Chapter XVI: Introduction (12)

_Tergum_ (2 _k_-2 _o_); this valve is here far more variable than in
any other species: in the commonest purple-striped forms (2 _l_), the
valve is rather broad, the basal margin lies in nearly a straight
line on the opposite sides of the spur, which is placed at rather
less than its own width from the basi-scutal angle; the spur is
rather short, and in width about one fourth of the entire valve; its
lower end is either bluntly pointed or more commonly nearly square
(2 _k_) and parallel to the basal margin: in young specimens it is
generally sharper than in older ones. Externally, in the line of
the spur, there is either a slight longitudinal depression, or more
rarely a deep furrow. The carinal margin is more or less convex, and
is formed by upturned lines of growth: the scutal margin is broadly
inflected. Internally, the articular ridge in the upper part is very
prominent: the crests for the tergal depressor muscle are moderately
prominent, but very variable. Sometimes the carinal portion of the
basal margin is slightly hollowed out. In _var. Stutsburi_ (2 _m_, 2
_n_, 2 _o_), and in some white varieties, which differ most in the
shape of the tergum from the commoner varieties, the whole valve is
narrower, the spur is much sharper and narrower, the carinal half of
the basal margin is much hollowed out and slopes down towards the
spur, with the crests for the depressor muscles depending beneath the
basal margin, and with the carinal margin sometimes extremely convex
or protuberant. But the shape and position of the spur, and the
outline of the carinal half of the basal margin vary much in nearly
all the varieties.

_Compartments._--The upper parts of the parietal pores are either
filled up solidly with, generally coloured, shell, or they are
crossed by thin transverse calcerous septa: the longitudinal parietal
septa occasionally bifurcate at their bases close to the outer
lamina, making an irregular outer row of minute pores. The _Radii_
have their septa rather fine, and finely denticulated on both sides,
but sometimes only on the lower side; the thickness of the septa
varies a little; the interspaces are filled up solidly; the summits
of the radii are jagged and oblique, and usually form an angle of
about 45° with the basis, not being added to above the level of the
opercular membrane; but not rarely they reach up much higher, and
are very nearly parallel to the basis, extending from tip to tip of
the compartments. Again, in some ordinary varieties, and always in
_var. Stutsburi_, the summits of the radii are extremely oblique, the
radii themselves forming a mere border to the compartments to which
they belong. In no other species have I seen so great an amount of
variation in the form of the summits of the radii. The _alæ_, in like
manner, have their summits either very oblique, not being added to
above the opercular membrane, or they are only slightly oblique; it
often happens that in those specimens in which the summits of the
radii are nearly parallel to the basis, the alæ are very oblique, and
the converse: in other individuals, both radii and alæ have equally
oblique summits. The sutural edges of the alæ vary in thickness,
being either very thin and obscurely crenated, or moderately
thick and ribbed. The _basis_ is porose; but I have never seen an
underlying cancellated layer of shell, as is so common in several
species.

_Mouth_: labrum, with from four to eight, generally with six, little
teeth: mandibles with three teeth, and two minute lower teeth, or
mere knobs: maxillæ with the edge straight, or with the inferior
part forming a slightly step-formed projection. _Cirri_: the rami
of the first pair are unequal by three or four segments, but in
some specimens by five or six segments, with the front surfaces of
the segments in the shorter ramus extremely protuberant. The second
pair of cirri are short, with the front surfaces of the segments
moderately protuberant: the third pair have a tuft of bristles at
their bases on the thorax. The segments in the sixth pair have from
four to six pairs of spines on the segments; equal-sized specimens
seem to vary in this latter respect. There is a small sharp
projection on the dorsal base of the penis.

_Varieties._

With respect to _var._ 1, _communis_, I have nothing further to
remark, except that I have seen specimens identically similar from
the Mediterranean, Natal, the Philippine Archipelago, and Sydney;
at the latter place it is said to be rare, but in most places it is
the commonest variety, and is often attached to ships' bottoms. Of
_var._ 2, _venustus_, I have seen specimens from the west coast of
Africa, Natal, and Ceylon, in groups by themselves, and associated
with _var. communis_; it is much less common than _var._ 1. The third
variety, _pallidus_, is not uncommon; I have seen many specimens
from the bottoms of ships, from the West Indies, and the west coast
of Africa. Of the _var._ 4, _niveus_, I have seen the most perfect
graduated series passing into _var._ 1, both from the West Indies,
Florida, and the Mediterranean: I have seen other specimens from the
Red Sea and Madagascar. Of the _var._ 5, _modestus_, I have seen
only one group from an unknown locality; it is only remarkable from
its uniform colouring. The _var._ 6, _Stutsburi_, is more remarkable
than the foregoing; until quite lately I did not doubt that it was
specifically distinct; but as I have seen every character graduate
into other varieties, I am now convinced that it is not a true
species: all the specimens which I have seen have come on shells,
or on ships' bottoms, from West Africa. Of _var._ 7, _obscurus_, I
have seen three or four groups of specimens from unknown quarters,
both on pebbles, shells, and on cork (probably from the Atlantic
ocean); and likewise some specimens taken from the bottom of Her
Majesty's ship "Fly," on the east coast of Australia; these latter
are intermediate in character with the next _var. variegatus_;
from the Australian seas, which I at first ranked as an undoubted
species, but I have subsequently failed in discovering any sufficient
diagnostic character. Lastly, of _var. cirratus_, I have seen several
groups of specimens from India and the Philippine Archipelago, and
a group intermediate in character between this and the first and
third varieties, from Australia; I retained this variety owing to
its peculiar freckled, pale brown colouring and beaded scuta (of
which, however, I have seen decided traces in the common variety),
as a distinct species, after I had given up all the foregoing forms.
I entertain some doubts whether I have now acted right; but when I
found some specimens which, I found it impossible to decide, whether
to rank as _amphitrite_ or _cirratus_, I determined to take the more
prudent course, and sink the latter as a species. This variety, also,
seems to connect _B. amphitrite_ and _concavus_ very closely.

20. BALANUS PŒCILUS. Pl. 5, fig. 3 _a_, 3 _b_.

_Shell dull red, freckled with white. Scutum internally without an adductor ridge; tergum with the spur, sharply truncated, almost one third of width of valve._

_Hab._--West coast of South America, Mus. Cuming; attached to an
Avicula.

