The Opercular Valves generally have their summits much worn down. The scuta are elongated in the line of the longer axis of the orifice; the articular ridge is very prominent, and is placed in the middle of the tergal margin. The terga are very narrow, as in some varieties of [C. stellatus]: they are remarkable in two respects, namely, in the depressor muscle being attached to a plate, formed apparently by the union of the usual crests, parallel to the outer lamina of the valve itself, a deep narrow cavity (fig. [2 d], p) being thus formed; and secondly, in the far more extraordinary circumstance of the existence of a small pit (q) at the extreme basi-scutal corner of the valve, in which about half of the scutal lateral depressor muscle is attached: I have observed no other instance in any cirripede of the partial attachment of a muscle properly belonging to one valve to another valve. The figures of the valves [2 b], [2 c], [2 d], are from specimens most unusually perfect, with the upper portion not worn away; the ordinary appearance of the valves as seen from above, is given in fig. [2 a]; at fig. [2 d], a view is given of the tergum seen from vertically beneath, showing the cavity for its own depressor muscle, and for part of the lateral depressor muscle of the scutum.
Mouth.—The crest of the labrum is hairy, without teeth: the palpi have long spines at the end, but none along the inferior margin: the mandibles have either four or five graduated teeth, the lower ones of which are plainly double laterally: the maxillæ have a very sinuous edge. Cirri: the first and second pairs are very short: on the four posterior pairs the segments support either four or five pairs of main spines, with the small intermediate spines rather larger than usual.
Branchiæ.—None; but where they ought to occur, there are two very slight ridges clothed with hairs, about the 1/100th of an inch in length. On the prosoma, there is a slight ridge, extending from the base of the first cirrus towards the adductor scutorum muscle, also clothed with hairs; this unusual character of the prosoma being hairy is common to [C. dentatus].
This species is the commonest cirripede on the shores of the Falkland Islands: many of the specimens are there crowded together, and rendered elongated and cylindrical, with the walls very thin, and the sutures often obliterated; as the opercular membrane is very narrow, the opercular valves are much influenced both in their outline and in their crests and articulations, by the varying form of the shell: I have even seen specimens with the scutum and tergum on one side twice as large as on the other side.
13. CHAMÆSIPHO—Nov. Genus.[132] Pl. [19].
[132] Χαμαι [Greek:Chamai], on the ground, and σιφων [Greek:siphôn], a tube.
Compartments four, with the sutures often much obliterated: basis membranous.
Distribution, Australia, China (?). Attached to littoral shells and rocks.