There can be no doubt that this species is the _B. nigrescens_ in Chenu, who had access to Lamarck's original specimens; and there can be equally little doubt that it is the _B. gigas_ of Ranzani, collected, during Baudin's expedition, at King George's Sound: it is essentially allied to _B. psittacus_, but in external appearance strikingly resembles some of the varieties of _B. tintinnabulum_. _General Appearance._--Shape tubulo-conical: walls smooth, sometimes longitudinally ribbed: colour ashy-gray tinged with blue, but many specimens are dark purplish-blue, owing to the disintegration of the outer lamina, and consequent exposure of the almost solidly filled up, dark blueish parietal tubes; on the other hand, some specimens are quite white. Ranzani describes the colour as earthy-violet, which is very characteristic of some of the specimens. The orifice is apt to be rather small, compared to the size of the specimens, and tends to be hexagonal. The radii are often rather narrow. The opercular valves are tinted pale blue. The basal diameter of the largest specimen is two inches, and its height two and a quarter. The _Scuta_ have their basi-tergal corner much rounded off, as in _B. psittacus_, so that the tergal margin does not extend more than half down the valve. The surface is somewhat prominent, along a line running from the apex to the point of chief curvature in the basal margin. The surface is not striated. Internally, the articular ridge is little prominent, and not reflexed; the lower end depends as a free, sharp style or point. The adductor ridge is moderately sharp, and stands some little way distant from the articular ridge: it is produced downwards, and forms a moderately deep and large cavity for the depressor muscle; but this cavity is not closed, and does not extend up, as in the two last species, to the apex of the valve. _Terga_, narrow, with a sharp, prominent, needle-like beak. Spur, long, narrow, placed at less than its own width from the basi-scutal angle: the basal margin on both sides slopes down to the spur: the scutal margin is not inflected. Internally, the articular ridge is very feebly developed, but extends down close to the basi-scutal angle. On the under surface in the upper part of the valve, there is a short, very slight ridge, extending on the carinal side, near and parallel to the articular ridge; this slight ridge plays an important part, as in the two foregoing species, in the formation of the beak or apex. Crests for the depressor muscle are hardly distinguishable.