Class—CRUSTACEA. Sub-Class—CIRRIPEDIA. (continued 2)

Female Organs.—M. Martin St. Ange has described how the peduncle[19] is gorged with an inextricable mass of branching ovarian tubes, filled with granular matter and immature ova. In Conchoderma and Alepas, the ovarian tubes run up in a single plane (Pl. IX, fig. 3,) between the two folds of corium round the sack. Here the development of the ova can be well followed: a minute point first branches out from one of the tubes; its head then enlarges, like the bud of a tulip on a footstalk; becomes globular; shows traces of dividing, and at last splits into three, four, or five egg-shaped balls, which finally separate as perfect ova. Within the peduncle, the ovarian tubes branch out in all directions, and within the footstalks of the branches (differently from what takes place round the sack), ova are developed, as well as at their ends. Close together, along the rostral (i. e., ventral) edge of the peduncle, two nearly straight, main ovarian tubes or ducts may be detected, which do not give out any branches till about half way down the peduncle, where they subdivide into branches, which inosculate together, and give rise to the mass filling the peduncle, and sometimes, as we have just seen, sending up branches round the sack. These two main unbranched ovarian ducts, followed up the peduncle, are seen to enter the body of the Cirripede (close along side the great double peduncular nerves), and then separating, they sweep in a large curve along each flank of the prosoma, under the superficial muscles, towards the bases of the first pair of cirri; and then rising up, they run into two glandular masses. These latter rest on the upper edge of the stomach, and touch the cæca where such exist; they were thought by Cuvier to be salivary glands. They are of an orange colour, and form two, parallel, gut-formed masses, having, in Conchoderma, a great flexure, and generally dividing at the end near the mouth into a few blunt branches. I was not able to ascertain whether the two main ducts, coming from the peduncle, expanded to envelope them, or what the precise connection was. The state of these two masses varied much; sometimes they were hollow, with only their walls spotted with a few cellular little masses; at other times they contained or rather were formed of, more or less globular or finger-shaped aggregations of pulpy matter; and lastly, the whole consisted of separate pointed little balls, each with a large inner cell, and this again with two or three included granules. These so closely resembled, in general appearance and size, the ovigerms with their germinal vesicles and spots, which I have often seen at the first commencement of the formation of the ova in the ovarian tubes in the peduncle, that I cannot doubt that such is their nature. Hence I conclude, that these two gut-formed masses are the true ovaria. I may add, that several times I have seen in the two long, unbranched ducts, connecting the true ovaria and the ovarian tubes in the peduncle, pellets of orange-coloured cellular matter (i. e., ovigerms) forming at short intervals little enlargements in the ducts, and apparently travelling into the peduncle.

The structure here described is quite conformable with that which we have seen in the larva; in the latter, two gut-formed masses of equal thickness extended from the cæca of the stomach to within the future peduncle, where the cement-ducts entered them, and where, after a short period, they were seen to expand into a mass of ovarian tubes. In the mature Cirripede, the cement-ducts can still be found united to the ovarian tubes in the middle of peduncle; and the cause of the wide separation of the true ovaria and ovarian tubes, can be simply accounted for by the internal, almost complete intersection of the animal, which takes place during the last metamorphosis.

The ova, when excluded, remain in the sack of the animal until the larvæ are hatched; they are very numerous, and generally form two concave, nearly circular, leaves, which I have called after Steenstrup and other authors, the ovigerous lamellæ (Pl. IV, fig. 2 b). These lamellæ lie low down on each side of the sack: in Conchoderma virgata, however, there is often only a single lamella, forming a deeply concave cup: in C. aurita there are generally on each side four lamellæ, one under the other. The ova lie in a layer from two to four deep; and all are held together by a most delicate transparent membrane, which separately enfolds each ovum: this membrane is often thicker and stronger round the margins of the lamellæ, where they are united, in a peculiar manner, presently to be described, to a fold of skin, on each side of the sack: these two folds, I have called the ovigerous fræna (Pl. IV, fig. 2 f).

M. Martin St. Ange, describes an orifice under the carina, by which he supposes the ova to enter the sack; this, after repeated and most careful examinations, I venture to affirm does not exist; on the contrary, I have every reason to believe that the ova enter the sack in the following curious manner. Immediately before one of the periods of exuviation, the ova burst forth from the the ovarian tubes in the peduncle and round the sack, and, carried along the open circulatory channels, are collected (by means unknown to me) beneath the chitine-tunic of the sack, in the corium, which is at this period remarkably spongy and full of cavities. The corium then forms or rather (as I believe) resolves itself into the very delicate membrane separately enveloping each ovum, and uniting them together into two lamellæ; the corium having thus far retreated, then forms under the lamellæ the chitine-tunic of the sack, which will of course be of larger size than the last-formed one, now immediately to be moulted with the other integuments of the body. As soon as this exuviation is effected, the tender ova, united into two lamellæ, and adhering, as yet, to the bottom of the sack, are exposed: as the membranes harden, the lamellæ become detached from the bottom of the sack, and are attached to the ovigerous fræna. To demonstrate this view, an individual should have been found, with both the old and new chitine tunic of the sack, and with the lamellæ lying between them; this, I believe, I have seen, but it was before I understood the full importance of the fact: a great number of specimens would have to be examined in order to succeed again, for the changes connected with exuviation supervene very quickly. I have, however, several times found the ova so loose under the sack, as to be detached with a touch from the ovarian tubes; and I have twice carefully examined specimens, which had just moulted, as shown by even the mandibles being flexible, in which the lamellæ had not become united to the fræna, but still adhered to the newly-formed chitine tunic of the sack; in these, the ova were so tender, that they broke into pieces rather than be separated from the membrane of the lamella, itself hardly perfectly developed, for pulpy cellular matter adhered outside some of the ova. These and other facts are quite inexplicable on any other view than that advanced.

As the lamellæ are formed without organic union with the parent, they would be liable to be washed out of the widely open sack of the Lepadidæ, if they had not been specially attached to the fræna. These fræna consist of a pair of more or less semicircular folds of skin, depending inside the sack, on each side of the point of attachment of the body. The fræna are often of considerable size, but in Ibla, they are very minute; they are formed of chitine tunic with underlying corium, like the rest of the sack; on their crests, there is a row, or a set of circular groups, or a broad surface, covered, either with minute, pointed, bead-like bodies mounted on long hair-like footstalks, or with staff-formed bodies on very short footstalks. I measured some of the bead-like bodies, in Lepas anserifera, and they were 1/2000th of an inch in diameter, and the footstalks three or four times as long as the elongated heads. These heads, of whatever shape they may be, have an opaque, and, I believe, glandular centre; I could not make out with certainty an aperture at their ends, but, I believe, such exists, and they seem to secrete a substance, which hardens into a strong membrane, serving to unite the crest of the frænum to the edges of the lamellæ. In one case, this bit of membrane seemed formed of a woven mass of threads. These little glandular bodies, with the membrane formed by them, are cast off at each exuviation, and new glands formed on the crest of the frænum underneath. In some species of Pollicipes, (viz., P. cornucopia and elegans,) the fræna, though present and large, are functionless and destitute of the glands: I believe, they exist in this same functionless condition, and in rather a different position in the sessile Cirripedes, and that in this family they serve as Branchiæ.

