PYRGOMA ANGLICA. _G. B. Sowerby._ (sine descript.) Genera of Recent
and Fossil Shells, fig. 7, No. 18, Sept. 1823.
MEGATREMA (ADNA) ANGLICA. _J. E. Gray._ Annals of Philosoph. (new
series), vol. x, Aug. 1825.
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.