Chapter XX: Introduction (16)

The _Radii_, when developed, are either narrow or broad, with their summits either oblique or extending in a straight line from the top of one compartment to that of another. In _T. serrata_, I have not seen a single specimen with the radii developed; in _T. porosa_, they are very seldom developed, and then, apparently, only in quite young specimens, in which they are narrow; in _T. purpurascens_, they seem to be about as often developed as not, and when present they are broad; in _T. costata_, _cœrulescens_, and _radiata_, they are always largely developed. In some specimens of the species, in which the radii are not developed, even the sutures do not reach the external surface; the outer lamina of the parietes being continuous all round, so that the shell seems formed of a single piece. Even in such specimens, the four compartments, viewed from within, can be seen to be distinct; and the sutures can generally be traced across the whole thickness of the parietal tubes; in this latter case, when the sutures are broken open, the radii are seen to be represented (Pl. 10, 1 _h_) by a few small sinuous ridges. Owing to the disintegration of the upper and outer part of the shell, and the consequent exposure of parts of the sheath and alæ, the radii sometimes appear as if developed, when such is not the case. With respect to the internal structure of the radii, they are formed, in _T. purpurascens_ and _costata_, of tubes, like those of the parietes, and therefore according to the normal plan; whilst in the other species they are formed by longitudinal sinuous ridges, sending out on each side irregular denticuli; and the interspaces between the ridges are filled up solidly during the growth of the radii, in all the species, except in _T. radiata_, in which they are left to a considerable extent open. These sinuous ridges, with their denticuli, homologically represent the branching septa which form the parietal tubes. The edges of the alæ are crenated in all the species, except in _T. costata_.

_Diametric growth._--When first examining groups of _T. porosa_, in none of which the radii had been developed, and in which, consequently, the shell could not have grown in diameter, but only at its basal margin, I was at first unable to comprehend, how the upper part of the shell and the orifice could have acquired their proper proportional width. The young shell, at its first formation, starts with an orifice so small that a pin could hardly be inserted in it; and this in many individuals is never increased in diameter by the diametric growth of the shell; but in place of this, as the conical shell is added to at its base, the whole upper part disintegrates and wears away, the orifice becoming thus enlarged. We thus see that the corrosion and wearing away of the upper part of the shell is a necessary element in its growth. The development of the radii, which in some of the species, as in _T. purpurascens_, at first seems to be quite capricious, really depends upon the fact, whether the specimens have been exposed to disintegration; for I have almost always found that when the outer lamina of shell has been well preserved, the radii have been developed, and the orifice has been enlarged by their growth, instead of by the wearing down of the upper part of the conical shell.

_Basis._--This consists of a very thin, flat, though irregular, translucent, calcareous plate, which towards the edges is sometimes membranous. In _T. purpurascens_, the basis is entirely membranous. When a portion of the calcareous base is dissolved in acid, a tissue is left, composed of several laminæ, to which numerous bifurcating cement-ducts are attached: even before dissolution, these delicate bifurcating ducts can just be perceived by the aid of a simple lens.

_Mouth._--The several organs present no particular characters. There are generally three teeth on each side of the notch in the labrum. The palpi usually have parallel sides, but are club-shaped in _T. purpurascens_ and _costata_. The mandibles have generally four teeth, but there are five in _T. vitiata_, and only three in _T. costata_. The maxillæ are notched. The outer maxillæ are bilobed in front.

_Cirri._--The segments of the three posterior pairs usually support only three pairs of main spines, but there are four pairs in _T. vitiata_ and _costata_: between each pair, there is either a tuft of fine spines, or a single fine spine. The rami of the first cirrus are unequal in length. In the third cirrus, the posterior ramus is sometimes much elongated, but sometimes both rami are short and blunt. Some of the segments in the third cirrus often support very coarsely and doubly pectinated spines. Under the head of _T. porosa_, it will be seen to what a remarkable degree the relative numbers of the segments in the several cirri vary, even in specimens taken out of the same cluster.

The _Branchiæ_ are well developed (at least in _T. porosa_ and _costata_), as a large, plicated, tapering fold, with a small second fold on the inner side at the base. In _T. porosa_ the _stomach_ is destitute of cæca. The _vesiculæ seminales_ in this same species are large, with their broad, blunt ends reflexed. The _ovarian_ tubes surround the sack, and cover the basal plate.

_Distribution and Habitats._--This genus is confined to the tropics, and to the warmer parts of the temperate seas: in the southern hemisphere, it ranges south, to the Cape of Good Hope and to Van Diemen's Land: in the northern hemisphere it does not appear to range so far; I do not know of any authentic case of a species having been found in the Mediterranean, or on the shores of the United States, north of the West Indies. _Tetraclita porosa_ is found round the whole world; _T. radiata_, also, has a very wide range, inhabiting the West Indies, the East Indian Archipelago, and New South Wales. This latter species, as well as _T. cœrulescens_, is often attached to the bottoms of ships, adhering to _Balanus tintinnabulum_. The several species live attached to tidal rocks, to littoral shells, or to massive corals. I have met with two instances, in the West Indies and the Philippine Archipelago, of _T. porosa_ adhering to wood. _Tetraclita porosa_ seems to feed chiefly on crustaceans: the number and the size of the amphipods, isopods, and entomostracans, together with an annelid, in the stomachs of some specimens from South America, was quite surprising. As many as five species occur in the same region, in the eastern half of the world; thus on the shores of New South Wales, we have _T. porosa_, _vitiata_, _radiata_, _purpurascens_, and _rosea_; in the Philippine Archipelago, we have _T. porosa_, _vitiata_, _costata_, and _cœrulescens_.

I have not seen any species of this genus fossil.