The appearance of the fragile shell, in the one group of specimens which I have seen, leads me to suspect that they may have grown under unfavorable circumstances. This species differs considerably in general aspect, but not much in essential characters, from _B. amphitrite_; the absence, however, of an adductor ridge to the scutum, and the sharply truncated spur of the tergum, are sufficient to distinguish them. In the opercular valves this species comes near to _B. vinaceus_, also from the west coast of South America; but the striated scuta of that species, the cancellated inner lamina of the parietes, the general colouring, and square porose radii, are amply diagnostic characters.

_General Appearance._--Shell fragile, tubulo-conical, orifice large,
passing from diamond-shaped into oval. Colour fine dark rose,
freckled with transverse, sharply pointed, fine zig-zag white lines:
the pink is also so arranged as to obscurely give to the walls a
longitudinally striped appearance: radii generally rather whiter than
the walls, and similarly freckled: terga similarly freckled: scuta
dull red, with a white band along the scutal margin. Basal diameter
of largest specimen half an inch.

_Scutum_, externally smooth: internally, articular ridge moderately
developed, slightly reflexed: there is no adductor ridge: there is
a distinct pit for the lateral depressor muscle. _Tergum_, with the
scutal margin unusually prominent, toothed: longitudinal furrow
shallow, the edges apparently having no tendency to fold in: spur
short, barely one third of width of valve, with the lower end sharply
truncated, parallel to the basal margin: articular ridge and crests
for the depressores moderately prominent.

_Compartments._--Walls very fragile, with the outer lamina not
thicker than the inner lamina. _Radii_ fragile, broad, with their
summits moderately oblique; their sutural edges have the septa
plainly denticulated on both sides, with the interspaces filled up
solidly nearly to the tips of the septa. _Alæ_, with their summits
more oblique than those of the radii; their sutural edges smooth.
_Basis_ with an underlying cancellated layer. _Mouth_: labrum with
three unusually large teeth on each side of the notch: mandibles with
the fourth tooth tolerably well developed, the fifth being confluent
with the inferior angle. _Maxillæ_ simple. _Cirri_,--first pair with
one ramus longer by about four segments than the other ramus, which
has considerably protuberant segments: second pair with segments only
moderately protuberant: sixth pair with segments much elongated, but
bearing only four pairs of spines.

21. BALANUS EBURNEUS. Pl. 5, fig. 4 _a_-4 _d_.

BALANUS EBURNEUS. _Aug. Gould_ (!). Report on the Invertebrata of
Massachussetts, 1841, fig. 6.

_Shell yellowish white. Scutum striated longitudinally: tergum with the spur truncated, the basi-carinal margin generally much hollowed out, and the carinal margin protuberant in the upper part._

_Hab._--United States, from about lat. 42° to Charlestown; West
Indies; Honduras; Venezuela; attached to shells and floating wood.
Attached to ships' bottoms from Trinidad and Jamaica, associated with
_B. tintinnabulum_, _amphitrite_, and _improvisus_. Brackish water,
Salem, Massachussetts, according to Mr. Stimpson. Mus. Aug. Gould,
Agassiz, Stutchbury, Cuming, W. Dunker, &c.; very common.

_General Appearance._--Shell conical, or almost tubular; white, with
the surface very smooth, covered by thin yellowish epidermis, but
with the radii naked. Orifice large, passing from rhomboidal into
pentagonal, moderately toothed. Average full size, about one inch in
basal diameter; I have seen a specimen 1.3 in basal diameter, and the
same in height.

_Scutum_, plainly striated longitudinally: the teeth on the occludent
margin small. Internally, the upper surface is roughened: the
articular ridge is prominent, and either slightly or not at all
reflexed: the pit for the adductor muscle is distinct; the adductor
ridge is prominent in a variable degree, and is almost confluent
with the articular ridge. In one specimen from Beverly Bay, U. S.,
the scuta were extraordinarily disintegrated, and I could perceive
no trace of the external radiating striæ. _Tergum_, with the basal
margin on the carinal side of the spur sometimes deeply (Pl. 5, fig.
4 _b_), and sometimes only slightly (fig. 4 _d_), and rarely hardly
at all, hollowed out: when much hollowed out the valve may almost
be said to be two-pronged, with the carinal prong narrower than
the spur. There is no distinct longitudinal furrow, but the whole
scutal margin projects above the general surface of the valve. In the
carinal margin, in the upper part, there is a remarkable convexity
or protuberance in the same plane with the valve, from which it
is separated by a very slight and narrow ridge. The spur is about
one fourth of the width of the valve, with its lower end abruptly
truncated. Internally, the upper surface is much roughened with
finely crenated ridges: the distinct crests for the depressores cover
the whole of the so-called carinal prong.

_Compartments_; the radii and alæ have their summits oblique,
sometimes a little rounded, but not smooth. The septa on the sutural
edges of the radii are remarkably fine, and closely approximate; the
denticuli are excessively minute. The sutural edges of the alæ are
most delicately crenated; the alæ are largely added to during the
diametric growth of the shell, and above the level of the opercular
membrane. The parietal pores are square and rather large: they are
crossed by transverse septa almost close down to the basis: the
longitudinal septa have tolerably large denticuli at their bases.
The pores in the basis are crossed by numerous transverse septa.
When specimens grow in a group, the basis is sometimes irregularly
cup-formed.

_Mouth_: _labrum_ serrated with small teeth, decreasing in size
downwards, on each side of the central notch. _Mandibles_ with the
third tooth rather thick and blunt, and with the fourth and fifth
knob-like. _Maxillæ_, with the inferior part projecting much beyond
the rest of the edge, and bearing two long single spines: between
these two spines and the large upper pair, there are, in a full-sized
specimen, about seven pairs of moderately long spines, feathered on
their sides. _Outer maxillæ_ thickly clothed with very fine spines,
and remarkably prominent.

