Chapter XIII: Introduction (9)

Besides the slight variation in the obliquity of the summits of the radii and alæ, dependent on the more or less cylindrical form of the shell, in some species, as in _B. tintinnabulum_, _amphitrite_, _improvisus_, _trigonus_, and _porcatus_, their obliquity also varies occasionally from unknown causes, and thus greatly affects the general appearance of the shell. In some few species, as in _B. perforatus_, the radii are often either not at all developed, or are of very variable width; in others, when the shell has become cylindrical, or when very old, the radii cease to grow, and from the disintegration of the whole upper part of the shell, with the continued growth of the lower part, the radii at last come to exist as mere fissures: I have seen instances of this in _B. psittacus_, _nigrescens_, and _porcatus_. Nevertheless, the obliquity of the upper margin, and the breadth of the radii are useful characters; and still more useful is the fact whether the upper margins are smooth and arched, or straight and jagged. The fact of the terga being more or less beaked is useful: as is, likewise, the presence of striæ, or furrows, or rows of pits, radiating from the apices of the scuta; but to ascertain the presence of these marks, it is almost invariably necessary to take out the scuta, clean, and examine them with a lens; these ridges and furrows, moreover, in some species, as is strikingly the case with _B. tintinnabulum_, and in less degree with _B. trigonus_, _lævis_, and _concavus_, appear and disappear, and vary without any apparent cause.

Now if we reflect that form, size, state and nature of the surface, presence of epidermis, relative size of the orifice, presence of longitudinal ribs, tint, and often the existence of any colour, are all highly variable in most of the species; and that the obliquity of the summits of the radii, and the presence of longitudinal striæ on the scuta, are variable in several species; we shall perceive how difficult it must ever be to distinguish the species from external characters. As some evidence of this, I may mention that, after having described nearly 40 species, and when my eye was naturally able to appreciate small differences, I began carefully to examine varieties of _B. tintinnabulum_, _amphitrite_, _improvisus_, _porcatus_, _vestitus_, &c., without even a _suspicion_ that they belonged to these species, at that time thoroughly well known to me; yet in the cases here referred to, there could be no doubt, when a perfect series was examined, that the specimens were only varieties. From this cause the labour of naming a collection is great. Let no one attempt to identify the species of this genus, without being prepared to disarticulate, clean, and carefully examine with a microscope the basis and parietes, and both the under and upper surfaces of the opercular valves; for I feel convinced, that he will otherwise throw away much labour. Moreover, in many cases, it is almost necessary, on account of the variability of the characters, to possess several specimens. From these facts, I have not hesitated to form my sections on characters which require close examination, though I would gladly have seized on external characters, could I have found such even moderately constant.

The least varying, and therefore most important characters, must be taken from the internal structure of the parietes, radii, and basis: not that these characters are absolutely invariable; thus the porosity of the parietes is slightly variable in _B. glandula_, and highly variable in the fossil _B. unguiformis_; it is also highly variable in _B. balanoides_, but under a systematic point of view this is unimportant, as the section including this latter species is well defined by the membranous basis. The porosity of the basis is in some degree variable in _B. nubilus_, _improvisus_, and _patellaris_; and in _B. flosculus_ we see signs of a passage from a calcareous to a membranous basis. Characters derived from the general shape, and from the ridges and depressions on the under side of the scuta and terga, especially of the scuta, are highly serviceable. The terga, indeed, in many species, as in _B. amphitrite_, vary considerably, and are affected by the general shape of the shell. Unfortunately the differences are not very great between the scuta of the different species. The cause of the opercular valves offering more useful characters, as far as outline is concerned, than do the walls of the shell, is no doubt due to their being almost independent of any influence from the nature of the surface of attachment. Even the ridges and depressions on the under side of the scuta, which are in direct connection with the muscles and soft parts of the animal, vary to a certain extent: thus the length and prominence of the adductor ridge is decidedly variable in _B. concavus_ and _tintinnabulum_, and in a less degree in _B. lævis_; the size and form of the little cavity for the lateral depressor muscle varies in many species; so does the exact shape and degree of prominence of the articular ridge. There is one character in the terga, which at first would be thought very useful, namely, whether an open longitudinal furrow, or a closed fissure runs down the valve from the apex to the spur; but it is found that the furrow almost always gradually closes up during growth; and as a consequence of this, the width of the spur compared to that of the whole valve, as well as its distance from the basi-scutal angle, and the form of its basal extremity, all vary in some degree. The length of the spur sometimes varies considerably, as in _B. concavus_ and _amphitrite_. The parts of the mouth are only occasionally serviceable; for the teeth on the labrum, and the state of the lower teeth on the mandibles, and the presence of a step-formed projection at the lower angle of the maxillæ, are all often variable. The relative lengths of the two rami of the first pair of cirri, the degree of protuberance of the segments, and the number of pairs of spines on the segments of the posterior pairs of cirri, are sometimes useful; but the relative lengths of the cirri, and more especially the numbers of pairs of spines on the posterior cirri, are apt to vary. Finally, I must express my deliberate opinion, that every part and organ, internal and external, in Cirripedes, is liable to some amount of variation in some of the species.

I must now point out the principal changes which supervene during growth, and which cannot properly be called variations. In the first place, I think, it is scarcely possible to recognise a species when under the 1/10th of an inch in diameter. In some cases, as in _var. d'Orbignii_ of _B. tintinnabulum_, the shell is invariably coloured when old, but quite white when very young. Generally the tints become very much darker with age. Some species, which usually or invariably have, when mature, longitudinally folded walls, as _B. flosculus_ and _balanoides_, are perfectly smooth in youth. The walls in _B. eburneus_, when young, have white, hyaline, longitudinal lines, and are naked; whereas, with advancing age, these lines disappear, and the subsequently formed shell becomes covered with membrane. The summits of the radii are apt to be oblique in the young of _B. Capensis_, _psittacus_, and _tintinnabulum_, whereas they are generally quite square in old specimens. In _B. eburneus_, _cariosus_, and in a lesser degree in _B. psittacus_, the scuta become longitudinally striated only with age. On the other hand, in very young specimens of _B. tintinnabulum_, the scuta sometimes are deeply impressed by little pits placed in rows. I have already alluded to the longitudinal furrow on the tergum so entirely changing its character, owing to the edges becoming, during growth, folded inwards; this likewise causes a decrease in the proportional breadth of the spur. In old specimens of _B. flosculus, var. sordidus_, the whole tergum is much more elongated than in young specimens. The basal margin of the sheath is hollow beneath in the young of _B. cariosus_ and of some other species, but in the old it is continuous with the inner surface of the walls. The inner lamina of the parietes generally loses, to a certain extent, its longitudinally ribbed character in old age. The basis is solid, instead of being porose, in very young specimens of _B. improvisus_. In all the species, the carino-lateral compartments, in early age, are very narrow in proportion to the width of the lateral compartments; and in all, at this early period, the operculum is large in proportion to the whole shell. The number of spines on the edge of the maxillæ, the number of segments in all the cirri, and the number of spines on each segment, are few in early youth, and go on increasing with each successive exuviation: the pedicels of the cirri are long in proportion to the rami at this same early age.[84]