_Variation._--The species vary in shape nearly, but not quite as much as in Balanus, for we very rarely here see cylindrical varieties; but in the same species, we have extremely depressed, steeply conical, and convex forms; the orifice varies in relative size; the state of the surface, whether ribbed or smooth, whether well preserved or corroded, the upfilled parietal tubes being thus exposed, varies more than in Balanus. The colour also varies; specimens of _T. porosa_ (Pl. 10, fig. 1 _a_ to 1 _f_) being dark purple, or even inky black, white, pale pinkish-purple, and green: as far as I have seen, the pinkish varieties of _T. porosa_ are confined to the eastern half of the world. Even the ridges and crests on the under side of the scutum vary in some degree; and the tergum in _T. porosa_ varies considerably, and in some of the other species, slightly, in general shape: I believe that the tergum becomes narrow and elongated, when the shell is steeply conical, with the orifice of small diameter. After having spent several days in disarticulating and closely examining the many specimens of _T. porosa_ in my possession, I concluded that its varieties formed at least four species, these being in external appearance extremely distinct; but ultimately the many intermediate forms compelled me to unite all into a single species. Again, I may instance the conical, ribbed variety of _T. purpurascens_ (Pl. 11, fig. 1 _b_), with the outer lamina of the shell preserved and with the radii widely developed, as having not the smallest resemblance to the other common depressed variety (fig. 1 _a_), having a granulated surface, produced by the exposed tips of the upfilled parietal tubes, and without a trace of the radii or even of the sutures; I may add that, according to the characters used by some authors, these two varieties would be classed in two separate genera.

To distinguish the species of this genus, the chief reliance must be placed (as in the case of most other sessile cirripedes) on the general outline of the opercular valves, and on the ridges and crests on their under sides: the internal structure, however, of the radii, and in a lesser degree of the parietes, must not be overlooked. I have not found the parts of the mouth, or the differences in the cirri, of much service; and it will be shown under _T. porosa_, that the relative numbers of the segments in the several cirri, and even their shape, is extraordinarily variable.

_Affinities._--All the species are pretty closely allied, and there is no ground for making any sectional division of the eight species, more especially not on the ground whether or no the radii are developed. _Tetraclita purpurascens_, taking into account all the characters, including the animal's body, is perhaps the most distinct species in the genus, but it is closely allied to _T. costata_. In the well-marked character of the parietes being formed of a single row of large tubes, _T. rosea_ differs from all the other species. The genus is closely allied to Balanus; I can point out no difference in the animal's body, nor any constant difference in the opercular valves. The ridges and crests on the under sides of the scuta are more prominent in Tetraclita; and all the species, excepting two, have crests (though sometimes very slight) for the attachment of the rostral depressor muscle, and these occur only in two species of Balanus: crests, also, for the attachment of the lateral depressor muscle are common in Tetraclita, but rare in Balanus. The main character, however, of the genus, as compared with Balanus, is derived from the existence of only four compartments, and in a lesser degree from the several rows of parietal pores; but, as just stated, _T. rosea_ has only a single row, and, on the other hand, in _Balanus crenatus_, there is a slight tendency exhibited, in the dividing of the longitudinal septa near the outer lamina, to form a second row of parietal pores; and in _B. cariosus_, moreover, we actually have two or three rows of irregular and very short pores. The thin, yet solid calcareous basis which occurs in all the species of Tetraclita, excepting _T. purpurascens_, resembles the basis in _Balanus flosculus_ and _imperator_, but I suspect that the structure of the cement-ducts is different in the two genera.

1. TETRACLITA POROSA. Pl. 10, fig. 1 _a_-1 _m_.

LEPAS POROSA. _Gmelin._ Syst. Naturæ, 1789.[107]

BALANUS SQUAMOSUS. _Bruguière._ Encyclop. Method., 1789, Pl. 165,
fig. 9, 10.

LEPAS FUNGITES. _Spengler._ Skrivter af Naturhist. Selskabet, 1 B.,
1790.

---- POROSA. _Wood's_ General Conchology, Pl. 9, fig. 4, 1815.

TETRACLITA SQUAMULOSA. _Schumacher._ Essai d'un Nouveau Syst., &c.,
1817.

BALANUS STALACTIFERUS. _Lamarck._ Animaux sans Vertèbres, 1818.

---- ---- _Chenu._ Illust. Conch., Pl. 4, fig. 6, 7.

ASEMUS POROSUS. _Ranzani._ Memoire di Storia Naturale, Tab. 3, fig.
32-35.

CONIA POROSA. _Sowerby._ Genera of Recent and Fossil Shells, Plate,
1823.

---- ---- _Leach._ (sine descript.) Encyclop. Brit. Supplement, vol.
3, 1824, Tab. 57.

[107] As Gmelin and Bruguière published the same year, I do not
know which comes first, but I have adopted the best known name.
Most authors give, amongst their references, Chemnitz, vol. 8,
Tab. 98, fig. 836, 837, but the accompanying description is more
applicable to _T. serrata_ of this work than to _T. porosa_;
without a figure or description, however, of the under side of the
scutum it is impossible to decide. Several authors, also, give
_Lepas cariosa_ of Pallas, as a synonym; this, however, is the
_Balanus cariosus_ of this work.

_Radii rarely present, when present narrow; even the sutures often absent: shell steeply conical, with the surface generally corroded, and having a stalactiferous appearance._

_Var._ (1) communis (Pl. 10, fig. 1 _a_): _outer lamina of shell
almost wholly removed; the portion preserved, as well as the exposed
parietal tubes, gray, or pale dirty brown, or dull purple_.

_Var._ (2) nigrescens (Pl. 10, fig. 1 _c_): _outer lamina of shell
almost wholly removed; the portion preserved, and the exposed
parietal tubes, very dark purple or inky black_.

_Var._ (3) viridis: _outer lamina of shell almost wholly removed;
the portion preserved, and the exposed parietal tubes, green; under
surface of opercular valves clouded green_.

_Var._ (4) rubescens (Pl. 10, fig. 1 _b_): _outer lamina of shell
almost wholly removed; the portion preserved, and the exposed
parietal tubes, pale reddish-purple, or peach-blossom purple; under
surfaces of opercular valves often reddish purple; terga often rather
narrow, with the spur somewhat pointed, and with the basal margin on
the carinal side sloping, or not making an angle with the spur_.

_Var._ (5) elegans (Pl. 10, fig. 1 _d_): _outer lamina preserved,
excepting sometimes near the summit of the shell; white, tinged
with yellowish brown from the epidermis; surface strongly ribbed
longitudinally; orifice rather small; sheath reddish-purple; terga
narrow, with the basal margin sloping as in var._ rubescens.

