described. The labrum is highly bullate, with the upper part forming a
rounded overhanging projection, and with the lower part much produced,
so that the mouth is placed far from the adductor scutorum muscle, and
consequently the orifice is directed more towards the ventral surface of
the thorax than in most other Cirripedes: on the crest of the labrum
there are some very small teeth in several of the species, but not in
all. The mandibles have either three or four main teeth, generally with
either one or two small teeth intermediate between the first and second
large teeth, and in the case of _S. Peronii_, with small teeth between
all the larger ones. The maxillæ have their edges furnished with many
spines, and are either straight or have the inferior part prominent and
step-formed. The outer maxillæ have the spines on their inner edges
either continuous or divided into two groups, of which latter structure
we have not hitherto had any very well characterised example. The
olfactory orifices are either highly or moderately protuberant.
In most of the species the prosoma is little developed, and the first
cirrus is placed far from the second. The _Cirri_ are generally but
little curled, and have elongated segments, with long, generally
serrated spines: the first cirrus varies in proportional length; the
second and third cirri have both their rami more thickly clothed with
spines than are the three posterior cirri, the spines being generally
arranged in three or four longitudinal rows: the cirri, however, of _S.
villosum_ in all respects resemble closely the cirri of _Pollicipes
sertus_ and _P. spinosus_.
The _Caudal Appendages_ are uniarticulate, small, and clothed with
spines: in _S. villosum_, however, differently from in all other allied
forms, there are no appendages.
The _Stomach_, in those species which I opened, is destitute of cæca.
There are no filamentary appendages.
_Generative System._ The ova are nearly spherical, and remarkably large,
as was stated to be the case in the introductory discussion, in which
the larva of _S. vulgare_, in the first stage of development, was
described: the ovigerous fræna are small. The testes are large, but the
vesiculæ seminales in some of the species extraordinarily small.
_Scalpellum ornatum_, and perhaps _S. rutilum_, are unisexual; the other
species are hermaphrodite, but most or at least some of the individuals,
are furnished with Complemental Males. These latter are fully described
under each species, so I will here only remark, that _S. ornatum_, which
alone (excepting perhaps _S. rutilum_) is unisexual, has less claim than
the other species to be generically separated: we have seen also, in
Ibla, that similar sexual differences occur in two most closely allied
species. It is very singular how much more some of the Males and
Complemental Males in Scalpellum differ from each other, than do the
female and hermaphrodite forms; this seems due to the different stages
of embryonic development at which the males have been arrested. In the
males, however, of _S. rostratum_, _S. Peronii_, and _S. villosum_,
compared one with another, but not with the males of the other species,
the parts of the mouth and apparently the cirri, resemble each other
more closely, than do the same organs in the hermaphrodites. At the end
of this genus I shall give a summary on the highly remarkable sexual
relations both in Scalpellum and Ibla.
_Distribution._--The species seem distributed over the whole
world, but as far as we can trust our present scanty materials,
are most common in the warmer temperate regions. The _S.
vulgare_ ranges from the Norwegian seas to Naples. Most of the
species are inhabitants of deep water.
_Affinities._--In the preliminary remarks, we have seen how this genus
blends into Pollicipes; and under the head of Oxynaspis, I have shown
its close affinity to that genus. If, indeed, we take _Pollicipes
spinosus_, and destroy all but six of the already minute and almost
rudimentary latera, we shall, as far as the capitulum is concerned,
convert it into a Scalpellum, closely similar to _S. villosum_. If we
take any species of Scalpellum, (excepting _S. villosum_ and _S.
rutilum_,) and destroy all the valves, but the scuta, terga and carina,
we shall convert it into an Oxynaspis. Lastly, I have shown under Ibla,
that in several most remarkable peculiarities of structure, there is a
manifest affinity between Scalpellum and that genus.
_Geological History._--Full details on this subject have been given in
the Memoirs of the Palæontographical Society. I will here only state,
that the oldest known form of Scalpellum occurs in the Lower Green Sand.
[=T= SUB-CARINÂ NULLÂ.]
