_Shell purple or dirty white, with the internal basal edges of the
parietes rough with irregular points and ridges; radii narrow or
absent; basis excessively thin, in appearance absent. Scutum with
crests for the lateral depressor muscle; tergum very narrow, with the
spur pointed._
_Var._ sordidus. (Pl. 8, fig. 5 _b_) _shell globulo-conical, dirty
white, with numerous sharp, narrow, longitudinal folds or ridges_.
_Hab._--Peru and Chile; generally attached to the _Concholepas
Peruviana_, or to _Balanus psittacus_, and associated with
_Chthamalus scabrosus_. _Var. sordidus_, inhabits Tierra del Fuego,
attached to littoral shells, wood, and rock, associated with _Ch.
scabrosus_.
_General Appearance._--Shell either extremely much depressed and
irregular, or globulo-conical, or more rarely cylindrical and
elongated. Walls, either with a few rather broad, smooth, irregular,
longitudinal folds, or, in _var. sordidus_, with numerous sharper
and more prominent longitudinal ridges; basal margin very sinuous.
Colour, either fine rich peach-blossom purple, or so pale as to be
almost white; or in _var. sordidus_ dirty white, generally stained
greenish from confervoid matter. Orifice small, oval, entire. Radii
very narrow, white, or not at all developed, and with even the
sutures not distinguishable. The purple coloured varieties, with
the narrow white radii, the small oval orifice, and folded walls,
have a very pretty appearance, which is far from the case with _var.
sordidus_. The largest specimens attained a basal diameter of .6
of an inch, but this is an unusual size: I have seen a cylindrical
specimen of _var. sordidus_ one inch in length.
The opercular valves are united to the sheath by unusually strong
membrane: internally, their upper parts are stained purple. _Scuta_,
these vary considerably in breadth, some being even broader than in
Pl. 8, fig. 5 _c_, and others as much elongated as in fig. 5 _d_:
these latter come from an elongated cylindrical shell. The valve
externally is unusually convex: the apex, also, projects freely to
an unusual degree. Internally, the articular ridge is moderately
prominent: the adductor ridge is prominent and much curved: in the
upper part it either lies close to, or at some little distance from
the articular ridge. The lateral depressores are attached to several
little crests, occupying a cavity, (often bordered above by a little
ridge) close beneath the adductor ridge. _Tergum_, extraordinarily
narrow and elongated; beak triangular, purple: a longitudinal furrow
runs down the valve: spur narrow, long, bluntly pointed, lying close
to the basi-scutal angle of the valve: the scutal margin is nearly
straight and parallel to the spur. Internally, the articular ridge
is prominent: the crests for the depressores are moderately well
developed: the upper part of the valve is marked by a purple patch,
bounded on one side by the articular ridge, and on the other side
by a very slight special ridge. There is some variability in the
narrowness of the whole valve, and in the sharpness of the spur.
_Parietes._--The under surface, in the more depressed varieties, is
roughened in a remarkable manner nearly or quite up to the sheath,
with very irregular, projecting, and branching ridges, and sometimes
with depending points. These ridges and points are granulated on
their under surfaces. The roughened surface in the more conical
varieties is confined to the basal inner margin. This structure is
nearly the same as that in _B. imperator_, represented (Pl. 8, fig.
4 _c_), but the little ridges are here more apt to be concentric,
instead of radiating. The lateral edges of the compartments on the
inside, especially the carinal edges, project inwards beyond the
inner surface of the shell. The sheath is but little hollow on its
under side. The diametric growth of the shell seems to be quite
capricious; in the same group, some individuals thus increasing, and
others not at all. When the radii are developed they are narrow and
white, with their upper margins nearly if not quite parallel to the
basis: their sutural edges are formed by large, irregular, branching
teeth or septa. The _alæ_, also, have their sutural edges coarsely
crenated; and when the shell increases by diametric growth, they are
added to above the opercular membrane, so as to be nearly square at
top.