_Cirri_: first cirrus, with one ramus having twenty-six segments,
and longer by ten segments than the shorter ramus, which has sixteen
segments: the shorter ramus, and both ramii of the second pair, have
their segments remarkably protuberant in front; the protuberance,
in the upper segments, equalling in length the supporting part of
each segment: rami of the second cirrus unequal in length by five
segments. Third cirrus with the segments only slightly protuberant;
rami considerably longer than those of the second cirrus: at the
dorsal base of the pedicel of this third cirrus there is no tuft of
fine hairs, as is common in many other species. _Sixth pair_, with
the upper segments elongated, bearing from six to seven pairs of
spines; dorsal spines short, thin, and few.

_Affinities_: in external appearance of the shell, this species can
hardly be distinguished from some of the white varieties of _B.
amphitrite_; and there is a considerable resemblance, in some of the
varieties, in the opercular valves; but the longitudinally striated
scuta of _B. eburneus_ suffice to distinguish these certainly very
distinct species. Equally, or even more like _externally_, is this
species to the _B. Hameri_, so that I have received from an eminent
naturalist in the United States both species mingled in the same lot,
all bearing the same name of _B. eburneus_; but when the internal
structure of the shell is examined, the species are at once seen to
be far removed from each other. Still more close is the affinity
of this species to _B. improvisus_, both in internal and external
characters: it agrees with this species in the singular habit of
being able to live in brackish water: these two species are the only
ones which have the labrum serrated with teeth, graduated in size, on
each side of the central notch. In the case of _young_ specimens of
the _var. assimilis_ of _B. improvisus_, an inhabitant of the same
seas with _B. eburneus_, the diagnosis is most difficult without long
practice; for in the young of _eburneus_, the compartments are only
partially covered by yellow epidermis, and have a striped appearance,
the radii are sometimes very oblique, the scuta externally have not
acquired their longitudinal striæ, and internally the adductor ridge
lies not so close to the articular ridge as it does subsequently;
hence I for some time mistook the _var. assimilis_ of _B. improvisus_
for the young of _B. eburneus_. But I found in the latter, that the
rami of the first pair of cirri, are always, even in the earliest
youth, more unequal in length, and that each segment of the posterior
cirri bears a greater number of pairs of spines, there being, even in
very minute specimens, seven pairs. Moreover, after having examined
scores of specimens, I found I could almost always distinguish the
two species by the smoothness and curvature of the summits of the
radii of _B. improvisus_; I entertain no doubt whatever about the
distinctness of the two species; indeed, when both are mature,
besides the greater size, striated scuta, &c. of _B. eburneus_, their
general aspect is very different.

22. BALANUS IMPROVISUS. Pl. 6, fig. 1 _a_-1 _c_.

_Shell white: radii narrow, with their upper margins smooth, slightly arched, very oblique. Tergum with a longitudinal furrow; spur with the end rounded._

_Var._ assimilis, _with longitudinal white hyaline lines_.

_Hab._--England, Scotland, Belgium (?), Nova Scotia, United States,
West Indies, Rio Plata, Southern Patagonia, Guayaquil, West Colombia;
attached to wood, shells, rocks, ships' bottoms, from low tidal level
to twenty fathoms depth.

_General Appearance._--Shell conical, with a rather large
diamond-shaped orifice, moderately or but little toothed; very
smooth; walls never folded longitudinally; white, with an extremely
thin pale-yellow persistent epidermis. The radii are very narrow,
with their summits very oblique, rounded, and smooth; the epidermis
is generally more persistent on the radii than on other parts, and
this is exactly the reverse of what is common with _B. eburneus_. The
specimens from nearly fresh-water in the R. Plata (hereafter to be
mentioned), are brownish, and have undergone a remarkable degree of
corrosion, the outer lamina of the walls having been entirely removed
to near the base; hence the external aspect of these specimens is
wholly different from ordinary individuals. The _var. assimilis_
has also a very different appearance, owing to the dead white of
the walls being relieved by narrow approximate longitudinal hyaline
lines, corresponding with and caused by the longitudinal parietal
septa being externally visible through the outer lamina of the
parietes; the epidermis on the radii is also of a rather brighter
yellow. The largest specimens which I have seen are those from the
Plata, and those attached to a ship from the West Indies, and they
had a basal diameter of .6 of an inch: from .4 to .5 of an inch is
the more usual full average size.

_Scuta_, with the lines of growth but little prominent: articular
ridge prominent, but little reflexed: adductor ridge straight and
very prominent, varying a little in its distance from the articular
ridge; there is scarcely any depression for the lateral depressor
muscle; the upper internal surface of the valve is roughened with
ridges. _Terga_, with a moderately deep longitudinal furrow; spur
short, rather narrow, with the end rounded, placed at less than its
own width from the basi-scutal angle; in the Rio Plata specimens the
spur is close to this angle: the basal margin is generally straight
on opposite sides of the spur, but sometimes on the carinal side it
is a little hollowed out. The lines of growth are upturned along the
carinal margin, which consequently is a little protuberant, but to a
varying degree. The crests for the depressores are extremely distinct
and prominent. In the varieties having the basi-carinal margin
hollowed out, and the carinal margin protuberant, there is a marked
resemblance to the peculiar tergum of _B. eburneus_.

_Walls_: the parietal pores are tolerably large, and are crossed by
numerous transverse septa: the longitudinal septa are very finely
denticulated at their bases, but occasionally almost smooth. The
_radii_ are, as stated, extremely narrow, and very remarkable from
their smooth rounded edges; their septa are barely denticulated.
The _alæ_ are remarkably protuberant; they have their summits much
less oblique than those of the radii, and sometimes they are almost
parallel to the basis: their sutural edges are coarsely crenated.
_Basis_, flat, thin, permeated by pores, but the pores do not
generally run to the very centre; they are, as usual, crossed by
transverse septa.

_Mouth_: the _labrum_ is the most remarkable part; on each side of
the central notch there are generally two teeth; and on the two
sides of the notch itself nine or eleven smaller teeth, decreasing
regularly in size downwards till they become so minute as to be
hardly visible even under the compound microscope; thus, in the two
specimens closely examined, there were altogether twenty-two and
twenty-six teeth on the labrum. _Mandibles_ with the two inferior
teeth reduced to mere knobs: _maxillæ_ with the lower part of the
edge bearing two large spines, and generally, but not always,
forming a step-formed projection. _Cirri_: the ramii of the first
pair are but slightly unequal; in one specimen examined there were
fifteen segments in one ramus and twelve in the other: segments very
protuberant in front. Second cirrus with the segments only slightly
protuberant; segments thirteen. Third cirrus longer than the second
pair, with the rami rather unequal in length: there is a tuft of long
spines on the basal segment of the pedicel of this cirrus. Fourth
cirrus twenty-two segments. Sixth cirrus, in the same individual,
thirty-four segments: on each of these segments there are five or six
pairs of spines. I may specify that the longer ramus of the first
cirrus of a large Rio Plata specimen had twenty-four segments.