1. SCALPELLUM VULGARE. Pl. V, fig. 15.
SCALPELLUM VULGARE. _Leach._ Encyclop. Brit. Suppl., vol. iii,
1824.
LEPAS SCALPELLUM. _Linn._ Systema Naturæ, 1767.
---- _Poli._ Test. utriusque Siciliæ, Pl. vi., fig. 16. 1795.
POLLICIPES SCALPELLUM. _Lamarck._ An. sans Vertebres, 1818.
POLYLEPAS VULGARE. _De Blainville._ Dict. Sc. Nat., Plate, fig. 4.
1824.
SCALPELLUM LÆVE, var. _Leach._ Zoolog. Journal, vol. ii, p. 215,
1825.
---- SICILIÆ, var. _Chenu._ Illust. Conch. Pl. iv, fig. 9.
SCALPELLUM VULGARE, (et var.) _Brown._ Illust. of Conch., 1844,
Pl. li., figs. 7 to 20.
_S. (Herm.) valvis 14, si rostrum pæne rudimentale includatur: lateribus
superioribus inæqualiter ovatis._
(Herm.) Capitulum with 14 valves, including the rudimentary rostrum:
upper latera irregularly oval.
Mandibles, with four or five teeth: maxillæ, with the edge straight,
bearing numerous spines.
COMPLEMENTAL MALE flask-formed, with four rudimentary valves; no mouth;
cirri not prehensile; attached to the occludent margin of the scutum,
near the umbo.
Great Britain, Ireland, France, Norway, Naples. Attached to
horny corallines, at from twenty to thirty, sometimes even to
fifty fathoms in depth, according to Forbes and MacAndrew.
HERMAPHRODITE.
_Description._--Capitulum much flattened with the apex produced, of a
pale brown colour, sometimes faintly tinted purple, composed of 14
valves, of which the rostrum is rudimentary and barely visible
externally; valves thin, white, translucent, smooth, slightly marked by
the lines of growth, separated from each other by rather wide
interspaces of colourless membrane, which is thickly clothed by small,
articulated spines of unequal length. The valves, excepting sometimes
their umbones, are also covered with membrane, bearing spines, placed in
rows parallel to the lines of growth; the spines are particularly
numerous round the orifice of the sack.
_Scuta_ slightly convex, thrice as long as broad; upper part much
acuminated; occludent margin almost straight; basal margin nearly at
right angles to the occludent margin; the tergal margin is separated
from the lateral margin by an angle more or less prominent; a slight
curved ridge runs from the umbo to this angle, and this deserves
especial notice, inasmuch as it indicates the outline which the valve
assumed in its earliest growth, and which is permanently retained in
most of the older fossil species. Along the occludent margin, there is a
trace of a ledge, developed in a variable degree, and which is noticed
only on account of the plainly visible ledge along this same margin, in
the allied genus Oxynaspis. The umbo, or centre of calcification, is
seated close to the occludent margin, and at about one fourth of the
length of the valve from the apex. Internally, (fig. 15, _a´_, Pl. V,)
the part above the umbo is flat; and beneath this upper part, there is a
large rounded hollow (_d_) for the adductor muscle: a fold or
indentation (_a_) running downwards from the umbo, extends in a very
oblique line across the occludent margin. This fold is of high interest
as giving lodgment to the Complemental Males, and will hereafter often
be referred to.
_Terga_, triangular, flat; occludent margin, very slightly arched.
_Carina_ much bent, with the umbo placed at barely one third of the
entire length of the valve from the apex. Two very slight ridges can be
perceived, one on each side, running from the umbo to the basal margin,
and separating the roof from the parietes of the valve; these ridges are
of great use in distinguishing the fossil carinæ of Scalpellum, from the
carinæ of Pollicipes. The part above the umbo is formed by the upward
production of a marginal slip along each side of the valve, which slips
in the fossil species (C in the woodcut, fig. 1, given in the
Introduction,) I have designated as the intra-parietes. The lower part
of the valve gradually widens from the umbo downwards; internally, the
whole is deeply concave, and continuously curved. The angle varies at
which the upper and lower portions externally meet each other; but is
never less than 135°. The upper part of the carina runs up between the
terga for three-quarters of their length; the basal margin does not
extend down low enough to pass between the carinal latera.