[84] In some specimens of _Balanus perforatus_ I made the following
enumeration of the number of segments in the cirri:--

+--------------+--------------+--------------+------------------+
| |Basal diameter|Basal diameter| Medium sized |
| | of shell | of shell | specimen about |
| | 1/20th of | 1/5th of |3/4ths of an inch |
| | an inch. | an inch. |in basal diameter.|
+--------------+--------------+--------------+------------------+
|First cirrus }| ? | 11 | 17 |
|shorter ramus}| | | |
| | | | |
|Second cirrus | 4 or 5 | 9 | 13 |
| | | | |
|Sixth cirrus | 9 or 10 | 19 |31, in another 36 |
+--------------+--------------+--------------+------------------+

In the specimen 1/5th of an inch in basal diameter, each segment
of the posterior cirri carried five pairs of spines; whereas,
in full-grown specimens, there are six or seven pairs. In the
1/20th of an inch specimen, on the inner maxillæ, there were
no spines between the upper large and the lower large pair of
spines; whereas, in the 1/5th of an inch specimen, there were five
intermediate spines, and in larger specimens nine or ten spines.

Notwithstanding the difficulties now enumerated, I hope that, owing to having examined a vast number of specimens of the most varying species, I have not fallen into very many errors. I have endeavoured to err on the side of making too few instead of too many species. In those cases, however, in which I have seen only a few specimens, I have been sometimes compelled to decide without sufficient evidence.

I would gladly have divided this genus, already including 45 species, into smaller genera; but so far from being enabled to do so, I have been compelled to form my Sections (immediately to be given) on characters not absolutely invariable, and far from obvious. I was particularly anxious to separate the elongated species with a boat-formed basis, which are attached to Gorgoniæ, and which form the genus Conopea of Say, but I was unable to effect their separation even as a sub-genus; for _B. navicula_ and _cymbiformis_ graduate in the most insensible manner through _B. galeatus_ (the type of Say's genus) and _B. calceolus_ into _B. stultus_, and this into _B. Ajax_; yet this latter species has even been described as a mere variety of the typical _B. tintinnabulum_! Indeed, so insensible is this graduation, that the first and second sections of the genus are hardly distinct. I fully admit, that if _B. stultus_ and _Ajax_ had never existed, _B. calceolus_ and its three allies might have formed as natural a little group, though difficult to be characterised, as does the sub-genus Acasta; or perhaps this group and Acasta might have been combined together. These same species, viz., _B. calceolus_ and its allies, are intimately allied to _B. terebratus_ and _inclusus_, which are contained in the last section (F) of the genus; and this shows that Dr. Gray's proposed genus Chirona, including the species with non-porose parietes in sections (E) and (F), could hardly have been instituted, even if the porosity of the parietes had not been variable in _B. unguiformis_, _balanoides_, and _glandula_. My fourth section (D), founded on the basis not being porose, is perhaps the weakest of the divisions, as may be seen in the list of exceptions appended to the sectional headings.

The arrangement of the species is, I think, as natural as a linear one could be made: every one knows how irregularly and in how many directions the lines of affinity in every natural genus branch out. Some few species stand rather isolated, as _B. declivis_; and _B. allium_, _cepa_, and _quadrivittatus_ in a little group by themselves. I have already shown how the species in the first and second sections (A and B) blend into each other; and that the blending species are likewise allied to some in the last section (F); furthermore, I shall have occasion to show that these same species can hardly be separated naturally from the sub-genus Acasta. The first section, moreover, passes into the third (C) by _B. tulipiformis_; and the third into the fourth (D) by _B. improvisus_, _nubilus_, _corrugatus_, and _patellaris_: the fifth and sixth (E and F) sections are closely connected together by _B. cariosus_ and _flosculus_; and these two sections blend into the fourth (D) through _B. unguiformis_ and _balanoides_, and lastly, into the third (C) section by _B. dolosus_ and _improvisus_.

The genus, as we have just seen, is hardly separated from the sub-genus Acasta; by _B. allium_ it tends to pass through the sub-genus Creusia into Pyrgoma; and by _B. imperator_ and _flosculus_ it graduates into Elminius and Tetraclita.

_Geographical Distribution._--This, which is much the largest genus of sessile cirripedes, has its species scattered over the whole world, from the arctic regions, in lat. 74° 48′, where we have _B. crenatus_ and _porcatus_, throughout the tropical seas, to Cape Horn, where _B. flosculus_ adheres to the coast-rocks. Many of the species have individually very wide ranges; thus _B. tintinnabulum_ and _amphitrite_ are found throughout the warmer seas; but the wide distribution of these species may be partly due to their frequent adhesion to ships' bottoms: _B. crenatus_ ranges from the frozen seas, in lat. 74° 48′ north, to the West Indies and Cape of Good Hope--a wonderful endurance of the most opposite climates. _Balanus improvisus_, again, extends from Europe to Nova Scotia, thence southward to Patagonia, and up the western coast of S. America, someway north of the Equator. Most of the species have considerable ranges; thus of the six species found on the eastern shores of northern America, five of them occur in Great Britain. Of the thirty-six species of which the habitats are known, exactly one third, or twelve, inhabit both the torrid and temperate zones, these being divided by the isocryme of 68°; nine are found exclusively in the torrid, and fifteen exclusively in the temperate zones. Within the warmer latitudes, and especially in the southern hemisphere, Tetraclita and Elminius to a certain extent supplant Balanus. In depth, the species range from the upper limits of the tidal zone to even fifty fathoms. _Balanus improvisus_ and _eburneus_ are able to survive in brackish water. The different species are attached to various surfaces--rocks, shells, timber, floating objects, sea-weed, lamelliform corals, Milleporæ, Gorgoniæ, and even to sponges. Mr. G. B. Sowerby has remarked[85] that in the species from the southern hemisphere it is the basis, and in the species from the northern hemisphere it is the parietes, which are elongated, when the individuals, from being crowded together, become cylindrical; but this is erroneous; _B. perforatus_, in the northern hemisphere, sometimes has an elongated basis; but no doubt the basis of our commonest species, as _B. balanoides_, _crenatus_, and _porcatus_, from being either membranous or thin, does not become cup-shaped; whereas this structure is conspicuous in _B. psittacus_ and _lævis_, the two commonest species in southern South America.

