the carinal latera; the surface of the valve between the notch and the
umbo is depressed.[56]

_Rostral Latera_, small, gradually widening from the umbo to the
opposite end, which is obliquely rounded.

_Infra-median Latera_, approaching to diamond-shaped, placed obliquely
to the longer axis of the capitulum; or the upper part may be described
as spear-shaped.

   [56] The only valve which I have seen at all like this, is a
   fossil specimen from the Upper Chalk of Scania; this is described
   in my memoir on the Fossil Lepadidæ (Palæontographical Society),
   under the name of _Scalpellum solidulum_ (Tab. 1, fig. 8, _e_,
   _f_), and is perhaps erroneously there considered as a carinal
   latus.

_Carinal Latera_: these appear as if formed of two valves united
together; the upper portion, widening as it ascends in a curved line,
terminates in a rounded margin, which enters the deep notch in the upper
latera; the other and lower portion is shorter, and terminates in a
square margin abutting against the infra-median latera; the umbones of
the carinal latera project beyond the line of the carina.

_Direction of the Lines of Growth in the Valves._--This should always be
carefully observed, on account of the great diversity there is in this
respect between the different species, especially when the recent are
compared with the older fossil species; moreover one of the chief
characters between the genus Scalpellum and Pollicipes, depends on the
direction of the lines of growth. In the scuta, terga, rostrum, and
upper latera of the present species, the chief growth is downwards; in
the carina, in mature specimens, it is both upwards and downwards; in
the carinal latera, both upwards and towards the infra-median latera; in
the infra-median latera chiefly upwards; and, lastly, in the rostral
latera, towards the infra-median latera.

_Peduncle_, short, not half as long as the capitulum; calcareous scales
imbricated as usual, tinged red, almost crescent-shaped, acuminated at
both ends, of remarkable length, so that in each whorl there are only
four scales: a full-sized scale equals in length one of the rostral
latera. The tips of two scales, in one whorl, lie under the middle
points of the carina and rostrum; and in the whorl, both above and
below, a single much curved scale occupies this same medial position.
The peduncle does not seem to have been attached in any definite
position to the horny coralline, as is the case with _S. vulgare_.

Length of capitulum in the largest specimen .2 of an inch.

The _Mouth_ is directed towards the ventral surface of the thorax. The
_Labrum_ is far removed from the adductor muscle, with the upper part
forming an overhanging projection; I believe there are some very minute
bead-like teeth on the crest. _Palpi_, small, narrow, thinly clothed
with bristles.

_Mandibles_, with three teeth, of which the first is distant from the
second; inferior angle not much acuminated, pectinated on both edges.

_Maxillæ_, small, narrow, produced, without any notch, with two large
upper spines, of which one is much thicker than the other; on the convex
upper margin there are some minute tufts of very small hairs.

_Outer Maxillæ_, with few bristles, arranged in a continuous line on the
anterior surface; on the external surface there is a tuft of long
bristles. Olfactory orifices situated laterally, forming two flattened,
tubular projections.

_Cirri._--First pair placed not far from the second; the three posterior
pair not very long, with their segments elongated, not protuberant,
bearing four pair of non-serrated spines, with a single short bristle
between each pair; dorsal tufts small, with one spine longer than the
others. First cirrus rather short, segments not very broad; second
cirrus with the rami nearly equal in length, anterior ramus rather
thicker than the posterior ramus, with three longitudinal rows of
spines.

_Caudal Appendages._--These are minute, rather broad, not half as long
as the lower segments of the pedicels of the sixth cirrus, with four
very long spines at the tip.

_Penis._--There is no trace of a probosciformed penis in the four
specimens examined; and as this organ is present in every ordinary
cirripede, with the exception of _Ibla Cumingii_ which we know to be
exclusively female, so we may infer with some confidence that the form
here described is female, although it is impossible in specimens once
dried to demonstrate the absence of the vesiculæ seminales and testes.

_Affinities._--This is a very distinct species; it is, however, much
more nearly related to _S. rutilum_, than to any other species; and next
to this, to _S. vulgare_; from this latter species it chiefly differs in
the large scales of the peduncle, in the scuta not being added to at
their upper ends, and in the membrane covering and connecting the valves
being spineless; but there is a greater difference in the trophi and in
the cirri. The peduncle of _S. ornatum_ presents some resemblance to
that of the singular cretaceous genus, _Loricula_.

MALE.

All the specimens, as already stated, were dry, but in an excellent
state of preservation, so that after having been soaked in spirits, they
could be minutely examined. In the four which I opened, I found, in a
transverse pouch on the under side of each scutum, a male lodged; in a
fifth dead and bleached specimen, the cavities in the shell for the
reception of the males, were present; and in a sixth young specimen,
also dead, cavities were in process of formation. As compared with
plants, the relation of the sexes in this species may be briefly given,
by saying that it belongs to the class _Diandria monogynia_. I will
first describe the males themselves, and then the cavities in the shell
of the female. The males differ in every point of detail, from the
complemental males of _S. vulgare_, but yet present so close a general
resemblance, that a comparative description will be most convenient.

The general shape of the whole animal is rather more elongated, and I
suspect flatter, but this latter point could not be positively
ascertained in dry specimens. The entire length is greater, being in the
largest specimen 13/400 (instead of at most 11/400), and the width,
7/400 of an inch. The orifice is not fimbriated; the four bristly points
over the calcareous beads are absent. The whole outer integument is much
thinner, owing evidently to its protected position, and is not covered
by little bristles, but with an extremely high power, minute points
arranged in transverse lines can be distinguished. The calcareous beads,
or rudimentary valves, are thin and regularly oval. It is remarkable
that in all the specimens, two on one side were smaller than the two on
the other side,--the smaller beads being 16/6000, and the larger,
22/6000 of an inch in diameter; therefore more than twice the size of
one of the beads in _S. vulgare_, which are only 9/6000 externally in
diameter. From the position of the eye, close to one margin, near the
upper end of the flattened animal, and from the manner in which the
little limbs and spines lay between two of the beads at the opposite
end, it was manifest that these latter, one large and one small,
corresponded with the terga of the other cirripedes, and that the other
two, near the eye, answered to the scuta. The valves being of unequal
sizes on the right and left-hand sides of the animal, is probably
connected with one side being pressed against the hard, shelly valve of
the female; in the same way as the valves in certain Pæcilasmas; are
smaller and flatter on the side nearest to the crustacean to which they
are attached. The eye, in being slightly notched on the upper and lower
edge, shows signs of really consisting of two eyes, which I believe is
always normally the case; it is rather larger, in the proportion of 13
to 11, being 13/12,000 of an inch in diameter, than in _S. vulgare_; and
from the almost perfect transparency of the integuments, is far more
conspicuous than in that species. Hence when the valves of the female
are opened, the black little eye is the first part of the male which
catches the attention. No vestige of a mouth could be discovered.

_Thorax and Abdomen._--The thorax, as in _S. vulgare_, is highly
extensible, and when stretched exhibits the same five transverse folds
or articulations; when contracted, it is broader, so that even the
truncated end of the abdomen is wider than the lower (properly anterior)
end of the thorax in _S. vulgare_. Its thin outer integument is studded
with excessively minute points in transverse rows. The four pair of
limbs are longer than in _S. vulgare_, but the spines on them much
shorter and thicker; each limb (including the first) supports three
spines, of which one is seated on a notch low down on the outside, and
is longer than the other two; of these two, the one on the same side
with the notch, is a little longer than the other. The spines on the
first and second pair of limbs are considerably shorter than those on
the third pair, and these latter, are a little shorter than those on the
fourth or posterior pair. Hence, the spines on the thoracic limbs,
compared with those of _S. vulgare_, present considerable differences,
both in their relative and absolute dimensions. The abdominal lobe is in
proportion rather shorter; its end is less abruptly truncated, and
supports a row of, I believe, six moderately long, and basally thick
spines; these spines are not so long as those surmounting the fourth
pair of limbs. On both lateral margins of the abdomen, rather on the
ventral face, there is a row of, I believe, seven long spines, but it is
very difficult to count the spines in specimens which have been once
dried. I was able to distinguish that the two lower pair of spines on
the ventral surface, are seated a little way one below and within the
other, as in _S. vulgare_. The abdominal spines altogether form quite a
brush, and there are certainly several more than in _S. vulgare_, and
those on the two sides are much longer.

_Antennæ._--The disc is hoof-like, with the upper surface forming a
straight line with the upper edge of the basal segment; the apex is
pointed and clothed with some fine down; there is a single spine
pointing backwards, which rises from the lower flat surface. The
ultimate segment was hidden in laminæ of cement; and I was not able to
make out its structure. There is a single spine on the outer edge of the
basal segment, in the usual position. The entire length of the limb,
measured from the end of the disc to the further margin of the basal
articulation, is 36/6000ths of an inch; measured to the inner margin, it
is; 21/6000ths of an inch; the disc itself is 12/6000ths of an inch
long; these measurements differ a little both absolutely ad
proportionally, compared with those of the antennæ of _S. vulgare_.

_Cavities in the Scuta of the Female for the reception of the
Males._--These extend nearly parallel to the tergal margin, transversely
across the valves, for three fourths of their width; they are seated
above the depression for the adductor muscle, and are more conspicuous
than it; they are deep and well defined, and each exactly contains one
male. The males are placed with their orifices in a little notch in the
occludent margin, and their prehensile antennæ at the further end. The
distance to which the cavities extend across the valve, and their
distance from the upper or tergal margin, varies a little, but chiefly
in accordance with the age of the specimens; for the valve continues to
increase in width, whilst the size of the cavity remains the same. The
occludent margin of the scutum in the largest female, was .1 of an inch
in length; of another, in which there was a fully developed cavity,
.084; of a third, in which there was no cavity, only a slight concavity,
with a preparatory impression, the length of the occludent margin was
.062. The larger and smaller of these three valves, are drawn of their
proper proportional sizes, in Pl. VI, figs. 1 _b´_, 1 _c´_. The
preparatory impression (fig. 1 _c´_, _b_), consists of a narrow, not
quite straight, extremely slight furrow, of slightly irregular width,
bordered on each side by a very minute ridge, which is distinctly
continuous with the inner edge of the occludent margin, both above and
below the cavity. The furrow appears to have been formed by calcareous
matter not having been deposited along this line, during the thickening
or growth of the internal surface of the valve: I suspect, that it
originates at a single period of growth, for I could see no signs of
successively-formed transverse lines. I believe that it is strictly
homologous with the fold, over which the complemental male is attached
in _S. vulgare_, but carried, for a special purpose, much further across
the valve and rectangularly inwards, for in structure and position both
are identical. In comparing the internal views of the scuta in _S.
vulgare_ and _S. ornatum_ (Pl. V, fig. 15 _a´_, and Pl. VI, fig. 1
_c´_), it must be borne in mind, that the latter should be compared, as
clearly shown by the lines of growth, with that portion alone of the
scutum in _S. vulgare_, which lies under the curved ridge connecting the
umbo and tergo-lateral angle. The deep cavity in which the male is
lodged, is formed subsequently to the preparatory furrow, simply by the
gradual thickening of the surrounding surface of the valve, more
especially of a ridge just above the pit for the adductor muscle, and of
another broad ridge just beneath the tergal margin. The deepest part of
the cavity lies parallel to the tergal margin along the upper side, and
here, in the older valves, the preparatory furrow can by care be
distinctly traced. In conformity with the shape of the cavity, the
orifice or notch in the occludent margin of the scutum, is situated at
the point where the preparatory furrow sweeps round and enters. I
believe that the cavity is lined by membrane, and that between the
cavity and the body of the female, there is a complex membranous
layer,--a pouch or bag being thus formed. An imaginary section of this
pouch (with the thickness of all the parts extremely exaggerated and in
a reversed position) is given in Pl. VI, fig. 1 _d´_: _a_ is the shell;
_x_ the cavity, converted, as I believe, into a pouch by, firstly, the
delicate tunic (_c_) lining the sack of the female; secondly, a double
layer (_d_) of corium; and, thirdly, by a special, rather thick
membranous layer (_b_), which thinning out round the cavity coats only
part of the under surface of the scutum. This latter membrane I have not
seen in any other Cirripede, and I believe it is nothing but the tissue,
here not calcified, which, in a calcified condition, ordinarily forms
the valves. On this view, the males may be said to be lodged in pouches,
formed in the thickness of the valves.

_Concluding Remarks._--The males from the absence of a mouth (and no
doubt of a stomach), must necessarily be short-lived, and, I suppose,
are periodically replaced by fresh males.[57] In one instance, the
remnants of the two great compound eyes of the larva, could be seen at
the end of the pouch, opposite the orifice. The larvæ, I conclude, crawl
in at the orifice, one side of which is formed, as we have seen, of
yielding membrane, and scratch out the dead exuviæ of the former
occupant: certainly, the males are less firmly attached to their
pouches, though some small quantity of cement is excreted, than are
other Cirripedes to the objects to which they are attached. The small
size of the female, and her valves not being thickly edged with chitine,
accounts for the males having pouches specially formed for them, instead
of being, as in _S. vulgare_, laterally imbedded in the chitine-border
of the scuta. In hereafter weighing the evidence on the nature of the
parasites in Ibla and in Scalpellum, the fact of the valves of the
supposed female being here modified for the special purpose of lodging
the males, will be seen to be important. If we imagine the male
parasites to be extraneous animals, and that by adhering to the sack of
the Scalpellum, they injure the corium and thus prevent the growth of
the shell over an area exactly corresponding to their own size, and so
form for themselves cavities; yet what can be said regarding the
preparatory furrows? surely these narrow lines cannot have been produced
by the pressure of the much broader parasites. Must we not see in the
furrows, the first marking out, if such an expression may be used, of
the habitation for the male, which has to be specially formed by the
independent laws of growth of the female?