_Rostrum_, (fig. 15 _b´_, seen externally, and highly magnified,)
minute, almost hidden by the enveloping membrane and by the small
prominent umbones of the rostral latera; in area equalling about one
fourth of the rostral latera; externally pyramidal, with the upper side
rather longer than the lower; internally slightly concave, square, with
the upper margin and sometimes with the lower margin, slightly hollowed
out. Umbo of growth nearly central.
_Upper Latera_, flat, irregularly oval, with an almost rectangular
shoulder under the basal angle of the terga; in area, about one third
larger than the largest valve of the lower whorl; the exact degree of
elongation of the oval figure varies a little. Umbo seated a little
above the central point.
_Lower Whorl_,--_Rostral Latera_, nearly twice as long as broad, lying
under the basal margins of the scuta: umbo seated over the rostrum;
opposite end, towards which the valve widens either sensibly or but
little, is either square or rounded; in area, less than any of the other
valves, excepting the rostrum; in breadth, equalling either half or one
third of the height of the infra-median latera; growth, directed chiefly
towards the infra-median latera. The freely-projecting umbo is about one
sixth part of the entire length of the valve.
_Infra-median Latera_, rather larger than the carinal latera; their
shape varies from elongated pentagonal with the angles rounded, to oval,
with the longer axis directed upwards. The umbo is seated a little above
the middle of the basal margin, so that there is some little growth
downwards, but the main growth is upwards. The upper point generally
stands a little above that of the carinal latera.
_Carinal Latera_, flat, less in area than the infra-median latera; basal
margin nearly straight; carinal margin slightly hollowed out, terminal
margin arched and protuberant. The umbones of the two valves almost
touch each other under the middle of the carina; main growth towards the
infra-median latera and upwards; umbones projecting not above one fifth
of the entire length of the valve.
_Peduncle_, much flattened, rarely as long as the capitulum, with the
upper end nearly as wide as it; the lower end is either blunt, or tapers
to a very fine point. The calcareous scales are transversely elongated,
and are about four times as wide as high; their internal surfaces are
slightly concave, and their external, convex; the two ends are pointed.
Viewed internally, the scales approach in shape to rhomboids. There are,
in a medium-sized specimen, about twenty scales in each whorl, their
tips overlapping each other: the whorls are placed not very near each
other and at rather unequal distances, except round the uppermost part,
where, being in process of formation, they are packed closely together.
The membrane uniting the scales, supports numerous transverse rows of
articulated spines, varying from 1/100th to 1/500th of an inch in
length, and each furnished with a long sinuous tubulus, 1/10,000th of an
inch in diameter, running through the membrane to the underlying corium.
