General Appearance.—The capitulum (seen from above in [Pl. III], [fig. 4 a]) is slightly compressed, almost globular, composed of thick membrane, with two large, ear-like, flexible, tubular, folded appendages, at the upper end, opening into the sack. These appendages are seated behind the rudimentary terga when such are present, or behind the spots which they would have held if not aborted. In a young condition they are tubular, but not folded; and often, according to Prof. Macgillivray, either one or both are at first imperforate. They are formed externally of the outer membrane of the capitulum (rendered thin where folded), and internally of a prolongation of the inner tunic of the sack; between the two, there is, as around the whole sack, a double layer of corium. A section across both appendages, near their bases, is given in [Pl. III], [fig. 4 b], showing how they are folded,—the chief fold being directed from below upwards, with a smaller fold, not always present, from between the two, outwards. The folds sometimes do not exactly correspond on opposite sides of the same individual; they are almost confined to the lower part, the orifice itself being often simply tubular. These appendages are sometimes very nearly as long as the whole capitulum: a section near their bases is sub-triangular. I shall presently make some remarks on their functions and manner of formation.

The Scuta, as well as the other valves, are imperfectly calcified: shape, variable. They usually consist of two lobes or plates, placed at above a right angle to each other, and rarely ([fig. 4 c]) almost in a straight line; the lower lobe is more pointed and narrower than the upper; the two correspond to the lower and middle lobes in the scuta of C. virgata, the upper one being here absent.

The Terga are developed in an extremely variable degree; they are often entirely cast off and absent. In very young specimens, they are of the same length with the carina, but after the carina has ceased to grow, the terga always increase a little, and sometimes to such a degree as to be even thirty or forty times as long as carina. When most developed ([fig. 4 a]) they are not above one third as long as the scuta, to which they lie at nearly right angles; they consist of imperfectly calcified plates, square at both ends, slightly broader and thinner at the end towards the carina, where they are a little curled inwards, than at the opposite end; they are not quite flat in any one plane; internally they are slightly concave; finally, I may add, they nearly resemble in miniature the terga of C. virgata. In full grown specimens, the terga almost invariably drop out and are lost; but even in this case, a long brownish cleft in the membrane of the capitulum, marks their former position. The orifice of the capitulum is usually notched between the terga, or between the clefts left by them; on each side of the notch there is a slight prominence. In some few cases, however, there is no trace of this notch. Behind the terga or the clefts, the great ear-like appendages, as we have seen, are situated.

Carina, rudimentary ([fig. 4.]) and often absent; it is pointed-elliptical, and is rarely above the 1/40th of an inch long. After arriving at this full size, calcareous matter is added to the under surface over a less and less area, so that it becomes internally pointed, and finally, in place of calcareous matter, continuous sheets of chitine are spread out beneath it; hence, during the disintegration of the outer surface, the carina comes to project more and more, and at last drops out; subsequently, even the little hole in which it was imbedded, disintegrates and disappears.

Peduncle, cylindrical, distinctly separated from the capitulum, and generally twice or thrice as long as it: the thickness of the outer membrane generally great, but variable: surface of attachment variable, either pointed, or widely expanded, or formed into divergent projections.

Filamentary Appendages, seven on each side, highly developed, long and tapering; there are two beneath the basal articulation of the first cirrus, and one on the posterior margin of the pedicel of each cirrus, excepting the sixth pair; the filaments on the pedicels are nearly twice as long as the cirri themselves.

Mouth,—mandibles, with the five teeth nearly equidistant, and towards their bases finely pectinated on both sides; inferior angle rudimentary, often represented by a single minute spine: in one specimen, there were only four teeth on one side. Maxillæ, with five steps, not very distinct from each other, with the first step much curved. The larger of the two upper great unequal spines is pectinated, like the teeth of the mandibles; there is a third long finer spine beneath the upper large pair.

Cirri rather short, broad, with the anterior faces of the segments protuberant, especially those of the first cirrus and of the anterior ramus of the second pair: spines on the anterior cirri doubly serrated. Posterior cirri, with the intermediate spines between the pairs, long; dorsal tufts, minute. On the lower segment of the pedicels of the four posterior cirri, there are two separate tufts of bristles.

Colours extremely variable; sometimes five longitudinal bands of dark purple can be distinctly seen (as in C. virgata) on the peduncle, these bands becoming more or less confluent on the capitulum; at other times, the capitulum is more or less spotted, or often nearly uniformly purple: the sack, cirri and trophi are, also, purple.

Size.—The largest specimen which I have seen was, including the peduncle and ears, five inches in length, the capitulum itself being rather above one inch in length, and 7/10ths of an inch in breadth.