[85] Darwin's 'Geology of S. America,' p, 264.

_Fossil Species._--Having already given, under the Family, some account of the geological history of sessile cirripedes, short as it is, I here only allude to the subject in order to state my conviction that species cannot be satisfactorily distinguished in a fossil state, and rarely in a recent state, without an examination of the opercular valves. Nothing, indeed, could have been easier than to have affixed names to many groups of specimens, having different aspects, but to feel sure that these were really distinct species requires better evidence than can be afforded by the shell, without the operculum. No doubt, in some of the smaller sections of the genus--for instance, in that characterised by a membranous basis--it would have been possible to have distinguished some or several fossil species; but such have not as yet been found. When the specimens are much fossilised, it is, indeed, difficult to make out the primary points of structure--namely, whether the parietes, radii, and basis are porose: to do this it is sometimes necessary to rub down, polish, and carefully examine, a transverse section of a piece of the shell.

_Sections of the Genus._

[A]

_Parietes, and basis, and radii permeated by pores._

[B]

_Parietes and basis sometimes permeated by pores, sometimes not; radii not permeated by pores; shell elongated in its rostro-carinal axis; basis boat-shaped, attached to Gorgoniæ and Milleporæ._

[C]

_Parietes and basis permeated by pores; radii not permeated by pores._

[D]

_Parietes permeated by pores. Basis and radii not permeated by pores._

[E]

_Basis membranous._

[F]

_Parietes and radii not permeated by pores. Basis sometimes permeated by pores, sometimes not, sometimes excessively thin and hardly distinguishable._[86]

[86] The following species might, owing to variation, or to the
obscurity of their structure, without care, be classed in the wrong
sections:--in A, _Balanus Ajax_, from living attached to Milleporæ,
is sometimes elongated in its rostro-carinal axis, and from having
its radii only finely porose, it might be classed in B: on the
other hand, _Bal. stultus_ is sometimes but little elongated, and
the basis hardly boat-formed, and hence might be classed in A. The
distinction between all the species in (B) and the sub-genus Acasta
is artificial.

In sections C and D, I have seen one specimen of _B. spongicola_
with a solid basis, and very young specimens of _B. improvisus_
are thus characterised, and therefore these species are liable to
be placed in the wrong section, D: _Bal. nubilus_, also, has part
of its base non-porose, and therefore likewise might be placed
in D: on the other hand, the circumference of the basis in _B.
patellaris_ is often porose, and hence this species, which belongs
to D, might be placed in C.

In _Bal. glandula_, in D, the parietes of the compartments, without
several were examined, might be thought to be solid, and therefore
this species might be wrongly placed in F; on the other hand, the
fossil _B. unguiformis_, in F, often has porose parietes, and such
specimens would naturally be placed in D. Lastly, without care, _B.
flosculus_ might be thought to have a membranous basis, and so get
placed in E.

The genus Pachylasma, without an examination of the animal's body,
might easily get misplaced in the wrong genus, amongst the species
in the last section (F) of Balanus, yet there can be no doubt that
Pachylasma belongs to the Chthamalinæ.

_Section_ A.

1. BALANUS TINTINNABULUM. Pl. 1, fig. _a_-_l_; Pl. 2, fig. 1 _a_-1 _o_.

LEPAS TINTINNABULUM. _Linn._ Syst. Naturæ, 1767.

---- ---- _Ellis._ Phil. Transact., vol. 50, 1758, Tab. 34, figs. 8
and 9.

---- ---- _Chemnitz._ Neues. Syst. Conch., 8 B. (1785),
Tab. 97, figs. 828-831.

BALANUS TULIPA. _Bruguière._ Encyclop. Meth., 1789; sed non _B.
tulipa alba_, in _Chemnitz_; neenon _B. tulipa_, _O. F.
Müller_, Zoolog. Dan.; neenon _B. tulipa_, Poli, Test. ut.
Siciliæ.

---- ---- _G. B. Sowerby._ Genera of Recent and Fossil Shells, Tab.
Genus Balanus.

LEPAS CRISPATA (_var._) _Schröter._ Einleitung Conch. vol. iii, Tab.
9, fig. 21.

---- SPINOSA (_var._) _Gmelin._ Linn. Syst. Nat.

---- TINTINNABULUM, SPINOSA, CRISPATA ET PORCATA. _W. Wood._ General
Conchology, 1815, Pl. 6, figs. 1, 2. Pl. 7, figs. 4, 5. Pl. 8,
figs. 1-5.

BALANUS TINTINNABULUM. _Chenu._ Illust. Conch.[87]

---- D'ORBIGNII (_var._) _Chenu._ Illust. Conch., Tab. 6, fig. 10,
sed non Tab. 4, fig. 13.

---- CRASSUS (Foss.) _Sowerby_ (!). Min. Conch., 1818. Tab. 84.

[87] Chenu gives several admirable figures of this species; but
he confounds some forms certainly distinct under this name, for
instance the _B. tulipiformis_ of this work.