_Attachment._--Specimens are attached to various horny corallines, and
occasionally to the peduncles of each other.[51] In both cases,
supposing the coralline to be erect, the capitulum is placed upwards,
with its orifice towards the branch to which it is attached, and
consequently with its carina outwards. Where several are crowded in a
group, their peduncles often become twisted and their positions
irregular, with their orifices facing in any direction. This uniform
position is simply the consequence of the larva attaching itself
head-downwards, and from the position of the prehensile antennæ,
necessarily with its sternal surface parallel and close to the branch of
the coralline; hence the dorsal surface, which afterwards is converted
into the carina, faces outwards. The peduncle, as already stated, often
tapers, at its basal extremity, to a sharp point. In very young
specimens, for instance in one with a capitulum only 1/20th of an inch
in length, the method of attachment is the same as in Lepas and many
other genera, namely, by cement proceeding exclusively from the antennæ
of the larva; but in older and full-grown specimens, instead of the
whole bottom of the peduncle becoming flattened and broadly attached,
which would be here impossible, the cement is poured out through a
straight row of orifices along the rostral edge, thus causing, by an
excellent adaptation, a narrow margin to adhere firmly to the thin and
cylindrical branches of the coralline. These orifices are represented,
magnified seven times, in Pl. IX, fig. 7, in which the lower attached
portion of the peduncle is split open and exhibited; they are circular,
and stand at regular intervals, in a straight line; the higher orifices
are larger, but further apart from each other than the lower ones; in
one full-grown specimen, I counted ten of these orifices in a length of
exactly a quarter of an inch. At each period of growth, the corium
recedes a little from the attached portion of the peduncle; of which
portion, the greater part is thus left empty and as incapable of further
growth, as are the larval antennæ at the extreme point: in the specimen
figured, the corium extended a little below the upper orifice. The
prehensile antennæ, however, I must remark, do not strictly rise from
the extreme point of the peduncle, but at a little distance from it, on
the rostral surface; this simply ensues from the antennæ in the larva,
being situated on the sternal surface, close to, but not actually on the
front of the head. The two cement glands are seated high up on the sides
of the peduncle, and remote from each other; they are small, unusually
globular and transparent. The two cement-ducts (fig. 7 _a_ _a_)
proceeding from them, are 3/2000ths of an inch in diameter, and run in a
zig-zag line; at the point where they pass through the corium to enter
the lower attached portion of the peduncle, they become closely
approximated, and partially imbedded in the membrane of the peduncle.
Together they run along the rostral edge, giving out through each
orifice a little disc of brownish cement, and finally they enter the
larval antennæ. The peduncle, just above the attached portion, where
still lined by corium, no doubt increases in diameter at each period of
growth, and must, I presume, become pressed against the almost parallel
branch of the coralline. The corium, at this same period, shrinks, or is
absorbed, and the two cement-ducts come in contact with, and adhere to,
the inner surface of the outer membrane of the peduncle; and then, by a
process which I do not understand in this or any other Cirripede,
apertures are formed both in the ducts and through the membrane, so that
the cement passes through, firmly fastening the outer surface of the
peduncle with its calcareous scales and spines, to the coralline.
[51] Mr. Peach, (Transact. Brit. Assoc., 1845, p. 65,) states
that this is sometimes the case in Cornwall; and I have seen a
similar instance in a fine group from Naples.
The structure of the larval prehensile antennæ will be most conveniently
described when we come to the Complemental male; and figures (10-12, Pl.
V) will be given.
_Size and Colours._--Montagu states (‘Test. Brit.,’ p. 18) that British
specimens rarely have a capitulum .62 of an inch in length; I have,
however, seen an Irish specimen, .7 long; and several specimens, from
the Bay of Naples, .8 long, and including the peduncle, 1.3 in length.
The valves in all the specimens are white, and the membrane connecting
them either nearly white, or dirty pale yellowish, or purplish-brown.
Within the sack the corium under the valves is tinted pale purple, and
two very faint bands of the same colour can generally be distinguished
running down the two sides of the peduncle. Body, coloured
yellowish-white, with the upper segments of the pedicels of the cirri,
tinted in front with purple.
_Body_, much flattened, the prosoma is very little developed; the mouth
placed far from the adductor muscle, and is directed in a remarkable
manner towards the ventral surface of the thorax: the first pair of
cirri stands far separated from the second pair.
_Mouth._--Labrum with the upper part highly bullate, forming an
overhanging projection equalling the longitudinal axis of the mouth;
basal margin much produced; crest with a row of bead-like teeth.
_Palpi_ rather small, with their external margin straight, and internal
margin oblique: the bristles on the two palpi just meet each other.
_Mandibles_, with five or six teeth, with the second, (or second and
third, when there are six teeth,) smaller than the others; in two
specimens, there were five teeth on one side and six on the other;
inferior angle rather broad and strongly pectinated.
_Maxillæ_ with the edge nearly straight, without any notch, but with the
inferior portion very slightly projecting; there are twelve or thirteen
pairs of unequal spines, of which some of the middle ones are rather
longer than the others, and almost as long as the two upper great
spines.