   [57] It is possible, though opposed to all analogy, that the
   females may be short-lived, and breed only once, in which case
   the males would not have to be periodically replaced.

3. SCALPELLUM RUTILUM. Pl. VI, fig. 2.

_S. (Foem. an Herm.) valvis 14 sub-rufis: carinæ tecto plano, utrinque
cristâ rotundatâ instructo; margine basali truncato: lateribus
superioribus latitudine duplo longioribus._

(Fem. or Herm.) Capitulum with 14 reddish valves: carina with the roof
flat, bordered on each side by a rounded ridge; basal margin truncated:
upper latera twice as long as broad.

Mandibles with three teeth: maxillæ narrow, bearing only four or five
pair of spines: segments of the second and third pair of cirri with one
side wholly covered with spines.

MALES, two, lodged in hollows, on the under sides of the scuta;
pouch-formed, with four (?) rudimentary valves; no mouth; cirri not
prehensile.

    Hab. unknown; associated with _Dichelaspis orthogonia_. British
    Museum.

FEMALE OR HERMAPHRODITE.

There is only a single specimen in the British Museum, and this had
nearly all its valves separated, and many of them in fragments: from its
state of decay, I think the specimen must have been dead, when
originally collected.

_Description._--The capitulum consists of fourteen valves, including
from analogy a rostrum.[58] Valves, apparently covered with membrane,
bearing some thin spines on the margins; clouded with a fine, though
pale, orange tint; surfaces plainly marked with lines of growth.

   [58] In my first, and as I thought careful examination of the
   separated valves (my only materials) of this species, I mistook
   one of the triangular rostral latera for the rostrum, and hence
   was unfortunately led into an error in my ‘Monograph on the
   Fossil Lepadidæ of Great Britain,’ in which I state that the
   present species has only twelve valves in the capitulum; and I
   inferred from this, that _S. quadratum_, _S. fossula_, &c., had
   only twelve valves; I still believe this to be correct, but the
   existence of fourteen valves in _S. rutilum_ and _S. ornatum_,
   the recent species to which the above fossils are most closely
   allied, no doubt is a strong argument in favour of this higher
   number.

_Scuta_, elongated, nearly three times as long as broad; apex, pointed;
basal margin extremely oblique, forming an acute angle with the
occludent margin; the lateral margin is slightly hollowed out, and is
separated from the tergal margin by a large rectangular projection or
shoulder. The occludent margin is nearly straight; externally, there is
a slight ridge running down the middle of the valve, from the apex to
the baso-lateral angle; and a second ridge running from the apex to the
tergo-lateral angle. The lines of growth do not end abruptly at the
tergo-lateral angle, as is the case with _S. ornatum_ and several fossil
species, but run up a little way along the tergal margin. The umbo is
seated at the uppermost point, and, therefore, the main growth is
downwards. There is a large rounded depression for the adductor muscle
(_a_, fig. 2 _a´_), and higher up, opposite the tergo-lateral angle,
there is another hollow (_b_), for the lodgment of the males; this
latter is of nearly the same shape as the hollow for the adductor
muscle, but rather more conspicuous than it. From the appearance of the
under surface of the scuta, it might readily have been thought, that
there had been two adductor muscles.

_Terga_, of large size, longer than the scuta, flat, triangular, with
the whole inferior part much produced and spear-like. A portion of the
apex, must have projected freely above the sack.

_Carina_ (Pl. VI, fig. 2 _b´_), simply bowed (_i. e._, not rectangularly
bent), with the umbo (and primordial valve) seated at the upper point;
rather massive, narrow, only slightly increasing in width from the upper
to the lower end; the two sides are flat, and at right angles to the
roof, which is bordered on each side by a rather broad, square-topped
ridge (_see section_ fig. 2 _c´_), or the roof may be said to have a
square-edged furrow running from the apex to the basal margin, and
widening downwards; these two ridges have their lines of growth oblique,
and hence have a twisted appearance; the central depressed portion of
the basal margin, which is square or truncated, descends lower down than
the two ridges. The sides of the valve close to the apex are broad, and
consist, as I believe, of intra-parietes, as well as of parietes, but
these parts are not separated from each other by ridges, as is commonly
the case, more especially with the fossil species. I have described the
carina in some detail, on account of its resemblance to that of the
cretaceous _S. fossula_, _S. trilineatum_, and _S. quadricarinatum_.

_Rostrum_, unknown; but one probably existed.

_Upper Latera_, of large size, elongated, quadrilateral, approaching to
diamond-shaped, with the angles rounded, nearly twice as long as broad;
almost flat; upper half acuminated, lying between the scuta and terga;
the lower half broad, forming a rectangular projection lying between two
latera of the lower whorl. The umbo is near the apex, the greater part
of the growth being downwards, but the valve is added to a little, round
the two sides of the apex; these additions do not take place in the
early stages of growth, (as explained under _S. vulgare_,) and,
therefore, they form a depressed rim.

_Rostral Latera_, almost exactly triangular, curved; basal margin
furnished with a just perceptible rim.

_Infra-median Latera_, quadrilateral, sides unequal in length; the
carino-basal margin being the longest; in area not quite twice double
the rostral latera; directed obliquely upwards.

_Carinal Latera_, sub-triangular, produced upwards, with the apex
rounded, and the two lateral margins hollowed out; the basal margin
exceeds a little in length the basal margin of the rostral latera. The
umbones of these two latera are seated at their basal outer angles, so
that the growth of the valves is towards each other and upwards. The
umbo of the infra-median latus is seated at the baso-rostral angle, and
hence the growth is obliquely upwards. The umbones of the rostral latera
must have been close together, over the unknown rostrum.

_Length_ of capitulum about 4/10th of an inch.

_Peduncle_, only small fragments are preserved; the calcified scales are
small, closely imbricated, several of them together only equalling in
length the basal margin of the rostral latera. Each scale is thin,
transversely elongated; basal imbedded portion straight; upper margin
rounded.

_Mouth._--Labrum with the upper part highly bullate, forming an
overhanging projection; palpi apparently small and narrow.

_Mandibles_, narrow, produced, with three teeth; inferior angle
pectinated, as is sometimes the third tooth; the distance between the
tips of the first and second teeth equals that between the second tooth
and the inferior angle.

_Maxillæ_, extremely narrow, produced, without any notch; spinose edge
exactly one third of the length of the mandibles: beneath the two upper
great spines there are only three or four pair of spines; on the convex
upper margin there are some minute tufts of the smallest hairs.

_Outer Maxillæ_, rounded with the inner margins very sparingly but
continuously covered with bristles. I could not ascertain whether the
olfactory orifices were tubular.

_Cirri._--These consisted, in the one specimen, of merely small
fragments. The segments of the posterior cirri are elongated, not
protuberant, and support, I believe, five pair of non-serrated spines,
and an exterior row of very minute spines: dorsal spines fine and long.
Either the second or third cirri, or probably both, are remarkable for
having the whole of one side of each segment covered with irregular rows
of long spines. Moreover, in the upper segments of these same cirri,
between each separate dorsal tuft, there is placed one or two long
bristles. The first cirrus appears to have had very broad segments, and
these are singular from the spines in the dorsal rows, being extremely
long. In some of the cirri, several of the basal segments are soldered
together.

_Caudal Appendages_, lost.

From the state of the specimen, it was quite impossible to ascertain
whether the individual here described was an hermaphrodite or female;
from the analogy of its nearest congener, _S. ornatum_, the latter is
the most probable; but the genus Ibla shows how the sexes may differ in
the most closely-allied forms.

_Affinities._--From the hollows on the under sides of the scuta, for the
lodgment of the males; from the umbones of the scuta and of the carina
being situated on the apices of these valves; and from all the
characters of the mouth, _S. rutilum_ is much more closely allied to _S.
ornatum_ than to any other species.

MALE, OR COMPLEMENTAL MALE.

In the concavity or hollow above the depression for the adductor muscle
(Pl. VI, fig. 2 _a´_), I found males, but in so extremely decayed a
condition, that they could hardly be examined. On one side, however, I
distinctly saw the larval prehensile antennæ, with pointed, hoof-like
discs; and part of the thorax, with its small limbs and long spines, as
in _S. vulgare_ or _S. ornatum_. I also saw clearly the eye. The four
calcified beads or rudimentary valves, I believe, were present; but in
removing the specimen, the whole fell to pieces and was lost. The outer
integument was covered with rather thick, very minute bristles, each
about, 2/10,000th of an inch in length, and therefore only half the
length of those on the complemental males of _S. vulgare_. The cavities
for the males are not formed, as in _S. ornatum_, by the thickening of
the internal surface of the valve round a defined space, but by the
scutum being externally convex and internally concave down the middle,
hollows being thus produced both for the lodgment of the males and for
the attachment of the adductor muscle. These hollows are separated from
each other by a slight transverse ridge. I do not know at which point of
the margin of the valve, the orifice of the male is situated, but I
presume close under the apex. In this species, as in _S. ornatum_, there
can be no question that the scuta of the female are specially modified
by their own growth for the reception of the males. It must be added
that, as it was not possible to ascertain whether the ordinary form of
_S. rutilum_ was hermaphrodite or female, so it must remain doubtful
whether the parasites are males or complemental males; but the former, I
think, is most probable.

[=TT= SUB-CARINÂ PRESENTE.]

4. SCALPELLUM ROSTRATUM. Pl. VI, fig. 7.

_S. (Herm.) valvis 15: rostro permagno: laterum paribus quatuor: pari
superiore pentagono._

(Herm.) Capitulum with 15 valves: rostrum very large: four pair of
latera; upper latera pentagonal.

Mandibles with four teeth; maxillæ with the inferior angle prominent.

_Complemental Male_, attached between the mouth and adductor scutorum
muscle; pedunculated; capitulum bearing a pair of elongated scuta and a
rudimentary carina; mouth and cirri prehensile.

    Philippine Archipelago; Island of Bantayan. Attached to a horny
    coralline: 20 fathoms. Mus. Cuming.

HERMAPHRODITE.

_Capitulum_, with the upper part narrow and produced.

_Valves_, 15 in number, placed close together, clouded pale red, covered
with membrane, which is thickly clothed with minute points.

_Scuta_ rather small, oval, with the upper end pointed; rather convex;
basal and lateral margins blending into each other; the upper produced
portion above the umbo is small; there is a deep pit for the adductor
muscle, and there is a fold on the occludent margin in the usual
position; occludent margin not straight.

_Terga_ large, one third of their own length longer than the scuta; fat,
sub-triangular; the three margins are not quite straight; the carinal
margin projects a little above the apex of the carina, and the scutal
margin is excised to fit the upper part of the scuta.

_Carina_ bowed, internally deeply concave; upper portion above the umbo,
about one fourth of the total length, extending between the terga for
two thirds of their length, up to the slight prominences on their
carinal margins: a ridge separates, on each side, the parietes from the
tectum.

_Rostrum_ (fig. 7 _a_) unusually large, about two thirds of the length
of the scuta, and twice as long as the rostral pair of latera;
internally concave, externally carinated; outline of the upper portion
acutely triangular, of the lower portion rounded; umbo seated at the
upper end.

_Upper Latera_ pentagonal, with the apex rounded.

_Rostral Latera_ flat, four-sided, with the basal margin the longest,
and the baso-carinal angle produced.

_Infra-median Latera_ nearly equalling in area the upper latera; not
descending so low down as the rostral and carinal latera; outline of
lower half semi-oval, of upper half rectangular.

_Carinal Latera_ flat, four-sided, with the basal margin the longest,
and slightly protuberant; baso-rostral angle produced; whole valve
larger than the rostral latus, but closely resembling it in form.

_Sub-carina_ minute, not above one third of the size of the rostral
latera, which are the smallest of the other valves; internally deeply
concave; externally solid, pyramidal, standing out beyond the surface of
the carina, with the umbo at the apex.

The umbones of the four pair of latera are seated a little above the
centre in each valve, on the summit of a raised triangular portion; this
arises from the valve at first growing only downwards, and when added to
at the upper end, the new part forms a ledge at a lower level round the
old part, which had already acquired some thickness.

_Peduncle_, short, about half the length of the capitulum; narrow;
thickly clothed with minute, longitudinally elongated, spindle-shaped,
calcareous scales or beads, which project but little.

_Length_ of the capitulum, rather under 3/10ths of an inch.

In a _Young Specimen_, with its capitulum, together with the peduncle,
only 1/10th of an inch long, the scuta, terga, and carina are very large
in proportion to the valves of the lower whorl. The latter project
more, and are externally more pointed, as in the genus Pollicipes. The
rostrum is well developed; the infra-median latera, in proportion, are
the least of all the valves. The carina is straight and pointed, and
not, relatively to the scuta, quite so long. The scuta are rather
broader in proportion to their length, which would naturally follow from
less having been added to their apices,--these valves at first growing
only downwards. The membrane covering and connecting the valves is
furnished with long thin spines.

_Mouth._--Labrum placed far from the adductor scutorum muscle, with the
upper part exceedingly prominent; apparently there are no teeth on the
crest. Palpi blunt.

_Mandibles_, narrow, with four teeth, of which the second is not smaller
than the others; inferior angle sharp and produced, barely pectinated.

_Maxillæ._--Under the two or three great upper spines, there is a tuft
of fine bristles; the inferior part of the edge is step-like, and much
upraised.

_Outer Maxillæ_, with the inner edge deeply notched, and the bristles
arranged in two quite distinct tufts; the bristles on the outer surface
are long. Olfactory orifices, thin, tubular, and projecting.

_Cirri._--The first pair is placed far from the second; the three
posterior pair are long and straight, with their segments much
elongated, not protuberant, bearing four or five pair of long spines,
with little intermediate tufts of minute spines, and with the minutest
spines on the lateral upper edges. Dorsal tufts with one spine extremely
long, equalling a segment and a half in length; the others very short.
Spines all serrated. First cirrus not very short; rami nearly equal,
with the four terminal segments of both tapering; all the basal segments
much thicker, and thickly covered with bristles. Second cirrus (as well
as the third in a less degree), with the anterior ramus thicker than the
posterior ramus, and with all the lower segments in both rami thickly
clothed with three or four longitudinal rows of spines.