The above-described method by which Cirripedia lay their eggs, namely, united together in a common membrane, placed between their old outer and new inner integuments, and the manner in which the lamellæ, when thus formed, are retained for a time fastened to the fræna, and are then cast off, appears to me very curious. In some of the lower Crustacea, it is known, that the ova escape by rupturing the ovisacs formed by the protruded ovarian tubes, and this is the nearest analogy with which I am acquainted. The ova are impregnated (as I infer from the state of the vesiculæ seminales), when first brought into the sack, and whilst the membrane of the lamellæ is very tender: the long probosciformed penis seems well adapted for this end. In the male of Ibla Cumingii, which has not a probosciformed penis, the whole flexible body, probably, performs the function of the penis: in Scalpellum ornatum, however, the spermatozoa must be brought in by the action of the cirri, or of the currents produced by them. That cross impregnation may and sometimes does take place, I infer from the singular case of an individual, in a group of Balani, in which the penis had been cut off, and had healed without any perforation; notwithstanding which fact, larvæ were included in the ova.

Exuviation; Rate of Growth; Size.—I have had occasion repeatedly to allude to the exuviation of the Lepadidæ: with the exception of the genus Lithotrya,[20] in which the calcareous scales on the peduncle, together with the membrane connecting them, is cast off, neither the valves nor the membrane uniting them, nor that forming the peduncle with its scales and styles, are moulted; but the surface gradually disintegrates and is removed, perhaps sometimes in flakes, whilst new and larger layers are formed beneath. In Scalpellum, I ascertained that the new membrane, connecting together the newly-formed calcified rims under the valves of the capitulum, was formed as a fold, with the articulated spines which it bears, all adpressed in certain definite directions. This fold of new membrane, when the old membrane splits and yields, of course expands, and thus the size of the capitulum is increased. In the peduncle, lines of splitting can seldom be perceived, except, indeed, in the sub-globular, embedded, downward-growing peduncle of Anelasma, as described under that genus. I do not understand what determines the complicated lines of splitting of the old membrane between the several valves of the capitulum,—without it be simply, that along these lines alone, the old membrane is not strengthened by the new membrane being closely applied under it, the new being formed, as we have just said, in a fold, in order to allow of increase in size. Although, as I believe, there is strictly no exuviation in the outer membranes of mature Lepadidæ, it seems that narrow strips of membrane are cast off from between the valves, for the few first moults, after the final metamorphosis of the larva. I may here remark that, in most sessile Cirripedes, the outside membrane connecting the operculum and shell, is regularly moulted.

The delicate tunic lining the sack, (a mere duplicature of that thick one, forming the outside of the capitulum, and generally transformed into valves,) and the integuments of the whole body, are regularly moulted. With these integuments, the membrane lining the œsophagus, the rectum, and the deep olfactory pouches, and the horny apodemes of the maxillæ, are all cast together. I have seen a specimen of Lepas, in which, from some morbid adhesion, the old membrane lining one of the olfactory pouches had not been moulted, but remained projecting from the orifice as a brown shrivelled scroll. The new spines on the cirri (and on the maxillæ) are formed within the old ones; but as they have to be a little longer than the latter, and as they cannot enter these up to their very points, their basal portions are not thus included, but are formed, running obliquely across the segments of the cirri; and what is curious, these same basal portions are turned inside out, like the fingers of a glove when hastily drawn off. After the exuviation of the old spines, the new spines have their inverted basal portions drawn out from within the segments, and turned outside in, so as to assume their proper positions.

All Cirripedia grow rapidly: the yawl of H. M. S. Beagle was lowered into the water, at the Galapagos Archipelago, on the 15th of September, and, after an interval of exactly thirty-three days, was hauled in: I found on her bottom, a specimen of Conchoderma virgata with the capitulum and peduncle, each half an inch in length, and the former 7/20ths in width: this is half the size of the largest specimen I have seen of this species: several other individuals, not half the size of the above, contained numerous ova in their lamellæ, ready to burst forth. Supposing the larva of the largest specimen became attached the first day the boat was put into the water, we have the metamorphosis, an increase of length from about .05, the size of the larva, to an whole inch, and the laying of probably several sets of eggs, all effected in thirty-three days. From this rapid growth, repeated exuviations must be requisite. Mr. W. Thompson, of Belfast, kept twenty specimens of Balanus balanoides, a form of much slower growth, alive, and on the twelfth day he found the twenty-first integument, showing that all had moulted once, and one individual twice within this period. I may here add, that the pedunculated Cirripedes never attain so large a bulk as the sessile; Lepas anatifera is sometimes sixteen inches in length, but of this, the far greater portion consists of the peduncle. Pollicipes mitella is the most massive kind; I have seen a specimen with a capitulum 2.3 of an inch in width.

Affinities.—Considering the close affinity between the several genera, there are, I conceive, no grounds for dividing the Lepadidæ into sub-families, as has been proposed by some authors, who have trusted exclusively to external characters. In establishing the eleven genera in the Lepadidæ, no one part or set of organs affords sufficient diagnostic characters: the number of the valves is the most obvious, and one of the most useful characters, but it fails when the valves are nearly rudimentary, and when they are numerous: the direction of their lines of growth is more important, and fails to be characteristic only in Scalpellum: with the same exception, the presence or abscence of calcified or horny scales on the peduncle is a good generic character. For this same end, the shape of the scuta and carina, but not of the other valves, comes into play. In three genera, the presence of filamentary appendages on the animal’s body is generic; in Pollicipes, however, they are found only on three out of the six species. The number of teeth in the mandibles, and the shape of the maxillæ, often prove serviceable for this end; as does more generally the presence of caudal appendages, and whether they be naked or spinose, uniarticulate or multiarticulate; in Pollicipes alone this part is variable, being uni-and multi-articulate; and in one species of Scalpellum they are absent, though present in all the others. The shape of the body, the absence or presence of teeth on the labrum, the inner edge of the outer maxillæ being notched or straight, the prominence of the olfactory orifices, the arrangement of the spines on the cirri, and the number and form of their segments, are only of specific value.

Comparing the pedunculated and sessile Cirripedes, it is, I think, impossible to assign them a higher rank than that of Families. The chief difference between them consists, in the Lepadidæ, in the presence of three layers of striæ-less muscles, longitudinal, transverse and oblique, continuously surrounding the peduncle, but not specially attached to the scuta and terga; and on the other hand, in the Balanidæ, of five longitudinal bundles of voluntary muscles, with transverse striæ, fixed to the scuta and terga, and giving them powers of independent movement. In the Lepadidæ, the lower valves, or when such are absent, the membranous walls of the capitulum, move with the scuta and terga when opened or shut; and the lower part of the capitulum is separated by a moveable peduncle from the surface of attachment; in the sessile Cirripedes, the lower valves are firmly united together into an immovable ring, fixed immovably on the surface of attachment. I will not compare the softer parts, such as the cirri and trophi, of the Lepadidæ with those of the Balanidæ, as my examination of this latter family is not fully completed: I will only remark, that there is a very close general resemblance, more especially with the sub-family Chthamalinæ.