_Outer Maxillæ._--On the inner margin the bristles are divided into two
separate tufts; exteriorly, near the base, there is a distinct rounded
swelling with bristles. The olfactory orifices are highly protuberant,
approximate, flattened, scarcely tapering towards their upper ends.
_Cirri._--The five posterior pair are elongated, very little curled,
with short pedicels; their segments are long, not at all protuberant in
front, bearing five or six pairs of long, slightly serrated spines, with
a very minute tuft of bristles between each pair, and with some short
lateral spines on the inner side of each segment; on the fourth pair of
cirri, these lateral spines are considerably developed; dorsal tufts
consist of fine spines, with one much longer than the others. _First
pair_ short, separated by a wide interval from the second; rami unequal
in length, by between two and four segments; longer ramus having nine
segments, scarcely half as long as the rami of the second cirrus;
shorter ramus with seven segments; in the same individual there were
twenty segments in the sixth cirrus. The segments in the shorter ramus
of the first cirrus are oblong in a transverse direction, and may be
compared to a set of shields placed transversely and strung together; in
the longer ramus the segments are longitudinally oblong; in both they
are thickly covered with spines. _Second cirrus_; the anterior ramus is
a little broader than the posterior ramus, with the segments bearing
about five rows of bristles; fifteen segments in the shorter ramus.
_Third pair_, with the two rami equal in thickness, and with the
segments differing very little from those of the posterior cirri,
excepting that the serrated spines in the external lateral rows are
rather larger. The fourth pair is remarkable by having, on the inner
side of the upper edge of each segment, a little tuft of minute smooth
spines, flattened, and a little enlarged near their ends, so as to be
spear-shaped; I could not see these singular spines on the other cirri.
The lower segments of the pedicels of all the cirri, excepting the sixth
pair, are remarkable from having their inner edges, in the middle,
produced into a considerable, abrupt, rounded projection, irregularly
covered with spines.
_Caudal Appendages_, (Pl. X, fig. 21,) very small, flattened, of nearly
the same width throughout; in a medium-sized specimen, only 1/100th of
an inch in length; each bears from ten to twenty small bristles placed
distantly from each other, of which those on the rounded apex are the
longest.
_Generative System._--The penis is remarkably acuminated; the vesiculæ
seminales are unusually small, and enter only for a short distance into
the prosoma; the testes are large. The ovarian tubes are of large
diameter; the ova are nearly spherical and large, namely, 9/400ths of an
inch in diameter; they are not numerous, and lie in single layers in the
two lamellæ. The ovigerous fræna are well developed, and lie under the
scuta; one I measured was 5/100ths of an inch in length and 2/100ths in
width; the margin is obliquely truncated and slightly sinuous. This
species breeds late in the autumn, and even in mid-winter; I have
examined a specimen from Cornwall with ova containing larvæ, taken on
the 26th of October; again, in another specimen from Belfast, sent to me
by Mr. Thompson, taken in January, there were ova in the lamellæ, and
therefore no doubt impregnated; and on February the 12th I received from
Mr. Peach, from Cornwall, specimens so very young that they must have
become attached during the first days of the month.
_Varieties._--The specimens from near Naples, (which I owe to the
kindness of the Rev. F. W. Hope,) are somewhat larger, and differ
slightly from those of Britain: they form, I imagine, the _S. Siciliæ_
of Chenu. After carefully examining them internally and externally, I
think it is quite impossible to consider them specifically distinct, for
although in several specimens, the valves were placed a little further
apart from each other,--the upper latera a little more elongated,--the
carinal latera rather narrower in their upper half,--the infra-median
latera rather more rounded,--and, lastly, in the scuta, the tergal
margin extended almost in the same line with the lateral margin;
nevertheless in other specimens, I could perceive no difference
whatever. It is, however, remarkable that in several full-grown
Neapolitan specimens there were no Complemental males, whereas I have
never seen a single full-grown British specimen without such being
present. In some specimens in the British Museum, without any given
locality, I have observed considerable variation in the breadth of the
carinal and rostral latera.
COMPLEMENTAL MALE. Pl. V, figs. 9-14.