being placed between the first and second, thus making five altogether;
inferior angle broad, pectinated.
_Maxillæ_, with its edge broad, straight, bearing about twenty pairs of
spines, shorter than the large upper spines.
_Outer Maxillæ_, with the bristles in front, continuous, and without any
notch; exterior surface with a prominence clothed with long spines.
Olfactory orifices slightly prominent.
_Cirri._--First cirrus placed near to the second; posterior cirri not
much elongated, with their segments slightly protuberant, bearing four
pairs of spines, of which the lower pair is small; spines slightly
serrated. In the lower segments, these spines are exceedingly unequal in
length, the inner spines on both rami, not being above one fourth of the
length of the outer corresponding spine in each pair. The tufts
intermediate between these pairs, are not very large: on the lateral
upper rims there are some strong, short spines: dorsal tufts with short,
thick spines. First cirrus about three fourths as long as the second
cirrus, with numerous tapering segments, three or four of the lower ones
being thick and protuberant: in the first cirrus there are eleven
segments, and in the sixth cirrus, seventeen. Second cirrus, with the
anterior ramus slightly thicker than the posterior ramus: a few of the
basal segments of both rami are protuberant, and thickly clothed with
spines. In the third cirrus, the two rami are nearly equally thick, with
some of the basal segments in both clothed, like a brush, with spines.
In these brushes on the first, second, and third cirri, most of the
spines are doubly toothed, each tooth being simply conical.
_Caudal Appendages_, small, much flattened, straight on the exterior
side, and curved on the inner side, with a row of short, rather thick
spines on the crest, and a few on the exterior margin.
The _Affinities_ of this species will be given under the head of the
following, _P. sertus_.
6. POLLICIPES SERTUS. Pl. VII, fig. 5.
_P. capitulo valvarum uno aut pluribus sub-rostro verticillis instructo:
laterum pari superiore vix inferioribus longiore: membranâ valvas
tegente (post desiccationem) fusco rufescente obscuro: rostro dimidiam
carinæ longitudinem æquante, superficiei internæ altitudine latitudinem
plus duplo superante: pedunculi squamis inæqualibus, non symmetricis:
verticillis longiusculè distantibus._
Capitulum with one or more whorls of valves under the rostrum: upper
pair of latera only slightly larger than the lower latera: membrane
covering the valves (when dried) dark reddish-brown: rostrum half as
long as the carina, with its inner surface more than twice as high as
broad: scales of peduncle of unequal sizes, unsymmetrically arranged in
rather distant whorls.
Maxillæ with two tufts of fine bristles, separated by larger spines:
caudal appendages uniarticulate: filamentary appendages none.
New Zealand; Mus. Cuming.
_Capitulum_, much flattened, broad, sub-triangular. Valves exceedingly
various in number; in the largest specimen with a capitulum 8/10ths of
an inch high, and 9/10ths of an inch wide, there were only thirty-one
valves, and these formed only a single whorl under the carina and
rostrum; whereas, in another specimen, which was barely 6/10ths of an
inch in length, there were fifty-two valves, and these formed two or
three distinct whorls under the carina. Scuta, terga, carina, and
rostrum, much larger than the other valves. All are moderately thick,
placed rather distant from each other, covered with thick membrane which
abounds with tubuli, arranged in rows; surface apparently smooth, but
with a very high power, extremely minute spines can be seen at the
extremities of almost all the tubuli. Little bunches of reddish fibrous
matter are imbedded in the membrane, like tufts of sea-weed floating in
water.
_Scuta_, triangular, basal margin curved, protuberant; the upper part of
the tergo-lateral margin is, also, slightly protuberant.
_Terga_, large, oval, basal angle broad, square; lower part of carinal
margin straight, upper part narrowed in; the apex is covered with
membrane and projects freely.
_Carina_, triangular, internally deeply concave, either straight, and
with the apex free, or inwardly and considerably curved; basal margin
nearly straight.
_Rostrum_, about half the length of the carina; either straight or
inwardly curved; it projects freely for full half its length; inner
growing surface triangular, more than twice as high as wide; basal
margin very slightly hollowed out. The _sub-carina_ and _sub-rostrum_
are larger than the largest of the latera; their inner surfaces are
transversely elongated, rounded at both ends, and slightly concave;
externally they are pointed, and project outwards; sometimes the
sub-carina, and sometimes the sub-rostrum is the largest.