Geographical Range; Habitats.—The Pedunculated Cirripedes extend over the whole world; and most of the individual species have large ranges, more especially, as might have been expected, those attached to floating objects; excepting these latter, the greater number inhabit the warmer temperate, and tropical seas. Of those attached to fixed objects, or to littoral animals, it is rare to find more than three or four species in the same locality. On the shores of Europe I know of only three, viz., a Scalpellum, Pollicipes, and Alepas. At Madeira (owing to the admirable researches of the Rev. R. T. Lowe), two Pæcilasmas, a Dichelaspis, and an Oxynaspis are known. In New Zealand, there are two Pollicipes and an Alepas, and, perhaps, a fourth form. From the Philippine Archipelago, in the great collection made by Mr. Cuming, there are a Pæcilasma, an Ibla, a Scalpellum, Pollicipes, and Lithotrya. Of all the Lepadidæ, nearly half are attached to floating objects, or to animals which are able to change their positions; the other half are generally attached to fixed organic or inorganic bodies, and more frequently to the former than to the latter. Most of the species of Scalpellum are inhabitants of deep water; on the other hand, most of Pollicipes,[21] of Ibla, and Lithotrya are littoral forms. The species of Lithotrya have the power of excavating burrows in calcareous rocks, shells, and corals; and the singular manner in which this is effected, is described under that genus. Anelasma has its sub-globular peduncle deeply embedded in the flesh of Northern Sharks; and I have seen instances of the basal end of the peduncle of Conchoderma aurita, being sunk into the skin of Cetacea; in the same way the point of the peduncle in the male of Ibla, is generally deeply embedded in the sack of the female. I believe in all these cases, the cementing substance affects and injures the corium or true skin of the animal on which the creature is parasitic, whilst the surrounding parts, being not injured, continue to grow upwards, thus causing the partial embedment of the Cirripede. In the case of Anelasma, we have growth at the end of the peduncle, and consequently downward pressure, and this may possibly cause absorption to take place in the skin of the shark at the spot pressed on.

Geological History.—Having treated this subject at length, in the volume of the Palæontographical Society for 1851, I will not here enter on it: I will only remark, that the Lepadidæ or Pedunculated Cirripedes are much more ancient, according to our present state of knowledge, than the Balanidæ. The former seem to have been at their culminant point during the Cretaceous Period, when many species of Scalpellum and Pollicipes, and a singular new genus, Loricula, existed; Pollicipes is the oldest genus, having been found in the Lower Oolite, and, perhaps, even in the Lias. The fossil species do not appear to have differed widely from existing forms.

Genus—Lepas. Plate I.

Lepas. Linnæus.[22] Systema Naturæ, 1767.

Anatifa. Brugière.[23] Encyclop. Method. (des Vers), 1789.

Anatifera. (Lister) et plerumque Auctorum Anglicorum.

Pentalasmis. (Hill.) Leach. Journal de Physique, July, 1817.

Pentalepas. De Blainville. Dict. des Sci. Nat., 1824.

Dosima. J. E. Gray. Annals of Philosophy, vol. x, 1825.

Valvæ 5, approximatæ: carina sursùm inter terga extensa, deorsùm aut furcâ infossâ aut disco externo terminata: scuta subtriangula, umbonibus ad angulum rostralem positis.

Valves 5, approximate: carina extending up between the terga, terminating downwards in an embedded fork, or in an external disc: scuta sub-triangular, with their umbones at the rostral angle.

Filaments seated beneath the basal articulation of the first cirri; mandibles with five teeth; maxillæ step-formed; caudal appendages uniarticulate, smooth.

Distribution.—Mundane; attached to floating objects.

Description.—Capitulum flattened, sub-triangular, composed of five approximate valves. The valves are either moderately thick and translucent, or very thin and transparent; and hence, though themselves colourless, they are often coloured by the underlying corium. Their surfaces are either smooth and polished, or striated, or furrowed, and sometimes pectinated. They are not subject to disintegration; they are generally naked, except on the borders, where they are coated, and held together by membrane; in L. fascicularis, however, the valves are covered with thin membrane, bearing very minute spines. The manner of growth of the valves will be best described under each. All the valves, even in the same species, are subject to considerable variation in shape, more especially the terga.

Scuta.—These valves are sub-triangular in outline, with the basal margin straight and rather short; and with occludent and tergo-carinal margins more or less protuberant; in L. fascicularis, however, the basal (Pl. I, fig. 6), and occludent margins are slightly reflexed and prominent. A ridge, generally runs from the umbo to the upper point. Internally, there is no conspicuous pit for the adductor muscle; under the umbones, there is generally either on both valves, or only on the right-hand side (Pl. I, fig. 1 c), a small calcareous projection or tooth, of variable size and shape, even in the same species; it is generally largest on the right-hand valve; these teeth at first sight appear to form a hinge, uniting the opposite scuta at their umbones, but this is not really the case, and their use appears to be only to give attachment to the membrane uniting the valves together, and to the peduncle. The basal margin is internally strengthened by a calcified rim, more or less developed. The umbones (and primordial valves when distinguishable,) are seated at the rostral angles; during growth the basal margin is not added to, and the occludent margin only to small extent; hence the main growth of the valve is at the upper end, and along the carina-tergal margin. In L. fascicularis, however, the basal reflexed margin is slightly added to beneath the umbo.

Terga,—flat, small compared with the scuta, usually of an irregular quadrilateral figure, with the two upper or occludent margins very short, in proportion to the two (carinal and scutal) lower margins; all the margins are nearly straight. The two occludent margins, generally meet each other at about right angles, forming a small triangular projection; in L. fascicularis, however, the occludent margin is formed by a single, slightly curved line. The umbones (and primordial valves when distinguishable) are not seated at the uppermost point, but at the angle where the carinal margin unites to the upper of the two occludent margins: during growth the terga are added to, both on the occludent and on the scutal margins, and slightly along the carinal margin; hence their growth is unequally quaqua-versal, except at one angle of the irregular quadrilateral figure.