_Caudal Appendages_, spinose, uni-articulate; but the specimen was
injured, and I could not exactly make out their shape: I believe it was
oval, and thickly fringed with fine spines.

_Penis_, very small, almost rudimentary, narrow, and hairy, scarcely
exceeding in length the pedicel of the sixth cirrus.

COMPLEMENTAL MALE. Pl. VI, fig. 5.

Before describing the parasite of the present species, which departs
entirely from the character of the males of the three preceding species,
it is proper to state that I consider it to be a Complemental Male
simply from analogy, as will hereafter be more fully shown at the end of
the genus. Had a specimen of the parasite been brought to me without any
information, I should have concluded that it was an immature individual
of a new genus of pedunculated Cirripedes, remarkable from the
rudimentary condition of the valves, and exhibiting, in one important
character, namely, in the form of the larval prehensile antennæ, an
alliance to Scalpellum. Had I been then told that three individuals in a
group, had been found attached to _S. rostratum_, not outside the
valves, but to the integument, in a central line, between the labrum and
the adductor scutorum muscle, in such a position that when the
Scalpellum closed its valves, these parasites were enclosed within the
capitulum, my surprise would have been great; for it is very improbable
that this singular and unparalleled position was accidental in this one
group of specimens, inasmuch as there seems to be a relation between the
naked condition of the capitulum of the parasite, and the protection
afforded to it by the capitulum of the Scalpellum. It further becomes
apparent on reflection, that these minute parasites, though having the
appearance of immaturity, can not increase in size, or but little, for
if they did grow, and acquired an ordinary size, they would either be
killed by the pressure of the scuta of the Scalpellum, or they would
destroy the latter, and in doing so soon lose their own support, and
thus necessarily perish!

The one full-grown specimen of _S. rostratum_, in Mr. Cuming’s
collection, was in a good state of preservation, but dry. The three
parasites were attached, as stated, close under the labrum, between it
and the adductor muscle. They are constructed like ordinary Cirripedia,
and have a mouth, thorax and cirri, enclosed in a capitulum, supported
on a peduncle of moderate length and narrow. The entire length of the
capitulum and peduncle, as far as could be ascertained in the shrivelled
condition of the specimens, was 35/1000ths, and the greatest width of
the capitulum 11/1000ths of an inch. Both capitulum and peduncle are
hirsute with spines, nearly 1/1000th of an inch in length, mingled with
shorter hairs in little rows of three and four together. The figure (5)
in Pl. VI is merely a restoration, as accurate as could be made from the
much shrivelled specimens. There are only three valves,--namely, an oval
carina (_a_), seated rather high up on the capitulum, in a rudimentary
condition and only 1/1000th of an inch in length, and a pair of scuta;
these latter consist of a narrow, slightly curved plate, 8/1000ths in
length, broadest at the lower end, where the breadth is 2/1000ths of an
inch. The prehensile antennæ, at the end of the peduncle, have pointed
hoof-like discs: I was not able to make out the other parts. It deserves
notice, that in the young specimen of the ordinary form of _S.
rostratum_, 1/10th of an inch in length, and therefore only thrice as
long as the parasites, all the valves were perfect, and seemed to have
followed the ordinary law of development.

_Mouth._--The largely bullate labrum is placed far from the adductor, in
the same manner as in the hermaphrodite. The mandibles have three large
sharp teeth, with the inferior point very sharp and small, so that there
is one less tooth than in the hermaphrodite. The maxillæ have two or
three large upper spines, the others being very thin; I believe the
lower part is upraised and step-like, as in the hermaphrodite. The
outer maxillæ are bilobed in front, with a few short bristles on the
outer side near the bottom. I was not able, from the dried state of the
specimens, to discover whether the olfactory orifices were tubular.
Altogether it was apparent, from this imperfect examination, that there
was a close similarity between the mouth of the parasite and of the
hermaphrodite.

The _Thorax_ is unusually elongated.

_Cirri._--The first pair is very short, and is distant from the second.
All have the appearance of immaturity, with their pedicels very long in
proportion to their rami; the latter are slightly unequal in length,
even in the sixth pair. There appeared to be six segments in the rami of
the sixth pair, each segment bearing two or three pair of long spines.

_Caudal Appendages_, with two or three little spines on their summits.

_Penis_, short, blunt, thick at the apex, with one or two spines on it.
I did not see any ovaria, but this could hardly have been expected in
specimens in a dried condition, without they had happened to have been
in a gorged condition. Certainly there were no ova.

In the general summary at the end of the genus, I shall give my reasons
for believing this parasite to be the Complemental Male of the
_Scalpellum rostratum_.

5. SCALPELLUM PERONII. Pl. VI, fig. 6.

  SMILIUM PERONII. _J. E. Gray._ Annals of Philosoph., new series,
        tom. x, 1825.

  ---- ---- . . . . . Spicilegia Zoologica, tab. iii, fig. 10, 1830.

  ANATIFA OBLIQUA. _Quoy_ et _Gaimard_. Voyage de l’Astrolabe, Pl.
        xciii, fig. 16, 1823-1834.

  POLLICIPES OBLIQUA. _Lamarck._ An. sans Vertebres (2d edition).

_S. (Herm.) valvis 13: laterum paribus tribus; pari superiore multùm
elongato: pedunculi squamis calcareis nullis._

(Herm.) Capitulum with 13 valves: three pair of latera; upper latera
much elongated: peduncle without calcareous scales.

Mandibles with 10 or 11 unequal teeth: maxillæ with the edge nearly
straight, bearing numerous spines.

COMPLEMENTAL MALE, attached externally, between the scuta and below the
adductor muscle; pedunculated; capitulum formed of six valves, with the
carina descending far beneath the basal angle of the terga; mouth and
cirri prehensile.

    Swan River, Australia, attached to a coralline; Mus. Cuming.
    Port Western, Bass’s Straits, as stated in the Voyage of the
    Astrolabe. Mus. Brit.

HERMAPHRODITE.

_Capitulum_ formed of 13 valves; namely, two scuta, two terga, a carina
and sub-carina, a rostrum, a pair of upper latera, and two pair of lower
latera; these latter valves, with the sub-carina and the rostrum, make a
whorl of six pieces. The upper part of the capitulum is, as usual,
produced. The upper valves are separated (in specimens which have not
been dried) by rather wide interspaces of membrane; they are covered
(excepting, generally, their umbones,) by membrane, which in the
interspaces is clothed with fine spines. The spines, or the marks where
they were once articulated, are visible over nearly the entire surface
of the membrane covering the valves. The spines are particularly
numerous round the orifice of the sack. The whole capitulum, (in a dried
condition), is coloured dull purplish-red, which is only in part due to
the underlying corium, for the valves themselves are pale red. After
having been long kept in spirits, the whole capitulum becomes
colourless. The valves are smooth, faintly marked by lines of growth.
The umbones of the lower valves project outwards, giving a denticulated
appearance to the base of the capitulum.

_Scuta_, slightly convex, oblong, breadth about two thirds of the
length, almost quadrilateral, with the upper portion produced into a
flat projection; this projection is almost spear-shaped, being
constricted a little on each side below the apex. There is a deep pit
for the adductor muscle. The umbo is near the apex, the part above not
being above one fifth of the whole length of the valve. As in _S.
vulgare_, the growth is at first downwards, and subsequently a little
upwards and downwards, thus producing the upper, small, spear-like
projection, which lies at a lower level than the umbo. There is a fold
on the occludent margin.

_Terga_, large, flat, triangular; carinal margin slightly hollowed out;
occludent margin slightly arched, with a small portion protuberant to a
variable amount. The apex is slightly curved towards the carina.

_Carina_, long, internally deeply concave, angularly bent, the lower
portion slightly longer and wider than the upper part; the two halves
meet each other at about an angle of 135°; the upper half is parallel to
the longer axis of the terga, between which it extends for three fourths
of their length. The external surface is rounded, except near the umbo,
where the edge is carinated; growth almost equally upwards and
downwards; the parietes and tectum are not separated by ridges.

The _Sub-carina_ lies close under the carina, and is placed almost
transversely to the longer axis of the capitulum; external surface
arched and smooth, the whole having the shape of half of a cone, with
the apex a little curved outwards; seen internally, it may be said to be
formed of two triangular wings placed at right angles to each other;
basal margin straight; in size equalling the carinal latera.

_Rostrum_, lying almost transversely to the longer axis of the
capitulum, under the basal margins of the scuta; in shape (fig. 6 _a_)
closely resembling the sub-carina, but about one third larger than it;
larger also than either the rostral or carinal latera; seen externally,
appears like a half cone; seen internally, is formed of two triangular
wings (with curved edges), placed at right-angles to each other.

_Upper Latera_, internally flat, oblong, twice as long as broad; upper
end square, truncated; upper half rather wider than the lower half;
fully twice as large as either of the lower latera. The basal points
extend below the basal margins of the scuta. The umbo is placed a little
above the centre.

_Rostral Latera_, minute, scarcely exceeding one third of the size of
the carinal latera, and very much less than the rostrum; they are placed
transversely under the basal point of the upper latus, or rather between
it and the baso-lateral angle of the scutum; basal margin, as seen
internally, straight; upper margin arched; rostral angle produced;
internally flat; the whole valve is very thick and solid, so that the
umbo which lies at the rostral end, projects rectangularly outwards.

_Carinal Latera_, oblong, nearly quadrilateral, with the upper angle
produced; placed obliquely, parallel to the lower half of the upper
latera; umbo slightly prominent, seated near the apex, with three
rounded ridges proceeding from it; internal surface very slightly
concave.

_Peduncle and Attachment._--The peduncle is short, not equalling the
capitulum in length. The whole surface is most thickly clothed with
minute spines, which are not visible when the specimen is dry; I think
it probable that they may sometimes all drop off before a new period of
exuviation. The peduncle does not (at least in the specimens which I
have examined, which were grouped in a bunch) taper at the lower end to
a point; and after careful examination, I feel sure that the cement does
not debouch from several successively formed orifices, as in _S.
vulgare_ and as in some Pollicipes, but only from the two original
orifices in the prehensile antennæ of the larva. In these latter organs,
the sucking disc is hoof-like and pointed, and is narrower than the
basal segment. The ultimate segment has on its inner side (supposing
this segment stretched straight forwards,) a notch or step bearing at
least three spines. The proportions of the different parts differ
slightly from those in _S. vulgare_; but, as I shall hereafter have to
give all the measurements, I do not think them worth repeating here. In
the one large group of specimens examined by me, in Mr. Cuming’s
possession, all were attached symmetrically to the coralline, as in the
case of _S. vulgare_, capitulum upwards, and their carinas outwards.

_Length_ of capitulum about three quarters of an inch; width about half
an inch; entire length, with peduncle, a little more than one inch.

The _Mouth_ is placed far from the adductor muscle.

_Labrum_, with its basal margin much produced; upper part highly
bullate, forming a rounded projection equalling the longitudinal axis of
the rest of the mouth; crest without any teeth.

_Palpi_, triangular, with the two margins, thickly clothed with
bristles; on each side of the mouth, near where the palpi are united to
the mandibles, there is a slight, orbicular, shield-like swelling.

The _Mandibles_ (Pl. X, fig. 3) have nine or ten very unequal teeth,
with the inferior angle rather broad and pectinated; of these, there are
four main teeth, of which the second is always the smallest, and between
the four, one or two small teeth are interpolated; so that the total
number is either nine or ten, and often varies on the two sides of the
same individual, as likewise does the shape of the inferior angle.

_Maxillæ_, with the edge nearly half as long as that of the mandibles,
supporting from seventeen to twenty pairs of spines; the upper pair is
only slightly larger than the others; a part near the inferior angle
projects slightly beyond the rest of the nearly straight edge. The
apodeme, at its base or point of origin, is unusually broad and flat.

_Outer Maxillæ_, large and triangular. The inner margin is slightly
concave, and continuously covered with short spines. The outer margin is
bilobed, as in _S. vulgare_, with the basal part supporting a great tuft
of long bristles, of which the greater number turn outwards, and almost
cover the olfactory orifices. The latter are slightly prominent, placed
some way apart from each other, with the above-mentioned tufts of
bristles between them. All the spines of the trophi are in some degree
doubly serrated.

_Cirri._--The first pair is seated rather far from the second pair, and
the prosoma being little developed, the shape of the body nearly
resembles that of _S. vulgare_. The posterior cirri are elongated, very
little curled, with the segments much flattened, not at all protuberant,
bearing from five to seven pair of long serrated spines, with a few
small spines in an exterior row; between each pair there is a very
minute tuft of small bristles; the upper lateral rim of each segment is
toothed with small spines; spines of the dorsal tufts, long, serrated.
_First pair_, elongated, having numerous segments, namely, seventeen,
whilst the sixth pair in the same individual had only twenty-one
segments; rami nearly equal; segments short, nearly cylindrical, thickly
clothed with long serrated spines. The _second_ and _third_ pair are
nearly equal in length; they have their anterior rami slightly thicker
than their posterior rami, both being much more thickly clothed with
spines, than are the three posterior pair of cirri. Pedicels, rather
short, with their inner edges not forming a projection, as in _S.
vulgare_.

_Caudal Appendages_ (Pl. X, fig. 20), uni-articulate, flat, rounded at
their ends and moderately long; clothed most thickly, like brushes, with
very fine bristles, which latter are serrated, and are longer than the
appendages themselves.

_Penis_, of small size, narrow, pointed, and thickly clothed with
delicate hairs; in length equalling only one fourth of the sixth cirrus.

_Ovigerous Fræna_, small, semicircular; entire edge thickly covered with
glands. Ovarian tubes, within the peduncle, fully developed as usual.