_Varieties, affinities._--When I first met with the _var. assimilis_,
misguided by its general aspect, I did not doubt that it was
specifically distinct; I was strengthened in this view by the
absolute identity of several hundred specimens attached to two
vessels from Jamaica and Trinidad, in the West Indies, with one
specimen from Charlestown, in the United States, sent me by Prof.
Agassiz, and with several in three lots from the western tropical
shores of South America: yet on close examination I can point out
no one distinguishing character, either in the shell or animal's
body, excepting the longitudinal hyaline lines on parietes, due to
the septa being externally visible. The presence of similar lines is
variable in white _vars._ of _B. amaryllis_ and _amphitrite_, and
they are seen in very young specimens of _B. eburneus_: hence it is
impossible to consider so trifling a character as specific; moreover,
lately I have seen a British specimen with hyaline lines, and some
few other specimens in an intermediate condition. Under the head
of _B. eburneus_, I have stated that although that species and _B.
improvisus_, which in the West Indies are associated together, are
most readily discriminated when old, yet when young, they so closely
resemble each other that the eye requires much practice to separate
them. On account of this species and _B. crenatus_ being sometimes
associated together on the shores of England, I have pointed out
under _B. crenatus_, the relative diagnostic characters of the two.
The chief affinity of _B. improvisus_ is certainly towards _B.
eburneus_; but in the narrow, oblique, rounded, and smooth-edged
radii, there is a relationship shown to the species in the last
section of the genus, such as _B. amaryllis_, and more especially to
the fossil _B. dolosus_: so close is the resemblance in the external
appearance of the shell, and in the structure of the opercular
valves, to the latter species, that I for some time did not discover
their distinctness. _Balanus improvisus_ has hitherto been overlooked
by naturalists, and has probably been confounded with _B. crenatus_
or _balanoides_.

_Range and habits._--This species, as far as my experience goes,
is commoner on the shores of Kent than on other parts of England:
the first specimens which I met with, I owed to the kindness of Mr.
Metcalf, they were attached to wooden stakes from Herne Bay, together
with a single specimen of _B. crenatus_: I have seen other specimens
from near Woolwich, from the Kentish oyster-beds, from Sandwich, and
from Ramsgate. The only other British specimens which I have seen
are from the River Itchen, in Hampshire, and from Loch Shieldaig,
in Ross-shire (Mus. Jeffreys), from a depth of twenty fathoms. This
species is often attached to wood. At Ramsgate, the specimens were
attached to a small coasting vessel, and they must have been immersed
five or six feet; they were associated with _B. crenatus_, and with
a few of _B. balanoides_. In the Brit. Mus. there are specimens
collected by Mr. Redman, from Nova Scotia, in North America. When
her Majesty's ship Beagle was beached at Santa Cruz, in Southern
Patagonia, numerous specimens were found adhering to her copper
bottom, some so small as to show that the species breeds in those
latitudes. Near Monte Video, in the estuary of La Plata, I found
many large, but much corroded specimens, adhering to some rocks in a
small _running_ stream of perfectly fresh water. The rise of the tide
is here small, but at high water the specimens apparently were for
a short time covered by the waters of the estuary, here itself only
brackish, and occasionally almost fresh. I took home some specimens,
and placing them in perfectly fresh water they continued for many
hours expanding and retracting their cirri with perfect regularity
and vigour. Here then we have a Balanus capable of living in fresh
water, and likewise in the saltest seas: even brackish water is a
deadly poison to several, probably to most, species of the genus; but
this, as we have seen, is not the case with the allied _B. eburneus_.
The water, I may add, at Woolwich, on the Thames, whence I have
received _B. improvisus_, must at times be very brackish. I have
already incidentally mentioned that the _var. assimilis_ was attached
in great numbers, associated with _B. eburneus_, _tintinnabulum_, and
_amphitrite_, on vessels from the West Indies: one specimen sent me
by Prof. Agassiz, from Charlestown, was attached to a specimen of _B.
eburneus_; and, lastly, I have seen three sets of the same identical
variety attached to shells from Guayaquil (in Mus. Brit. and Cuming),
and from West Colombia. Here, then, we have the same species with
an enormous range, from Nova Scotia and Great Britain to South
Patagonia; and, which is the case with scarcely a single mollusc, it
lives both on the eastern and western tropical shores of the South
American continent.

23. BALANUS NUBILUS. Pl. 6, fig. 2 _a_-2 _c_.

_Shell white, rugged: basis in parts imperfectly porose. Scutum with the articular ridge minute; adductor ridge prominent, forming a deep pit for the lateral depressor muscle: tergum with an internal patch of purple; apex produced, purple._

_Hab._--California, Mus. Brit. and Aug. Gould; associated with _B.
glandula_, and attached to wood.

I have seen two specimens of this species, brought by Lady K. Douglas from California; and two from Monterey, sent me by Dr. Aug. Gould. This is a very distinct species, coming nearer to _B. porcatus_ than to any other species: it is also allied to _B. cariosus_. In the basis being in parts solid or not permeated by pores, it has claims to be placed in the next section, in which I at one time included it.

_General Appearance._--Shell conical, rugged, sometimes furnished
with sharp longitudinal ribs; dirty white. Orifice not large, oval,
toothed. Radii rather narrow, with their summits oblique, much
jagged. Basal diameter of largest specimen 2.1; height only 1.3 of an
inch.