Carina.—This is always very narrow and curved, concave within, often carinated and barbed exteriorly; it extends upwards between the terga for one half or two thirds of their length: at the lower extremity it ends (with the exception of L. fascicularis), in a small fork (Pl. I, fig. 1, a, b) rectangularly inflected and embedded in the membrane, beneath the basal margin of the scuta. From comparing this lower part of the carina in L. australis (fig. 5 a), with the same part in some of the species of the allied genus Pæcilasma, it would appear that the fork is formed by an oblong disc, more and more notched at the end, and with the rim between the two points more or less folded backwards: conformably with this view, in very young specimens of L. australis, instead of a large and sharp fork, there is a small disc. The only use of the fork appears to be to give firm attachment to the membrane uniting the valves and peduncle. In L. fascicularis, instead of a fork, there is a broad, oblong disc (figs. 6, 6 a), rectangularly inflected; it is much longer than the fork, in proportion to the upper part of the carina; the disc is not more deeply embedded than the upper part. The umbo (and primordial valve when distinguishable,) of the carina is seated just above the embedded fork (or disc in L. fascicularis), at the point where the inflection takes place; hence the main growth of the carina is upwards,—the fork, however, being of course, likewise added to at its point: in L. fascicularis, the growth is both upwards and downwards.

Peduncle and Attachment.—The peduncle is generally quite smooth: though with a high power its surface may be seen to be studded with minute beads, or larger discs, of yellowish and hard chitine; in the young of L. australis, and I suspect of some other species, it is covered with very minute spines. The peduncle in this genus attains its greatest development. The cement-tissue debouches, I believe, only through the functionless larval antennæ, except in one species, L. fascicularis, in which a ball of this substance is formed in a most peculiar manner round the peduncle (Pl. I, fig. 6), apparently for the purpose of serving as a float, as will be presently described.

Size and Colour.—The species of this genus are the largest of the Pedunculata, with the exception of some Pollicipes: even in the smallest species (L. pectinata), the capitulum sometimes attains a length of about half an inch. The peduncle varies much in length in the same species: in L. anatifera, it is occasionally above a foot long. The colours of L. anatifera, L. Hillii, and L. anserifera, are very bright and striking; the membrane bordering the valves and that round the top of peduncle in two of the species, is of the brightest scarlet-orange; the valves, owing to the underlying corium, are pale blueish-grey, and the interspaces between them dark leaden-purple. The cirri and trophi are generally dark purple or lead-colour.

Filamentary Appendages.—These are attached to beneath the basal articulation of first pair of cirri; they vary in the several species, from one to five or six on each side, the lowest being always the longest. Several of them are occupied by testes. In L. pectinata, generally, not even one is developed. They are subject to great variation in their proportional lengths, and in number, in the same species. These organs have generally been considered to serve as branchiæ; I see no reason to believe that they are more especially designed for this end, than is the general surface of the body.

Mouth.—The labrum is moderately bullate, the longitudinal diameter of this part equalling about one third, or half of that of the rest of the mouth. The palpi are moderately developed. The mandibles (Pl. X, fig. 5) have five teeth with the inferior point either broad, or very narrow and tooth-like. The maxillæ are step-formed (Pl. X, fig. 9); the first step is sometimes indistinct and curved; and in L. pectinata, all the steps vary much, and are more or less blended together. The outer maxillæ (like those at Pl. X, fig. 16), are internally clothed continuously with spines. The olfactory orifices are not at all prominent.

Cirri.—The first pair is placed near the second pair, and is of considerable length; the second has the anterior ramus thicker than the posterior ramus, and the segments brush-like; the segments (Pl. X, fig. 26) of the four posterior cirri bear from four to six pair of long spines, with a row of small intermediate spines: in the posterior cirri of L. australis the lateral rim spines are much developed; and in those of L. fascicularis, the usual pairs of large spines are lost in a broad triangular brush, formed by the increase of the lateral marginal, and intermediate spines.

Caudal Appendages (Pl. X, fig. 18 b), very small, either blunt or pointed, and quite destitute of spines.

The prosoma is well developed. The stomach is surrounded in the upper part by a circle of large branching cæca. The generative system is highly developed; the testes coating the whole of the stomach, entering the filamentary appendages and the pedicels of the cirri; the two ovigerous lamellæ contain a vast number of ova; they are united to rather large fræna, of which the sinuous margin supports either a continuous row or separate tufts of glands.

Distribution.—The species abound over the arctic, temperate and tropical parts of the Atlantic, Indian and Pacific Oceans, and are always, or nearly always, attached to floating objects, dead or alive. The same species have enormous ranges; in proof of which I may mention that of the six known species, five are found nearly all over the world, including the British coast; and the one not found on our shores, the L. australis, apparently inhabits the whole circumference of the southern ocean.

General Remarks and Affinities.—The first five species form a most natural genus; they are often sufficiently difficult to be distinguished, owing to their great variability. The sixth species (L. fascicularis) differs to a slight extent in many respects from the other species, and has considerable claims to be generically separated, as has been proposed by Mr. Gray, under the name of Dosima; but as it is identical in structure in all the more essential parts, I have not thought fit to separate it. As far as external characters go, some of the species of Pæcilasma have not stronger claims, than has L. fascicularis, to be generically separated; and I at first retained them altogether, but in drawing up this generic description, I found scarcely a single observation applicable to both halves of the genus; hence I was led to separate Lepas and Pæcilasma. If I had retained these two genera together, I should have had, also, to include the species of Dichelaspis and Oxynaspis; and even Scalpellum would have been separable only by the number of its valves; this would obviously have been highly inconvenient. Although some of the species of Pæcilasma so closely resemble externally the species of Lepas, yet if we consider their entire structure, we shall find that they are sufficiently distinct; as indirect evidence of this, I may remark that Conchoderma (as defined in this volume), includes two genera of most authors, and yet certainly comes, if judged by its whole organisation, nearer to Lepas than does Pæcilasma.

1. Lepas anatifera. Tab. I. fig. 1. (var.)

L. anatifera. Linnæus. Systema Naturæ, 1767.

Anatifa vel anatifera vel pentalasmis lævis[24], plerumque auctorum.

———— engonata (!).[25] Conrad. Journal Acad. Nat. Sc. Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 15.

———— dentata (var.) Brugière. Encyclop. Meth. (des Vers), 1789.

Pentalasmis dentatus (var.) Brown. Illust. Conch., Pl. lii, fig. 5.

Anatifa . . . . . . . . . . . . Martin St. Ange. Mem. sur l’organisation des Cirripedes, 1835.

L. valvis aut lævibus aut delicate striatis: è duobus scutis, dextro solùm dente interno umbonali instructo; pedunculi parte superiore fuscâ.

Valves smooth, or delicately striated. Right-hand scutum alone furnished with an internal umbonal tooth: uppermost part of peduncle dark-coloured.

Filaments, two on each side.

Var. (a). Fig. 1. Scuta and terga with one or more diagonal lines of dark greenish-brown, square, slightly depressed marks.

Var. (b). (Fig. 1 b.) Carina strongly barbed.

Extremely common; attached to floating timber, vessels, sea-weed, bottles, &c., and to each other, in the Atlantic Ocean, Mediterranean, West Indies, Indian Ocean, Philippine Archipelago, Sandwich Islands, Bass’s Straits, Van Diemen’s Land.