_Shell varying from pink to blackish purple, often striped and ribbed longitudinally: orifice generally entire, sometimes toothed. Scutum with the articular ridge broad and reflexed. Tergum with the basal margin generally forming a straight line on opposite sides of the spur._

_Var._ (1) communis (Pl. 1, figs. _a_, _b_, _f supra_; Pl. 2, figs. 1
_a_, 1 _c_, 1 _d_, 1 _e_, 1 _i_, 1 _k_): _conical or tubulo-conical;
smooth or moderately ribbed longitudinally; colours varying from
purplish-pink to blackish-purple; often in obscure longitudinal
stripes; orifice of shell rounded-trigonal_.

_Var._ (2) vesiculosus (_young_) (Pl. 2, fig. 1 _h_): _exterior
surface of the scuta impressed with small square holes, arranged in
two or more rows, radiating from the apex of the valve_.

_Var._ (3) validus (Pl. 1, figs. _c_, _f infra_): _globulo-convex;
coarsely ribbed, ribs flexuous; either smooth or rugged; pale
chocolate purple or pink; shell extremely strong; orifice almost
circular_.

_Var._ (4) zebra (Pl. 1, fig. _g_): _conical; rich chocolate purple
with broad snow-white ribs; sheath bright chesnut colour; summits of
alæ oblique; orifice almost circular_.

_Var._ (5) crispatus (_Schröter_) (Pl. 1, fig. _h_): _pale blueish
or pinkish-purple, with irregular rough projections, or with short,
sharp, needle-like points; scuta with their exterior surface either
plain, or with radiating lines formed of hood-like projecting points_.

_Var._ (6) spinosus (_Gmelin_) (Pl. 1, fig. _i_): _globulo-conical
or cylindrical; shell rather thin, with long, upcurved, nearly
cylindrical, very sharp points; colours very pale; attached to other
specimens, and to Lepas anatifera_.

_Var._ (7) coccopoma (Pl. 1, fig. _d_; Pl. 2, fig. 1 _f_, 1 _l_,
1 _o_): _globulo-conical; orifice small, rounded; walls generally
smooth, thick; intense rose-colour, sometimes most faintly striped
longitudinally with varying shades of pink; radii tinged with
purple; scutum sometimes as in_ var. communis, _sometimes with its
basi-tergal corner much cut off, with the adductor ridge prominent,
the pit for the depressor muscle deep, and the articular ridge broad
and hooked; tergum sometimes as in_ var. communis, _sometimes with a
broader spur, placed nearer to the basi-scutal corner of the valve_.

_Var._ (8) concinnus (Pl. 1, fig. _e_; Pl. 2, fig. 1 _g_):
_globulo-conical; walls finely ribbed; dull purple, tinged and
freckled with white; scutum, with a broad, hooked, articular ridge,
with an extremely sharp plate-like adductor ridge, and with a cavity,
bordered by a plate, for the rostral depressor muscle; tergum as in_
var. 1.

_Var._ (9) intermedius: _radii with their summits slightly oblique;
parietes pale blueish purple, with narrow dark purplish-blue
longitudinal lines; sheath with the internal surface of the rostrum
and lateral compartments much darker colored than the internal
surface of the carina and carino-lateral compartments; scuta and
terga as in_ var. communis.

_Var._ (10) occator (Pl. 1, fig. _k_; Pl. 2, 1 _b_): _radii with
their summits slightly oblique; parietes smooth, or ribbed, or
spinose; very pale blueish-purple, with narrow darker longitudinal
lines; sheath with the internal surface of the rostrum and lateral
compartments dull blue, whilst the corresponding parts of the carina
and carino-lateral compartments are white; scuta with small, sharp,
hood-formed points, arranged in straight radiating lines; terga with
the spur placed at either its own width, or less than its own width,
from the basi-scutal angle_.

_Var._ (11) d'Orbignii (_Chenu_) (Pl. 1, fig. _l_; Pl. 2, 1 _m_, 1
_n_): _radii with their summits oblique, and the orifice of the shell
rather deeply toothed; shell conical or tubulo-conical, smooth, or
rugged; colour dull purplish-lilac, with the tips of the parietes and
a band along one side of the radii quite white; sheath rather darker
at the rostral than at the carinal end; scuta as in_ var. 1; _terga
as in_ var. occator.

_Habitat._--West coast of Africa, on mytili; Madeira, on rocks; West
Indies; Cape of Good Hope, on a patella and on kelp; mouth of the
Indus; East Indian Archipelago; Sydney, Australia, attached to Lepas
anserifera, adhering to a floating cane; Peru; Galapagos Islands;
West Mexico; California. Extremely common on ships' bottoms arriving
from West Africa, India, and China, often associated with _B.
amphitrite_.

_Fossil_ Red Crag, England; Mus. S. Wood and J. de C.
Sowerby.--Touraine (?); Mus. Lyell.

_General Remarks._--This, the first species of Balanus, is, perhaps
with the exception of _B. amphitrite_, the most difficult and
variable in the genus. There are some other species which vary quite
as much in external appearance; for instance, _B. perforatus_; but
_B. tintinnabulum_ also varies in far more important points, as in
the proportions and structure of the opercular valves. The difficulty
in determining whether or not the differences are specific, is
wonderfully increased by whole groups of individuals varying in
exactly the same manner. I have seen three most distinct varieties
taken from the bottom of the same vessel, so that I did not at first
entertain the least doubt that they were three distinct species. I
may mention, as showing the vacillations which I have experienced
on this subject, that beginning with the impression, that the above
three varieties were really distinct species, after going over the
several immense collections of specimens placed at my disposal,
I came to the conclusion that the above three, and several other
forms presently to be described, were only varieties; yet after an
interval of some months, having to look at some of these specimens
again, I could not but think that I had come to a false conclusion,
and so went into all the details again, and satisfied myself that I
had followed a right course; after another interval, I had to repeat
the same process, and even now I can never look at a group of the
beautifully coloured shells with their small rounded orifices of
_var. coccopoma_ attached to the _Avicula margaritifera_, or again
at _var. d'Orbignii_, with its toothed orifice and white tips to
the compartments, without thinking that they must be specifically
distinct from the dull-coloured specimens with large entire orifices
so common on ships' bottoms; yet I can produce a full series of
intermediate forms, and I can further show, in each variety, that
the several points of difference by which each is characterised, are
variable. I may be permitted to add, in order to show that it has
not been from indolence that I have combined so many forms, that I
had named and already written out full descriptions of most of the
varieties, before determining to sacrifice them.

