General Appearance and Structure of Shell.—Shell extremely rugged, irregular, massive, generally much corroded, steeply conical or even sub-cylindrical: orifice large, broad, rhomboidal, of nearly equal breadth at both ends. Colour dirty white, often slightly tinted yellow from the investing membrane, and from thin layers of punctured membrane alternating with the laminæ of shell. The parietes, in old specimens, have very irregular longitudinal ridges, or rather plates projecting out, sometimes much branched, and generally curved inwards so as to meet each other, thus forming round the basal margin a circle of cylindrical apertures. In old large specimens the radii are not developed, and till the compartments are disarticulated there is no trace of the toothed structure of their sutural edges: in this condition the sutures exist as deep, rugged, narrow fissures. In younger shells, the radii, though narrow, are distinct, and have their surfaces transversely ribbed, and their edges toothed and interlocked with the teeth of the recipient furrow. Some of the specimens present a curiously deceptive resemblance to Elminius plicatus. Basal diameter of largest specimen, one inch and a quarter; height one inch.

The parietes are remarkably thick, but the compartments separate easily: I have, however, seen one instance in which they were partially calcified together. Their internal surfaces are very smooth. The sheath does not descend low. The alæ project rectangularly; they have thick edges, and these are coarsely crenated in transverse lines. Of the radii sufficient has been said.

Scuta (fig. 2 b): these, in all the specimens seen by me but one, have been deeply corroded, and their outline, as in Chthamalus, considerably modified: in the one specimen well preserved, the exterior growth-ridges were extremely prominent. The articular ridge does not project much, nor is the articular furrow very deep. There are more or less distinct crests for the lateral depressor muscles. The Terga are rather narrow, with a small rounded spur, moderately distinct. The tips of the crests for the depressor muscle barely depend beneath the basal margin.

Mouth: labrum considerably bullate, with the crest hairy and furnished with a few most minute teeth. Palpi small, with their tips not nearly touching each other. Mandibles with four teeth, of which the lower ones are laterally double: inferior pectinated portion small. The maxillæ are notched, but their outline differed on opposite sides of the individual examined. Outer maxillæ bilobed on their inner face.

Cirri.—The first pair has the rami unequal in length by about three segments, having six segments on one and nine on the other ramus. In the second pair the anterior ramus is remarkably short and extremely broad; the five segments of which it is composed being thickly covered with bristles, some of which are very coarsely and doubly pectinated: the posterior ramus is nearly twice as long as the anterior ramus, and has eleven segments; of these, excepting the two basal segments which are rather thickly covered with spines, the others resemble in the arrangement of their spines the four posterior pairs of cirri, with the exception that there is a single transverse row of rather long spines along the upper and inner lateral edge of each segment. The segments in all the four posterior pairs of cirri resemble each other in bearing each four pairs of main spines (of which the two lower pairs are short), with a tuft of small intermediate spines.

The penis is remarkable from its very small size and shortness, not being more than once and a half as long as the pedicel of the sixth cirrus.

General Appearance and Structure.—Shell circular, much depressed; coloured brown, with an orange-red tint; surface regularly and narrowly furrowed in longitudinal lines, the intermediate rounded ridges projecting at the basal margin in finger-like points. The eight compartments, when disarticulated, are of nearly equal sizes; the carino-lateral and rostro-lateral compartments being rather smaller than the others. The radii are neatly toothed; but with the exception of these teeth, which are equally developed on both sides of the sutures, and which closely interlock in the lower part of the shell, but stand a little apart in the upper part, the radii can hardly be said to be developed. The alæ do not form a rectangular shoulder, the lower margin being regularly curved into the parietes; the upper margin is only slightly oblique; the external surface is furrowed by lines of growth. The shell increases a little in diameter, chiefly by the growth of the alæ. The parietes are not very thick, with the inner surface smooth, but with punctures placed in rows for the entrance of the tubuli: the laminæ of shell alternate with layers of yellow finely punctured membrane. Basis formed of thin membrane, in concentric slips. Basal diameter of largest specimen, .6 of an inch.

Scuta broad, with the lines of growth few in number, but extremely prominent, so as to form folds: basal margin with a very slight angular bend: articular ridge not very prominent. Terga, with a narrow slip along the scutal margin, having the lines or folds of growth so prominent as almost to form a series of small transverse pits: the basal margin of this portion forms an angle with the rest of the basal margin: no spur can be said to exist: the crests for the depressor muscle depend a little beneath the basal margin: articular ridge very prominent.

Mouth: labrum and palpi as in the last species. Mandibles with three main teeth, apparently single, of which the lower tooth has its upper edge pectinated: the inferior part of the mandible is pectinated as usual. The maxillæ have two notches, one beneath the two upper large spines, and the other in the middle, separating some thicker and thinner spines.

Cirri: first and second pairs short, with the anterior rami in each longer by about two segments than the posterior rami; all the segments thickly covered with bristles. The third cirrus is much longer than the second cirrus, with the posterior ramus longer than the anterior ramus; on the latter the three basal segments, and on the posterior ramus the two basal segments are thickly covered with bristles; the other segments have bristles arranged as on the three posterior pairs of cirri, namely, each segment has four pairs of main spines, of which the two lower pairs are short.

The unarticulated support, whence the articulated portion of the penis arises, is unusually long, equalling the pedicel of the sixth cirrus.