_Var._ (6) communis (young) (Pl. 10, fig. 1 _e_): _radii developed,
very narrow; outer lamina of shell preserved, gray or dull purple;
surface slightly ribbed longitudinally_.

_Var._ (7) patellaris (Pl. 10, fig. 1 _f_): _radii developed,
very narrow, white; outer lamina of shell preserved, generally
reddish-purple; steeply conical, with the orifice extremely small;
surface smooth, with longitudinal white ribs. Terga very narrow, with
the spur sharply pointed, and with the basal margin on the carinal
side sloping towards it, or not making an angle with it. Scuta, with
the adductor ridge very prominent. Attached to a ship's bottom_.

_Hab._--West Indies, Brazil, West Colombia, Panama, Galapagos
Archipelago, California, Philippine Archipelago, China, East coast of
Australia, Red Sea; generally attached to tidal rocks, sometimes to
shells, sometimes to wooden posts. Very common.

_General Appearance._--This, the widest-distributed and much
the commonest species of the genus, varies greatly in external
appearance. The usual shape is steeply conical, but some individuals
are much depressed. In the common varieties the outer lamina of
shell has been removed even close to the basal edge; the upfilled
parietal tubes being thus exposed (fig. 1 _b_), as flattened
adpressed points. These points are largest in large specimens, but
they vary somewhat in size in specimens of equal growth. When the
outer surface is preserved, it is generally ribbed longitudinally,
but is sometimes quite smooth. The most general colour is dirty gray
or dark purple; but many specimens are pale pinkish-purple, owing
to the exposure of the parietal tubes upfilled with shelly matter
of this tint: there are also, as given under the characters of the
_vars._, black, white and green varieties. The sheath is always
tinted by the prevailing colour. The radii are rarely developed,
but generally the four sutures are distinct; sometimes these are
externally quite obliterated, the shell, as seen from the outside,
consisting of a single piece like a patella or fissurella. When the
radii are developed they are very narrow, with their upper edges
oblique: their development seems always coincident with the more or
less perfect preservation of the shell, and their function is to
enlarge the orifice; the enlargement being usually effected by the
disintegration and removal of the whole upper part of the conical
shell. The size of the orifice varies considerably; in the seventh
variety it was extraordinarily small: in outline it varies from oval
to rounded trigonal or rhomboidal; in some specimens, with the radii
well developed, it was rounded pentagonal.

_Size._--_Tetraclita porosa_ is the largest species of the genus;
I have seen specimens attached to a large pebble of granite in the
British Museum, which measured two inches in basal diameter, and
nearly one inch and a half in height.

_Scuta_: these are sub-triangular and generally a little elongated,
but they vary slightly in relative breadth (fig. 1 _i_, 1 _l_), and
likewise in the degree to which the basi-tergal angle is rounded off.
The under surface is clouded with dull or pinkish-purple, or with
green, or is nearly white. The articular ridge is not prominent, and
the articular furrow is narrow. The adductor ridge is prominent, and
runs upwards for some distance close and parallel to the articular
ridge; and sometimes it extends nearly or quite up to the apex of
the valve; in one single specimen the adductor ridge had an abraded
appearance, and was very little developed. The crests for the rostral
and lateral depressores are sharp and distinct. Along the occludent
margin, the ends generally of the alternate lines of growth are
enlarged into knobs, serving to lock the two valves together; but in
many specimens only two or three knobs, at intervals of several lines
of growth (fig. 1 _b_), are developed.

_Terga_: when the upper end of the valve is not corroded, there is
a distinct beak, hollow within for a thread of corium. The scutal
margin is not much inflected, and the articular ridge not very
prominent. The spur is placed quite close to the basi-scutal angle
of the valve, so that there is no basal margin on that side of the
valve. The width of the valve and of the spur, and the acumination of
the extremity of the latter, varies in a remarkable manner. In the
broad and commonest variety (fig. 1 _k_), the basal margin of the
valve form an angle of about 130° with the carinal side of the spur,
and the basal end of the spur is broad and truncated. In the less
common and narrow variety (1 _m_), the basal margin in some extreme
cases forms very nearly a straight line with the carinal side of
the spur; and the spur itself is bluntly pointed: in _var._ 7 it is
sharply pointed.

_Structure of the parietes and radii._--In all cases the four sutures
are quite distinct, from top to bottom, on the internal lamina of
the shell, and generally they run through the whole thickness of
the walls, and are visible externally. Often they do not quite
reach the outer lamina, and then the shell externally consists of a
single piece, like a patella. Sometimes the sutures can be traced
running through the parietal tubes only for a short distance from
the internal surface; where they cease, the two walls of the suture
become fused together. When a perfect suture is split open, the
radius is represented (fig. 1 _h_) by a few narrow, sinuous ridges,
sending out on each side little branches or denticuli; these are
received into corresponding furrows in the opposed compartment. These
ridges run nearly parallel to each other, and somewhat obliquely,
from the outer lamina of the shell to the basis. When the radii are
developed, their edges are similarly formed, by sinuous denticulated
ridges, with the interspaces between them filled up solidly. The alæ
are but little prominent.

The _mouth_ does not deviate from the generic type. The _cirri_
are remarkable from the variability in the several pairs of the
relative numbers of their segments, as shown in the following table.
The segments do not correspond even on opposite sides of the same
individual, as may be seen in the two lower lines of the table. I
believe that variability to this degree is very uncommon in other
cirripedes, though, as stated in the Introduction, the number of the
segments always increases with the growth of the individual. The
terminal segments in the longer rami of both the first and third
cirrus are antenniformed,--being elongated, and of a different
shape, with fewer bristles, compared with the basal segments of
the same cirri. It is apparently these terminal segments which
are particularly liable to vary in number. In both rami of the
third cirrus, some of the segments, from the sixth to the eleventh
inclusive, (counting from the bottom), more especially the eighth,
ninth, and tenth, carry a few spines coarsely and doubly pectinated;
but as some of the adjoining segments carry spines which may be
called doubly serrated, it is not easy to draw an exact line of
demarcation. Sometimes, though rarely, a few of the nearly terminal
segments in the second cirrus are furnished with similar, doubly
pectinated spines.