_Affinities._--This species differs from all the others in the absence
of calcareous scales on the peduncle; but it has no other character
which at all justifies its generic separation. In the shape of the scuta
and carina it comes nearest to _S. vulgare_. Taking all the characters
together, it is scarcely possible to say to which of the other species
it is most closely allied, having close affinities with all. In the
entire structure, however, of the Complemental Male, immediately to be
described, this species certainly comes nearer to _S. villosum_ than to
any other species. I may add, that in _S. villosum_ the latera are
almost rudimentary, and therefore tend to disappear, whereas in _S.
Peronii_ it is the calcareous scales on the peduncle which have actually
disappeared.

COMPLEMENTAL MALE. Pl. VI, fig. 3.

I examined, owing to the great kindness of Mr. Cunning, six dry
specimens of the hermaphrodite _S. Peronii_, from Swan River, and one in
spirits from another locality, in the British Museum. Out of these seven
specimens, only three appeared to have had parasites attached to them,
and these I infer, from reasons to be more fully given at the end of the
genus, are Complemental Males. One of the three specimens, however, had
two males close together. These parasites were firmly cemented to the
integument of the hermaphrodite, in a fold, in a central line between
the scuta, a little below (the animal being in the position in which it
is figured) the adductor scutorum muscle, and therefore some way below
the umbones of these valves. When the scuta are closed, the parasites,
from their small size, are enclosed and protected. In every detail of
structure, they are obviously pedunculated Cirripedia.

The _Capitulum_ (Pl. VI, fig. 3) has six valves; namely, a pair of scuta
and of terga, a carina, and a rostrum, all united by finely-villose
membrane, furnished near the orifice with some much longer and thicker
spines. The capitulum is truncated in a remarkable manner, the orifice
not being, as in the hermaphrodite, in the same line with the peduncle,
but almost transverse to it, and therefore almost parallel to the
surface of attachment. The largest specimen measured transversely,
through the scuta and terga, was 30/1000ths of an inch in breadth;
another was only 26/1000ths to 27/1000ths: this latter specimen,
measured longitudinally, from the base of the carina to the tips of the
terga, was 15/1000ths of an inch. A scutum of the largest specimen was
17/1000ths in length. The scuta and terga are broadly oval, with the
primordial valves very plain at their upper ends. I may here mention,
that in a central line between the scuta, I observed the _apparently_
single, minute, black eye, as in ordinary Cirripedia.

The _Carina_ is straight, triangular, and internally slightly concave;
its basal margin descends far below the basal points of the terga.

The _Rostrum_ is shorter, and internally more concave than the carina: I
believe it projects more abruptly outwards than is represented in the
figure.

The _Peduncle_ commences some little way below the scuta: it is narrow
and very short: it is finely villose: it is lined by delicate transverse
striæ-less muscles, within which there are the usual stronger,
longitudinal muscles. The base is flat and truncated. I examined, and
carefully compared, the prehensile antennæ with those of the
hermaphrodite, and found every part and every measurement the same. The
full importance of this identity will hereafter be more fully insisted
on. The antennæ are represented of their proper proportional size in
fig. 3.

_Mouth._--The labrum, as in the hermaphrodite, is highly bullate, and
far removed from the adductor scutorum muscle. The _Palpi_ are small and
triangular, with their blunt apices clothed with a very few scattered
bristles.

_Mandibles_, with only three teeth, and the lower angle minute, slightly
pectinated; the first tooth is distant from the second, and larger than
it. Width of the whole organ, .0021 of an inch.

_Maxillæ_, bearing only a few spines, furnished with a long apodeme;
beneath the upper large pair there is a notch, under which there are two
spines of considerable size and a small tuft of fine bristles; width
.001 of an inch, and therefore only 1/16th of the size of the same organ
in the hermaphrodite: the relative sizes of the maxillæ and mandibles
are the same in the male and hermaphrodite.

_Outer Maxillæ_ blunt, triangular, with a few thinly-scattered bristles
on the inner face; those on the outside being longer.

_Cirri._--The First pair is far removed from the second; the rami are
very short, barely exceeding the pedicel in length; they are formed of
only four segments, each bearing a pair of spines; but on the end of the
terminal segment, there are three spines, of which the central one is
very long. Second pair also short. In the sixth pair there are five or
six elongated segments, each bearing three pair of long spines; dorsal
tufts large. The cirri are furnished with transversely-striated muscles.

The _Caudal Appendages_ exist as two very minute plates, with a few
bristles at their apices.

The _Penis_ is not acuminated, with four bristles at the end; it is
short, equalling only the lower segment of the pedicel of the sixth
cirrus. In the one specimen preserved in spirits, I unfortunately
omitted to search for the vesiculæ seminales; I cannot doubt that such
existed, but it would have been important to have ascertained whether
they contained spermatozoa. I made out, most distinctly, that there was
no trace of ovarian tubes within the peduncle; and my assertion may be
believed when I state, that I traced the two much finer and more
transparent cement-ducts, from the prehensile antennæ up to the body of
the animal: in Lepas I have _repeatedly_ detected, with ease, the
ovarian tubes within the peduncle, before the calcification of the
valves had even commenced, and therefore at a much earlier period of
growth than in these parasites. Consequently I am prepared to affirm,
that these parasites are not females, but that, as far as can be judged,
from external organs, they are exclusively males.

_Concluding Remarks._--In comparing the capitulum of the hermaphrodite
with that of the complemental male (Pl. VI, figs. 6 and 3), we must be
struck with the differences in their shape, in the number, relative
sizes, and forms of the several valves. It should, however, be borne in
mind, that the scuta and carina in the hermaphrodite at first grow
exclusively downwards; so that if we remove the upper portions
subsequently added, the difference in shape in these valves is not so
great as it at first appears. The rostrum in the male is of much larger
relative size; whilst of the upper latera there is not a trace, although
in the hermaphrodite these valves are larger than the rostrum. The
terga, compared with those of the hermaphrodite, differ more essentially
than do the other valves; and the manner in which the primordial valves
project, shows that from the first commencement of calcification, the
lines of growth have followed an unusual course. The great breadth and
shortness of the terga is evidently related to the shortening of the
whole capitulum, and the transverse position of the orifice; and this
shortening of the capitulum, no doubt, is rendered necessary for its
reception and protection within the shallow furrow between the scuta of
the hermaphrodite. Finally, if we compare the internal parts of the
hermaphrodite and male, the differences are considerable, though partly
to be accounted for by the youth of the latter: the form and position of
the labrum, and the distance between the first and second pair of cirri,
is the same in both; but the mandibles and maxillæ differ considerably.

To put the case as I have before done, if a specimen of one of these
parasites had been brought to me to class without any information of its
habits,--the downward direction of growth in all the valves, the
presence of a rostrum, the villose outer integument, all the details of
the prehensile antennæ, the form of the animal’s body, and the position
of the labrum, would have convinced me that, though a quite new genus,
it ought to have stood close to Scalpellum, and nearer to it than to
Ibla.

6. SCALPELLUM VILLOSUM. Pl. VI, fig. 8.

  POLLICIPES VILLOSUS on Plate (TOMENTOSUS in text). _Leach._
        Encyclop. Brit., Suppl., vol. iii, 1824, Pl. lvii.

  ---- VILLOSUS.[59] _G. B. Sowerby._ Genera of Shells, Pollicipes,
        fig. 3, 1826.

  CALANTICA HOMII. _J. E. Gray._ Annals of Phil., vol. x, p. 100,
        1825.

   [59] As Mr. Sowerby has adopted the name _villosus_, I have
   followed him; though as _tomentosus_ is used through some mistake
   by Leach in the text, both names have equal claims as far as
   priority is concerned.

   In Lamarck, ‘Animaux Sans. Vert.,’ the _P. villosus_ of Sowerby
   is made synonymous with _Anatifa villosa_ of Brugière, which is
   certainly incorrect, although the _A. villosa_ of this latter
   author is not positively known.

_S. (Herm.) valvis 14: sub-rostro præsente: carinâ pæne rectâ: laterum
paribus tribus; pari superiore triangulo._

(Herm.) Capitulum with 14 valves: sub-rostrum present: carina nearly
straight: three pair of latera; upper latera triangular.

_Mandibles_ with four teeth, of which the second is the smallest:
maxillæ with a projection near the inferior angle: no caudal appendage.

COMPLEMENTAL MALE, attached externally between the scuta, below the
adductor muscle; pedunculated; capitulum formed of six valves, with the
carina not descending much below the basal angles of the terga: mouth
and cirri prehensile.

    Eastern Seas[60] (?) attached to shells and rocks. Mus. Brit.;
    College of Surgeons; Cuming.

   [60] No habitat is attached to any of these specimens; but Mr.
   Sowerby informs me that he has seen specimens attached to the
   _Modiola albicostata_ of Lamarck, which shell is said by the
   latter author to be found in the seas of India, Timor, and New
   Holland.

HERMAPHRODITE.

_Capitulum_ with fourteen valves, consisting of a pair of scuta and of
terga, a carina, (which five valves are much larger than the others,) a
rostrum, sub-rostrum, sub-carina, and three pair of small latera. All
the valves are covered by membrane, as are the calcareous scales on the
peduncle; and this membrane everywhere is densely clothed with spines.
The upper valves are not very thick; they stand rather close together.
The eight valves of the lower whorl are more solid, and are placed far
apart; they are small, tending to become rudimentary. None of the valves
are added to at their upper ends, in which respect this species differs
remarkably from the others of the genus, and approaches in character to
Pollicipes.

_Scuta_, with a deep hollow for the adductor muscle, triangular, with
the basal margin elongated, and protuberant.

_Terga_, large, flat, triangular, basal point blunt, with the carinal
margin slightly hollowed out, and the scutal margin protuberant. Apex
solid.

_Carina_, rather longer than the terga, straight, gradually widening
from the upper to the basal end, deeply concave. In young specimens the
upper part is slightly bowed inwards. Apex solid.

_Sub-carina_, with the inner surface crescent-shaped; the umbo points
transversely outwards; in width it exceeds the largest of the latera.

_Rostrum_, triangular, internally (fig. 8 _a_) concave; basal margin
slightly hollowed out, and deeply notched; rather less in width than the
carina; short, with the umbo pointing upwards and outwards. In young
specimens the apex curves a little inwards.

_Sub-rostrum_, with the inner surface transversely elongated (fig. 8
_b_), slightly crescent-shaped, about two thirds as wide as the rostrum.
The apex points transversely outwards.

_Latera_, three pair; the middle pair apparently corresponds with the
upper latera of the other species of the genus. The two other pair of
latera, together with the rostrum and sub-carina, form a whorl. The
sub-rostrum lies by itself, a little beneath this whorl. The latera are
smaller than the rostrum or the sub-carina. They are placed far distant
from each other; their inner surfaces are triangular; their umbones
point upwards; the rostral pair is smaller than the other two pair,
which are of equal size. The exact position of the rostral latus
differed on the two sides of the specimen examined; apparently its
normal position is at the baso-lateral angle of the scuta.

_Peduncle_, wide at the summit, longer than the capitulum; calcified
scales small, not arranged very regularly; flattened, spindle-shaped,
rather far separated from each other; imbedded in membrane, so that even
their summits are rarely uncovered. The surface of the membrane is
thickly clothed with spines, which are strong, thick, yellow, pointed,
and furnished with large tubuli running to the underlying corium. These
spines are arranged in groups of from three or four, to five or six.
Besides these larger spines, the whole surface is villose with very
minute colourless spines, not above 1/20th of the length of the larger
ones. The surface of attachment is broad. This species, not being
symmetrically attached to a coralline, the peduncle does not curve, as
in most of the other species, towards the rostrum.

The capitulum is above half an inch in length.

_Mouth._--The labrum is much produced downwards, but yet the mouth is
not very far distant from the adductor muscle: the upper part is
bullate, forming a small overhanging point, and in longitudinal diameter
equals the rest of the mouth. _Palpi_ blunt.

_Mandibles_ with four teeth, strong, short, thick, the second tooth much
smaller than the others; inferior angle broad, pectinated.

_Maxillæ_ with a long, rather sinuous edge, which, near the inferior
angle, has a narrow projecting point, bearing rather finer spines; there
is, also, apparently, a very minute tuft of small spines close under the
two large upper spines: there are, altogether, about twenty pair of
spines, without counting the smaller ones.

_Outer Maxillæ_, with the inner edge slightly concave, continuously
covered with bristles; exteriorly, with a prominence covered with longer
bristles. Olfactory orifices prominent, protected by a slight punctured
swelling between the bases of the first pair of cirri.

_Cirri._--Prosoma moderately developed; first pair of cirri rather far
removed from the second pair. The segments of the three posterior pair
are not elongated, short, slightly protuberant in front, bearing four or
five pairs of strong spines; a little below each pair, there is an
intermediate tuft of very fine straight bristles, of which the upper
tuft is the largest; on the lateral upper rims there are some short,
strong spines; dorsal tufts rather small and thick; spines all more or
less serrated, especially on the broad basal segments of the three
anterior cirri. Pedicels of the cirri not particularly protuberant in
front. First cirrus with rami, slightly unequal in length; not short;
basal segments much thicker and more protuberant than the upper
segments. Second cirrus; anterior ramus with six or seven basal segments
highly protuberant, and crowded with spines; posterior ramus with about
six segments, similarly characterised. Third cirrus with the anterior
ramus having six, and the posterior ramus five segments, also similarly
characterised.

_Caudal Appendages_ absent, there being only a slight swelling on each
side of the anus.

The _oesophagus_ runs parallel to the labrum, and enters obliquely the
summit of the stomach, which is destitute of cæca: the biliary envelope
is longitudinally plicated.

There are no _Filamentary Appendages_.