Seeing that _B. tintinnabulum_ and _amphitrite_ are the two most
variable species in the genus, more especially in the important
characters derived from the opercular valves, and knowing that these
species are attached so very frequently to ships' bottoms, one is led
to suspect that their extreme tendency to vary may be due to their
being exposed to varying and peculiar conditions, whilst transported
to new and distant localities. It is even just possible, as may be
inferred from the facts given in the Introduction (p. 102) in regard
to certain monstrous specimens of _Bal. balanoides_ having been
apparently impregnated by adjoining individuals, that the varieties
may interbreed, and so produce numerous intermediate forms. Whether
or not this could take place, I am inclined to look at these two
species, as in an almost analogous condition with our domestic
animals, which give rise to such infinitely numerous varieties. It
appears to me probable, that several of the varieties keep true
to their peculiarities, as long as they continue to breed in the
same locality; but that when their larvæ become attached to ships'
bottoms, and are thus transported and exposed to new conditions, they
give rise to new and ever-varying varieties. I will first give a full
description of the more common forms of _B. tintinnabulum_, which
undoubtedly belong to the same species, only alluding to the less
frequent points of difference, and then separately describe the more
marked varieties.

_General Appearance._--Shape of shell generally tubulo-conical, or
conical, or globulo-conical, rarely depressed. Orifice either large
and rounded-trigonal, or small and oval, either entire or less
frequently toothed. Surface quite smooth, or longitudinally ribbed;
ribs of variable strength, not unfrequently flexuous or branching,
sometimes roughened with blunt or sharp projecting, irregular points,
or more rarely with almost cylindrical, upturned, long spines; the
simple longitudinal ribs are generally most strongly marked in
young specimens. _Colour_, generally varying from pink, to pink
tinged with purple, to dark, inky purple, more or less striped,
longitudinally, with white or pale tints; rarely the shell is of the
brightest rose-colour, either uniform or longitudinally striped;
sometimes it is pale purplish, or dark blue; and sometimes dark
chocolate-purple: the ribs, when present, are generally more or less
white, sometimes snow-white. That there is much variation in colour,
and in the prominence of the longitudinal ribs, is quite certain,
as the two sides of the same individual sometimes differ greatly in
these respects. The radii are generally rather darker coloured than
the parietes, but sometimes they are lighter, even in the darkest
tinged specimens. The surfaces of the radii are occasionally finely
plaited in lines parallel to the basis. In some infrequent varieties
the radii have oblique summits, making the orifice of the shell to
be toothed. The sheath is generally feebly coloured, but sometimes
bright chesnut-brown, and sometimes blueish. The _strength_ of the
shell varies considerably; some of the globulo-conical varieties are
extremely massive. _Size_; basal diameter of largest specimen very
nearly three inches; height of the highest specimen three inches.

Young specimens are apt to have a peculiar aspect; for their shell
is often strongly ribbed longitudinally, and the summits of their
radii are sometimes oblique. Their scuta are sometimes deeply
pitted in radiating lines. Their colours are generally pale. I
have seen specimens attached to kelp from the Cape of Good Hope,
with their parietes white and ribbed, and their radii mottled with
pinkish-purple; I have seen other young specimens from the Galapagos
Archipelago, of a uniform grayish-blue.

The _Scuta_ generally have their lines of growth moderately
prominent; occasionally they are longitudinally striated, with the
lines of growth flexuous and upturned at intervals into small,
sharp, hood-liked projections, which are symmetrically arranged in
straight lines radiating from the apex of the valve; I have seen
this structure in some specimens of _var. crispatus_ and in _var.
occator_ (Pl. 2, fig. 1 _b_); and I have noticed an intermediate
state in _var. communis_. The degree to which the basi-tergal corner
of the valve is rounded off varies much even in _var. communis_ (Pl.
2, fig. 1 _a_, 1 _d_, 1 _e_). The articular ridge (1 _c_, 1 _e_)
is broad and much reflexed; and often, but not always, distinctly
hooked (1 _f_). The adductor ridge is confluent with the articular
ridge, and runs straight down the valve, bounding the cavity for
the depressor muscle; generally the adductor ridge is blunt, and so
little prominent as barely to deserve notice; but I have seen it
sharp and prominent in one specimen of _var. communis_, and it is
generally prominent in _var. coccopoma_ (1 _f_), and most remarkably
so in _var. concinnus_ (1 _g_). The cavity for the lateral depressor
muscle is generally very slight; but in the two vars. just mentioned,
and sometimes in _var. communis_, it is deep. In _var. concinnus_ (1
_g_) there is a remarkable plate developed for the attachment of the
rostral depressor muscle. The scuta are coloured either dull-purple
or reddish, or striped longitudinally white and blue. The surface is
sometimes externally depressed in the line of the adductor ridge; and
in young specimens there is sometimes, along this line, a chain of
pits (1 _h_), as in full-grown specimens of _B. trigonus_ and _lævis_.

The _Tergum_ (Pl. 2, figs. 1 _i_ to 1 _o_) is broad, with a generally
closed longitudinal furrow; this furrow is open in young specimens,
and it is often, but not always, open in rather large specimens of
_var. occator_; it is always open in _var. d'Orbignii_ (Pl. 2, fig. 1
_m_), and sometimes in _var. concinnus_. Apex barely beaked, except
in _var. spinosus_, in which it is sensibly produced. Spur placed
either very nearly in the middle of the basal margin, or when least
medial, it stands at above its own width from the basi-scutal angle;
yet in some specimens of _var. occator_ the spur is less than its own
width from this angle. The basal margin (1 _i_), on opposite sides of
the spur, either forms a nearly straight line, or the scutal portion
descends lower than the carinal portion, and curves very regularly
towards the spur; this is the case in _var. d'Orbignii_ (1 _n_), and
in some specimens of _var. occator_. The carinal half of the basal
margin generally forms an angle with the spur of only a little above
a rectangle. The spur varies a little in length and breadth, but
never exceeds one fourth of the greatest breadth of the valve. The
scutal margin is broadly inflected, the inflected portion forming
either a right angle, or somewhat less than a right angle, with the
exterior surface of the valve. Internally the articular ridge is
prominent, and is either considerably or slightly curved; it extends
down either about half, or three fourths, of the length of the valve.
The spur is produced for a considerable distance up the internal
surface of the valve as a prominence. The crests for the tergal
depressor muscle are very feeble. In one specimen, in which both the
shell and operculum had undergone much disintegration, the scuta and
terga were calcified together.