_Scuta_, broad, with the lines of growth prominent; internally,
articular ridge very little prominent, sometimes hardly developed,
but thick, ending downwards in a small free point. Adductor ridge
prominent, blunt, produced straight downwards, making a deep
longitudinal cavity for the lateral depressor muscle; in some
specimens this cavity is almost arched over, so as to tend to be
tubular, with a short ridge in the middle (Pl. 6, fig. 2 _a_): in
other specimens there is no trace of this tubular structure. _Terga_,
with the apex beaked, beak triangular, dull purple; the longitudinal
furrow is so shallow as hardly to exist. The basal margin slopes
down on both sides, with a nearly equable curvature towards the
spur; hence the spur is broad in its upper part, and narrow at its
obliquely truncated lower end. Internally, there is an elongated dark
purple patch: the shallow articular furrow is of quite remarkable
breadth; the articular ridge is medial, and the inflected scutal
margin is not wide. The internal surface of the spur is formed into
a ridge, which runs a little way up the valve, and is sometimes
partially separated from the spur itself (fig. 2 _c_), making the
basal extremity toothed or double. The crests for the depressores are
pretty well developed.

_Walls_, moderately strong: inner lamina slightly ribbed: the
denticuli on the bases of the parietal longitudinal septa are sharp:
I could not see any transverse septa in the parietal tubes. The
_radii_ are rather narrow; their summits are remarkably jagged and
very oblique; the septa are plainly denticulated on both sides, but
chiefly on the lower side; each septum itself, towards the inner
lamina of the radius, branches and divides: the interspaces are
filled up nearly solidly. The _alæ_ have apparently their summits
less oblique than those of the radii: their sutural edges are finely
crenated. The lower edge of the sheath is hollow underneath. The
_basis_ is flat; it is rather thin, and imperfectly porose; in parts
it is not at all porose, in others it is traversed only by very
minute pores: there is nevertheless, in some parts, even where the
upper layer is not porose, an underlying, cancellated layer.

_Animal's body_ unknown.

24. BALANUS CORRUGATUS. Pl. 6, fig. 3 _a_, 3 _b_.

_Shell white, longitudinally folded; radii narrow. Scutum internally without an adductor ridge._

_Fossil_, Sub-Appennine formations; Colle in Tuscany; Mus. Greenough.

I have seen only two specimens of this species attached to rock, collected by Mr. Greenough, at Colle, and kindly given by him to me. The species comes near to the living _B. crenatus_, also found fossil in deposits of this same age; it differs, however, distinctly from that species, in having its basis permeated by pores, and, in a less degree, in the sutural edges of the radii being more plainly crenated: the opercular valves of the two species closely resemble each other. This may be the _B. stellaris_ of Bronn, but it is futile attempting to identify the species of this genus merely by external characters, even when aided, as in this case, by an excellent drawing of the shell.

_General Appearance._--Shell conical, with broad rounded longitudinal
folds; orifice of moderate size, oval; radii narrow, with their upper
margins oblique; but the summits of both specimens had been much
broken. Colour, as it appears, originally white. Basal diameter of
largest specimen 3/4 of an inch.

_Scuta_, with the upper portion much reflexed; the articular
ridge is very prominent, and the articular furrow of great width;
when the valve is viewed from the outside the articular ridge is
very conspicuous: there is no adductor ridge. _Terga_, with the
longitudinal furrow very slight; the spur is from one third to
one fourth of the width of the valve, and its basal end is blunt
and almost truncated; it stands about half its own width from the
basi-scutal angle. Internally, the articular ridge is very prominent,
and the articular furrow narrow and deep, extending down the valve in
the line of the spur.

_Parietes_: the parietal tubes are remarkably large, and I think
this can hardly be an individual peculiarity: the tubes are crossed
by many transverse septa, close down to the basis. The _radii_ are
narrow, and have jagged, oblique summits: their sutural edges have
very distinct septa, barely denticulated, with the interspaces filled
up solidly. The _alæ_ have oblique summits; I was unable to make out
the structure of their sutural edges. The _Basis_ is very distinctly
permeated by pores, which are crossed by transverse septa.

The shell and opercular valves of _B. corrugatus_ so closely resemble the same parts in _B. crenatus_, that I should not be much surprised at seeing the two species graduating into each other, if a larger series of specimens, from beds intermediate in age between the Sub-Appennine formations and the present time, were obtained. If indeed the basis of _B. crenatus_ were permeated by pores, the two species could hardly be discriminated.

_Section_ D.

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

25. BALANUS PORCATUS. Pl. 6, fig. 4 _a_-4 _e_.

BALANUS PORCATUS. _Emanuel da Costa._ Hist. Nat. Test. Brit., p. 249
(1778).

LEPAS BALANUS. _Linn._ Syst. Naturæ (1767).

---- ---- _Born._ Testacea Mus. Cæs. Desc., Tab. 1, fig. 4, (1780).

---- ---- _Chemnitz._ Syst. Conch., 8 Band., Tab. 97, fig. 820,
(1785).

BALANUS ARCTICA PATELLIFORMIS. _Ellis._ Philosoph. Transact., vol.
50, Tab. 34, fig. 18 (1758).

---- SULCATUS. _Bruguière._ Encyclop. Method., Tab. 164, fig. 1
(1789).

LEPAS COSTATA and BALANUS. _Donovan._ British Shells, 1802-1804, Tab.
30, fig. 1, 2.

LEPAS SCOTICA. _W. Wood._ General Conchology, Pl. 6, fig. 3, sed non
_Lepas balanus_, Pl. 7, fig. 3, (1815).

BALANUS ANGULOSUS. _Lamarck_ (1818), in _Chenu_, Illust. Conch., Tab.
11, fig. 11.

---- TESSELATUS. _Sowerby_ (!). Mineral Conchology, Tab. 84 (1818).

---- SCOTICUS. _Brown._ Illust. Conch. Great Britain, Pl. 7, fig. 2,
sed non, Pl. 6, fig. 9 et 10 (1827); 2d edit., Pl. 53, fig.
1-3, 22, 23 et Pl. 54, fig. 1-3.

---- GENICULATUS. _Conrad._ Journal Acad. Philadelphia, vol. 6, part
2, p. 265 (1830), Tab. 11, fig. 16.

---- ---- _Aug. Gould_ (!). Report on the Invertebrata of
Massachussetts, fig. 9 (1841).