_Testes_ large, branched like a stag’s horns, attached in a sheet to the
ventral surface of the stomach: the vesiculæ seminales enter the
prosoma, and have their reflexed ends not very blunt. The _Penis_ is
rather narrow, with the terminal half plainly ringed, and bearing tufts
of fine bristles arranged in circles, one tuft below the other; on the
basal half there are only a few scattered minute bristles.

_Affinities._--In the downward growth of all the valves, in the presence
of a sub-rostrum, in the shape of the scuta, carina, and more especially
of the triangular latera, in the form of the peduncle, with its
irregularly-scattered calcified scales, in the shape of the animal’s
body, in the structure both of the mandibles and maxillæ, in the
arrangement of the spines, both on the anterior and posterior cirri,
_Scalpellum villosum_ most closely resembles, or rather is identical
with, Pollicipes. Had it not been for the formation of the valves
forming the capitulum, and from the presence of Complemental Males, I
should have placed this species alongside of _Pollicipes spinosus_ and
_sertus_. In not having caudal appendages, _S. villosum_ differs from
all the species of Scalpellum and Pollicipes; but this organ is variable
to an unusual degree in Pollicipes.

COMPLEMENTAL MALE. Pl. VI, fig. 4.

From the kindness of Professor Owen, Mr. Gray, and Mr. Cuming, I have
been enabled to examine six specimens of this species; and on two of
them I found Complemental males. They were attached in the same position
as in _S. Peronii_; namely, beneath the adductor muscle, in the fold
between the scuta, so as to be protected by the latter when closed. This
parasite is six-valved, and has a close general resemblance with that of
_S. Peronii_, but differs in very many points of detail. It is
represented of the natural size at _á_ fig. 4. The capitulum is
43/1000ths of an inch, measured across the scuta and terga; and the same
measured from the base of the carina to the top of the capitulum; hence
it is broader, by a quarter of the above measurement, and considerably
higher than the male of _S. Peronii_. From the capitulum being higher,
that is, not so much truncated, the orifice is placed more obliquely.
The membrane connecting the valves is finely villose, and is besides
furnished with spines, conspicuously thicker and longer than those on
the male _S. Peronii_. The scuta and terga are much more elongated, a
scutum being here 35/1000ths of an inch in length. The carina descends
only just below the basal points of the terga, instead of far below
them. The rostrum is a little broader and more arched than the carina;
it is 2/1000ths in length, and therefore more than two thirds of the
length of the carina, the latter being 28/1000ths of an inch from the
apex to the basal margin. The primordial valves, with the usual
hexagonal tissue, are seated on the tips of the scuta, terga, and
carina, but not on the rostrum; so that these valves follow the same law
of development, as in the ordinary and hermaphrodite form of Scalpellum.
The scuta (_a_, fig. 4, greatly enlarged), the terga (_b_), and carina
(_c_) of the male, resemble the same valves in the hermaphrodite, much
more closely than do these valves in the male and hermaphrodite _S.
Peronii_. The rostrum has not its basal margin hollowed out, and is very
much larger relatively to the carina, than in the hermaphrodite. The
large relative size of the rostrum in the complemental male both of this
species and of _S. Peronii_, is a remarkable character, which I can in
no way account for.

The peduncle is narrow and short, but in a different degree in the two
specimens examined. It is naked. The prehensile antennæ were not in a
good state of preservation: the disc is narrower than the basal segment,
and only slightly pointed, in which important respect it differs from
the same part in the foregoing species; at its distal end, rather on the
inner side, there are two or three spines, apparently in place of the
excessively minute hairs, which are found at the same spot in some or in
all the other species of Scalpellum, and in Ibla: similar strong spines
occur in Pollicipes. Unfortunately, for the sake of comparison, I was
not able to find the prehensile antennæ in the hermaphrodite _S.
villosum_.

_Mouth._--Labrum bullate, with teeth on the crest. _Palpi_ blunt,
spinose.

_Mandibles_, with three teeth; inferior point rather strongly
pectinated.

_Maxillæ_, with a considerable notch under the upper pair of large
spines; inferior part of the edge not prominent.

_Outer Maxillæ_, with the spines on the inner edge arranged into two
groups. Olfactory orifices tubular and prominent, with some long
bristles near their bases. In the mandibles having only three teeth, in
the maxillæ being notched and in the lower part not being prominent,
and, lastly, in the bristles on the inner face of the outer maxillæ
being arranged in two groups, these several organs differ from those in
the hermaphrodite.

_Cirri._--First pair short, with only three or four segments in each
ramus: second cirrus, with the basal segments not very thickly clothed
with spines: sixth cirrus with seven segments, not protuberant in front,
each bearing four pairs of spines, without intermediate tufts.

_Caudal appendages_, none. This is an interesting fact, considering that
these organs are likewise absent in the hermaphrodite _S. villosum_,--an
absence highly remarkable, and confined to the genus Conchoderma and the
one species of Anelasma.

_Penis_ thick, not tapering, rather exceeding in length the pedicel of
the sixth cirrus, square at the end, and furnished with some spines. In
one specimen, I believe I distinguished the vesiculæ seminales: if so,
they contained only pulpy matter, and not spermatozoa. There were no
ovarian tubes within the peduncle, which was lined by the usual muscles;
I traced the two delicate cement-ducts, running from within the antennæ
close up to the animal’s body. Hence in this case, as in that of _S.
Peronii_, I dare positively affirm that ovarian tubes do not occur; for
it is out of the question that I could have traced the cement-ducts,
and, at the same time, overlooked the far larger and more conspicuous
ovarian tubes, into which, moreover, the ducts, had they existed, would
have run. Consequently, these parasites are not females; but judging
from the probosciformed penis, and from the presence, as I believe, of
vesiculæ seminales, they are males.

The complemental males of the present species, and of _S. Peronii_, so
closely resemble each other, that what I have stated regarding the
affinities of the latter, are here quite applicable. It is singular how
much more alike the parts of the mouth and the cirri of these two
complemental males are, than the corresponding parts in the two
hermaphrodites: this no doubt is due to the two males having been
arrested in their development, at a corresponding early period of
growth. Several of the characters, by which the hermaphrodite _S.
villosum_ so closely approaches, and almost blends into the genus
Pollicipes,--such as the thicker cirri, with the intermediate tufts of
bristles, the small second tooth of the mandibles, and the little
brush-like prominence on the maxillæ,--are not in the least apparent in
the complemental male.

SUMMARY ON THE NATURE AND RELATIONS OF THE MALES AND COMPLEMENTAL MALES,
IN IBLA AND SCALPELLUM.

Had the question been, whether the parasites which I have now described,
were simply the males of the Cirripedes to which they are attached, the
present summary and discussion would perhaps have been superfluous; but
it is so novel a fact, that there should exist in the animal kingdom
hermaphrodites, aided in their sexual functions by independent and, as I
have called them, Complemental males, that a brief consideration of the
evidence already advanced, and of some fresh points, will not be
useless. These parasites are confined to the allied genera Ibla and
Scalpellum; but they do not occur in Pollicipes,--a genus still more
closely allied to Scalpellum; and it deserves notice, that their
presence is only occasional in those species of Scalpellum which come
nearest to Pollicipes. In the genera Ibla and Scalpellum, the facts
present a singular parallelism; in both we have the simpler case of a
female, with one or more males of an abnormal structure attached to her;
and in both the far more extraordinary case of an hermaphrodite, with
similarly attached Complemental males. In the two species of Ibla, the
complemental and ordinary males resemble each other, as closely as do
the corresponding hermaphrodite and female forms; so it is with two
sets of the species of Scalpellum. But the males of Ibla and the males
of Scalpellum certainly present no special relations to each other, as
might have been expected, had they been distinct parasites independent
of the animals to which they are attached, and considering that they are
all Cirripedes having the same most unusual habits. On the contrary, it
is certain that the animals which I consider to be the males and
complemental males of the two species of Ibla, if classed by their own
characters, would, from the reasons formerly assigned, form a new genus,
nearer to Ibla than to the parasites of Scalpellum: so, again, the
assumed males of the three latter species of Scalpellum would form two
new genera, both of which would be more closely allied to Scalpellum,
than to the parasites of Ibla. With respect to the parasites of the
first three species of Scalpellum, they are in such an extraordinarily
modified and embryonic condition, that they can hardly be compared with
other Cirripedes; but certainly they do not approach the parasites of
Ibla, more closely than the parasites of Scalpellum; and in the one
important character of the antennæ, they are identical both with the
parasitic and ordinary forms of Scalpellum. That two sets of parasites
having closely similar habits, and belonging to the same sub-class,
should be more closely related in their whole organisation to the
animals to which they are respectively attached, than to each other,
would, if the parasites were really distinct and independent creatures,
be a most singular phenomenon; but on the view that they differ only
sexually from the Cirripedes on which they are parasitic, this
relationship is obviously what might have been expected.

The two species of Ibla differ extremely little from each other, and so,
as above remarked, do the two males. In Scalpellum the species differ
more from each other, and so do the males. In this latter genus the
species may be divided into two groups, the first containing _S.
vulgare_, _S. ornatum_ and _S. rutilum_, characterised by not having a
sub-carina, by the rostrum being small, by the constant presence of four
pair of latera, and by the peculiar shape of the carinal latera; the
second group is characterised by having a sub-carina and a large
rostrum, and may be subdivided into two little groups; viz., _S.
rostratum_ having four pairs of latera, and _S. Peronii_ and _villosum_
having only three pairs of latera: now the males, if classed by
themselves, would inevitably be divided in exactly the same manner,
namely, into two main groups,--the one including the closely similar,
sack-formed males of _S. vulgare_, _ornatum_, and _rutilum_, the other
the pedunculated males of _S. rostratum_, _Peronii_, and _villosum_; but
this latter group would have to be subdivided into two little
sub-groups, the one containing the three-valved male of _S. rostratum_,
and the other the six-valved males of _S. Peronii_ and _S. villosum_. It
should not, however, be overlooked, that the two main groups of
parasites differ from each other, far more than do the two corresponding
groups of species to which they are attached; and, on the other hand,
that the parasitic males of _S. Peronii_ and _S. villosum_ resemble each
other more closely, than do the two hermaphrodite forms;--but it is very
difficult to weigh the value of the differences in the different parts
of species.

Besides these general, there are some closer relations between the
parasites and the animals to which they are attached; thus the most
conspicuous internal character by which _Ibla quadrivalvis_ is
distinguished from _I. Cumingii_, is the length of the caudal appendages
and the greater size of the parts of the mouth; in the parasites, we
have exactly corresponding differences. Out of the six species of
Scalpellum in their ordinary state, _S. ornatum_ is alone quite
destitute of spines on the membrane connecting the valves; and had it
not been for this circumstance, I should even have used the presence of
spines as a generic character; on the other hand, _S. villosum_, in
accordance with its specific name, has larger and more conspicuous
spines than any other species. In the parasites we have an exactly
parallel case; the parasite of _S. ornatum_ being the only one without
spines, and the spines on the parasite of _S. villosum_ being much the
largest! This latter species is highly singular in having no caudal
appendages, and the parasite is destitute of these same organs, though
present inn the parasites of _S. rostratum_ and _S. Peronii_. Again, _S.
villosum_ approaches, in all its characters, very closely to the genus
Pollicipes, and the parasite in having prehensile antennæ, with the disc
but little pointed, and with spines at the further end, departs from
Scalpellum and approaches Pollicipes! Will any one believe that these
several parallel differences, between the Cirripedial parasites and the
Cirripedes to which they are attached, are accidental, and without
signification? yet, this must be admitted, if my view of their male sex
and mature be rejected.

One more, and the most important special relation between the parasites
and the cirripedes to which they are attached, remains to be noticed,
namely that of their prehensile larval antennæ. I observed the antennæ
more or less perfectly in the males of all, and except in _S. villosum_,
in all the species, though so utterly different in general appearance
and structure, I found the peculiar, pointed, hoof-like discs, which are
confined, I believe, to the genera Ibla and Scalpellum. In the
hermaphrodite forms of Scalpellum, I was enabled to examine the antennæ
only in two species, _S. vulgare_ and _S. Peronii_, (belonging,
fortunately, to the two most distinct sections of the genus,) and after
the most careful measurements of every part, I can affirm that, in _S.
vulgare_, the antennæ of the male and of the hermaphrodite are
identical; but that they differ slightly in the proportional lengths of
their segments, and in no other respect, from these same organs in _S.
Peronii_,--in which again the antennæ of the male and of the
hermaphrodite are identical. The importance of this agreement will be
more fully appreciated, if the reader will consider the following table,
in which the generic and specific differences of the antennæ in the
Lepadidæ, as far as known to me, are given. These organs are of high
functional importance; they serve the larva for crawling, and being
furnished with long, sometimes plumose spines, they serve apparently as
organs of touch; and lastly, they are indispensable as a means of
permanent attachment, being adapted to the different objects, to which
the larva adheres. Hence the antennæ might, _à priori_, have been deemed
of high importance for classification. They are, moreover, embryonic in
their nature; and embryonic parts, as is well known, possess the highest
classificatory value. From these considerations, and looking to the
actual facts as exhibited in the following table, the improbability that
the parasites of _S. vulgare_ and _S. Peronii_, so utterly different in
external structure and habits one from the other, and from the
Cirripedes to which they are attached, should yet have absolutely
similar prehensile antennæ with these Cirripedes, appears to me, on the
supposition of the parasites being really independent creatures, and
not, as I fully believe, merely in a different state of sexual
development, insurmountably great.