_Numbers of the segments in the rami of the Cirri, in different specimens._

+------------------+--------------+--------------+--------------+-------+
| |First cirrus. |Second cirrus.|Third cirrus. |Sixth |
| | | | |cirrus.|
| |--------------+--------------+--------------+-------|
| |Shorter|Longer|Shorter|Longer|Shorter|Longer|Either |
| |ramus. |ramus.|ramus. |ramus.|ramus. |ramus.|ramus. |
|------------------+-------+------+-------+------+-------+------+-------|
|Specimen from | | | | | | | |
|Pernambuco, Brazil| 9 | 19 | 10 | 11 | 15 | 27 | 26 |
|(_var._ 1) | | | | | | | |
|------------------+-------+------+-------+------+-------+------+-------|
|Another specimen | | | | | | | |
|from the same | 12 | 23 | 12 | 14 | 14 | 19 | 23 |
|cluster | | | | | | | |
|(_var._ 1) | | | | | | | |
|------------------+-------+------+-------+------+-------+------+-------|
|From the Galapagos| | | | | | | |
|Archipelago, | 10 | 16 | 10 | 11? | 11 | 16 | 25 |
|(_var._ 1) | | | | | | | |
|------------------+-------+------+-------+------+-------+------+-------|
|From the | | | | | | | |
|Philippine | 10 | ? | 10 | 10 | 11 | 19 | 18 |
|Archipelago, | | | | | | | |
|(_var._ 4) | | | | | | | |
|------------------+-------+------+-------+------+-------+------+-------|
|From California | 15 | 24 | - | - | - | - | 22 |
|(_var._ 5) | | | | | | | |
|------------------+-------+------+-------+------+-------+------+-------|
|From the bottom | | | | | | | |
|of a ship | - | - | 9 | 9 | 10 | 17 | 14 |
|(_var._ 7), | | | | | | | |
|young | | | | | | | |
|------------------+-------+------+-------+------+-------+------+-------|
|From South America| | | | | | | |
|(_var._ 1) | 11 | 18 | 11 | 12 | 13 | 21 | 22 |
|British Museum | | | | | | | |
|------------------+-------+------+-------+------+-------+------+-------|
|Another specimen | | | | | | | |
|from the | 16 | 25 | 13 | 18 | 15 | 23 | 27 |
|same cluster with | | | | | | | |
|the last specimen | | | | | | | |
|------------------+-------+------+-------+------+-------+------+-------|
|Same individual, | | | | | | | |
|but the cirri | 15 | 28 | 15 | 21 | 16 | 23 | - |
|from the opposite | | | | | | | |
|side of the body | | | | | | | |
+------------------+-------+------+-------+------+-------+------+-------+

_Varieties._--Under the generic description, I have stated that after
having spent some time in examining a very large suite of specimens
of _T. porosa_, I concluded that at least four of the varieties were
true species. It so happened that all the specimens which I first
examined of the _var._ (4) _rubescens_, had the narrow sloping terga,
and scuta with only two or three great teeth on their occludent
margins; but ultimately, in a group thus characterised, I found one
or two individuals with terga precisely of the shape of those in
_var._ (1) _communis_. Again, in a group of dull purple specimens of
_var. communis_, a few had the narrow sloping terga, and scuta with
teeth on their occludent margins, intermediate in size and number
between the varieties with only one or two great teeth, and those
with every alternate growth-ridge enlarged into a tooth. Hence _var.
rubescens_ completely broke down as a species.

With respect to _var._ (5) _elegans_ (a M.S. specific name of Leach)
I inferred at first, from external appearance alone, that it was
distinct; the outer lamina of the shell and even the epidermis is
preserved; the surface is strongly ribbed, and the whole shell,
excepting the sheath, is nearly white; the terga are narrow, with a
sloping basal margin as in _var._ (4) _rubescens_. Whole groups of
specimens are thus characterised. But as _var. communis_ is often
white, and as the surface, when the outer lamina is preserved, is
generally, as we shall presently see, ribbed longitudinally, the
differences in _var. elegans_ are quite unimportant.

The (6th) _var._ differs from _var. communis_ only in the narrow
radii having been developed, and consequently in the orifice being
pentagonal, and in the outer, longitudinally ribbed lamina of the
shell having been preserved. In the same group of specimens, I have
seen every intermediate stage between this and the common form. It
must not, however, be supposed that the young of _var. communis_
always pass through these stages, for such is not the case. In the
genus _Balanus_ it has been seen, how capricious in some species is
the development of the radii.

Of the other varieties, enumerated at the beginning, no further
mention is required, excepting with respect to _var._ (7), the most
singular of all. I have seen only three specimens, sent to me by Dr.
Aug. Gould, of Boston, United States, and these from the appearance
of their bases I have no doubt had been attached to a ship,--the
only instance which I have met with, in the present species. The
shell is steeply conical, with the orifice so small as to be reduced
to a mere pore; the radii are extremely narrow and white; the shell
is thin, with the surface smooth, but ribbed longitudinally and
regularly; the outer lamina of the shell and the epidermis are
perfectly preserved; the upper part of the shell is reddish purple,
which dies away towards the base: careful examination of the apex
shows that at the first growth the young shell was blueish-green.
The terga are narrow, with a sloping basal margin, as in _var.
rubescens_, but with the point of the spur sharper. I have formerly
remarked that the shape of the terga seems influenced by the size
of the orifice. The lower edge of the sheath depends freely: I have
seen no other instance of this latter structure, so common, but so
variable, in _Balanus_, in the present species, except to a partial
extent in one distorted specimen, in Mr. Stutchbury's collection,
adhering to _Balanus tintinnabulum_, and probably taken from a ship's
bottom. I may add that this distorted specimen was remarkable from
its radii being wider than in any other instance,--from its smooth
uncoloured surface without longitudinal ribs,--and from the perfect
preservation of the epidermis over its entire surface. Although Dr.
Gould's specimens, in external aspect, are absolutely and entirely
different from the common varieties of _T. porosa_, there are so many
intermediate forms, and the differences are so little important that
I feel no hesitation in attributing them to variation, consequent on
the individuals having been exposed to unusual conditions, attached
to the bottom of a ship.