_Shell white, generally sharply ribbed longitudinally: radii with their summits almost parallel to the basis. Scutum longitudinally striated: tergum with the apex produced and purple._

_Var._ (_a_): _Walls without longitudinal ribs_. Mus. Brit., Cuming,
Stutchbury, Jeffreys.

_Hab._--South shores of England, Ireland, Scotland, Shetland Islands,
Iceland, Davis's Straits, 66° 30′ N.; Lancaster Sound, 74° 48′ N.
(Mr. Sutherland). Maine and Massachussetts, United States. China (?).
In deep water, common on shells, crustacea, and rocks, sometimes
imbedded in sponges.

_Fossil_ in the glacial deposits of Scotland, Uddevalla, and Canada;
in the mammaliferous and Red Crag of England; Mus. Lyell, Sowerby, S.
Wood, &c.

_General Appearance._--Shell conical, somewhat convex; white,
sometimes tinted yellowish, from the thin investing membrane;
the produced tips of the terga are purple: the parietes of each
compartment have from two to four strong, prominent, sharp, straight
longitudinal ribs; these are sometimes irregular, and rarely, as will
presently be described, they are absent. The radii are smooth and of
considerable breadth; their summits are nearly parallel to the basis
or only slightly oblique: hence the orifice is entire; it is rather
small and ovate, being broad at the rostral end, and very sharp and
narrow at the carinal end.

_Dimensions._--The largest specimens which I have seen from Great
Britain or Ireland, have been 1.3 of an inch in basal diameter:
in Mr. Cuming's collection, however, there was one much depressed
specimen from the Shetland Islands, 2.1 in basal diameter: a
regularly conical specimen from the coast of Massachussetts attained
a nearly equal diameter; out of the glacial deposits in the Isle of
Bute, Scotland, several specimens had this same diameter, namely, two
inches, and were even more steeply conical, being 1.85 in height;
some glacial specimens from Uddevalla and Canada, in Sir C. Lyell's
collection, were 1.7 in basal diameter. Hence, it appears, as we
shall presently see is likewise the case with _B. crenatus_ and
_Hameri_, that northern specimens, and those from the United States
and from the glacial deposits, often exceed in dimensions those from
Great Britain or Ireland.

_Scutum_: the lines or ridges of growth are broad and prominent;
they are divided into square beads by fine striæ, radiating from the
apex: and hence the valve is longitudinally striated. Internally,
the articular ridge is extremely little prominent; the adductor
ridge, or what must be called such, runs straight down under the
articular ridge, making a deep longitudinal pit for the lateral
depressor muscle. _Tergum_: the apex is a little produced, and
coloured purple, as well as the upper internal surface of the valve;
there is no longitudinal furrow, only a very slight depression: the
spur is placed close to the basi-scutal angle; it is rather long,
and measured across the upper part, is half as wide as the valve:
its lower end is truncated and rounded; the basal margin slopes
towards it. Internally, a very small portion of the scutal margin is
inflected: the articular furrow is shallow and broad: the crests for
the depressores are feeble. In young specimens the spur is bluntly
pointed.

The _Parietes_ (4 _e_) have large square parietal tubes: in the
upper part these are filled up solidly without transverse septa:
the longitudinal septa are finely denticulated at their bases, and
the denticuli extend unusually close to the outer lamina. In very
young specimens the inner lamina of the parietes is ribbed, in lines
corresponding with the longitudinal septa, as is the case with most
species of the genus; but in medium and large-sized specimens,
there are between the ribs, thus produced, from one to four smaller
ribs, which do not correspond with any longitudinal septa; they are
finely denticulated at their bases, and may be considered as the
representatives of longitudinal septa which have not been developed
and reached the outer lamina. I have seen no other instance of this
structure, namely, the presence of a greater number of ribs, on
the inner lamina of the walls, than there are longitudinal septa.
The _radii_ have their summits generally parallel to the surface
of attachment, as is usual in the first section of the genus, but
sometimes they are slightly oblique: the septa sometimes rudely
branch a little, but they exhibit scarcely a trace of denticuli: the
interspaces are filled up quite solidly. The _alæ_ have their summits
very oblique; their sutural edges are finely crenated.

_Basis_, rather thin, translucent, not permeated by pores; obscurely
furrowed in lines radiating from the centre: the circumference is
marked in a peculiar manner by the longitudinal septa, and by the
tips of those intermediate, denticulated ribs, which occur on the
inner lamina of the parietes.

_Mouth_: labrum with six teeth: mandibles with the fourth and fifth
teeth small and rudimentary: maxillæ, with a small notch under
the upper pair of spines; in the lower part there is a single
large spine. _Cirri_, dark brownish purple, making a singular
contrast with the white operculum and shell; first pair, with one
ramus, having twenty-six segments, and about twice as long as the
shorter ramus, having twelve or thirteen segments, with their front
surfaces protuberant. In the second pair the segments are but little
protuberant: third pair about one third longer than the second pair:
sixth pair, elongated, having in the same individual forty-six
segments; these segments have shield-shaped fronts, bearing five
pairs of spines, with some minute intermediate bristles. There is the
usual point at the dorsal base of the penis.

_Range: Geological History._--This species is common on the shores
of Scotland and Ireland; the most southern point of Europe whence I
have happened to see a specimen is Tenby, in South Wales: but I have
no doubt it is found further south; and Mr. Jeffreys, who knows this
species well, has found it common on the extreme southern shores of
England. In the United States, it is found on the shores of Maine and
Massachussetts: northward, I have seen specimens from Iceland, from
Davis's Straits, and from Lancaster Sound, in lat. 74° 48′ north;
these latter I owe to Sir J. Richardson. It is an inhabitant of deep
water; in Mr. Thompson's collection there are several specimens from
the Bay of Belfast, marked twenty-five fathoms, and one group said
to have come from "about fifty fathoms, on the coast of Antrim:" one
specimen from Cape St. Anne, Massachussetts, is marked as having come
from only five fathoms. This species is commonly associated, on both
sides of the Atlantic, with _B. crenatus_, and sometimes with _B.
Hameri_ and _Verruca Strömia_: mollusca, such as pectens, modioli,
and oysters, offer the most usual surfaces of attachment: I have,
however, seen many specimens on crustaceans, on rocks, and even on
the roots of the larger sea-weeds. This species is very common in the
glacial deposits of Uddevalla, of Skien in Norway, and of Canada, and
is associated with the same species as in the living state: I have
seen, also, specimens from the same formation in the Island of Bute,
Scotland. I have seen numerous specimens from the mammaliferous crag,
and a few from the Red Crag of England. I owe to the kindness of Mr.
J. de C. Sowerby an inspection of the original specimens of the _B.
tesselatus_ of the Mineral Conchology, which is certainly the present
species.