The parasites of _S. vulgare_ take advantage of a pre-existing fold on
the edge of the scutum, where the chitine border is thicker; and in this
respect there is nothing different from what would naturally happen with
an independent parasite; but in _S. ornatum_ the case is very different,
for here the two scuta are specially modified, _before the attachment of
the parasites_, in a manner which it is impossible to believe can be of
any service to the species itself, irrespectively of the lodgment thus
afforded for the males. So again in _S. rutilum_, the shape of the
scutum seems adapted for the reception of the male, in a manner which
must be attributed to its own growth, and not to the pressure or
attachment of a foreign body. Now there is a strong and manifest
improbability in an animal being specially modified to favour the
parasitism of another, though there are innumerable instances in which
parasites take advantage of pre-existing structures in the animals to
which they are attached. On the other hand, there is no greater
improbability in the female being modified for the attachment of the
male, in a class in which all the individuals are attached to some
object, than in the mutual organs of copulation being adapted to each
other throughout the animal kingdom.

  Generic Characters of the larval prehensile ANTENNÆ, in the Lepadidæ,
  as far as known from their imperfect state of preservation, and the
  number of species examined.

      |Name of Species.
      |    |Length of, from end of disc to the further margin of the
      |    |oblique basal articulation: Scale, fractions of the 1/6000ths
      |    |of an inch.
      |    |    |Length of, from end of disc to the inner margin of the
      |    |    |basal articulation. Scale same.
      |    |    |    |Width of basal segment, in widest part. Scale same.
      |    |    |    |    |Disc, length of. Scale same.
      |    |    |    |    |    |Disc, width of. Scale same.
      |    |    |    |    |    |    |Ultimate segment, length of. Scale
      |    |    |    |    |    |    |same.
      |    |    |    |    |    |    |    |Ultimate segment, width of.
      |    |    |    |    |    |    |    |Scale, fractions of the
      |    |    |    |    |    |    |    |1/20,000ths of an inch.

  LEPAS: disc large, thin, almost _circular_, slightly elongated, with
  several long spines on the hinder margin; end segment with three very
  long, plumose spines on the upper _exterior_ angle.[61]

      |_L. anatifera_ (?)
      |    |62
      |    |    |--
      |    |    |    |20
      |    |    |    |    |23
      |    |    |    |    |    |22
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

      |_L. australis_,
      |    |111
      |    |    |--
      |    |    |    |40
      |    |    |    |    |42
      |    |    |    |    |    |39
      |    |    |    |    |    |    |18
      |    |    |    |    |    |    |    |30

      |_L. pectinata_,
      |    |51
      |    |    |--
      |    |    |    |23
      |    |    |    |    |16
      |    |    |    |    |    |14
      |    |    |    |    |    |    |9
      |    |    |    |    |    |    |    |16

      |_L. fascicularis_,
      |    |60
      |    |    |40
      |    |    |    |22
      |    |    |    |    |16
      |    |    |    |    |    |15
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

  DICHELASPIS: disc _small_, thin, circular, with several spines on the
  hinder margin; end segment, with two long spines on the upper _exterior_
  angle.

      |_D. Warwickii_,
      |    |54
      |    |    |--
      |    |    |    |11
      |    |    |    |    |7-8
      |    |    |    |    |    |7-8
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |13-14

  CONCHODERMA: disc large, thin, _transversely_ elongated, with several
  long spines on the hinder margin; end segment, with two excessively
  long, plumose spines on the upper _exterior_ corner.

      |_C. virgata_,
      |    |82
      |    |    |40
      |    |    |    |28
      |    |    |    |    |25
      |    |    |    |    |    |35
      |    |    |    |    |    |    |12
      |    |    |    |    |    |    |    |26

      |_C. aurita._
      |    |--
      |    |    |--
      |    |    |    |--
      |    |    |    |    |28
      |    |    |    |    |    |40
      |    |    |    |    |    |    |11
      |    |    |    |    |    |    |    |26

  ALEPAS: disc small, slightly elongated, with two or more spines on the
  hinder margin; end segment, with two long spines on the upper _inner_
  corner, and four shorter ones on the exterior corner.

      |_A. cornuta_,
      |    |60
      |    |    |--
      |    |    |    |24
      |    |    |    |    |14
      |    |    |    |    |    |12
      |    |    |    |    |    |    |8
      |    |    |    |    |    |    |    |20

  IBLA (parasitic males of): disc, _hoof-like_, _pointed_, elongated, with
  a single spine on the hinder margin; end segment, with four short spines
  on the upper exterior corner.

      |_I. Cumingii_,
      |    |22
      |    |    |--
      |    |    |    |7-8
      |    |    |    |    |7
      |    |    |    |    |    |--
      |    |    |    |    |    |    |3-4
      |    |    |    |    |    |    |    |7-8

      |_I. quadrivalvis_,
      |    |32-33
      |    |    |--
      |    |    |    |10
      |    |    |    |    |8
      |    |    |    |    |    |5
      |    |    |    |    |    |    |4
      |    |    |    |    |    |    |    |8

  SCALPELLUM: disc _hoof-like_, generally _pointed_ and elongated, with a
  single spine on the hinder margin; end segment, with a notch on the
  inner[61] side, bearing two spines, longer than on the exterior corner.

      |_S. vulgare_,
      |    |39
      |    |    |19
      |    |    |    |10
      |    |    |    |    |10-11
      |    |    |    |    |    |5-6
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |7

      |_S. ornatum_,
      |    |36
      |    |    |21
      |    |    |    |10
      |    |    |    |    |12
      |    |    |    |    |    |--
      |    |    |    |    |    |    |--
      |    |    |    |    |    |    |    |--

      |_S. Peronii_,
      |    |30
      |    |    |19
      |    |    |    |--
      |    |    |    |    |9
      |    |    |    |    |    |6
      |    |    |    |    |    |    |5
      |    |    |    |    |    |    |    |10

  POLLICIPES: disc small, _hoof-like_, not pointed, with a single spine on
  the hinder margin; end segment, as in _Scalpellum_.

      |_P. cornucopia_,
      |    |20
      |    |    |--
      |    |    |    |6
      |    |    |    |    |6
      |    |    |    |    |    |6
      |    |    |    |    |    |    |6
      |    |    |    |    |    |    |    |8

   [61] In the diameter of the disc, the thin membranous border,
   which is present in the first three genera, is included; but I
   have some doubts, whether this border be not the first rim of
   cementing tissue, as all the specimens, of which measurements are
   here given, had been removed after attachment. In using the terms
   inner and outer sides of the end segment, it is supposed, that
   this segment is stretched straight forwards, instead of being
   bent rectangularly outwards, as in its natural position; and then
   there can be no doubt which is the inner and outer sides.

It should be observed that the evidence in this summary is of a
cumulative nature. If we think it highly, or in some degree
probable,--from the ordinary form of _Ibla Cumingii_ having been shown
on good evidence to be exclusively female,--from the absence of ova and
ovaria in the assumed males of both species of Ibla, at the period when
their vesiculæ seminales were gorged with spermatozoa,--from the close
general resemblance between the parts of the mouth in the parasites and
in the Iblas to which they are attached,--from the differences between
the two parasites being strictly analogous to the differences between
the two species of Ibla,--from the generic character of their prehensile
antennæ,--and from other such points,--if from these several
considerations, we admit that these parasites really are the males of
the two species to which they adhere, then in some degree the occurrence
of parasitic males in the allied genus Scalpellum is rendered more
probable. So the absolute similarity in the antennæ of the males and
hermaphrodites both in _S. vulgare_ and _S. Peronii_; and such relations
as that of the relative villosity of the several species in this same
genus, all in return strengthen the case in Ibla. Again, the six-valved
parasites of _S. Peronii_ and _S. villosum_ are so closely similar, that
their nature, whatever it may be, must be the same; hence we may add up
the evidence derived from the identity of the antennæ in the parasite
and hermaphrodite _S. Peronii_, with that from the antennæ in the male
_S. villosum_, approaching in character to Pollicipes, to which genus
the hermaphrodite is so closely allied; and to this evidence, again, may
be added the singular coincident absence of caudal appendages in the
male and hermaphrodite _S. villosum_. If these two six-valved parasites
be received as the complemental males of their respective species, no
one, probably, will doubt regarding the nature of the parasite of _S.
rostratum_, in which the direct evidence is the weakest; but even in
this case, the particular point of attachment, and the state of
development of the valves, form a link connecting in some degree, the
parasites of the first three species with the last two species of
Scalpellum, in accordance with the affinities of the hermaphrodites.

When first examining the parasites of _S. rostratum_, _S. Peronii_, and
_S. villosum_, before the weight of the cumulative evidence had struck
me, and noting their apparent state of immaturity, it occurred to me
that possibly they were the young of their respective species, in their
normal state of development, attached to old individuals, as may often
be seen in Lepas; this, however, would be a surprising fact, considering
that _S. rostratum_ and _S. Peronii_ are ordinarily attached, in a
certain definite position, to horny corallines, and considering that the
exact points of attachment in these three parasites, (of which I have
seen no other instance amongst common Cirripedes,) namely, between the
scuta, would inevitably cause their early destruction, either directly
or indirectly, by their living supports being destroyed. Nevertheless, I
carefully examined a young specimen of _S. rostratum_ only thrice as
large as the parasite; and not having very young specimens of _S.
Peronii_ and _villosum_, I procured the young of closely-allied forms,
namely, of _S. vulgare_, (with a capitulum only 4/100th of an inch in
length,) and of _Pollicipes polymerus_, (with a capitulum of less size
than that of one of the parasites,) and there was not the least sign of
anything abnormal in the development of the valves. In _S. vulgare_, at
a period when the calcified scuta could have been only 1/100th of an
inch in length, (and therefore considerably less than the scuta in the
parasites,) the upper latera must have been as much as 4/1000ths of an
inch in length, and the valves of the lower whorl certainly
distinguishable.

To sum up the evidence on the sex of the parasites, I was not able to
discover a vestige of ova or ovaria in the two male Iblas; and I can
venture to affirm positively, that the parasites of _S. Peronii_ and _S.
villosum_ are not female. On the other hand, in the two male Iblas, I
was enabled to demonstrate all the male organs, and I most distinctly
saw spermatozoa. In the parasitic complemental male of _S. vulgare_, I
also most plainly saw spermatozoa. In the parasites of _S. rostratum_,
_S. Peronii_, and _S. villosum_, the external male organs were present.
I may here just allude to the facts given in detail under Ibla, showing
that it was hardly possible that I could be mistaken regarding the
exclusively female sex of the ordinary form of _I. Cumingii_, seeing how
immediately I perceived all the male organs in the hermaphrodite _I.
quadrivalvis_; and as the parasite contained spermatozoa and no ova, the
only possible way to escape from the conclusion that it was the male and
_I. Cumingii_ the female of the same species, was to invent two
hypothetical creatures, of opposite sexes to the Ibla and its parasite,
and which, though Cirripedes, would have to be locomotive! I insisted
upon this alternative, because if the parasite of _I. Cumingii_ be the
male of that species, then unquestionably we have in _I. quadrivalvis_ a
male, complemental to an hermaphrodite,--a conclusion, as we have seen,
hardly to be avoided in the genus Scalpellum, even if we trust
exclusively to the facts therein exhibited.

With respect to the positions of the parasitic males, in relation to the
impregnation of the ova in the females and hermaphrodites, it may be
observed that in the two male Iblas, the elongated moveable body seems
perfectly adapted for this end; in the males of the first three species
of Scalpellum, the spermatozoa, owing to the manner in which the thorax
is bent when protruded, would be easily discharged into the sack of the
female or hermaphrodite; this would likewise probably happen with the
complemental male of _S. rostratum_, considering its position within the
orifice of the capitulum, between the mouth and the adductor scutorum
muscle. The males of _S. Peronii_ and _villosum_ being fixed a little
way beneath the orifice of the sack, below the adductor muscle, are less
favorably situated, but the spermatozoa would probably be drawn into the
sack by the ordinary action of the cirri of the hermaphrodite, and
therefore would at least have as good a chance of fertilising some of
the ova, as the pollen of many dioecious plants, trusted to the wind,
has of reaching the stigmas of the female plants. Regarding the final
cause, both of the simpler case of the separation of the sexes,
notwithstanding that the two individuals, after the metamorphosis of the
male, become indissolubly united together, and of the much more singular
fact of the existence of Complemental males, I can throw no light; I
will only repeat the observation made more than once, that in some of
the hermaphrodites, the vesiculæ seminales were small, and that in
others the probosciformed penis was unusually short and thin.

Viewing the parasitic males, in relation to the structure and appearance
of the species to which they belong, they present a singular series. In
_S. Peronii_ and _S. villosum_, the internal organs have the appearance
of immaturity; the shape of the capitulum is specially modified for its
reception between the scuta of the hermaphrodite, and several of the
valves have not been developed. This atrophy of the valves, is carried
much further in _S. rostratum_. In Ibla, many of the parts are embryonic
in character, but others mature and perfect; some parts, as the
capitulum, thorax, and cirri, are in a quite extraordinary state of
atrophy; in fact, the parasitic males of Ibla consist almost exclusively
of a mouth, mounted on the summit of the three anterior segments of the
21 normal segments of the archetype crustacean. In the males of the
first three species of Scalpellum, some of the characters are
embryonic,--as the absence of a mouth, the presence of the abdominal
lobe, and the position of the few existing internal organs; other
characters, such as the general external form, the four bead-like
valves, the narrow orifice, the peculiar thorax and limbs, are special
developments. These three latter parasites, certainly, are wonderfully
unlike the hermaphrodites or females to which they belong; if classed as
independent animals, they would assuredly be placed not in another
family, but in another Order. When mature they may be said essentially
to be mere bags of spermatozoa.

In looking for analogies to the facts here described, I have already
referred to the minute male Lerneidæ which cling to their females,--to
the worm-like males of certain Cephalopoda, parasitic on the
females,--and to certain Entozoons, in which the sexes cohere, or even
are organically blended by one extremity of their bodies. The females in
certain insects depart in structure, nearly or quite as widely from the
Order to which they belong, as do these male parasitic Cirripedes; some
of these females, like the males of the first three species of
Scalpellum, do not feed, and some, I believe, have their mouths in a
rudimentary condition; but in this latter respect, we have, amongst the
Rotifera, a closely analogous case in the male of the Asplanchna of
Gosse, which was discovered by Mr. Brightwell[62] to be entirely
destitute of mouth and stomach, exactly as I find to be the case with
the parasitic male of _S. vulgare_, and doubtless with its two close
allies. For any analogy to the existence of males, complemental to
hermaphrodites, we must look to the vegetable kingdom.