_Latera_, small, with their inner surfaces transversely elongated, the
larger being the most elongated. Externally they are acuminated, and
directed upwards; they project but very little beyond the thick membrane
in which they are imbedded. Neither the number, size, nor shape of the
latera agree on opposite sides of the same individual; and it would
appear that, occasionally, some of them cease to grow, and disappear. In
the large specimen with only thirty-one valves, the three pairs of
latera, corresponding to the upper, rostral, and carinal latera in
Scalpellum, were larger in a marked manner than the others; but in the
specimen with fifty-four valves, this could hardly be said to be the
case. In this latter specimen, some of the valves in the lowermost whorl
were exceedingly minute.
_Peduncle_, broad, about as long as the capitulum; surface of attachment
wide; calcareous scales minute, placed in transverse rows, which become
less and less regular in the lower part. The scales do not stand very
close together; they are of unequal sizes and irregular outline;
generally spindle-shaped; calcareous matter is added regularly only to
the scales in the uppermost row, and irregularly to some of the lower
scales. The latter, consequently, are the largest, and often much
elongated; they are sometimes of singular and irregular shapes.
_Colour._--The membrane covering the valves and forming the peduncle,
(after having been long kept dry, and not having been in spirits,) is
dark reddish chocolate-brown; corium of sack dark purple; cirri banded
with dark purplish-brown, with the lower parts of the trophi similarly
coloured.
_Filamentary Appendages_, none, but on the prosoma there are scattered
some small papillæ, which are roughened by finely spinose scales, like
combs; these papillæ certainly seem to represent the filaments in
_Pollicipes cornucopia_ and its two allies.
_Ovigerous Fræna_, seated in the same position as in _P. spinosus_, but
rather longer, with an elliptical _tuft_ of glands on the crest.
_Mouth_, not placed far from the adductor muscle.
_Labrum_, moderately bullate, with the upper part not overhanging; no
teeth on the crest. _Palpi_, short, broad, blunt.
_Mandibles_, with three main teeth, with either one or two smaller teeth
inserted between the first and second, making four or five altogether;
inferior angle rather narrow, pectinated with long and fine spines.
_Maxillæ_, rather broad, with two long upper spines; beneath which there
is a very small prominence bearing a minute tuft of fine bristles;
beneath this, there are eleven pairs of rather long and strong spines;
and the inferior angle is formed by a rather broad, upraised, and
obliquely rounded prominence, bearing a broad tuft of fine spines.
_Outer Maxillæ_, with the inner surface continuously clothed with short
spines; exteriorly there is a slight prominence with long hirsute
spines.
_Olfactory Orifices_ barely prominent.
_Cirri._--First pair placed near the second; the segments of the three
posterior pairs are slightly protuberant, and bear three or four pairs
of finely serrated spines; intermediate tufts long, the middle spines
being the longest; spines on the upper lateral edges long and strong;
dorsal tufts rather short. _First cirrus_, long, multiarticulate, having
fourteen or fifteen segments, whilst the sixth cirrus had nineteen
segments; rami unequal in length by about two segments; basal segments
protuberant brush-like. _Second_ and _third cirri_ with five basal
segments of both rami protuberant and brush-like; but the anterior rami
in both cirri are broader than the posterior rami. Spines on the
protuberant segments of both rami of both cirri, coarsely and doubly
pectinated.
_Caudal Appendages_ (Pl. X, fig. 19), minute, uniarticulate,
club-shaped, with the enlarged ends directed inwards, or towards each
other; summits sparingly clothed with very short spines.
_Penis_, small.
_Affinities._--This species makes a very close approach in the general
form and relative sizes of all the valves, and in the variability of the
number of the whorls, to _P. spinosus_; there is a still closer and more
important resemblance, in the inequality and manner of growth of the
calcareous scales on the peduncle. These species differ, in the colour
of the membrane covering the valves, and in the greater development of
both rostrum and sub-rostrum in _P. sertus_. The rostrum of the latter
is longer than half the length of the carina, and its inner surface is
more than twice as high as wide; and the sub-rostrum is twice as large
as any of the latera,--all points of difference from P. _spinosus_.
