LEPAS POROSA. _Gmelin._ Syst. Naturæ, 1789.[107]_A Monograph on the Sub-class Cirripedia (Volume 2 of 2) The Balanidæ, (or Sessile Cirripedes); the Verrucidæ, etc., etc.

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._

+------------------+--------------+--------------+--------------+-------+

| |--------------+--------------+--------------+-------|

|------------------+-------+------+-------+------+-------+------+-------|

|Pernambuco, Brazil| 9 | 19 | 10 | 11 | 15 | 27 | 26 |

|(_var._ 1) | | | | | | | |

|------------------+-------+------+-------+------+-------+------+-------|

|from the same | 12 | 23 | 12 | 14 | 14 | 19 | 23 |

|(_var._ 1) | | | | | | | |

|------------------+-------+------+-------+------+-------+------+-------|

|Archipelago, | 10 | 16 | 10 | 11? | 11 | 16 | 25 |

|(_var._ 1) | | | | | | | |

|------------------+-------+------+-------+------+-------+------+-------|

|Philippine | 10 | ? | 10 | 10 | 11 | 19 | 18 |

|(_var._ 4) | | | | | | | |

|------------------+-------+------+-------+------+-------+------+-------|

|From California | 15 | 24 | - | - | - | - | 22 |

|(_var._ 5) | | | | | | | |

|------------------+-------+------+-------+------+-------+------+-------|

|of a ship | - | - | 9 | 9 | 10 | 17 | 14 |

|(_var._ 7), | | | | | | | |

|------------------+-------+------+-------+------+-------+------+-------|

|(_var._ 1) | 11 | 18 | 11 | 12 | 13 | 21 | 22 |

|------------------+-------+------+-------+------+-------+------+-------|

|from the | 16 | 25 | 13 | 18 | 15 | 23 | 27 |

|------------------+-------+------+-------+------+-------+------+-------|

|but the cirri | 15 | 28 | 15 | 21 | 16 | 23 | - |

+------------------+-------+------+-------+------+-------+------+-------+

_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.

A Monograph on the Sub-class Cirripedia (Volume 2 of 2) The Balanidæ, (or Sessile Cirripedes); the Verrucidæ, etc., etc. · 第 107 / 417 题