The remarkable feature of this genus resides in the vibracula, which here appear to attain their utmost development.  Each vibraculum appears to belong not to a single cell as in Scrupocellaria, but to be common to, or applied to the backs of several.  They are more or less pyriform or long oval in shape, and the two rows decussate with each other along the middle of the branch—­giving in the narrower species, especially, much the aspect of an ear of barley, and in the wider of a straw plait.  The walls of the vibracula are usually thin, and very transparent, so as to allow the outlines of the cells to be seen imperfectly through them.  The upper and outer extremity of the vibraculum is bifid, and to the inner horn is articulated the seta, and from the notch between the two horns there is continued nearly, if not quite, to the inner extremity of the organ, and along its upper border, a shallow groove, in which is lodged the seta when in a state of rest.  In most species the seta is serrated with distant teeth on one side.

Where there are more than two rows of cells, the marginal cells differ in conformation from the central.

As in Scrupocellaria, the opening of the cell is sometimes protected by a pedunculate operculum.  The genus, therefore, may, like that, admit of being divided into sections, distinguished respectively by the presence or absence of a pedunculate operculum.

a.  Operculatae.

1.  C. rudis, n. sp.

Multiserial; opening of cells oval, margin much thickened, with a strong projecting upturned spine on each side in the central cells, and with three strong and long similar spines on the outer side, and a smaller one on the inner side in the marginal cells.  Operculum spatulate, or pointed above, entire.  Each cell of the central rows with two small avicularia in front, immediately below the mouth.  Each marginal cell with a single large vibraculum in front below the mouth.  Vibracula slender, very transparent.  Setae short, not serrated.

Habitat:  Bass Strait.

Colour dirty white:  forms a broad frondose polyzoarium 1 1/2 to 2 inches, or perhaps more, in height.  The branches, all disposed in the same plane, are flat, thick, and about 1/8th of an inch wide, composed of from four to six rows of comparatively small cells, which viewed behind appear lozenge or diamond-shaped, and arranged quincunically.  It is not always easy to observe with accuracy the outline of the vibracula, owing to the extreme tenuity of their walls, but the groove along the upper border is very distinct and most usually has the seta lying in it.  The avicularia on the marginal cells are very large, but not uniform in size.  Along each border of the branches runs a bundle of radical tubes, the number of which diminishes as the branch ascends, each terminating in a vibraculum.

2.  C. zelanica, Busk.

Selbia zelanica, Gray.  Dieffenbach’s New Zealand, volume 2 page 292.