2. TETRACLITA SERRATA. Pl. 10, fig. 2 _a_-2 _d_.

_Shell dark greenish-gray, with narrow, longitudinal, serrated ribs: radii absent: scutum with the adductor and articular ridges forming a cavity, which runs up to the apex of the valve._

_Hab._--Cape of Good Hope; Algoa Bay; attached to sandstone and to
Patellæ; Mus. Brit., Cuming, and Stutchbury.[108]

[108] I have seen three separate lots of this species all from the
Cape of Good Hope; one lot was collected by Dr. Krauss, at Algoa
Bay, and I strongly suspect is the species described by him in his
'Südafrikanischen Mollusken' as _Conia porosa_. If the species,
figured by Chemnitz, and mentioned in a note (p. 329), under _T.
porosa_, be the present species, the specimens probably did not
come from Tranquebar, on which point Chemnitz speaks only from
memory. I have seen one specimen ticketed New South Wales, it is
possible, considering the case of _T. rosea_, that this may be
correct, but I should like to have further confirmation before
giving it as a habitat.

_General Appearance._--Colour dark greenish gray; form steeply
conical; surface covered, especially in the lower half of the shell,
by numerous, narrow, sharp, longitudinal ridges, but slightly
prominent, and serrated or transversely divided into small teeth:
when the shell has been much disintegrated, the upper part of the
surface consists of the exposed, smooth, rather large, upfilled
parietal tubes. I have seen no instance of the development of
the radii; sometimes even the sutures are with great difficulty
distinguishable, though I believe they always reach the outer
surface; sometimes the sutures are wide from the disintegration of
the edges of the compartments. Orifice rounded or oval.

_Scuta._--The scuta and carinal half of the terga are blueish-green.
In the scuta neither the articular ridge or furrow are much
developed: the adductor ridge is prominent, and is united to the
articular ridge, about half way up the latter, thus forming a rather
large, triangular cavity, which runs up to the apex of the valve.

The _Terga_ are beaked. The spur, measured across the upper part,
is half as wide as the valve; it is bluntly pointed; it is placed
quite close to the basi-scutal angle of the valve, so that there
is no basal margin on that side; it curves towards the scutum, its
extremity extending beyond the basi-scutal angle.

_Structure of the Shell and Radii._--The parietal tubes are rather
large, especially those adjoining the inner lamina of the walls. The
shell is of singularly little specific gravity, which is due to the
parietal tubes not being filled up with shelly matter nearly to so
great an extent as in the other species; even in the uppermost part
the tubes are not solidly filled up, only their external sides are
thickly coated with greenish-black shell, which by corrosion becomes
grayish. The radii, as stated, are not developed: the shell breaks
with singular facility along the sutures, and the radii are then seen
to be most feebly represented by a few very small branching ridges.
The alæ have their edges plainly crenated. The sheath is dark green,
with the lower edge free.

The _Mouth_ presents no particular characters. With regard to the
_Cirri_, I am doubtful whether any confidence can be placed in the
numbers of the segments being constant; but I may state that the
second cirrus contained thirteen and sixteen segments in its two
rami; the third cirrus only fourteen in both rami; and the sixth
cirrus twenty-six segments in both rami. Whereas in every specimen
of _T. porosa_, the longer ramus of the third cirrus contained more
segments than either ramus of the second. About half the segments,
namely, those in the middle of both rami of the third cirrus, are
furnished with coarsely and doubly pectinated spines, like those in
_T. porosa_.

_Affinities._--Upon the whole, this species is more nearly allied
to _T. porosa_ than to any other. In the cavity formed by the
union of the adductor and articular ridges, it is allied to _T.
cœrulescens_. This species differs from all, in its little specific
gravity, consequent on the parietal tubes being only slightly filled
up, and in the peculiarly serrated, narrow, approximate ridges on
the external surface of the walls. The character derived from the
adductor ridge, just alluded to, is remarkable. In the shape of the
terga, in the absence of radii, and in the structure of the body,
this species approaches closely to _T. porosa_.

3. TETRACLITA ROSEA. Pl. 10, fig. 3 _a_-3 _d_.

CONIA ROSEA.[109] _Krauss_ (!). Die Südafrikanischen Mollusken, Tab.
6, fig. 28, 1848.

BALANUS CUMINGII. _Chenu._ Illust. Conch., Tab. 4, fig. 5.

[109] I am greatly indebted to Professor Krauss for having sent
me, for examination, the unique specimen collected by himself in
Algoa Bay. There can be no doubt of the identity of the African and
Australian specimens. It is a singular circumstance that the same
species should occur in these two distant places, and, as far as at
present known, not in the intermediate, more tropical coasts.

_Shell dirty white, tinged with pink; parietes formed by a single row of large tubes: radii generally narrow: tergum with the spur rather short and broad._

_Hab._--New South Wales, Moreton Bay in lat. 27°, Port Jackson, and
Twofold Bay; South Africa, Algoa Bay. Attached, in Australia, to
littoral rocks and shells; often associated with _T. purpurascens_,
_Chthamalus antennatus_, and _Catophragmus polymerus_; Mus. Brit.,
Cuming, Krauss, Darwin, Stutchbury.

_General Appearance._--Shell steeply conical, often rather convex;
dirty or brownish white, feebly tinted with pink; external surface
generally much disintegrated, and having in the upper part a pillared
appearance, owing to the exposure of the upfilled, large, square,
parietal tubes, and, in the lower part, a striated (and sometimes
serrated) appearance, from the exposure of the parallel, approximate
plates, with which the outer lamina of the shell is internally
strengthened. In only a few young specimens, the whole outer lamina
of the shell was well preserved; and in these the surface was very
smooth, and even glossy, giving to the specimens a quite different
aspect; even in partially corroded specimens, the lower part of the
shell sometimes is quite smooth. Generally, the radii are developed;
in most specimens they are narrow, but sometimes of moderate width;
their summits are oblique, and their edges often notched or toothed.
The recipient furrow, in each opposed compartment, is often almost
as wide as the radius itself, and is equally notched. In some much
corroded specimens there were no radii. Basal diameter of largest
specimen, 1.1 of an inch.

