_General Appearance._--Shell, sometimes with the rostrum, and sometimes with the carina, and corresponding portions of the basal cup, elongated; but not, apparently, to so great a degree as in the foregoing species; basis not furrowed, from not clasping the branches of the Gorgonia. Colour pale blueish-purple, with the radii whiter. The surface is studded with small calcareous points. The carino-lateral compartments are very narrow, not more than one tenth of the width of the lateral compartments; they are, moreover, scarcely wider at the base than at the summit. The summits of the radii are, apparently, a little oblique, or at least not so square as in the foregoing species. The shell is not nearly so strong as in the last three species; and the compartments separate by gentle force, and from the action of caustic potash. The largest specimen was .4 of an inch in basal diameter. Internally, the parietes are not very strongly ribbed, or they are almost smooth, and there are no pores. The basis is concave and smooth within, and is not porose. The sutural edges of the radii are quite smooth, or sometimes they exhibit, in the lower part, mere traces of septa,--a character by itself sufficient to separate this from the foregoing species. The alæ have oblique summits, and the rather narrow portion added during the diametric growth of the shell, is white. The _Scutum_, externally (6 _d_), has raised striæ, radiating from the apex; valve rather thick; internally, the articular ridge is but slightly prominent, and its lower end is rounded off: the depression for the lateral depressor muscle is slight; between this depression and that for the adductor muscle, the surface of the valve is prominent. _Tergum_, somewhat beaked; externally, the surface is depressed in the line of the spur: the carino-basal margin slopes towards the spur. _Animal's body_ unknown. _Section_ C. _Parietes and basis permeated by pores. Radii not permeated by pores._ 14. BALANUS TRIGONUS. Pl. 3, fig. 7 _a_-7 _f_. _Parietes ribbed, mottled purplish-red; orifice broad, trigonal, hardly toothed. Scutum thick, with from one to six longitudinal rows of little pits. Tergum without a longitudinal furrow; spur truncated, fully one third of width of valve._ _Hab._--Java; East-Indian Archipelago; Peru; West Columbia; California; Sydney; New Zealand. Mus. Brit., Cuming, Stutchbury, Dunker, &c.