PYRGOMA SULCATUM. Philippi. Enumeratio Molluscorum Siciliæ, Tab. 12, fig. 24, (1836).
------ ANGLICA. Brown. Illustrations of Conchology, (2d edit., 1844), Tab. 53, fig. 27-29.
Shell steeply conical, purplish red: orifice oval, narrow: basis permeated by pores, generally exserted out of the coral: scutum and tergum sub-triangular.
Hab.—South coast of England and of Ireland, (12 to 45 fathoms, Forbes and MacAndrew); Sicily; Madeira; St. Jago, Cape de Verde Islands; generally attached to the edge of the cup of a Caryophyllia, in deep water, but at St. Jago within the tidal limits; Mus. Brit., Cuming, Lowe, &c.
Fossil in the Coralline Crag, Ramsholt; Mus. S. Wood.
General Appearance.—Shell steeply conical, slightly compressed, the lower part with rounded, approximate, radiating ribs: colour dull purplish-red: orifice oval, small, and narrow. The basis is not deeply conical, and occasionally is even flat. Generally it stands exserted; but in the Coralline Crag specimens, it is almost wholly imbedded. Externally it is furnished with ribs corresponding with those on the shell. The largest recent specimen which I have seen, from St. Jago, was .22 of an inch in basal diameter; but some few of the British specimens are nearly as large, and one of the fossils from the Coralline Crag a little larger.
The Scuta and Terga are of the ordinary shape of these valves in [Balanus] and its allies. Scuta triangular, with the basal margin a little curved and protuberant: adductor and articular ridges distinct from each other, moderately prominent: there is a small hollow for the lateral depressor muscle. Terga triangular, with the spur rather narrow, moderately long, placed near, but not confluent with the basi-scutal angle of the valve. The basal margin forms an angle rather above a right angle with the spur. Internally, the articular ridge and crests for the depressor muscles, feebly developed.
Internal Structure of the Shell and Basis.—Internally, the shell is ribbed more or less prominently. The lower edge of the sheath, which is reddish, and extends far down the walls, seems always to project freely. In several specimens there were on each side, at the carinal end of the shell, a trace of a suture, which could be perceived only on the sheath. The basis appears always to be permeated by minute tubes or pores, though these are sometimes rather difficult to be seen.