_Affinities._--This species is very distinct from every other; it
comes nearest, as shown in all the characters derived from its
opercular valves, to _B. nubilus_, and in this latter species we
have seen the basis plainly tending to lose its pores and thus
become solid. _B. porcatus_ is perhaps allied in some degree to _B.
trigonus_, and slightly to _B. crenatus_. The rather broad radii,
with their summits hardly oblique, give this species a very different
aspect from those species of the genus amongst which it must be
placed.

_Varieties._--A conical specimen, sent to me from the coast of
Massachussetts, is remarkable from the radii not having been at all
developed, being represented by mere fissures. I have seen a few
specimens of _var._ (_a_), (one collected by Sir E. Parry in the
arctic seas) which had a remarkably different aspect from the common
forms, but which, after a careful examination of the opercular valves
and of the animal's body, I feel convinced are not specifically
distinct: they are characterised by the walls being smooth and
absolutely destitute of the external longitudinal ribs; by the shell
being more cylindrical, with broader radii, and with the orifice
larger and more rhomboidal; the walls and radii are much thinner, and
the internal lamina is less plainly ribbed: the beak of the tergum is
not purple. As most of these specimens had grown in a group crowded
together, the difference of shape, and perhaps the thinness of the
walls, is thus explained. In a specimen from Davis's Straits, in
Mr. A. Hancock's collection, most of the above characters are in an
intermediate condition; there are only a few external longitudinal
ribs on the parietes; and the terga have not purple apices. In Mr.
Cuming's collection there are some fine, brilliantly white specimens
(_without opercula_) from the coast of China; these have thin walls
and radii, and the walls are not longitudinally ribbed, but they are
not smooth: the orifice is not large, nor the shape of the whole
shell cylindrical. It is just possible that these latter specimens
may be a distinct and representative species, but I do not think so.

26. BALANUS PATELLARIS. Pl. 6, fig. 5 _a_-5 _c_.

LEPAS PATELLARIS, (_Gmelin_). _Spengler._ Schriften der Berlin.
Gesellschaft, &c. b. i (1780), Tab. 5; Chemnitz, Neues Syst.
Couch., Tab. 98, fig. 839.

_Shell depressed; brown, generally with obscure longitudinal violet stripes: radii (in full-grown specimens) with their summits rounded and surfaces finely ribbed parallel to the basis: basis sometimes permeated by imperfect pores. Scutum internally with an adductor ridge._

_Hab._--Bengal, on wood, Mus. Brit.; on a shell, Mus. Stutchbury;
Philippine Archipelago (young specimen), Mus. Cuming. According to
Spengler, on the Coromandel and Malabar coasts.

_General Appearance._--Shell depressed, sometimes much depressed:
orifice elongated, rhomboidal, but little toothed; surface smooth,
but in old specimens sometimes with the walls slightly folded
longitudinally. The radii are rather narrow, with their summits
oblique; in old specimens their summits are rounded, and their
whole surface finely ribbed parallel to the basis. Colour, in old
specimens dirty brown, tinged with violet, sometimes in longitudinal
bands, and with whiter irregular marks in the upper parts owing to
disintegration: in young specimens the walls are regularly banded
longitudinally, with violet-brown and dirty white; the radii being
generally of a paler dirty red or violet. Basal diameter of largest
specimen .9 of an inch.

_Scuta_, externally rather smooth; internally, articular ridge
prominent, reflexed, with the lower edge hollowed out so as to be
slightly hook-formed: adductor ridge small; there is a slight pit
for the lateral depressor. _Tergum_, with the spur bluntly pointed,
placed at about its own width from the basi-scutal angle; there is no
longitudinal furrow, only a slight depression; carinal margin arched
and protuberant: internally, articular ridge extremely prominent,
running down in the direction of the middle of the spur: crests for
the tergal depressores well developed.

_Parietes_, with the pores rather large; the internal lamina is very
strongly ribbed, the ribs being but slightly denticulated at their
bases: the parietal pores do not appear to be crossed by transverse
septa: sheath closely attached to the walls. The radii have jagged
oblique summits forming an angle of about 45° with the horizon; in
old specimens they become more oblique and narrow: and are then
very remarkable from their summits being arched and rounded, with
a crenated edge, and with their whole surface transversely ribbed
in horizontal lines; this is likewise the case with the recipient
furrow in the opposed compartments: in young specimens the radii are
externally quite smooth: the septa on the sutural edges are bluntly
denticulated; the interspaces being filled up solidly. The alæ have
their summits oblique, but much less oblique than the summits of the
radii; their sutural edges are very finely crenated.

_Basis_ thin, either quite solid, that is, not permeated by pores,
but only furrowed in lines radiating from the centre, or permeated
by pores towards the circumference, the pores being of very small
diameter;--so that we here have an important character variable
within the limits of the same species. Base flat, and this holds
good, as remarked by Spengler, even when the specimens are attached
to cylindrical pieces of wood.

_Animal's body_ unknown.

_Affinities._--In the basis being sometimes permeated towards the
circumference by pores, and by the colouring (the other species in
this and the next section being dirty white), _B. patellaris_ has
almost as strong a claim to be ranked in the last as in the present
section: in the rounded summits of the radii, and in the state of
the basis, it, perhaps, shows more affinity to _B. improvisus_ than
to any other species; it is, however, almost equally allied to _B.
glandula_.

27. BALANUS CRENATUS. Pl. 6, fig. 6 _a_-6 _g_.

B. CRENATUS. _Bruguière._ Encyclop. Method. (des Vers) 1789.

LEPAS FOLIACEA, _var. a_. _Spengler._ Skrifter af Naturhist.
Selskabet, b. i, 1790.

---- BOREALIS. _Donovan._ British Shells, Pl. 160 (1802-1804).