General Appearance.—Valves white, more or less translucent and thick, with a tinge of blueish-grey, from the underlying corium; sometimes brownish cream-coloured, rarely with a tint of purple. Surfaces smooth, with traces of very fine lines radiating from the umbones, sometimes rather plain on the basal part of the scuta. Length in proportion to the breadth of the capitulum variable, owing to the varying degree to which the scuta and terga have their apices produced. Scuta with the occludent margin either considerably curved or nearly straight. The internal tooth of the right-hand scutum, close to the umbo, varies in size and form, being either pointed, square, or obliquely truncated on either side, or it has a notch on the summit; internal basal rim of the scuta either plainly developed or nearly absent. In many specimens (Pl. I, fig. 1), on the scuta, or on the scuta and terga, (and sometimes more on one side of the individual than on the other,) a nearly straight line, running diagonally across the capitulum, of slight, quadrilateral depressions, of a dirty greenish colour, with the edges blending away, is either conspicuously developed, or can only just be discerned. These marks increase in size from the umbones to the margins of the valves. There are sometimes two or even three rows on the scuta. They are formed by the retention of a portion of the chitine membrane, which is cast off the rest of the surface; the margins of the valves are occasionally notched slightly on the line of marks; there is no difference along this line in the underlying corium. Specimens both with and without a barbed carina are thus characterised. Carina; the interspace between the carina and the scuta and terga is not wide. The carina exteriorly, is either convex and smooth, or furnished with knobs or with extremely sharp, long teeth (Pl. I, fig. 1 b); small specimens, with the capitulum under half an inch in length, are generally most strongly barbed.[26] Apex more or less acuminated; width and thickness variable; sides strongly furrowed. Fork (fig. 1 a) generally less wide than the widest upper part of the valve, with the two prongs diverging from each other at less than a right angle; their sharpness and precise form variable; rim between them reflexed (figs. 1 a and b), making a slight notch behind. Peduncle smooth, wrinkled, length in proportion to that of the capitulum varying, from barely equalling it, to six or seven times as long. I have noticed a specimen including mature ova, with a capitulum under half an inch long.

Filamentary Appendages;—never more than two on each side, with sometimes only one developed; of variable length; one seated on the flank of the prosoma, under the first cirrus; the second close under the basal articulation of this cirrus, on the posterior face of a slight swelling: these appendages correspond with g and h in Fig. 4, Pl. IX.

Mouth.—Mandibles (Pl. IX, fig. 5), with, as usual, five teeth, all pointing downwards. Maxillæ (Pl. IX, fig. 9), with the lower step of variable width compared to the two upper steps. Cirri; posterior cirri with segments (fig. 26) bearing six pair of spines; intermediate fine spines rather long; first cirrus, anterior ramus longer by only about two segments than the posterior ramus; second cirrus with anterior ramus, with very broad transverse rows of bristles; spine-bearing surfaces considerably protuberant; caudal prominences smooth, rounded.

Size.—The largest specimen which I have seen had a capitulum two inches in length; the longest, including the peduncle, was sixteen inches.

Colours.—Calcareous valves already described. Edges of the orifice bright scarlet orange; basal edges of the scuta, and sometimes of all the valves, with a torn border of orange membrane. Interspaces between the valves dull orange-brown. Peduncle darkish purplish-brown, with the lower part sometimes pale; chitine membrane itself tinted orange; in young specimens, peduncle pale, the colour first appearing in the uppermost part, close under the capitulum; this upper part is often darker than the other parts, and never orange-coloured, as in L. Hillii and L. anserifera. Sack internally dark purplish lead-colour, sometimes with a tinge of orange, darkest under the growing edges of the valves; body of animal pale purplish lead-colour. The four posterior cirri blackish purple; the second, and often the third cirrus, appear as if the colour had been laterally abraded off; these latter cirri have sometimes a tinge of orange. In very young specimens, the cirri are only barred with purple. The ova and the contents of the ovarian tubes are of a beautiful azure blue, becoming yellow in spirits.

In museums a vast amount of difference is seen in the colours of this species, caused by the method of preparation: if dried without having been in spirits, and subsequently kept dry, the orange tint round the orifice is preserved; if kept long in spirits, this is quite lost; but sometimes in specimens in spirits the colour of the membrane of peduncle is preserved and rendered pinker. The colours of the sack and animal are either quite discharged or rendered extremely dark. The valves themselves also often become more opaque. In some specimens well preserved in spirits, the sack and cirri were purplish-brown or lead-colour, tinted with dirty green, or orange, or bright yellow, or brick-red.

General Remarks.—From the foregoing description it will be seen how extremely variable almost every part of this species is. I find, in the British Museum, ten distinct specific names given by Dr. Leach to different varieties, or rather to different specimens, for some of them are undistinguishable. A specimen from the Sandwich Islands, sent by Mr. Conrad to Mr. Cuming, is marked A. engonata.

In looking over a large collection of specimens in a museum, the most distinctive characters appear at first to be the colours, the dentation or barbed condition of the carina, the row of square marks on the scuta and terga, and the more or less produced form of the whole capitulum: all these characters are absolutely worthless as distinctive characters, and blend into each other. In a fresh condition, the colours of this species, and of L. anserifera and L. Hillii are surprisingly alike, though in L. anatifera alone, the uppermost part of the peduncle is dark. As far as I have seen, the smoothness of the valves, together with the presence of a tooth beneath the umbo, on the right-hand scutum, and its entire absence on the left side, (in other species it is smaller on this, than on the right-hand side,) is an unfailing diagnostic mark. I believe this species is always attached to floating objects, though there are some very young specimens in the British Museum, collected by Sir G. Grey, adhering to sandstone, but this may have been buoyed up by some large sea-weed. Mr. Peach has given me the particulars of two instances, in which, after gales of wind, this species, of nearly full size, adhering to apparently freshly broken-off Laminariæ, has been cast upon the coast of England and Scotland.

2. Lepas Hillii. (Pl. I, fig. 2).

Anatifa vel pentalasmis lævis (!) plerumque auctorum.

Pentalasmis Hillii (!). Leach. Tuckey’s Congo Expedit. p. 413, 1818.

—————— cheloniæ (!) Ib. Ib.

Anatifa tricolor (?). Quoy et Gaimard. Ann. des Sc. Nat., 1st series, tom. x, 1827, Pl. vii, fig. 7, et Voyage de l’Astrolabe, Pl. xciii, fig. 4.

———— substriata (!). Conrad. Journal Acad. Nat. Sc., Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 14.

L. valvis lævibus; scutorum dentibus internis umbonalibus nullis; carinâ à cæteris valvis, furcâ etiam a scutorum basali margine, paululum distante; pedunculi parte superiore aut pallidâ aut aurantiacâ.

Valves smooth; scuta destitute of internal umbonal teeth; carina standing a little separate from the other valves, with the fork not close to the basal margin of the scuta; uppermost part of peduncle either pale or orange-coloured.

Filaments three on each side.

Extremely common; attached to ships’ bottoms, from all parts of the world; on floating timber; associated with L. anatifera and L. anserifera. Mediterranean. Attached to turtles, in the Atlantic, lat. 30° north. West Indies. Falkland Islands. “South Seas,” collected by A. Menzies. Port Stephen, Australia.

