The _Carina_, in outline is triangular, with the basal margin in some species extremely protuberant. In the first four species, the internal surface is concave, in _L. truncata_ and _L. Valentiana_ it is convex, with a central raised ridge, and consequently the upper freely-projecting portion of the valve, has a prominent central crest or ridge; in _L. Nicobarica_ and _L. Rhodiopus_ there is only a trace of this ridge. The rostrum, as before stated, is always very small; it, as well as the latera, are most developed in _L. Nicobarica_, and least in _L. truncata_ and _L. Valentiana_; generally only a few zones of growth are preserved, and from their being enlarged at their basal serrated rims, the rostrum sometimes appears like a few beads of a necklace strung together. The _Latera_ are remarkable from being placed over the carinal half of the terga, in an oblique position, parallel to the lower carinal margin of the terga. A section, parallel to the growth layers, varies in the different species from elliptic to broadly oval, and in _L. Nicobarica_ it is triangular. Only a few layers of growth are ever preserved. In _L. truncata_, where the latera are represented by mere stiles, (like strings of beads), and are even less in width than the rostrum, they are imperfectly calcified. _Microscopical Structure of the Valves._--The shelly layers are white, and generally separate easily, so that in _L. dorsalis_ it is rare to find a specimen with the upper part of the valves perfect. The valves are so translucent, that in the thin margins, even the tubuli could be sometimes distinguished. The valves are coated by strong yellow membrane, which, after the shelly matter in _L. dorsalis_ had been dissolved in acid, separated into broad slips, answering to each zone of growth. On the lower margin of each slip, there is a row of closely approximate spines, generally slightly hooked, pointed, 1/650th of an inch in length, and 1/10000th of an inch in diameter; they arise out of a little fold; all are furnished with tubuli of the same diameter with themselves, running through the whole thickness of the shelly layers, and attached, apparently, by their apices, to the underlying corium. As the spines are very numerous, so are the parallel rows of tubuli. After the shelly layers had been dissolved, there was left in _L. dorsalis_ (well seen in the latera), an extraordinary, conferva-like mass of branching, jointed, excessively thin tubes, sometimes slightly enlarged at the articulations, and appearing to contain brown granular matter: other portions of the valves, instead of this appearance, exhibited membranes or films with similar, branching, articulated tubes or vessels attached to them: I have not seen this appearance in any other cirripede. The yellow exterior enveloping membrane, with its spines, is present in all the species of the genus; in _L. Rhodiopus_ these spines are much larger than in _L. dorsalis_, and on the inner sides of the