_Compartments_: their exterior appearance has been already described.
The parietal tubes are not large; they are generally crossed by
transverse septa in their uppermost part; but they are sometimes
almost solidly filled up by dark shelly layers. The internal surface
of the parietes is more or less plainly ribbed; in old specimens,
however, it generally becomes smooth. The _radii_ have their septa
denticulated on both sides; and they are porose, that is, the
interspaces between the septa are not filled up solidly. The radii
generally extend from tip to tip of the adjoining compartments, that
is, their summits are parallel to the basis; but in three not common
varieties, viz., _vars. intermedius_, _occator_, and _d'Orbignii_
(the former of which at least must, without the smallest doubt,
be ranked as a mere variety), their summits are oblique. I have
occasionally met with specimens of _var. communis_ with oblique
radii; and this is not very infrequent in young shells. Exteriorly
the radii are generally smooth, but sometimes finely ribbed
horizontally, owing to the projection of the septa. The _alæ_ have
their sutural edges smooth; their summits are usually parallel to
the basis, but they are often much broken; in _var. zebra_, however,
in every specimen which I examined, the summits were oblique. The
sheath varies much in colour: in _var. occator_, and in a less
degree in _var. intermedius_ and _var. d'Orbignii_, the portion
lining the rostrum and lateral compartments is much darker than
the other parts of the sheath. The _Basis_ generally has a thick,
underlying, cancellated layer. Sometimes the basis (Pl. 1, fig. _b_)
is irregularly cup-formed.

_Mouth_: labrum with four or six minute teeth: mandibles with five
graduated teeth; inferior point more or less spinose. Maxillæ, either
with or without a small notch, beneath the upper pair of spines; in
the lower part there are two spines longer than those immediately
above them. _Cirri_, the first pair has the rami unequal, in the
proportion of about 19 segments in the longer ramus, to 16 in the
shorter. The segments in the latter have their anterior surfaces very
protuberant. The second pair is short, with the anterior surfaces of
the segments protuberant. On the thorax (Pl. 25, fig. 1), on each
side, at the bases of third pair of cirri, there is a projecting
membranous plate fringed with fine bristles. The three posterior
pairs have their segments shield-shaped in front, generally bearing
four pairs of spines, of which the lower pair is minute; between
these pairs there are some minute spines. In some young specimens
from the Cape of Good Hope, and in _var. concinnus_, I found six
pairs of spines on the segments of the posterior cirri.

_Geographical Distribution._--This species is extremely common over
the whole of the warmer seas. It ranges from the Island of Madeira
to the Cape of Good Hope, and on the west coast of America, from
Monterey, in lat. 37° N., in California, to Peru. It is attached to
rocks and sub-littoral shells, to floating timber, to kelp, and to
_Lepas anatifera_. It is attached in wonderful numbers to ships'
bottoms arriving at our ports, from West Africa, the West Indies,
the East Indian Archipelago, and China. It is generally associated
with _B. amphitrite_ and _amaryllis_. I have already stated that,
on the bottoms of vessels, the different varieties are generally
grouped together; and this makes me believe that they are local. In
Mr. Stutchbury's collection there are numerous specimens taken from
a ship which first went to the west coast of Africa for guano, and
then to Patagonia for the same object, and it was interesting to see
the manner in which numbers of _B. psittacus_, a Patagonian species,
had become attached on the African _B. tintinnabulum_. The varieties
from the west coast of America seem eminently peculiar; we there find
_var. coccopoma_ and _concinnus_; and a blueish, rugged variety, with
peculiar opercular valves.

_Geological History._--I have seen specimens in Mr. S. Wood's
collection from the Red Crag of England, which, though not
accompanied by opercular valves, I cannot doubt belong to this
species. The specimens named by Mr. Sowerby, in the 'Mineral
Conchology,' as _B. crassus_, and which I have seen through the
kindness of Mr. J. de C. Sowerby, also belong to this species. I
further believe that a specimen in Sir C. Lyell's collection, given
to him by M. Dujardin under the name of _B. fasciatus_ from Touraine,
is likewise _B. tintinnabulum_.

_Varieties._

With respect to _var. communis_, I have nothing to remark. The
second, _var. vesiculosus_ (Pl. 2, fig. 1 _h_), is confined to young
specimens, and may, perhaps, be due to a want of calcareous matter.
With respect to _var. validus_ (Pl. 1, figs. 1 _c_, 1 _f infra_),
I may observe that some of the coarsest and strongest specimens
which I have seen were said to have been attached to a surface of
iron. I have seen two large lots of _var. zebra_ (1 _g_), taken by
Mr. Stutchbury, from the bottoms of ships, arriving from Bengal and
China, and in both cases associated with _var. communis_, and in one
case with _var. coccopoma_. I at first thought that this variety,
_zebra_, was specifically distinct, but now I feel no doubt, that it
is a mere variety; its body was in every respect identical with that
of _var. communis_.

Nor have I any doubt that _var. crispatus_, of Schröter (Pl. 1, fig.
_h_), is only a variety, although the scuta in some specimens have a
peculiar appearance, externally like these valves in _var. occator_
(Pl. 2, fig. 1 _b_): the scutum is here broader and flatter than in
_var. communis_, and the adductor ridge is very feebly developed,
but we shall see how variable this ridge is in all the varieties:
externally, the sharp, hood-like points formed by the upturned lines
of growth, have a very remarkable appearance, from being arranged in
quite straight radiating lines. This structure is evidently caused by
the same tendency which produces on the walls the sharp, upturned,
irregular points; but it is singular that the scuta are smooth in
some specimens with very rough parietes; and, on the other hand,
bristling with the symmetrically arranged, hood-like projections, in
other specimens on which I could with difficulty detect only a few
exceedingly minute points on the walls. In _var. communis_ I have
seen a few specimens with a slight tendency in the scuta to become
striated longitudinally. The tergum in _var. crispatus_ presents no
difference from that in _var. communis_. Some of the roughest and
best characterised specimens of _var. crispatus_ appear to have come
off copper-sheathed vessels.