General Appearance.—Capitulum laterally flat; length varies in proportion to the breadth; valves white, somewhat translucent, moderately thick, very smooth, but with faint traces of radiating lines; in some varieties, surface rather irregular along the zones of growth. Scuta without any internal teeth, and with scarcely any trace of the internal basal rim; upper angle little acuminated; the occludent margins of the two scuta stand rather separate from each other, showing a wide space of corium between them: these margins are arched and protuberant, but with the lower part a little hollowed out; basal margin a little curved. In one specimen alone, I saw a trace of a diagonal line of square coloured marks, like those common in L. anatifera. Terga rather broad, with the basal angle not much acuminated. The degree of prominence and outline of the double occludent margin varies very much. Carina, separated by a rather wide space from the scuta and terga; of very varying shape, the upper part not much acuminated, generally very flat, sometimes exteriorly marked by a central depressed line; never barbed; occasionally, (in a specimen from Australia,) middle part so wide as almost to become spoon-shaped; on the other hand occasionally of nearly the same width throughout; somewhat constricted above the fork. Fork deeply embedded as usual; situated, in fresh specimens, a little way beneath the basal margins of the scuta, instead of touching them, as in the other species; forks of varying width, not so abruptly inflected as in many species; sometimes much narrower than the upper widest part of the valve, sometimes nearly twice as wide; prongs of fork not very sharp, diverging at about a right angle, with the rim between them reflexed. The apex of the carina extends up between the terga for barely half their length, instead of up fully three fourths of their length, as in L. anatifera.

The chitine membrane at the base of the capitulum, especially at the anterior and posterior ends, is covered with beautiful, little, embedded, yellowish beads, about 3/2000th of an inch in diameter; above this, on each side of the carina, there is a space with similar but smaller little spheres, and still higher up still minuter ones; others occur on different parts of the capitulum; these spaces are seen to be distinctly separated from each other, and present a beautiful appearance under a high power.

Peduncle, as long as, or rather longer than, the capitulum: in one set of specimens, however, it was thrice or four times as long as the capitulum. The peduncle, in some specimens, was conspicuously covered with transverse plates of yellowish hard chitine.

Filamentary Appendages.—Three on each side; one on the flank of the prosoma, with a pair beneath the basal articulation of the first cirrus; relative lengths various, but the posterior filament of the pair under the cirrus, is the shortest. Mouth; palpi not much acuminated; maxillæ step-formed, but with the upper or first step in some specimens indistinct, or forming a curve. Cirri; the segments of the first cirrus and of the posterior arm of the second cirrus are highly protuberant, the protuberances sometimes equalling half the thickness of the segments themselves. Caudal appendages smooth, rounded.

Size.—The largest specimen which I have seen, in the collection of Mr. Cuming, had a capitulum 1-1/10th of an inch long, and 1-1/4 wide; therefore not quite equalling in size the largest specimens of L. anatifera.

Colours.—When fresh, valves blueish-grey from the underlying corium, edges of all the valves and round the orifice, and round the top of the peduncle, bright orange-yellow, passing into the finest scarlet, and varying slightly in tint in different specimens. Space between the carina and the other valves, and between the occludent margins of the scuta, rich purplish-brown; peduncle either pale or purplish-brown, or only clouded on the sides with the same. In young specimens, peduncle nearly colourless; and in those under a quarter of an inch long in the capitulum, the top of the peduncle has not acquired its orange tint. Sack pale, leaden-purple, body the same, but paler and more reddish; cirri (but only the tips of first pair) tinted with fine golden orange. Immature ova in peduncle beautiful blue. After being long kept in spirits, the colours are changed, weakened, or discharged, as in L. anatifera and L. anserifera, and the valves become opaque. In some long-kept specimens the corium everywhere had become pale brown; more usually it assumes a dirty purplish lead-colour.

Monstrous Variety.—Amongst a set of ordinary specimens from a ship from Genoa, sent me by Mr. Stutchbury, there were three, one full-grown and two very young, with the whole capitulum, (and likewise with the scuta and terga taken separately,) not above half the usual length in proportion to the breadth. Neither the colours nor animal in this variety presented any difference.

General Remarks.—This species is almost universally confounded with L. anatifera. Quoy and Gaimard, however, appear to have distinguished it, under the name of A. tricolor, from its colours. Leach named it accidentally, for he specifies not one distinctive character, and besides his two published names, he has appended two other names to specimens in the British Museum. A specimen, from the Sandwich Islands, sent by Mr. Conrad to Mr. Cuming, is marked A. substriata. In a dry state, from the shrinking of the membranes, and consequent approach of the carina to the other valves, and of the fork to the basal margin of the scuta, it is most difficult to distinguish this species, though so decidedly distinct, from L. anatifera; the absence, however, of a tooth on the under side of the right-hand scutum is at once characteristic. Even in specimens kept in spirits, in which there has been no shrinking, but in which the colours have changed, and taking into account the variation in the carina and upper part of the terga, this species is not always readily distinguished from L. anatifera, without opening the valves and looking for the right-hand tooth of the latter. In fresh specimens, the orange ring at the top of the peduncle, and the broad purplish interspace between the carina and other valves, are characteristic. In all states, the filamentary appendages offer a good character.

3. Lepas anserifera. Pl. I, fig. 4.

L. anserifera. Linnæus. Syst. Naturæ, 1767.

Anatifa striata. Brug. Encyclop. Meth. (des vers), Pl. clxvi, fig. 3.

Pentalasmis dilatata! (young). Leach. Tuckey’s Congo Expedit., p. 413, 1818.

Anatifa sessilis (?). Quoy et Gaimard. Voyage de l’Astrolabe, Pl. xciii, fig. 11.

Lepas nauta.[27] Macgillivray. Edin. New Phil. Journ., vol. xxxviii, p. 300.

Pentalasmis anseriferus. Brown. Illust. Conch., 1844, Pl. li, fig. 1.

L. valvis approximatis leviter sulcatis (tergis præcipuè); scuto dextro dente forti interno umbonali, lævo aut dente exiguo, aut merâ cristâ instructo; margine occludente arcuato, prominente: pedunculi parte superiore aurantiacâ.

Valves approximate, slightly furrowed, especially the terga; right-hand scutum with a strong internal umbonal tooth; left-hand with a small tooth, or mere ridge; occludent margin arched, protuberant: uppermost part of peduncle orange-coloured.

Filaments five or six on each side.

Var. (dilatata, young); valves rather thin, finely furrowed, often strongly pectinated; scuta broad, with the occludent margins much arched, making the space wide between this margin and the ridge connecting the umbo and the apex: carina often barbed.

Common on ships’ bottoms from the Mediterranean, West Indies, South America, Mauritius, Coast of Africa and the East-Indian Archipelago. Central Pacific Ocean. China Sea. Chusan. Sydney. Attached to pumice, various species of fuci, Janthinæ, Spirulæ; often associated with L. anatifera and L. Hillii, and, in a young state, with L. fascicularis.