_Basis._--When a shell is removed from the surface of attachment,
and inspected even under a lens, there appears to be no basis
whatever, either adhering to the shell, or to the supporting surface:
but when a more careful examination is made, with a higher power,
an excessively thin, translucent, calcareous, irregular layer, or
rather film, can almost always be discovered. This would be more
easily distinguished if the specimens had adhered to rock instead of
to the rugged shells of molluscs. At one time I thought the basis
was partially membranous, for I have certainly scraped off small
fragments of membrane from the supporting surface; but these, when
examined under the compound microscope, seemed always to consist of a
thin sheet of the yellow cementing tissue; and in some instances, a
brittle film of shell, representing the true basis of the cirripede,
still adhered to the upper surface of the membranous bits of cement.
Nevertheless, so imperfect is the calcareous basis, that I should not
be surprised if portions of a true membranous basis did really in
some cases exist.
_Mouth_: labrum with the notch wide, generally with a few little
teeth; mandibles with three teeth, and some inferior knobs; maxillæ
notched. _Cirri_, first pair with one ramus shorter by three segments
than the other ramus. Second and third pairs short, of nearly
equal length, thickly clothed with spines; segments very little
protuberant. Posterior cirri, having elongated segments, supporting
seven pairs of spines.
_Var. sordidus._--This form is very common on the tidal shores of
the Strait of Magellan, and of the southernmost parts of Tierra del
Fuego, near Cape Horn: it lives attached to rocks, mytili, and logs
of wood, and is associated with _Chthamalus scabrosus_. It almost
certainly is the most antarctic form of the genus Balanus. If I were
guided by external appearance alone, I should certainly separate
this form specifically from _B. flosculus_, but, as will be seen in
the following description, the differences consist only in _var.
sordidus_ being much duller and rather differently coloured, in the
longitudinal folds being sharper and more prominent, and in the whole
shell being rather more globular, and on an average rather larger;
but in the true _B. flosculus_ there is considerable variation in
all these respects, as there likewise is in _var. sordidus_; thus
some of the cylindrical varieties of the latter have less prominent
ridges than even _B. flosculus_. In general appearance I have seen
some _nearly_, but not exactly, intermediate forms; therefore, I do
not feel positive that these forms may not be specifically distinct,
but have failed, after careful examination, to find any sufficient
diagnostic _characters_. Moreover, in the case of _Balanus lævis_,
I was led to believe that there is an equal and somewhat analogous
amount of variation in the specimens inhabiting Tierra del Fuego and
northern Chile; and in this case I was enabled to show the existence
of strictly intermediate forms in the intermediate districts.
The shell in _var. sordidus_ is generally globulo-conical, dirty
white, frequently with a green tinge, from the growth of confervoid
matter. Orifice small. The exterior surface is covered with numerous
prominent, narrow, sharp ribs or folds, the basal margin being
serrated with projecting points where the folds terminate. When
the radii are not developed, the sutures are very often obscure.
Internally, the shell is faintly tinted of a port-wine purple. In
all points of structure this form is identical with the true _B.
flosculus_. In some few specimens the whole exterior surface was
disintegrated and smooth; and this is generally the case with the
upper parts of the shell. Some other specimens, which had grown
crowded together on wood, had become cylindrical, and consequently
the orifice was as large in diameter as the shell, namely, half an
inch: in some of these cylindrical varieties the sheath was entirely
soldered to the walls. The largest specimens which I have seen were
.6 of an inch in diameter; and above one inch in height.
_Affinities._--This species, in its opercular valves, even in such
trifling characters as the strength of the opercular membrane,
and in its cirri, approaches closely to _B. cariosus_. We even
see on the under side of the scutum, in that species, a single
little ridge, foreshadowing, as it were, the crests for the lateral
scutal depressores, so remarkable in our present species. In the
structure of the shell and of the basis, _B. flosculus_ is much
more closely related to the last species, or _B. imperator_. If it
had been possible to have arranged the species in a single line,
_B. flosculus_ ought undoubtedly to have been placed between _B.
cariosus_ and _imperator_.