I believe _var. spinosus_ of Gmelin (Pl. 1, fig. _i_), has been
correctly considered by me as a variety, but I have unfortunately
seen only one set of specimens with their opercular valves preserved:
these were attached to _Lepas anatifera_. The colour of the shell
varies from reddish-purple to nearly white; the radii are sometimes
quite white; the walls are slightly ribbed. The scuta in the above
specimens, externally were smooth; the adductor ridge was rather more
distinct from the articular ridge than in any other variety; and the
terga rather more plainly beaked. The tubular, up-curved, calcareous
spines sometimes occur only on one side of the shell, and often only
in the lower part. These spines are often coloured brighter than
the walls. Their presence cannot be accounted for (any more than
the state of the scuta in the foregoing _var. crispatus_) by the
nature of the surface to which they are attached; for I have seen one
set attached to a large rugged specimen of _B. tintinnabulum_, and
another to the very smooth valves of _Lepas anatifera_. I believe
that this form is almost always associated with _var. communis_,
which is an argument that it is only a variety.

To _var. coccopoma_ (Pl. 1, fig. _d_) I alluded in my introductory
remarks as having so strongly the aspect of a distinct species. I
possess a beautiful group, with a globulo-conical, smooth shell, of
the finest rose colour, with a rather small, rounded orifice. These
specimens were attached (mingled with _B. trigonus_) to _Avicula
margaritifera_, from, as Mr. Cuming believes, Panama. I can never
look at this set of specimens without doubting the correctness of the
determination at which I have arrived. In the British Museum there
are two sets of specimens taken off a vessel, on the west coast of
South America, almost identical in external appearance with those in
my possession, but rather more rugged. Mr. Stutchbury has sent me
some specimens from a ship, direct from China, which are rather paler
pink, and more striped, and come near to some ordinary varieties of
_B. tintinnabulum_. The scuta (Pl. 2, fig. 1 _f_) in the above three
sets of specimens agree in having the adductor ridge more developed,
and the pit for the lateral depressor muscle deeper than is usual.
The tergum (1 _l_, 1 _o_) in most, but not in all these specimens,
has a rather broader spur; and some of the specimens have the
carinal portion of the basal margin considerably hollowed out; the
spur, also, is placed nearer the basi-scutal angle than in ordinary
cases. On the other hand, in Mr. Cuming's collection, there are two
specimens taken off a vessel, identical in external appearance with
the foregoing, but which have scuta and terga in every character
exactly as in _var. communis_; hence I am compelled to consider all
these specimens as mere varieties.

_Var. concinnus_ (Pl. 1, fig. _e_) is, perhaps, the most remarkable
of all the varieties; I have seen three sets of specimens from the
west coast of South America,--all identical in appearance, having
longitudinally-ribbed walls, either rosy or of a dull purple, striped
and freckled in a peculiar manner with white. I have, however,
seen an approach to this colouring in some few specimens of _var.
communis_; and the shell itself offers no other peculiarities. The
scutum (Pl. 2, fig. 1 _g_) resembles, in general shape, that of _var.
coccopoma_; but the adductor ridge is here much sharper and more
prominent; and the rostral depressor muscle, instead of being lodged
in a little cavity formed by the folding over the occludent margin,
has, in addition, a small plate on the under side, which tends to
convert the pit into a tube. The tergum exactly resembles that of
_var. communis_. The segments in the sixth cirrus bear six, instead
of four, pairs of spines,--a circumstance which I have noticed
only in some young specimens of _var. communis_, from the Cape of
Good Hope. From these several peculiarities, until quite lately, I
resolved to keep this form specifically distinct; but I have finally
concluded that they are not sufficient. For firstly, I have seen a
scutum in _var. communis_ (Pl. 2, fig. 1 _d_), with the adductor
ridge nearly as sharp; and this ridge is always strongly pronounced
in _var. coccopoma_; secondly, with respect to the plate for the
rostral depressor muscle, although I have not seen this in any other
variety, yet in _Bal. concavus_ a closely analogous plate, situated
in the lateral depressor cavity, is highly variable, and I am not
willing to found a new species on one minute point of structure,--a
structure which is variable in another species of the same genus.

I have seen some cylindrical and conical specimens of _B.
tintinnabulum_, from the coast of Mexico and California, only
noticeable, as far as the shell was concerned, from being rugged,
and of a dull blueish-purple; but which had opercular valves
exactly like those of _var. coccopoma_, and therefore, as far as
the scutum is concerned, approaching closely in structure to _var.
concinnus_,--all three from the west coast of America. Hence I was
at one time led to believe that there existed a species on this line
of coast, which represented _B. tintinnabulum_, and which varied in
external shape and colour in an analogous manner to that species. But
as the opercular valves in _var. coccopoma_ are sometimes identical
with those of _var. communis_, and as this is always the case with
the tergum of _var. concinnus_, and as the shell itself presents
no differences, it is scarcely possible to admit the existence on
the west coast of America of this supposed representative of _B.
tintinnabulum_.

With respect to _var. intermedius_ I have little to say in addition
to the character given above: I have seen only two groups of
specimens in Mr. Cuming's collection: the chief interest in this
variety is that it shows that the next form must be ranked as a
variety, and not as a distinct species.

Of _var. occator_ (Pl. 1, fig. _k_) I have seen several specimens,
mostly taken off the bottoms of vessels, and one specimen, marked
in Mr. Cuming's collection "South Seas." After having carefully
examined these specimens, I came to the conclusion, that the slightly
oblique radii--the general colouring, and more especially that of the
sheath--the scuta (Pl. 2, fig. 1 _b_), with their sharp hood-like
points, in radiating lines--and the terga, with the spur so near to
the basi-scutal angle, were amply sufficient to distinguish it as
a good species. Subsequently, however, I found that the scuta in
_var. crispatus_ presented, both externally and internally, exactly
the same peculiar appearance. In _var. intermedius_, I found the
summits of the radii equally oblique, and the general colouring
nearly the same, and more especially a close approach to the singular
circumstance of the sheath differing in colour towards the opposite
ends of the shell. So that the position of the spur of the tergum was
the chief remaining character; and this evidently varied considerably
in the four or five specimens examined by me, being either its own
width, or much less than its own width, from the basi-scutal angle:
the outline, also, of the small portion of basal margin, between the
spur and the basi-scutal angle, likewise varied much, being either
angularly indented, or gradually curved down towards the spur: so
also the tip of the spur varied in shape. The longitudinal furrow
is unusually apt, in this variety, to remain open. We know that the
position of the spur varies considerably in _var. communis_. Hence,
although the spur, on an average, lies closer to the basi-scutal
angle in this than in any other variety, even than in _var.
d'Orbignii_, it would, I conceive, be preposterous to found a species
on this one character. In the animal's body, every part agrees
perfectly with that of _var. communis_.