_Scuta_, generally thick, sometimes very thick, with the external
surface usually much corroded: articular furrow rather wide;
articular ridge not very prominent; adductor ridge prominent. The
rostral depressor muscle is attached in a small oblong pit, sometimes
including little crests; and the lateral depressor muscle is attached
to what may be described either as three or four parallel furrows or
crests.

_Terga_, with the spur placed close to the basi-scutal angle, so that
there is no basal margin on that side; spur short, with its lower end
truncated and rounded; broad, even exceeding, when measured across
the upper part, half the width of the valve. Articular furrow wide.
Apex not beaked.

_Structure of Walls and Radii._--This species differs from all the
others of the genus in having only a single row (fig. 3 _d_) of
parietal tubes; these are large, quadrangular, but elongated in the
ray of the circle. They are not filled up, even at the very top of
the shell, but they become thickly lined all round with compact
shelly matter. When the surface of the shell is disintegrated,
these upfilled tubes greatly affect, as already stated, the
external appearance. The outer lamina near the basis is internally
strengthened by longitudinal, sharp, approximate ridges or plates,
which, also, often affect, after corrosion, the external appearance.
The _radii_ have their sutural edges formed by a set of narrow,
branching ridges or septa; the ends of which, seen externally, often
give a notched outline to this edge; the recipient furrows in the
opposed compartments are deep, and their edges likewise are often
notched: the interspaces between the branching ridges are filled up
solidly. The _alæ_ have their edges coarsely crenated. The lower edge
of the sheath is not free.

The _mouth_ and _cirri_ present no particular characters: the third
cirrus has both its rami elongated, with the terminal segment
tapering. In the three posterior pairs of cirri, the tufts of little
spines between the main pairs are rather large.

_Affinities._--This species has no particular affinity with any
other. The circumstance of there being only a single row of parietal
tubes is not so important a difference as might at first be thought,
inasmuch as in the other species, during their quite early youth, the
walls are formed of only a single row of tubes or pores.

4. TETRACLITA PURPURASCENS. Pl. 11, fig. 1 _a_-1 _d_.

LEPAS PURPURASCENS.[110] _Wood's_ General Conchology, p. 55, Pl. 9,
fig. 42, 1815.

BALANUS PLICATUS. _Lamarck._ Animaux sans Vertèbres, 1818.

---- ---- ET PUNCTURATUS. _Chenu._ Illust. Conch., Tab. 4, fig. 3 et
12.

CONIA DEPRESSA (!). _J. E. Gray._ Appendix, Dieffenbach's Travels in
New Zealand, 1843 (sine descript. vel figurâ).

[110] The descriptions given by Wood and Lamarck are fuller and
more accurate than is usual in the case of Cirripedes, and I have
no doubt regarding these two names. The _Conia depressa_ of Dr.
J. E. Gray is, as I know from having seen the original specimens,
the young of this same species; the name is unaccompanied by any
description or figure.

_Shell depressed, pale purple or dirty white, with the surface longitudinally ribbed, or corroded and granulated: radii or even sutures none, or radii well developed and broad, with their summits parallel to the basis: basis membranous: scutum transversely elongated: tergum small, with the spur extremely short and rounded._

_Hab._--Sydney, New South Wales; Flinder's Lagoon, Sir C. Hardy's
Island, Barrier Reef; King George's Sound, Western Australia; Van
Diemen's Land; New Zealand, adhering to _Pollicipes spinosus_;
Mus. Brit., Cuming, Stutchbury, Darwin, &c. China (?) attached to
_Pollicipes mitella_, Mus. Brit. and Stutchbury. Generally attached
to tidal rocks, sometimes to shells. Very common.

_General Appearance._--Shell generally much depressed, in a few
cases rather steeply conical, in one single instance cylindrical,
but not much elongated. Colour, when alive, pale, but fine purple; I
presume, judging from some dried specimens, sometimes dirty white.
The state of the surface varies remarkably: about half the specimens
(fig. 1 _a_) which I have seen, had the outer lamina of shell quite
removed, and the surface granulated, owing to the projecting and
exposed tips of the upfilled parietal tubes; the radii are not
developed, and often even there is no trace of the four sutures;
the rather large orifice is somewhat rounded, and the two scuta,
with their surfaces disintegrated, have their middle parts deeply
indenting the terga. The shell, in the other and perhaps more common
condition (fig. 1 _b_), has the outer lamina preserved, and is
longitudinally ribbed with generally at least five or six ribs on
each compartment: the radii are here very wide, and extend from tip
to tip of the compartments, so that their summits are parallel to the
basis; they are generally covered by a brownish epidermis, thickly
clothed with little spines; the orifice is neatly diamond-shaped;
the apices of the opercular valves meet at a common point: these
specimens are almost always smaller and younger than the granulated
specimens. Altogether the specimens in the two opposite states have,
in their external appearance, nothing in common, and no one, without
careful examination, would ever suspect that they were specifically
identical; this, however, was proved by the intermediate forms,
and, in one instance, three of the compartments had their surfaces
granulated, and were entirely destitute of the radii, whilst the
fourth by some chance had been preserved from corrosion, was
longitudinally ribbed, and had its epidermis-covered radius fully
developed. The difference in the appearance of the opercular valves,
in the two states, is simply owing to the degradation of their upper
parts in the granulated specimens.

The basal diameter of the largest specimen was one inch, but the
height only .35 of an inch.

_Scuta_, transversely elongated, so that the basal margin is nearly
twice as long as the tergal margin: articular ridge very little
prominent; articular furrow wide but shallow; adductor ridge very
blunt, slightly prominent, sometimes almost absent, almost parallel
to the basal margin: there are no distinct crests for the rostral
or lateral depressor muscles, but some small irregular pits for the
latter. In one young specimen, the lines of growth were crenated,
showing a tendency in the valve to become longitudinally striated, as
in the allied _T. costata_. In some young and immature specimens, the
basal margin was deeply sinuous.