Finally, the simple fact of the diversity in the sexual relations,
displayed within the limits of the general Ibla and Scalpellum, appears
to me eminently curious; we have (1st) a female, with a male (or rarely
two) permanently attached to her, protected by her, and nourished by any
minute animals which may enter her sack; (2d) a female, with successive
pairs of short-lived males, destitute of mouth and stomach, inhabiting
two pouches formed on the under sides of her valves; (3d) an
hermaphrodite, with from one or two, up to five or six similar
short-lived males without mouth or stomach, attached to one particular
spot on each side of the orifice of the capitulum; and (4th)
hermaphrodites, with occasionally one, two, or three males, capable of
seizing and devouring their prey in the ordinary Cirripedial method,
attached to two different parts of the capitulum, in both cases being
protected by the closing of the scuta. As I am summing up the
singularity of the phenomena here presented, I will allude to the
marvellous assemblage of beings seen by me within the sack of an _Ibla
quadrivalvis_,--namely, an old and young male, both minute, worm-like,
destitute of a capitulum, with a great mouth, and rudimentary thorax and
limbs, attached to each other and to the hermaphrodite, which latter is
utterly different in appearance and structure; secondly, the four or
five, free, boat-shaped larvæ, with their curious prehensile antennæ,
two great compound eyes, no mouth, and six natatory legs; and lastly,
several hundreds of the larvæ in their first stage of development,
globular, with horn-shaped projections on their carapaces, minute single
eyes, filiformed antennæ, probosciformed mouths, and only three pair of
natatory legs; what diverse beings, with scarcely anything in common,
and yet all belonging to the same species!

   [62] ‘Annals of Natural History,’ vol. ii, (2d series, 1848,) p.
   153, Pl. vi. Mr. Dalrymple has published a very interesting paper
   on the same subject in the ‘Philosophical Transactions,’ (p.
   342,) 1849; and there is another Memoir by Mr. Gosse in the
   ‘Annals of Natural History,’ vol. vi, (1850,) p. 18.

_Genus_--POLLICIPES. Pl. VII.

  POLLICIES. _Leach._ Journal de Physique, tom. lxxxv, Julius,
        1817.[63]

  LEPAS. _Linn._ Systema Naturæ, 1767.

  ANATIFA. _Brugière._ Encyclop. Méthod. (des Vers), 1789.

  MITELLA. _Oken._ Lehrbuch der Naturgeschichte, 1815.

  RAMPHIDIONA. _Schumacher._ Essai d’un Nouveau Syst. &c., 1817
        (ante Julium).

  POLYLEPAS. _De Blainville._ Dict. des Sc. Nat., 1824.

  CAPITULUM (secundum Klein). _J. E. Gray._ Annals of Philos., tom.
        x, new series, Aug. 1825.

   [63] This is one of the rare cases in which, after much
   deliberation, and with the advice of several distinguished
   naturalists, I have departed from the Rules of the British
   Association; for it will be seen that _Mitella_ of Oken, and
   _Ramphidiona_ of Schumacher, are both prior to _Pollicipes_ of
   Leach; yet, as the latter name has been universally adopted
   throughout Europe and North America, and has been extensively
   used in geological works, it appears to me to be as useless as
   hopeless to attempt any change. It may be observed that the genus
   _Pollicipes_ was originally proposed by Sir John Hill (‘History
   of Animals,’ vol. iii, p. 170), in 1752, but as this was before
   the discovery of the binomial system, by the Rules it is
   absolutely excluded as of any authority. In my opinion, under all
   these circumstances, it would be mere pedantry to go back to
   Oken’s ‘Lehrbuch der Naturgeschichte’ for the name _Mitella_,--a
   work little known, and displaying entire ignorance regarding the
   Cirripedia.

_Valvæ ab 18 usque ad 100 et amplius: lateribus verticilli inferioris
multis; lineis incrementi deorsùm ordinatis: sub-rostrum semper adest:
pedunculus squamiferus._

Valves from 18 to above 100 in number: latera of the lower whorl
numerous, with their lines of growth directed downwards: sub-rostrum
always present: peduncle squamiferous.

Hermaphrodite; filamentary appendages either none, or numerous and
seated on the prosoma and at the bases of the first pair of cirri;
labrum bullate; trophi various; olfactory orifices generally highly
prominent; caudal appendages uni-articulate and spinose, or
multi-articulate.

    Attached to fixed, or less commonly to floating objects, in the
    warmer temperate, and tropical seas.

It has been remarked, under Scalpellum, how imperfectly that genus is
separated from Pollicipes; and we have seen under _Scalpellum villosum_
that the addition of a few small valves to the lower whorl, would
convert it into a Pollicipes, most closely allied to _P. sertus_ and
_spinosus_. It has also been shown, that the six recent species of
Pollicipes might be divided into three genera, of which _P. cornucopia_,
_P. elegans_, and _P. polymerus_, would form one thoroughly natural
genus, as natural as Lepas and the earlier genera; _P. mitella_ would
form a second; and _P. sertus_ and _P. spinosus_ a third; but I have
acted to the best of my judgment in at present retaining the six species
together. As far as the valves of the capitulum are concerned, it would
be very difficult to separate _P. mitella_ from _P. sertus_ and
_spinosus_.

_Description._ The number of valves in the capitulum has in this genus
acquired its maximum. The number varies considerably in the same
species, and even on opposite sides of the same individual, and
generally increases with age. It is more important, that the number of
the whorls in _P. cornucopia_, and in the two following closely-allied
forms, also increases with age. In _P. sertus_ and _P. spinosus_, even
the number of the whorls varies in different individuals, independently
of age. The valves are arranged alternately with those above and below;
they are generally thick and strong, making the capitulum somewhat
massive; in some species they are subject to much disintegration; but in
others, the apices of the several valves, especially of the carina and
rostrum, are well preserved, and project freely: they are covered with
membrane, which, differently from in most species of Scalpellum, either
does not bear any spines, or only exceedingly minute points. In all the
species there is a sub-rostrum and sub-carina, and often beneath these a
second sub-rostrum and sub-carina. In medium-sized specimens there are
at least 20 valves in the lowermost whorl. The carina is either straight
or curved, but never rectangularly bent, and is always of considerable
breadth. None of the valves are added to at their upper ends. The scuta
have a deep pit for the adductor muscle. The valves lie either some
little way apart, or more commonly close together. In _P. mitella_ the
scuta and terga are locked together by a fold, and the valves of the
lower whorl overlap each other in a peculiar manner, resembling that in
which the compartments in the shells of Sessile Cirripedes fold over
each other.

The _Peduncle_ is of considerable length in some of the species, and
rather short in others; it is, in every case, clothed with calcified
scales. The scales in the first four species are placed alternately and
symmetrically; they are formed and added to in the same manner as in
Scalpellum; they differ in size according to the size of the individual,
and consequently the lower scales on the peduncle, formed when the
specimen was young, are smaller than the upper scales; the lower scales
are separated from each other by wide interspaces of membrane, owing to
the continued growth of the peduncle by the formation of new layers of
membrane, and the disintegration of the old outer layers. Each scale is
invested by tough membrane (or has been, for it is often abraded off),
in the same manner as the valves; each is furnished with one or more
tubuli, in connection with the underlying corium. In _P. sertus_ and _P.
spinosus_, the scales are small, spindle-shaped, and not of equal sizes,
and the rows are distant from each other, so that their alternate
arrangement is not distinguishable; in these two species, new scales are
formed round the summit of the peduncle, and the growth of each is
completed whilst remaining in the uppermost row; but, besides these
normal scales, such as exist in the other species of Pollicipes and in
Scalpellum, new scales are formed in the lower part of the peduncle,
which are generally of very irregular shapes, are often larger than the
upper ones, are crowded together, and sometimes do not reach the outer
surface of the membrane. This formation of scales in the lower part of
the peduncle, independently of the regular rows round the uppermost
part, is perhaps a feeble representation of the calcareous cup at the
bottom of the peduncle in the genus Lithotrya. The prehensile antennæ
will be described under _P. cornucopia_.

_Size._--Most of the species are large: and _P. mitella_ is the most
massive of the Pedunculated Cirripedes.

The _Mouth_ is not placed far from the adductor muscle. The labrum is
highly bullate. The mandibles have either three or four main teeth (Pl.
X, fig. 1), with often either one or two smaller teeth inserted between
the first and second. The maxillæ (Pl. X, figs. 13, 14), have their
edges either straight and square, or notched, or more commonly with two
or three prominences bearing tufts of finer spines. The outer maxillæ
(fig. 17) generally have a deep notch on their inner edges, but this is
not invariable. The olfactory orifices in most of the species are highly
prominent.

_Cirri._--The first pair is never placed far distant from the second.
The posterior cirri have strong, somewhat protuberant segments; and
between each of the four or five pair of main spines (Pl. X, fig. 27),
there is a rather large tuft of straight, fine, short bristles. The
second and third pair have the basal segments, either of the anterior
rami, or of both rami, so thickly clothed with spines (fig. 25), as to
be brush-like: in _P. mitella_, however, the third pair is like the
three posterior pair in the arrangement of its spines, in this respect
resembling the sessile Chthamalinæ. The caudal appendages are either
uni-articulate and spinose, or multi-articulate: it is remarkable that
there should be this difference in such closely allied species as _P.
cornucopia_ and _P. polymerus_: the short, obtuse, obscurely-articulated
caudal appendage of the former species (fig. 22) makes an excellent
passage from the uni-articulate (fig. 19) to the multi-articulate form,
as in _P. mitella_.

The stomach, in those species which I opened, is destitute of cæca; the
hepatic glands are arranged in straight lines; the rectum is unusually
short. The prosoma is well developed.

In _P. cornucopia_, _P. elegans_, and _P. polymerus_, there are numerous
filamentary appendages both on the prosoma, and at the bases of the
first pair of cirri: these appendages are occupied by testes, and I
suspect stand in relation to the length of the peduncle and consequent
great development of the ovaria. In order to give space for the
filamentary appendages, the sack (generally roughened by small
inwardly-pointing papillæ) penetrates more deeply than usual into the
upper part of the peduncle. There are small ovigerous fræna in _P.
sertus_, _P. spinosus_, and _P. mitella_: in the three other species,
the frænum or fold occupies the usual position on each side, and is
large; but in one specimen carefully examined by me, I was unable to see
any glands; and in another specimen, the ovigerous lamellæ were not
attached to the fræna; hence I conclude that the fræna are functionless
in these three species.

_Affinities._--I have already remarked on the close relationship between
this genus and Scalpellum; there is also some affinity with Lithotrya.

    _Distribution._--All over the world. The _P. cornucopia_ ranges
    from Scotland to Teneriffe: the _P. polymerus_ is found in
    opposite hemispheres in the Pacific Ocean, extending from
    California to at least as far as 32° south of the Equator.

_Geological History._--Having so lately given, in the ‘Memoirs of the
Palæontographical Society,’ a full account of all the fossil species
known, I will not repeat here the conclusions there arrived at. I will
only state, that species of Pollicipes are found in all the formations,
extending from the Lower Oolite to the Upper Tertiary beds.

1. POLLICIPES CORNUCOPIA. Pl. VII, fig. 1.

  POLLICIPES CORNUCOPIA. _Leach._ Encyclop. Brit. Supp., vol. iii,
        1824.

  ---- SMYTHII, var. _Leach_. Ibid.

  LEPAS POLLICIPES. _Gmelin._ Systema Naturæ, 1789.

  ---- GALLORUM. _Spengler._ Skrivter Naturhist. Selskabet, Bd. i,
        Tab. vi, fig. 9, 1790.

_P. capitulo, valvarum duobus aut pluribus sub-rostro verticillis
instructo: valvis albis, aut glaucis: pedunculo, squamarum densis
verticillis symmetricè dispositis._

Capitulum with two or more whorls of valves under the rostrum; valves
white or gray; scales on the peduncle symmetrically arranged in close
whorls.

Maxillæ with three tufts of fine bristles, separated by larger spines:
segments in the first cirrus less than half the number of those in the
sixth cirrus: caudal appendages multi-articulate: filamentary appendages
attached to the prosoma.

    Coast of Portugal; mouth of the Tagus. England,[64] Ireland, and
    the Frith of Forth in Scotland. Mediterranean (according to
    Brugière): Teneriffe: Mogador, Africa.

   [64] This species is said by Montagu (‘Test. Brit. Supplement’)
   to have been found attached to drift timber in the Frith of
   Forth, and to the bottom of a wrecked vessel towed into
   Dartmouth. According to Mr. W. Thompson (‘Annals of Nat. Hist.’
   vol. xiii, p. 436), it has been found attached to wood-work near
   Dublin.

Capitulum, obtusely triangular, massive: valves close together, rather
thick, with their exterior surfaces convex, naked, except in the lower
parts, where united together by tough, greenish-brown membrane,
destitute of spines. The edges of the orifice are widely bordered by
membrane, coloured fine crimson red. The valves, in a specimen with a
capitulum above three quarters of an inch long, were 52 in number; in a
specimen one fifth of an inch long, only between 20 and 30. Two whorls
of valves are distinct beneath the carina and rostrum. In one specimen
in Mr. Cuming’s collection, with a capitulum 1.4 of an inch long, there
were three whorls beneath the rostrum, and four beneath the carina. The
scuta, terga, and carina are much larger than the other valves.

_Scuta_, oval, the basal and tergo-lateral margins sweeping into each
other, and the apex pointed; internally (Pl. VII, fig. 1 _a_) the pit
for the adductor muscle is deep.