Lastly, we come to _var. d'Orbignii_ (Pl. 1, fig. _l_): until quite
recently I did not even suspect that this form was only a variety
of _B. tintinnabulum_: I have examined a great number of specimens
in Mr. Stutchbury's collection, which had come attached on a vessel
from Java, and likewise a few other specimens in other collections.
They all closely resemble each other in shape, and even in size,
and differ only in tint of colour, and in the surface being either
very smooth, or longitudinally ribbed, sometimes with rugged, sharp
points. From this circumstance--from the peculiarity of the tint,
with the tips of the parietes and one side of the radii perfectly
white--and from the obliquity of the summits of the radii, I was led
to think this form specifically distinct. But the colour does not
differ from that of some other varieties of _B. tintinnabulum_; the
circumstance of the colour being uniform or not striped, is common
to the sub-varieties of several varieties, and the white tips to
the parietes, and the white borders to the radii, result simply
from the shell, whilst young, having been wholly white, and this is
not rarely the case with _var. communis_. Dismissing, therefore,
colour, it will be found that hardly any other characters remain by
which this form can be separated from _var. occator_; in both the
summits of the radii are oblique, in both the sheath is coloured in
nearly the same manner, in both the opercular valves, especially the
terga (Pl. 2, figs. 1 _m_, 1 _n_), resemble each other; the scuta,
however, are smooth in _var. d'Orbignii_ and rough in _var. occator_.
This latter form, certainly, cannot be specifically separated from
_var. intermedius_, and this assuredly is only a variety of _B.
tintinnabulum_. Hence I am led to conclude that _Balanus d'Orbignii_
of Chenu, peculiar as its whole aspect is, must be ranked only as a
variety of _B. tintinnabulum_; its oblique radii resulting from the
same cause, whatever that may be, which has given this structure
to _var. intermedius_ and _occator_; and its peculiar colouring to
having been exposed (owing probably to having been transported on
vessels) to different conditions, whilst young and old.

2. BALANUS TULIPIFORMIS. Pl. 2, fig. 2 _a_-2 _d_.

BALANUS TULIPIFORMIS EX CORALLIO RUBRO. _Ellis._[88] Philosoph.
Transactions, vol. 50 (1758), tab. 30, fig. 10.

LEPAS TULIPA. _Poli._ Test. utriusque Siciliæ, tab. 5, fig. 1. et 6
(1791).

BALANUS TINTINNABULUM (_var._) _Chenu._ Illust. Conch., tab. 3, f. 5.

[88] According to the letter of the Rules of the British
Association, Ellis's name ought to be retained, as it was published
in 1758, the same year during which the 10th edition of the
'Systema Naturæ' appeared, in which edition the binomial method
was first used. But as Ellis himself did not then know of, or
follow this method, it might be disputed whether, according to the
_spirit_ of the law, his name ought to stand. The only other name
given to this species is that of _tulipa_, affixed by Poli in 1791,
but this name had been previously used by Müller in 1776, and by
Chemnitz in 1785, for another species, the _B. Hameri_ of this
work; and likewise, also previously to Poli, by Bruguière in 1789,
for still another species, viz., _B. tintinnabulum_ of this work:
under these complicated causes of confusion, I think it is highly
advisable to adopt Ellis's name. I may add that the _B. tulipa_ of
Mr. G. B. Sowerby is the _B. tintinnabulum_ of this work. It is
possible that the _B. conoides_ of Brown, 'Illustrations Conch.'
(1st edit. pl. 6, fig. 7), may be our present species; but without
details of structure it is hardly possible to identify, in many
cases, the species of Balanus.

_Shell dark rose-coloured, sometimes tinged with purple; orifice toothed. Scutum externally very smooth, covered by membrane. Tergum with distinct crests for the depressor muscles._

_Hab._--Sicily, Malta, Malaga, (associated with _B. perforatus_),
Madeira. Often growing in clusters and associated with _Pachylasma
giganteum_. Attached to _Millepora aspera_, oysters, and other
shells. According to Poli, an inhabitant of deep water; yet in mus.
Cuming there are two fine specimens attached to the always floating
_Lepas anatifera._ Mus. Lowe, Macandrew, Stutchbury.

_General Appearance._--Shell tubulo-conical or conical: orifice
large, toothed, approaching to pentagonal. Surface moderately smooth,
naked. Colour rosy, or tile-red, with a slight tinge of purple; or
beautiful rich purple. Radii nearly as dark as, or darker than, the
parietes. The portion of the alæ seen externally is generally white.
Internally the whole shell is nearly white. Generally the tints
outside vary in transverse fasciæ; sometimes there are very fine,
dark, longitudinal lines. Largest specimen (from Malta), 1.4 of an
inch in basal diameter; usually full-sized specimens are about three
quarters of an inch in basal diameter.

_Scuta_ (Pl. 2, fig. 2 _a_, 2 _c_) very smooth, with the
growth-ridges very little prominent, sometimes there are obscure
traces of longitudinal striæ; surface covered by an unusually thick
and persistent yellow membrane: valve narrow, with the upper part
commonly reflexed: the basal margin forms, with the occludent margin,
a smaller angle than is usual: the tergal margin of the valve is
rectangularly inflected, instead of being, as is usual, merely
bowed inwards. Internally, the articular ridge is rather prominent.
The depth of the _slight_ pit for the lateral depressor muscle is
variable; it sometimes includes a minute, central, longitudinal ridge.