_Terga_, small in area, not above half that of the scuta: spur
extremely short, broad, placed close to the basi-scutal angle of the
valve, so that there is no basal margin on that side of the spur. The
lower end and sides of the spur form one uniform curve. Articular
ridge barely developed. Crests for the tergal depressores sharp and
prominent.

_Structure of the Shell and Radii._--The walls are very thick, and
the parietal tubes small and numerous; there are sometimes from
twelve to fifteen rows of tubes in the thickness of the wall. The
tubes in their whole upper part are filled up solidly; and, as
we have seen, are often exposed by disintegration. In very young
specimens, of that size in which in _T. porosa_ there would be only
a single row of parietal tubes, there were here two or three rows.
The development of the radii, as we have seen, is very capricious;
the sutures even sometimes being lost. The radii, when developed,
are broad, square on the summit, and covered by brownish hirsute
epidermis: internally they are formed of tubes like those forming the
parietes; in this respect differing from all the species except the
following, _T. costata_. The tubes in the radii run obliquely down
towards the basis; instead of in a transverse line, directly towards
the opposite compartment, as might have been expected from the
structure of the radii in Balanus. The alæ have their edges finely
crenated. The sheath in all the specimens which I have observed is
colourless; its lower edge is not free. The corium entering the
parietal tubes, and lining the opercular valves, the mouth, and the
anterior cirri, is generally of an extremely dark purple colour.

The _Basis_ is entirely membranous, in which respect this species
differs from all the others in the genus.

_Mouth_: all the trophi are unusually hairy or spinose. The labrum is
deeply notched and apparently destitute of teeth on the crest. The
palpi are club-shaped or enlarged at their extremities. The mandibles
have the fourth tooth rudimentary.

In the _Cirri_, the second and third pairs are remarkably short
and blunt. In one specimen the two rami of the first cirrus had
respectively six and sixteen segments; those of the second, six and
seven; those of the third, seven and seven; and those of the sixth
cirrus twenty rather elongated segments, with a small tuft of spines
between each main pair of spines.

_Affinities._--This species differs from all, in its membranous
basis, and in its transversely elongated scuta. It resembles _T.
costata_, and differs from all the other species, in its radii
(when developed) being square on the summit, and in being formed of
tubes,--in the smallness and number of the parietal tubes,--in the
absence of crests on the under side of the scuta for the rostral
and lateral depressor muscles,--in the shortness and rounded form
of the spur to the terga,--and, lastly, in the club-shaped palpi
and small size or absence of the fourth tooth in the mandibles. _T.
purpurascens_ differs from _T. costata_ in those points, namely, in
its membranous basis and transversely elongated scuta, in which it
differs from all the other species, and, moreover, in its scuta not
being plainly striated longitudinally, in having more ribs on the
external surface of the parietes of its shell, and in having only
three pairs of main spines on the three posterior cirri.

5. TETRACLITA COSTATA. Pl. 11, fig. 2 _a_-2 _c_.

_Shell depressed, whitish, generally with ten very prominent longitudinal ribs: radii broad, with their summits parallel to the basis: basis calcareous: scutum externally striated longitudinally: tergum with the spur short and rounded._

_Hab._--Philippine Archipelago, Mus. Cuming. Attached to various
shells, within the tidal limit.

_General Appearance._--Shell whitish, probably tinged, when alive,
with reddish-purple; depressed; surface perfectly preserved, smooth,
but having longitudinal very prominent ribs, almost invariably ten
in number; namely, three on both the rostrum and carina, and two on
the two lateral compartments, with ten corresponding projections
round the basal margin. Orifice passing from rounded-trigonal to
diamond-shaped. The radii are very broad and square at the summit,
and extend from tip to tip of the compartments. Basal diameter of
largest specimen under half an inch, generally from .3 to .4 of an
inch.

_Scuta_, of the usual sub-triangular shape, and not transversely
elongated, as in _T. purpurascens_. External surface striated
longitudinally; in many specimens there is a medial depression, or
a row of very small pits, such as occur on the scuta of _Balanus
trigonus_ and _lævis_. The adductor ridge is moderately developed,
and runs nearly parallel to the occludent margin; there are no crests
for the rostral and lateral depressor muscles.

_Terga_: these in area equal two thirds of the scuta: the spur is
short and rounded, and placed as described under _T. purpurascens_;
but the articular ridge seems to be more prominent than in that
species.

_Structure of the Shell and Radii._--The parietal tubes are small,
and very numerous, as in _T. purpurascens_. The radii are wide,
square on the summits, but not so conspicuously covered by hirsute
epidermis as in that species. Internally, the tubes forming the radii
are smaller, and run more transversely than in _T. purpurascens_,
that is in the normal course, as in Balanus. The edges of the alæ are
nearly or quite smooth. The _Basis_ is as distinctly calcareous, as
in the other species of the genus.

_Mouth_: the trophi are not so hairy as in _T. purpurascens_; the
labrum seems destitute of teeth; the palpi are club-shaped at their
ends; the mandibles have only three teeth. The second and third
cirri are not so short and blunt relatively to the others as in _T.
purpurascens_. In the posterior cirri, the elongated segments carry
four main pairs of spines, between which there is no intermediate
tuft of fine spines.

The _Affinities_ of this species have been fully pointed out under
the last and closely related species. In external appearance, _T.
costata_ can at first hardly be distinguished from those young and
pale-coloured varieties of _T. purpurascens_, which have their
external surface not corroded, and their radii well developed.

6. TETRACLITA VITIATA. Pl. 11, fig. 3 _a_-3 _e_.

_Shell white, generally tinged in the upper part with pink; surface irregular: parietal tubes very irregular: radii moderately wide, with their summits oblique: alæ with very thick crenated sutural edges: tergum with the spur not joined to the basi-scutal angle; spur with its extremity equably rounded._

_Hab._--Philippine Archipelago; Barrier Reef, (Raine's Islet),
Australia; Mus. Cuming and Stutchbury. Attached to massive corals, to
coral-rock, to a Tridacna, and to _Tetraclita cœrulescens_.

