2. Scalpellum ornatum. Pl. VI, fig 1.

S. (Fœm.) valvis 14, sub-rufis: lateribus superioribus quadranti-formibus, arcu crenâ profundâ notato.

(Fem.) Capitulum with 14 reddish valves: upper latera quadrant-shaped, with the arched side deeply notched.

Mandibles with three teeth; maxillæ narrow, bearing only four or five pair of spines.

Males, two, lodged in cavities on the under sides of the scuta; pouch-formed, with four unequal, rudimentary valves: no mouth: cirri not prehensile.

FEMALE.

Capitulum oblong, with the upper portion much produced; valves, 14, thick, naked, closely locked together, irregularly clouded with pale crimson; the membrane connecting the valves is not furnished with spines. On most of the valves there are furrows and ridges diverging from the umbones, and the lines of growth are plainly marked: in the valves of the lower whorl, the umbones are slightly protuberant.

Scuta, convex, unusually thick, oblong, quadrilateral, with the occludent margin the longest; lateral margin slightly hollowed out. The umbo (and primordial valve) is situated at the uppermost point of the valve, and consequently the growth is exclusively downwards. On the under side (Pl. VI, figs. 1 b´ and 1 c´), in about the middle of the valve, there is a pit (a) for the adductor scutorum muscle, the depth and distinctness of which varies a little; above the pit, and between it and the apex, there is a transverse, oblong, deeper depression (b), within which, the male is lodged. A small portion of the apex of the valve projects over the terga.

Terga, large, nearly equalling the scuta in area, flat and sub-triangular; the scutal margin is not quite straight. The apex of the valve is thick and solid, and must have projected freely for a length equalling one third of the occludent margin.

Carina, laterally broad, angularly bent; slightly widening from the apex to the base; internally, deeply concave. The position of the umbo varies, in young specimens it is seated at the uppermost point, and consequently in such there is no upward growth; in older specimens, from the junction and upward production of that part on each side of the valve, which I have called in fossil specimens the intra-parietes, the valve is added to above the umbo, but to a lesser degree than in S. vulgare. Slight ridges separate the roof from the parietes, and the parietes from the intra-parietes.

Rostrum, minute, narrow, widening a little from the apex downwards, inserted like a wedge between the umbones of the rostral latera, and hardly projecting above their upper margins, so as to be easily overlooked: internally concave.

Upper Latera (fig. 1 á), quadrant-shaped, with a deep square notch cut out of the arched margin, which notch receives the upper point of 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.

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?

3. Scalpellum rutilum. Pl. VI, fig. 2.

S. (Fœm. 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.

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.

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.

[† † 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.

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.