General Appearance.—Capitulum more or less elongated relatively to its breadth; in two specimens, with scuta of equal width, one was longer than the other by the whole of the occludent margin of the terga. Valves white, thick, (in young specimens sometimes diaphanous and thin,) closely approximate to each other; surfaces furrowed to a very variable amount. Terga generally more plainly furrowed than the scuta, of which the basal portion is generally less furrowed than the upper part; ridges, often rough, generally much narrower than the furrows: in half-grown specimens (var., dilatata of Leach,) the ridges are frequently denticulated, and there is even sometimes a row of bead-like teeth along the basal margins of the scuta. The ridges vary much, sometimes alternately wide and narrow; in two specimens of equal size, there were, in one, thirty-two ridges, and in the other only eighteen, on the scutum.

Scuta, with the occludent margin rounded and protuberant to a variable degree, but always leaving a rather wide space between the margin, and the ridge which runs from the umbo to the apex; apex pointed. Right-hand internal tooth considerably larger than that on the left, which is often reduced to a mere ridge; internal basal rim thick, sometimes furrowed along its upper edge, but of variable thickness, sometimes not extending as far as the baso-carinal angle. Terga, sometimes equalling, sometimes only two-thirds of, the length of the scuta; in young specimens, the two occludent margins form a right-angle with each other; in older specimens they form less than a right-angle, and hence the portion of valve thus bounded is unusually protuberant. Carina, within deeply concave; exterior sides finely furrowed longitudinally, generally denticulated; valve only slightly narrowed in above the fork, of which the prongs diverge at an angle of 90°, or rather more, and are wider than the widest upper part of the valve; rim between the prongs reflexed; the heel or external angle, just above the fork, sometimes considerably prominent. I have seen only a single large specimen with its carina barbed. In half-grown specimens, (var. dilatata, Leach,) the carina is often strongly barbed, with the upper point much acuminated, the fork about twice as wide as the widest upper part, and the prongs diverging at rather more than a right-angle. In some specimens, especially very young ones, there are at the base of the carina, above the fork, some strong, downward-pointed, inwardly-hooked, calcareous teeth; such occur also in some specimens along the basal margins of the scuta, two of these hooked teeth under the umbones of the scuta being larger than the rest: specimens conspicuously thus characterised came from the Navigator Islands; in these, I may add, the acutely triangular primordial valves were quite plain.

Peduncle, generally about as long as the capitulum; in young specimens generally short.

Filamentary Appendages, generally five, sometimes six, on each side; one is seated on the side of the prosoma, and the four others placed in pairs beneath the basal articulation of the first cirrus; the lowest posterior filament of the four generally is the largest. In young specimens, having a capitulum only half an inch long, the upper pair of the four often is not developed, or is represented by mere knobs. The mouth presents no distinctive characters. Cirri, with the longer ramus of the first pair almost equal to the shorter arms of the second pair; spine-bearing surfaces only slightly protuberant. Caudal appendages smooth, curved, pointed.

Size.—The largest specimen which I have seen, had a capitulum one inch and a half in length.

Colours.—The white valves are edged with bright orange membrane; and are so close to each other that no interspaces, coloured from the underlying corium, are left. Peduncle, dark orange-brown, with the uppermost part under the capitulum bright orange all round; the chitine membrane itself being thus coloured. Sack, internally, dark purplish lead-colour. Body and cirri, either nearly white or pale purplish-lead colour, with the arms of the second, third, and fourth cirri, and pedicels of the fifth and sixth, more or less tinted with orange. A specimen preserved during fourteen months in good spirits had only a tinge of orange left round the orifice and round the upper part of peduncle, and on the cirri. In some other specimens, badly preserved, the chitine membrane was quite colourless, and sack and cirri dirty lead-colour. Fresh ova, peach-blossom-red; immature ova, in ovarian tubes, pale pink.

Monstrous Variety.—In Mr. Stutchbury’s collection, there was a specimen, with the scuta, broad, smooth, thin, and fragile, without any ridge running from the umbo to the apex, and with the occludent margin reflexed. This seemed caused by the shell having been attacked by some boring animal, and from having supported Balani. In the same specimen the first cirrus on one side was monstrously thick and curled; the second cirrus had its posterior ramus in a rudimentary condition. In Mr. Cuming’s Collection, there are small specimens with the zones of growth overlapping each other, with thick irregular margins, and with the carina distorted.

This species has cost me much trouble: I have examined vast numbers of specimens, from a tenth to half an inch in length, attached to light floating objects, such as Janthinæ and Spirulæ from the tropical oceans, which all resembled each other, and slightly differed from the common appearance of L. anserifera: this variety is the Pentalasmis dilatata of Leach; and for a long time I considered it as a distinct species. It differs from L. anserifera, in the less thickness of the valves, in their being more finely and yet plainly furrowed; in the greater width of the scuta; and more especially, of that part of the valve lying between the occludent margin, and the ridge running from the umbo to the apex; in the less elongation of the area in the terga, bounded by the two occludent margins; and, lastly, in the less size of the whole individual. The trophi and cirri are absolutely identical. Lately, however, in carefully going over a great suite of specimens, all the above few distinctive characters broke down and insensibly graduated away; and I am convinced that this form is only a variety of L. anserifera; its different aspect being caused partly by youth, but chiefly, I suspect, from being attached to light objects floating close to the surface of the sea.

The Lepas anserifera can be distinguished by the slight furrows on its valves from all the other species, excepting L. pectinata: this latter species can be readily known, by the close proximity in the scuta of the occludent margin, and the ridge extending from the umbo to the apex; by its carina being very narrow above the fork; by the prongs of the fork diverging at an angle of from 135° to 180°; by the thinness of its valves; by the coarseness of the furrows on them; and lastly, by there being at most in L. pectinata only one filamentary appendage beneath the first cirrus.

4. Lepas pectinata. Pl. I, fig. 3.

Lepas pectinata. Spengler. Skrifter Naturhist. Selbskabet, 2, B. 2, H., 1793, Tab. X, fig. 2.

——— muricata (var.) Poli. Test. Utriusque Scicil., vol. i, Pl. vi, figs. 23, 29, 1795.

Lepas anserifera. Poli. Test. Utriusque Scicil., vol. i, Pl. vi, figs. 25-27.

——— sulcata. Montagu. Test. Brit., Pl. i, fig. 6, 1803.

Pentalasmis sulcata. Leach. Encyclop. Brit. Suppl., tom. iii, Pl. lvii, 1824.

——————— spirulæ (!) (var.) Leach. Tuckey’s Congo Expedit. Appendix, 1818.

——————— radula (var.) et sulcatus. Brown. Illust. of Conchology, Pl. li, figs. 3-6, 1844.

——————— inversus. Chenu. Illust. Conchy., Pl. i, fig. 14.

Anatifa sulcata. Quoy et Gaimard. Voyage de l’Astrolabe, Pl. xciii, figs. 18, 20.[28]

L. valvis tenuibus, crassè sulcatis, sæpe pectinatis; scutorum cristâ prominente ab umbone ad apicem juxta marginem occludentem pertinente: furcæ carinalis cruribus inter angulos 135° et 180° divergentibus.

