_Compartments._--Walls moderately strong; parietal tubes small, with transverse septa in their upper ends; inner surface of the walls much less strongly ribbed than is usual. _Radii_ broad, with their summits parallel to the basis; their septa are strongly denticulated. _Alæ_ with their summits oblique; their sutural edges are barely crenated. _Basis_, thin, flat, or cup-formed. _Body_ unknown. _Affinities._--In general appearance this species comes near to _B. psittacus_; but in all essential characters it comes much closer to the following species, from which, however, it can easily be distinguished by colour, and by the inner lamina of the parietes not being cancellated. 7. BALANUS VINACEUS. Pl. 2, fig. 7 _a_-7 _d_. _Shell purplish dark brown: inner lamina of the parietes cancellated. Scutum finely striated longitudinally. Tergum with the longitudinal furrow shallow and open; basal margin on both sides sloping towards the spur._ _Hab._--West Coast of South America. Mus. Cuming. _General Appearance._--Shell conical, with a large, rhomboidal orifice; walls rather thin, coloured, together with the radii and operculum, dark purplish-brown; sheath nearly colourless. Walls smooth, slightly irregular, very finely striated longitudinally. Basal diameter of largest specimen .8 of an inch. _Opercular Valves_, unusually smooth, that is without prominent growth-ridges. _Scuta_, finely striated longitudinally, with the sharp striæ closely approximate. The teeth on the occludent margin are sharp, and stand some way apart from each other. Internally, the whole surface is remarkably flat and smooth: the articular ridge is of moderate breadth, and slightly reflexed: there is no adductor ridge, and the oval depression for the lateral depressor muscle is extremely slight. _Terga_, with the longitudinal furrow very slight; the bottom of this furrow is feebly striated longitudinally, and there is a trace of a fine, rounded ridge on the scutal margin, as in _B. decorus_. The basal margin slopes on both sides towards the spur, which is of moderate length and breadth, with its lower end truncated and parallel to the carino-basal margin; the spur stands at about once and a half its own width from the basi-scutal angle. Internally, the valve is lined by very dark, purplish-brown corium; the articular ridge is prominent; in the upper part of the valve, parallel to the articular ridge, there are two or three feeble ridges; there are no crests for the tergal depressores.