In the characters of the mandibles, and more especially of the outer
maxillæ; in the length of the first pair of cirri; in both rami of the
second and third cirri having their basal segments brush-like, with
pectinated spines; and in the shape of the caudal appendages, there is a
close relationship to _P. spinosus_, and through this species to
_Scalpellum villosum_. In the little prominence of the olfactory
orifices, P. _sertus_ differs from most of the allied forms, excepting
_P. spinosus_. In the maxillæ having two prominences bearing fine tufts
of bristles, in the roughened knobs on the prosoma, and in the presence,
in some individuals, of two or three whorls of valves under the carina
and rostrum, there is a marked tendency in _P. sertus_ to approach _P.
cornucopia_, _P. elegans_, and _P. polymerus_.
_Genus_--LITHOTRYA. Pl. VIII, IX.
LITHOTRYA. _G. B. Sowerby._ Genera of Shells, April 1822.
LITHOLEPAS. _De Blainville._ Dict. des Scienc. Nat., 1824.
ABSIA.[65] _Leach._ Zoological Journal, vol. ii, July 1825.
BRISNÆUS et CONCHOTRYA. _J. E. Gray._ Annals of Philosophy, vol.
x, (new series,) August 1825.
LEPAS. _Gmelin._ Systema Naturæ, 1789.
ANATIPA. _Quoy_ et _Gaimard_. Voyage de l’Astrolabe, 1832.
[65] The description of Absia is so inaccurate, that I should not
have recognised it, had not the _Lithotrya Nicobarica_, in a
bottle in the British Museum, borne this name.
_Valvæ 8, si inter eas parvum (sæpe rudimentale) rostrum et duo parva
latera numerentur; incrementi lineis concinnè crenatis: pedunculus
squamis calcareis parvis vestitus, in verticillis superioribus crenatis;
aut calyci basali calcareo aut discorum ordini affixus._
Valves 8, including a small, often rudimentary rostrum and a pair of
small latera: lines of growth finely crenated. Peduncle covered with
small calcareous scales, those of the upper whorls crenated; attached
either to a basal calcareous cup, or to a row of discs.
Body lodged within the peduncle: mandibles with three teeth, the
interspaces being pectinated; maxillæ various: olfactory orifices
slightly prominent: caudal appendages multiarticulate.
Lodged in cavities, bored in calcareous rocks, or shells, or
corals; generally within the Tropics.
_Description._--The capitulum is not much compressed, a horizontal
section giving an oval figure; it is placed obliquely on the peduncle,
the scuta descending lower than the terga and carina. There are eight
valves, of which the scuta, terga, and carina are large; the rostrum and
a pair of latera are very small and often rudimentary. These three
latter valves are essentially distinguished from the scales of the
peduncle, the upper ones of which they sometimes hardly exceed in size,
by not being moulted at each period of exuviation. The latera overlie
the carinal half of the terga; I presume that they are homologous with
the carinal latera in Scalpellum. Each successive layer of shell forming
the valves is thick, and extends over nearly the whole inner surface;
hence the carina and terga, and to a certain extent the scuta, either
actually do project freely much beyond the sack, or would have done so,
had not their upper ends been removed; for the upper and old layers of
shell, in most of the species, either scale off or disintegrate and wear
away. A rectangularly projecting rim, serrated by small teeth, is formed
at the bottom of each fresh layer of growth, along the external surfaces
of each valve (see upper part of fig. 1 _b´_ Pl. VIII.) This structure,
as well as that of the crenated scales on the peduncle, is important,
for by this means the animal, as we shall presently see, forms and
enlarges the cavity in the rock or shell in which it is imbedded.
The scutum overlaps either about one third or even one half of the
entire width of the tergum, and abuts against a prominent longitudinal
ridge on its exterior surface. In _L. truncata_ and _L. Valentiana_,
this ridge on the tergum being folded over towards the scutum, forms a
conspicuous furrow, receiving the tergal margin of the latter. In _L.