B. RUGOSUS. _Pulteney_ (?) Catalogue of Shells of Dorsetshire,
1799.

---- ---- _Montagu_ (?) Test. Brit. 1803.

---- ---- _Gould_ (!). Report on Invertebrata of Massachussetts
(1841), fig. 10.

B. GLACIALIS (?) _J. E. Gray._ Suppl. Parry's Voyage, 1819.

B. ELONGATUS (!), CLAVATUS (!), _Auctorum variorum_.

_Shell white: radii with their oblique summits rough and straight. Scutum without an adductor ridge: tergum with the spur rounded._

_Hab._--Great Britain, Scandinavia, Arctic Regions as far as
Lancaster Sound, in 74° 48′ N. (Mr Sutherland); Behring's Straits
(Captain Kellett); United States; Mediterranean; West Indies, (Mus.
Brit.); Cape of Good Hope, (Mus. Krauss). Generally attached to
shells and crustacea in deep water; sometimes to ships' bottoms. Very
common.

_Fossil_ in glacial deposits of Scandinavia and Canada, Mus. Lyell;
in the mammaliferous, and Red, and Coralline Crags, Mus. S. Wood, J.
de C. Sowerby, Bowerbank; Miocene formation, Germany, Mus. Krantz.

I find, in most collections, this species confounded with _B. balanoides_; I have even seen the two species, placed by Leach, on the same tablet in the British Museum: _B. balanoides_ is, moreover, generally confounded with _Chthamalus stellatus_; nor has any one hitherto separated the present species from _B. improvisus_. On the other hand, trifling varieties, both of _B. balanoides_ and _B. crenatus_, have commonly been considered as specifically distinct. From these facts it will be seen in what confusion our commonest British species of Balanus have been left. After due deliberation, I have little doubt that this is the _B. crenatus_ of Bruguière, and probably the _B. rugosus_ of Montagu, but this latter author omits all reference to the really important diagnostic characters between this species and _B. balanoides_. The _B. crenatus_ is certainly the _B. rugosus_ of Dr. Aug. Gould. In various collections, I find specimens of _B. crenatus_, when coming from the arctic regions, called _B. glacialis_, _arcticus_, and _borealis_; though I have not met with an authentic specimen of the _B. glacialis_ of Gray ('Supp. Parry's Voyage,' 1819, p. ccxlvi), I have little doubt that it would prove to be the present species.

_General Appearance._--White, usually of a dirty tint, from the
yellowish or brownish persistent epidermis: conical, generally
(fig. 6 _a_) with the parietes rugged and irregularly folded
longitudinally; but sometimes much depressed and extremely smooth (6
_b_); often cylindrical and very rugged; occasionally club-shaped (6
_c_), the upper part being much wider than the lower: specimens in
this latter condition sometimes have extremely narrow parietes, like
mere ribs, and wide radii. The orifice in the cylindrical varieties
is often most deeply toothed. The radii are generally narrow, and
have jagged oblique summits; but not infrequently they are so narrow
as to form mere linear borders to the compartments. The orifice is
rhomboidal, passing into oval, either very deeply or very slightly
toothed.

_Dimensions._--The largest British specimen which I have seen was
only .55 of an inch in basal diameter: specimens from Greenland
and the northern United States frequently attain a diameter of
three-quarters of an inch, and I have seen one single somewhat
distorted specimen actually 1.6 of an inch in basal diameter. The
specimens from the glacial deposits of Uddevalla and Canada appear,
on an average, to attain as large or larger dimensions than those
from the United States: on the other hand, the specimens from the
mammaliferous and Red Crag are smaller, the largest being only .35 in
basal diameter. When individuals have grown crowded together, their
length is often twice, and even occasionally thrice, as great as
their greatest diameter; thus I have seen a Greenland specimen 1.6 of
an inch in length, and only .75 in diameter. In the British Museum
there are some arctic specimens, one and a half inch in length, only
half an inch in diameter at the summit (fig. 6 _c_), thence tapering
downwards to a blunt point.

_Scuta_; the lines of growth are but little prominent: the surface
is generally covered by disintegrating membrane. The upper ends
are usually a little reflexed, so that the tips project freely as
small flattened points. Internally, the articular ridge is highly
prominent and somewhat reflexed: there is no adductor ridge, but a
very distinct impression for the adductor muscle: the depression for
the lateral depressor muscle is small, but variable. The _terga_
are rather small: the spur is short, and placed at rather less than
its own width from the basi-scutal angle; the basal margin slopes a
little towards the spur, of which the lower end is rounded or bluntly
pointed in a variable degree. There is no longitudinal furrow, hardly
even a depression. Internally, the articular ridge is very prominent
in the upper part; the crests for the tergal depressores are well
developed, but variable.

_Compartments._--The internal carinal margin of each compartment,
from the sheath to the basis, generally, but not invariably, projects
a little inwards beyond the general internal surface of the shell,
in a manner not common with the other species of the genus: the
basal edge of this projecting margin rests on the calcareous basis,
and is crenated like the basal edges of the longitudinal parietal
septa. The whole internal surface of the shell is ribbed, but the
ribs are not very prominent. The parietal tubes are large, and are
crossed in the upper part, and often low down, by transverse thin
septa: the longitudinal parietal septa are only slightly denticulated
at their bases; occasionally they divide at the basis close to the
outer lamina of the parietes, making some short outer subordinate
pores. In the circular furrow beneath the lower edge of the sheath,
there are sometimes little ridges, dividing it into small cells:
sometimes, however, this furrow is filled up by irregular knobs of
calcareous matter. The _radii_ are always rather narrow, and often
they form mere linear ribbons of nearly uniform width along the
edges of the compartments. Their summits or edges are always more or
less irregular and jagged: they form an angle with the horizon of
generally above 40°. Their septa are fine, and barely or not at all
denticulated. The alæ have oblique summits: their sutural edges are
rather thick and distinctly crenated. _Basis_ flat, calcareous, very
thin, with the surface slightly marked by radiating furrows, which
furrows answer to the radiating pores that occur in the bases of most
species. In a club-shaped arctic specimen, one inch and a half in
length, the summit being half an inch and the base only one fifth of
an inch in diameter, the basis was still calcareous, thick, and not
permeated by pores.