_Terga_, larger than the scuta, internally (fig. 1 _a_) slightly
concave; carinal margin much curved and protuberant; basal angle blunt;
scutal margin either curved with the upper part straight, or formed of
two almost distinct lines, corresponding with the tergal margin of the
scutum, and with one of the sides of the upper latus.

_Carina_, much curved, extending far up between the terga, internally
deeply concave, widening much from the top to the bottom; basal margin
highly protuberant, with a central portion either truncated and very
slightly hollowed out, or bluntly and rectangularly pointed, with the
apex itself rounded.

_Rostrum_, not one third of the length of the carina, concave,
triangular, with the basal margin slightly protuberant. Of the other
valves, including the sub-carina and sub-rostrum, the shape of their
inner surfaces is sub-triangular, with the basal margin convex;
externally the umbones are pointed, and slightly curled inwards, so as
to overlap each other like tiles: the smaller valves, however, of the
lower whorls (fig. 1 _a_) are more or less transversely elongated, so as
to become almost elliptic instead of triangular. Of the latera, the
upper pair, which corresponds to the interspace between the scuta and
terga, is the largest, but barely exceeds in size the pair answering to
the carinal latera in Scalpellum, which lie between the terga and
carina: the next largest pair is the rostral, or that between the scuta
and rostrum. Some, however, of the lower latera are of nearly equal
size.

_Peduncle_, narrower, but generally longer than the capitulum; upper
part encased with small calcareous scales, with their apices curved
inwards, and overlapping each other. The inner surface of each scale is
triangular, with the basal margin protuberant. The scales continue to
grow or be added to, only in about the ten upper whorls, which form but
a small part of the whole peduncle; in the lower part, the scales become
further and further separated from each other. The surface of
attachment, in full-grown specimens, is broad; but in two very young
specimens, which I removed with great care after the action of potash, I
found the peduncle ending in a filiform prolongation, such as often
occurs in _Scalpellum vulgare_ and in _Lepas fascicularis_. At the
extremity of the pointed peduncle, there were seated the larval
prehensile antennæ, of which the following measurements are given to
show how minute they are.

                                                            _Inch._
  Length, from apex of disc, to the further
      edge of the basal articulation                       20/6000
  Breadth of basal segment, in broadest part                6/6000
  Hoof-like disc, length of                                 6/6000
  Ultimate segment, entire length of                        6/6000
      “       “     breadth, in broadest part               6/20000

The disc resembles a broad, rounded hoof, very little longer than broad,
and narrowed in at the heel; the apex is not at all pointed, and bears
some minute and thin spines. There is one large spine on the under side
of the disc; and another on the basal segment, on the outside, in the
usual position. The ultimate segment is long and thin; it has a notch on
the inner side (the segment supposed to be stretched forward), bearing
two or three long flexuous spines; and there are three or four other
spines on the summit: altogether there is a close resemblance with the
antennæ in Scalpellum, excepting that the hoof-like disc is not here
pointed.

_Colours._--Valves internally tinted, in parts, grey; peduncle, brown;
corium of sack, purplish-brown, of peduncle, rich coppery brown; cirri,
banded dorsally, and with the front surfaces of the segments,
purplish-brown. Edge of the orifice of sack, fine crimson red. The
specimen here described had been dried for a few weeks, and was then
moistened.

_Dimensions._--The largest specimen which I have seen, in Mr. Cuming’s
collection, had a capitulum 1 and 4/10ths of an inch long; a fine
specimen, from Teneriffe, was 9/10ths in length. In a specimen with a
capitulum 1/20th of an inch long, and about the same in breadth, there
were eighteen valves; so that, besides the principal valves, five pair
of latera, the sub-carina, and sub-rostrum, were already developed, and
on the upper part of the peduncle, there were many calcareous scales.

_Filamentary Appendages._--The prosoma is well-developed, with thirteen
or fourteen pair of short, blunt filaments, placed close together in two
longitudinal rows; those nearest the thorax are the longest; outside
this double row, on each side, there is a row of papillæ, indicating a
tendency to the formation of two other rows of filaments. There is a
pair of longer filaments, one on each side of the mouth, pointing
upwards, and thinly clothed with long spines; at the bases of the first
pair of cirri there is a second pair of filaments, shorter and bearing a
few minute spines. The bottom of the sack is studded with small rounded
papillæ, with roughened summits.

_Mouth_, not placed very far from the adductor muscle.

_Labrum_, highly bullate, equalling, in its longitudinal diameter, the
rest of the mouth; upper part square, not overhanging the lower part;
there are some small teeth on the crest.

_Palpi_, oval, outer and inner margins nearly alike, thickly clothed
with spines.

_Mandibles_, with three very strong, yellow teeth; inferior point broad,
coarsely pectinated. In one specimen, on one side, the third tooth was
represented by two smaller teeth.

The _Maxillæ_ bear three conspicuous tufts of fine bristles, separated
by larger spines; the first tuft is placed close to the two, upper,
large, but unequally-sized spines; the second tuft is placed in the
middle, and the third at the inferior angle. The two latter tufts stand
on prominences; between the two upper tufts there are three pair, and
between the two lower tufts four or more pair of rather strong spines:
(see the figure, 13, Pl. X, in the allied _P. polymerus_.)

_Outer Maxillæ_, with the inner edge divided in the middle by a
conspicuous notch, and with the bristles above and below short, making
two _equal_ combs. On the exterior surface, the bristles are longer and
more spread out. Olfactory orifices prominent, protected by a punctured
swelling between the bases of the first pair of cirri.

_Cirri_, short and rather thick; the first pair is not far removed from
the second. The segments of the three posterior pair are somewhat
protuberant, bearing six pair of short, strong spines, graduated in
length, between which there is a very thick, longitudinal brush of
short, fine, straight bristles, of which the lower ones are the longest;
some thick, minute spines arise from the upper lateral edges of the
segments. The spines in the dorsal tufts are short, much crowded, and of
nearly equal length; see figure, 27, Pl. X, in the allied _P.
polymerus_. In a specimen in which the sixth cirrus had seventeen
segments, the first cirrus had, in the shorter ramus, eight segments, of
which the lower four were thick and protuberant, with the spines doubly
serrated. In this same specimen, the anterior ramus of the second cirrus
had twelve segments, of which the five basal ones were highly
protuberant, and thickly clothed with non-serrated spines. In the third
cirrus the basal segments of the anterior ramus are highly protuberant.
The basal segments in the posterior rami of both these cirri, are
slightly protuberant, but otherwise resemble the segments in the three
posterior pair.

The _Caudal Appendages_ (Pl. X, fig. 22), in full-grown specimens, just
exceed in length the lower segments of the pedicels of the sixth cirrus;
they are nearly cylindrical, bluntly pointed, with five oblique
imperfect articulations; the lower or basal articulations cannot be
traced all round, being distinct only on the ventral surface. There is a
row of short spines round the upper edge of each segment, with a little,
short tuft on the point of the terminal segment. In a rather young
specimen, however, with its capitulum one fifth of an inch long, each
appendage certainly consisted of a single segment, with spines only on
the summit.

_Penis_ purple, with excessively short and fine spines in tufts, chiefly
near the extremity. In a specimen with a capitulum only one fifth of an
inch long, the penis consisted of a mere pointed papilla, not so long as
the caudal appendage, and therefore equalling in length only the lower
segment of the pedicel of the sixth cirrus.

_Ovigerous fræna._--I could see none, though there were two large
lamellæ in the sack. The ova were flesh-coloured, but they had been
dried and then placed in spirits. The ova were wonderfully numerous,
oval, much elongated, and 1/100th of an inch in length.

2. POLLICIPES ELEGANS.

  POLLICIPES ELEGANS. _Lesson._ Voyage de la Coquille, tom. ii, p.
        441, 1830, et Illust. Zool., Pl. xxxix, 1831.

  ---- RUBER. _G. B. Sowerby._ Zoolog. Proc., 1833, p. 74.

_P. capitulo, valvarum duobus aut pluribus sub-rostro verticillis
instructo: valvis et pedunculi squamis rufo-aurantiacis: squamarum
verticillis densis symmetricè dispositis._

Capitulum with two or more whorls of valves under the rostrum: valves
and scales of peduncle reddish-orange; the latter symmetrically arranged
in close whorls.

Maxillæ with three tufts of fine bristles, separated by larger spines;
segments is in the first cirrus more than half the number of those in
the sixth cirrus; caudal appendages multi-articulate; filamentary
appendages attached to the prosoma.

    Coast of Peru, Payta, attached to wooden posts, according to
    Lesson: Lobos Island, Peru, Mus. Cuming: West Coast of Mexico,
    Tehuantepec, on an exposed rock, according to Hinds.

The resemblance of this species is so close to _P. cornucopia_, that it
is quite useless to do more than point out the few points of difference.
Valves of the capitulum and scales of the peduncle, coloured (after
having been in spirits,) reddish-orange. In a specimen in which the
capitulum was 1.3 of an inch in length, there were three whorls of
valves below the carina; in this large specimen altogether there were
about eighty valves; in medium-sized specimens, the number is about the
same as in _P. cornucopia_. The upper latus, (viewed internally,) has an
area about twice as large as that latus, which corresponds to the
interspace between the carina and terga; whereas in _P. cornucopia_ the
upper latus is only slightly larger than this same valve. The apex of
the basal internal margin of the carina is here rounded, instead of
being square, as is generally the case with _P. cornucopia_. The strong
membranous margin of the orifice of the sack, in its upper part, is
almost one third as wide as the widest part of the terga, whereas in _P.
cornucopia_ it is only one fourth of this same width. The peduncle
apparently is rather longer, compared with _P. cornucopia_, and the
calcareous scales on it perhaps a little larger in proportion.

In a very young specimen, with the capitulum barely exceeding 1/20th of
an inch in length, I could distinguish the sub-rostrum, sub-carina, the
upper, and some of the lower latera.

_Filamentary Appendages._--These, in a medium-sized specimen, are
arranged on the prosoma in four longitudinal approximate rows, there
being twelve in each row; those in the two outer rows are only half the
length of those in the two inner rows; those nearest the thorax are the
longest; there are some papillæ outside the outer rows. In a very large
specimen with its capitulum 1.3 in length, these filaments were very
much more numerous, and some were placed on the first segment of the
thorax, and at the bases of several of the posterior cirri. Some of the
filaments are bifid, trifid, and even branched. In all the specimens, at
the bases of the first pair of cirri, there are, on each side, a pair of
filaments, (one below the other,) pointing upwards, less than half as
long as those on the prosoma: also on each side of the mouth, there is a
longer and thicker filament, pointing upwards, with a few very minute
scattered spines on it; the apices of these three pair of filaments, as
well as of some of the others, are roughened with very minute pectinated
scales. All these filaments were gorged with the branching testes.

_Mouth._--The parts are closely similar to those in _P. cornucopia_; in
the mandibles, the interspace between the third tooth and the inferior
angle, is slightly pectinated: in the maxillæ, there are six or eight
pairs of spines between the two upper tufts of fine spines.

_Cirri._--These are in most respects similar, to those of _P.
cornucopia_. In a specimen in which the sixth cirrus had eighteen
segments, the shorter ramus of the first pair had ten segments, of which
the five lower segments were thick and clothed with doubly serrated
spines. In the second cirrus the anterior ramus had fifteen segments, of
which the four basal ones were highly protuberant, and thickly clothed
with spines. These spines, and some on the third cirrus, and a few on
the first cirrus, have peculiar bent teeth, presently to be described
under _P. polymerus_. These singularly toothed spines are absent in _P.
cornucopia_. From the above numbers, we see that the first and second
pairs of cirri have more segments in proportion to the sixth pair, than
in _P. cornucopia_; and in the second pair, a fewer proportional number
of the basal segments are protuberant and thickly clothed with spines.

_Caudal Appendages_, shorter than the lower segments of the pedicels of
the sixth cirrus, with only four articulations; rather constricted near
the base.

The _Ovigerous Fræna_ consist of very long and prominent folds, thinning
out to nothing towards the bases of the scuta, but not furnished, as far
as I could see, with glands, and therefore not normally functional.

_Diagnosis with P. cornucopia._--The reddish-orange colour of the valves
alone suffices. There is a very slight difference, in the larger
proportional size of the upper latera, and in the outline of the basal
margin of the carina. In the maxillæ there is, in _P. elegans_, a
greater width between the two upper tufts of fine spines. In the cirri,
the segments in the first pair, are more than half as many as those in
the sixth pair; in the anterior ramus of the second pair, only 4/15ths
of the segments are protuberant and brush-like, whereas in _P.
cornucopia_ 5/12ths are in this condition.

3. POLLICIPES POLYMERUS. Pl. VII, fig. 2.

  POLLICIPES POLYMERUS.(!) _G.B. Sowerby._ Proc. Zool. Soc., 1833,
        p. 74.

  --MORTONI. (!) _Conrad._ Journal Acad. Nat. Sci. Philadelphia,
        vol. vii, p. 261, Pl. xx, fig. 12, 1837.

_P. capitulo, valvarum duobus, tribus, aut pluribus sub-rostro
verticillis instructo: valvis sub-fuscis: lateribus à supremo ad infimum
gradatim quoad magnitudinem positis: carinæ margine basali (introrsùm
spectanti) ad medium excavato: pedunculi squamarum verticillis densis,
symmetricè dispositis._

Capitulum with two, three, or more whorls of valves under the rostrum:
valves brownish: latera regularly graduated in size from the uppermost
to the lowest: carina with the basal margin, (viewed internally,)
hollowed out in the middle: scales of the peduncle symmetrically
arranged in close whorls.

Maxillæ with three tufts of fine bristles, separated by larger spines;
caudal appendages uniarticulate; filamentary appendages attached to the
prosoma.

    Upper California, St. Diego and Barbara, 32° to 35° N.,
    according to Conrad; Mus. Cuming: Low Archipelago, Pacific