Valentiana_, there is a second furrow on the carinal side of the tergum,
receiving the upper end of the corium-covered or growing surface of the
carina. Besides these provisions for holding together the valves, there
are, apparently, others for a similar purpose; thus in each scutum,
under the rostral angle, there is a roughened knob-like tooth, which
touches the under side of the little rostrum, and no doubt serves to
give attachment to the membrane uniting the three valves together. In
some species, the adjoining basal margins of the scuta and terga, where
touching each other, are inflected and roughened; again in _L.
Rhodiopus_, the carinal angles of the terga are produced into points,
and in _L. truncata_ and _L. Valentiana_ into prominent roughened knobs,
which touch two corresponding small knobs, on the upper part of the
growing surface of the carina. Moreover, considerable portions of the
inner surfaces of the scuta and terga, are roughened with minute sharp,
imbricated points, apparently for the firmer attachment of the corium.
The roughened knobs at the rostral angles of the scuta, no doubt are
homologous with the teeth in a similar position on one or both scuta in
Lepas, and in some fossil species of Pollicipes, as in _P. validus_. The
other projections and roughened surfaces are peculiar to Lithotrya. The
growth of all the valves is, as in Pollicipes, simply downwards.
The _Scuta_ are triangular, with their umbones or centres of growth at
the apex; the tergal margin, as seen from within, is either nearly
straight or much hollowed out, accordingly as the scuta simply overlap
the terga, or are received in a furrow. In some of the species there is
a distinct pit for the adductor muscle, and in others this cannot be
distinguished.
_Terga._--These present great differences in shape; but all appear to be
modifications, (as seen internally,) of a rhomboidal figure, which seems
to be the normal form of the terga in the Lepadidæ. Of the lower part of
the valve, the whole exterior surface, with the exception of a narrow
ridge running from the apex down to the basal angle, is hidden by the
overlapping of the scuta, latera, and carina.
The _Carina_, in outline is triangular, with the basal margin in some
species extremely protuberant. In the first four species, the internal
surface is concave, in _L. truncata_ and _L. Valentiana_ it is convex,
with a central raised ridge, and consequently the upper
freely-projecting portion of the valve, has a prominent central crest or
ridge; in _L. Nicobarica_ and _L. Rhodiopus_ there is only a trace of
this ridge. The rostrum, as before stated, is always very small; it, as
well as the latera, are most developed in _L. Nicobarica_, and least in
_L. truncata_ and _L. Valentiana_; generally only a few zones of growth
are preserved, and from their being enlarged at their basal serrated
rims, the rostrum sometimes appears like a few beads of a necklace
strung together.
The _Latera_ are remarkable from being placed over the carinal half of
the terga, in an oblique position, parallel to the lower carinal margin
of the terga. A section, parallel to the growth layers, varies in the
different species from elliptic to broadly oval, and in _L. Nicobarica_
it is triangular. Only a few layers of growth are ever preserved. In _L.
truncata_, where the latera are represented by mere stiles, (like
strings of beads), and are even less in width than the rostrum, they are
imperfectly calcified.
_Microscopical Structure of the Valves._--The shelly layers are white,
and generally separate easily, so that in _L. dorsalis_ it is rare to
find a specimen with the upper part of the valves perfect. The valves
are so translucent, that in the thin margins, even the tubuli could be
sometimes distinguished. The valves are coated by strong yellow
membrane, which, after the shelly matter in _L. dorsalis_ had been
dissolved in acid, separated into broad slips, answering to each zone of
growth. On the lower margin of each slip, there is a row of closely
approximate spines, generally slightly hooked, pointed, 1/650th of an
inch in length, and 1/10000th of an inch in diameter; they arise out of
a little fold; all are furnished with tubuli of the same diameter with
themselves, running through the whole thickness of the shelly layers,
and attached, apparently, by their apices, to the underlying corium. As
the spines are very numerous, so are the parallel rows of tubuli. After
the shelly layers had been dissolved, there was left in _L. dorsalis_
(well seen in the latera), an extraordinary, conferva-like mass of
branching, jointed, excessively thin tubes, sometimes slightly enlarged
at the articulations, and appearing to contain brown granular matter:
other portions of the valves, instead of this appearance, exhibited
membranes or films with similar, branching, articulated tubes or vessels
attached to them: I have not seen this appearance in any other
cirripede. The yellow exterior enveloping membrane, with its spines, is
present in all the species of the genus; in _L. Rhodiopus_ these spines
are much larger than in _L. dorsalis_, and on the inner sides of the
carina they are trifid and quadrifid, and large enough to be conspicuous
with a lens of weak power.
