CHTHAMALUS DENTATUS. _Krauss_ (!). Die Südafrikanischen Mollusken,
1848, tab. 6, fig. 27.
_Shell dirty white or brownish: sutures formed by interlocking teeth:
tergum with the carinal margin protuberant._
_Hab._--South Africa, Natal; West Africa, Loanda and the Gold Coast;
West Indies (?). Attached to ships' bottoms and to littoral shells,
and to _Tetraclita serrata_, _Balanus perforatus_, and _amphitrite_;
often attached to _Balanus tintinnabulum_ and _amphitrite_ on ships'
bottoms.
_General Appearance and Structure of Shell._--Shell dirty white,
pale brown, or gray: conical, moderately depressed: walls either
broadly and irregularly folded (fig. 3 _a_), with the surface
corroded, or (when attached to ships' bottoms and sometimes to other
Cirripedes) narrowly and regularly folded (3 _b_), with the surface
well preserved, smooth, and generally covered by thin brown membrane.
These latter specimens generally have the shell more steeply conical,
with the orifice rather smaller, and the radii broader, than in
the first-mentioned specimens, which are attached to coast-rocks
and shells, and have had their summits worn down. The sutures in
all cases are tolerably distinct, and have their edges toothed and
interlocked: the crenations are visible before the compartments are
disarticulated, when viewed either internally or externally, but
occasionally they are obscure. The radii, when best developed, are
rather narrow, and of equal width on both sides of the sutures, with
their summits rounded: their surfaces are finely ribbed transversely,
each rib corresponding with, or rather forming a point of, the
toothed edge. On the under side these teeth usually are a little
hollow or are pitted: the radii, in fact, may be said to be folded,
like the parietes, only more symmetrically and narrowly, so that the
points in the opposed edges interlock. The edges of alæ are serrated,
but more finely than the radii. The parietes are rather thin, with
their under surfaces generally smooth. The sheath does not descend
far down the shell. The colour of the corium lining the sack and the
animal's body varies considerably, being either almost black or pale
purple; and the specimens adhering to ships' bottoms are internally
almost white. Of these latter specimens, I have seen some .6 of an
inch in basal diameter: of corroded specimens attached to littoral
shells, I have not seen one quite .4 of an inch in basal diameter.
_Scuta_, with the articular ridge very prominent: the pit for the
adductor is deep, and there are generally some distinct, though
minute, pits for the lateral depressores. The _Terga_ (fig. 3 _c_)
have the articular ridge very prominent; and the carinal margin is
rather more arched and protuberant than in the other species.
_Mouth._--The crest of the _labrum_ is toothed: the palpi are short,
truncated, with long spines arising from their ends, and along the
basal exterior margin. In the mandibles the first tooth is seated
rather far from the succeeding teeth: the inferior part is coarsely
pectinated: the maxillæ are deeply notched. The tips of second pair
of _Cirri_ have many coarsely pectinated spines: the shorter ramus
had six segments, whilst the shorter ramus of the third pair had
eighteen segments: the segments on the posterior cirri carry five
pairs of main spines.
_Branchiæ, &c._--These consist of a double fold, the outer one being
the largest, and the inner semi-circular, as has been described under
the genus. In a young specimen, only one tenth of an inch in basal
diameter, the branchiæ consisted of a single fold; in a specimen a
little larger, there were two folds, but these were of equal size:
ultimately the outer fold increases in size so as to become nearly
double the inner fold. The _Ovarian tubes_ are remarkable from their
large diameter. I was surprised to observe in the specimen only one
tenth of an inch in basal diameter, that the larvæ were ready to
escape. On the prosoma, there are some longish _hairs_ arranged in
short rows, and some few on the membrane lining the sack, and some on
the opercular membrane and valves.
It may be seen in Pl. 18, fig. 3 _a_, and 3 _b_, that I have here
united two varieties considerably different in external aspect: I have
done this without hesitation, inasmuch as there are intermediate forms,
and as the differences are analogous with those so commonly occurring
in sessile cirripedes; dependent on whether or not the specimens
have been exposed to corrosion. I have seen both varieties from
Natal, and both from the west coast of Africa; although the smooth,
well-preserved, narrowly plicated varieties seem more common in western
than in southern Africa. With respect to the range of the species, I
have seen a specimen from the West Indies, but it was the variety
which so commonly adheres to ships' bottoms. This variety often arrives
alive in British ports; and I have seen a specimen picked up dead on
the beach near Dublin.