_Shell reddish, with six large, membrane-covered apertures between the
sutures, above the basal cup: carino-lateral parietes half as broad as
lateral parietes; internally, parietes and edge of basis smooth; tergum
with the articular ridge short and prominent; spur pointed._
_Hab._--Philippine Archipelago, Mus. Cuming.
_General Appearance._--Shell rather elongated or tubular; with the
upper part reddish, and the surface roughened with very minute
points. The basal cup is generally as deep as the shell is high,
ending downwards in a blunt point, often curved to one side. The
summits of the radii, as usual, are oblique. The parietes of the
carino-lateral compartments are about half as wide as the parietes of
the lateral compartments, and are therefore of greater proportional
width than in the foregoing or any other species of the genus.
The large membrane-covered openings, or, as they may be called,
windows, presently to be described, between the lower halves of the
compartments, is much the most remarkable character of this species.
The largest specimen which I have seen was only .23 in diameter, and
.6 of an inch in height, measured from the basal point of the cup to
the tips of the compartments.
_Scuta._--These barely exhibit a trace of longitudinal striæ. The
valve is rather thick and convex. The basi-tergal angle is much
rounded off. Internally, the articular ridge is thick and rather
prominent. _Terga_: the valve is furrowed in the line of the spur:
the spur is pointed and rather long; it is distinctly separated from
the basi-scutal angle of the valve, and the basal margin on the two
sides of the spur forms a straight line. The articular ridge is
prominent, and short.
_Structure of the Parietes, Radii, and Basis._--The parietes are
internally quite smooth down to its basis. The edges of the radii are
also smooth, as is the edge of the basal cup. The alæ project less
than usual. The radii are of moderate breadth, they extend downwards
only a little below the sheath, namely, about half way down the
shell, where they terminate, as usual, in a point. The increase in
width, during growth, of the radii, and their not extending down to
the basis, would necessarily cause a gap between the opposed edges
of the walls, in the portion beneath the radii; but besides this,
the edges of the walls themselves, beneath the radii, and on the
opposed side beneath the alæ, are hollowed out, but on the latter
side or beneath the alæ sometimes in a lesser degree. The result of
this is, that the compartments, in their lower halves, are separated
from each other by membrane-covered windows or apertures, arched at
their upper ends, and of considerable size, namely, about as wide as
the parietes of the carino-lateral compartments. I have only further
to remark, that during the downward growth of the parietes, the
apertures increase in size, but at the same time become closed up at
their upper ends; and the arched layers of shell added at these upper
ends, assume a very different aspect from the rest of the parietal
surface,--appearing like two wedges, with their points upwards, let
in, on one side of the suture, between the ordinary parietal surface
and the radius, and, on the other side of the suture, between the
ordinary parietal surface and the recipient furrow of the radius.
The _animal's body_ was in a bad state of preservation; but, as far
as I could make out, the cirri resembled those of _A. glans_.
_Affinities._--This species differs from _A. glans_ in not having the
internal margins of the compartments projecting inwards. It differs
from all the ordinary varieties of _A. spongites_, in the smoothness
of the basal edges of the parietes and of the edge of the cup; in
the greater width of the carino-lateral compartment, though this is
a variable point in _A. spongites_; slightly in the shape of the
scuta and terga; and, lastly, in the large, membrane-covered openings
between the compartments.