_Peduncle._--The most remarkable fact concerning this part, is that the
outer tunic, together with the calcareous scales with which it is
covered, is moulted at each successive period of exuviation and growth.
I demonstrated this fact in _L. dorsalis_ and _L. truncata_, by removing
the old tunic and finding a new membrane with perfect calcified scales
beneath; and as these two species, (I obtained, also, pretty good
evidence in _L. Nicobarica_,) are at the opposite extremes of the genus,
no doubt this fact is common to the whole genus. I know of no other
instance, amongst Cirripedia, in which _calcified_ valves or scales are
moulted. I am not certain that the whole skin of the peduncle is thrown
off in a single piece; though this almost certainly is the case with the
uppermost and lowest portions. The animal’s body is partly lodged within
the peduncle, which is generally from one to three times as long as the
capitulum, and in the upper part is fully as broad as it. The scales
with which it is clothed, extend up in the triangular interspaces
between the basal margins of the valves. The scales of the upper whorl,
or of the two or three upper whorls (Pl. VIII, figs. 1 _b´_ and 3 _d_)
are larger than those below; and these latter rapidly decrease in size,
so as to become low down on the peduncle, almost or quite invisible to
the naked eye. The scales in each whorl, are placed alternately with
those in the whorls, above and below. All the upper scales are packed
rather closely together; those in the uppermost row are generally nearly
quadrilateral; those in the few next succeeding whorls, are triangular,
with their basal margins protuberant and arched; the scales, low down on
the peduncle, stand some way apart from each other, and generally
consist of simple rounded calcareous beads, of which some of the
smallest in _L. dorsalis_ were only 1/400th of an inch in diameter. In
the lowest part of the peduncle these scales, after each fresh
exuviation, are apparently soon worn entirely away by the friction
against the sides of the cavity; hence in most specimens this part of
the peduncle is quite naked. This same part, however, is furnished with
nail- or rather star-headed little projections of hard, yellow, horny
chitine (fig. 3 _e_). The star on the summit seems generally to have
about five irregular points; one star which I measured was 7/6000th of
an inch in total width, the footstalk being only 2/6000th of an inch in
diameter; the whole projected 10/6000ths of an inch above the surface of
the peduncle; from the footstalk a fine tubulus runs through the
membrane to the underlying corium. These star-headed little points are
often much worn down; in one specimen which was on the point of
exuviation, there remained, in the lower part, close above the basal
calcareous cup, only some hard, smooth, yellow, little discs, on a level
with the general surface of the membrane,--these being the intersected
or worn down footstalks, with every trace of the calcareous beads gone.
But in this same specimen, under the old peduncular membrane, there was
a new one, studded with the usual circular calcareous beads, slightly
unequal in size, generally about 1/400th of an inch in diameter, and
each furnished with a tubulus; but as yet none of the star-headed points
of chitine had been formed. I believe that these latter are developed
from the tubuli leading to the calcified beads, and, therefore, are
formed directly under them. In _L. cauta_ the lowest scales on the
peduncle are a little larger than in _L. dorsalis_, giving a frosted
appearance to it, and all of them are serrated (fig. 3 _d_) round their
entire margins. Generally only the scales in the uppermost, or in the
three or four upper rows are serrated, and this only on their arched and
protuberant lower margins. The state of the serrated edge varies
extremely in the same species, from elongated conical teeth to mere
notches, according to the amount of wear and tear the individual has
suffered since the last period of exuviation; so also do the teeth or
serrated margins on the valves of the capitulum. Each scale has a fine
tubulus passing from the corium through the membrane of the peduncle to
its bluntly-pointed imbedded fang or base. The membrane is transparent,
thin, and tender, to a degree I have not seen equalled in the other
Lepadidæ, except, perhaps, in Ibla. It is much wrinkled transversely.