_General Appearance._--Shell conical, moderately steep: white,
generally with a tinge of pinkish-purple in the upper part, owing to
the exposure of the tips of the upfilled parietal tubes. The lower
part of the surface is generally well preserved, and is formed by
very irregular, branching, longitudinal, slightly prominent, ridges.
Radii of moderate width, with their summits oblique. Orifice rather
large, rounded trigonal.

_Scuta_, rather narrow, with the upper part acuminated: the external
surface generally much disintegrated, and marked with some irregular
blotches of dark red. Articular ridge not prominent; articular furrow
rather deep: adductor ridge, distinct from the articular ridge,
pretty well developed, as are the crests for the rostral and lateral
depressor muscles. In young and well preserved scuta, there is an
external, medial, hyaline band, corresponding with the hollow under
the adductor ridge, and caused by the thinness of the valve along
this line.

_Terga_: externally, the carinal half is longitudinally and very
feebly striated. Internally, the articular furrow is very wide, but
shallow, and of unusual length, owing to the preservation of the
upper part of the valve; the articular ridge is not prominent. The
spur does not actually join, as in all the foregoing species, the
basi-scutal angle, but is separated from it by a short piece of basal
margin; its two sides are more nearly parallel than is usual, and
the end is regularly rounded. It is always rather narrow, though the
width varies considerably (fig. 3 _d_, 3 _e_). It extends in the same
straight line with the middle of the articular furrow. The terga,
though not possessing any striking characters, differ considerably in
appearance from those of the other species.

_Structure of the Shell and Radii._--The parietal tubes are
remarkable from their irregular shapes, and unequal sizes (fig. 3
_b_),--hardly two resembling each other. Sometimes a single elongated
tube will reach across the whole thickness of the walls. The septa
between the tubes are rather thick and rugged. The tubes are
generally darkly coloured from the adhering corium; they are solidly
upfilled, but only in the uppermost part, by dark chocolate-red
shelly matter. The radii are formed by irregularly branching ridges,
with the interspaces filled up solidly. The square edges of the alæ
are much thicker than in any other species, and are furnished with
transverse ridges, which are sometimes slightly branched. The inner
lamina of the walls near the basis, in most of the specimens, is
irregularly and longitudinally ribbed, the ribs being longitudinally
striated. The sheath and the upper part of the inner lamina of the
parietes are clouded with chocolate-red.

The animal's _Mouth_ and _Cirri_ were ill-preserved; but I was able
to make out that the labrum had some strong teeth, and that the
mandibles were furnished with five teeth, a greater number than in
any other species. The palpi had parallel sides as usual. In the
sixth cirrus, the segments had four pairs of main spines, instead of
the usual number of three.

_Affinities._--This species does not appear to be particularly
related to any other one: perhaps it is rather nearer to the two
following than to the foregoing species. The irregular parietal
tubes, thick-edged alæ, form of terga, five teeth to the mandibles,
and four pairs of spines to the segments of the posterior cirri, are
its chief characteristics.

7. TETRACLITA CŒRULESCENS. Pl. 11, fig. 4 _a_-4 _d_.

LEPAS CŒRULESCENS. _Spengler._ Skrivter af Selskabet, 1 Bind.,
1790.[111]

[111] The longitudinally folded walls, as described by Spengler,
the blue colour, the habitat, namely, associated with _B.
tintinnabulum_ from the East Indies, and more especially the
expression "Valvulæ operculi cardine dentato mobilis," apparently
referring to the highly prominent articular ridge of the scutum,
leave little doubt on my mind that I have rightly named the present
species.

_Shell with the upper part tinged greenish-blue, longitudinally ribbed: radii moderately wide, with their summits oblique: scutum with a small adductor and extremely prominent articular ridge, united together and so forming a small sub-cylindrical cavity: tergum with the spur not joined to the basi-scutal angle._

_Hab._--Philippine Archipelago, attached to _Balanus tintinnabulum_;
attached to a ship's bottom, and to _Balanus tintinnabulum_, both
from the Pacific Ocean; attached to a massive coral, and associated
with _T. vitiata_, and therefore from the tropical eastern seas; Mus.
Brit., Cuming, Stutchbury.

_General Appearance._--Shell conical, sometimes depressed; surface
with rather broad, smooth, longitudinal ridges; whitish, with the
upper part greenish-blue, sometimes very feebly tinted with pink;
radii white, or mottled with blueish-green, or with pink. When the
outer lamina of shell has been corroded, the upfilled parietal tubes,
of a dull blueish-gray colour, are exposed. The radii are moderately
wide, with their summits very oblique. In basal diameter, one
specimen was 1.8, and another 1.5 of an inch.

_Scuta_, externally furrowed very slightly in a longitudinal
direction, causing the lines of growth to become a little sinuous.
The valve is strong and thick; and the epidermis, when preserved,
is hirsute with spines. The articular ridge is extraordinarily
prominent; it projects, as measured from the external surface of
the valve, to an amount equalling half the width of the valve in
its widest part. The adductor ridge is very short, and is united
to the bottom of the articular ridge, thus forming a small, nearly
cylindrical tube, which runs up to near the apex of the valve. The
inflected occludent margin is broad and coarsely toothed. The crests
for both depressor muscles are not very prominent. When the scuta
and terga are articulated together, owing to the great projection of
the articular ridge of the scutum, its upper part is separated from
the tergum (fig. 4 _b_), by a remarkably wide and deep, fissure-like
hollow. The scutum, in some distorted specimens from a ship's bottom,
was narrow in proportion to its ordinary breadth.

_Terga._--These are large. Externally, there is a broad, longitudinal
depression, bounded on each side by a ridge. The carinal half is
feebly striated longitudinally. A large upper portion (fig. 4 _b_)
projects freely, and stands, when the two valves are articulated
together, above the apex of the scutum, but does not form a beak as
in _T. porosa_. Internally, the tergal margin is widely inflected;
the articular furrow is very deep, but the articular ridge is not
prominent. The spur is not very broad; it is separated from the
basi-scutal angle by a small space of basal margin, which forms a
straight line with the basal margin on the opposite side of the spur.
The end of the spur is truncated, and is parallel to the basal margin.