Part 21

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_.