Valves thin, coarsely furrowed, often pectinated. Scuta with a prominent ridge extending, from the umbo to the apex, close to the occludent margin; fork of the carina with the prongs diverging at an angle of from 135° to 180°.

Filaments absent, or only one on each side.

Var. (Pl. I, fig. 3 a), upper part of the terga (bounded by the two occludent margins) produced and sharp; surface of all the valves often coarsely pectinated, and with the carina barbed.

Atlantic Ocean, from the North of Ireland to off Cape Horn; common, under the tropics; Mediterranean: attached to wood, cork, charcoal, sea-weed, a reed-like leaf, spirulæ, cuttle-fish bones, to a bottle together with L. anatifera; to a ship’s bottom, Belfast, (W. Thompson.) Often associated with L. fascicularis. Montagu states (‘Test. Brit.,’ p. 18) that this species is sometimes attached to the fixed Gorgonia flabellum.

General Appearance.—The capitulum varies considerably in length compared to its breadth, caused chiefly by the greater or less production of the occludent portion of the terga; valves thin, brittle; the furrowed surface varies much in character, narrow and broad ridges often alternating; frequently each ridge (but more especially the ridge running from the umbo to the apex of each scutum, and sometimes that alone,) is covered with prominent, curled, flat, calcareous spines, giving the shell an appearance like that of many mollusca. Other specimens show no trace of these calcified projections. From the thinness of the valves and the depth of the furrows, the margins of the valves are sinuous. Scuta: the ridge running from the umbo to the apex is unusually prominent and curved; it runs very close to the occludent margin, so that, differently from in all the other species, only a very narrow space is left between this margin and the ridge. Internal teeth, under the umbones, either sharp and prominent, or mere knobs; sometimes that on the right side is much larger than that on the left; sometimes they are nearly equal; sometimes that on the left is scarcely distinguishable. Internal basal rim absent, or barely developed.

Terga: these valves have a conspicuous notch to receive the apex of the scuta; the two occludent margins either meet each other at a rectangle, or at a much smaller angle, causing the portion thus bounded to vary much in outline, area, and degree of prominence. This at first led me to think that the P. spirulæ of Leach, in which the point is very sharp and prominent, was a distinct species; but there are so many intermediate forms, that the idea must be given up. I may remark, that in all the species of Lepas, the upper part of the tergum seems particularly variable. The degree of acumination of the basal portion of the tergum also varies; the internal surface sometimes has small crests radiating from the umbo.

Carina, broad, within deeply concave; edges sinuous, externally sometimes strongly barbed; narrow above the fork, which latter is wider than the widest upper part of the valve; prongs sharp, thin, diverging at an angle of from 135° to 180°; the rim connecting the prongs not, or only slightly, reflexed.

Peduncle, narrow, shorter than the capitulum.

Filamentary Appendages, none, or only one, short, obtuse projection on each side, on the posterior face of the swelling under the first cirrus.

Mouth.—Mandibles, with the inferior point produced into a single pectinated tooth, rarely into two pectinated teeth; on one side of one specimen, there were only four instead of five teeth. Palpi very narrow. Maxillæ highly variable; they may be described as formed of five steps, of which the two lower ones are generally united into a single one, divided by a mere trace of a notch; or with the three lower steps blended into an irregular, projecting surface, and with even the fourth step indistinct. I have seen these two extreme forms on opposite sides of the mouth of the same individual,—on one side the maxillæ being regularly step-form, on the other the whole inferior part forming an almost straight edge, standing high up above the first notch or step which bears the two upper great spines.

Cirri.—First pair rather far removed from the second pair, with the longer ramus about three-fourths of the length of shorter ramus of second cirrus; spine-bearing surfaces, hardly at all protuberant; lateral marginal spines on the posterior cirri rather long; caudal appendages smooth, rounded, extremely minute: penis very spinose.

Size.—Capitulum in the largest specimen, six-tenths of an inch long; only a few arrive at this size.

Colours, after having been kept in spirits,—sack and cirri, especially first cirrus, clouded with pale purple; peduncle brownish; valves appear blueish in specimens not long preserved, but in specimens kept longer they become perfectly and delicately white.

General Remarks.—Under the head of L. anserifera, I have made some remarks on the diagnostic characters of this species. In the thinness of the valves,—form of the carina, with the rim connecting the prongs being not, or scarcely, reflexed,—and in the shortness and narrowness of the peduncle, there is some approach to L. australis, and thence to L. fascicularis. In the form of the maxillæ,—in one specimen having the mandible on one side bearing only four teeth,—and in the frequent absence of filamentary appendages, there is some approach to the genus Pæcilasma; but there is no such approach in the characters derived from the capitulum. We have seen that, as in so many other species of this genus, most of the parts are variable, and this is the case to a most unusual extent in the form of the maxillæ. Dr. Leach has attached eight specific names to the specimens preserved in the British Museum.

5. Lepas australis. Pl. I, fig. 5.

L. valvis glabris, tenuibus, fragilibus; scutorum dentibus umbonalibus utrinque internis; carinæ parte superiore latâ, planâ, suprâ furcam valdè constrictâ; furcæ cruribus latis, planis, tenuibus, acuminatis, intermedio margine non relexo.

Valves smooth, thin, brittle; scuta with internal umbonal teeth on both sides. Carina with the upper part broad, flat; much constricted above the fork, which has wide, flat, thin, pointed prongs, with the intermediate rim not reflexed.

Filaments, two on each side.

Common on Laminariæ in the whole Antarctic Ocean: Bass’s Straits, Van Diemen’s Land: Bay of Islands, New Zealand, lat. 35° S.: lat. 50° S., 172° W.: coast of Patagonia, lat. 45° S.: attached to bottom of H. M. S. Beagle, lat. 50° S., Patagonia: attached to a Nullipora, (I presume a drift piece,) British Museum.

General Appearance.—Capitulum rather obtuse and thick; valves thin, brittle, approximate, either white and transparent, or dirty-brown and opaque; or sometimes tinted internally with purple (perhaps the effects of being preserved in spirits); surface plainly marked by lines of growth, rarely marked with traces of lines radiating from the umbones. Scuta with teeth on both sides, nearly equal; internal basal rim rather wide, sometimes furrowed; basal margin considerably curved inwards. Terga rather wide; basal angle blunt; angle formed by the two occludent margins blunt and rounded. Carina (fig. 5 a) with the apex blunt, flat; the middle part generally very broad; much constricted above the fork, where it is internally deeply concave, and externally carinated; fork twice as broad as the broadest upper part of the valve; with the prongs flat, broad, thin, pointed, diverging at about an angle of 75°, with the intermediate rim not at all reflexed; the fork generally not deeply imbedded in the chitine membrane of the peduncle, so as to be quite easily visible externally; sometimes there is an internal, transverse, depressed line on the fork. In young specimens, with the capitulum about a quarter of an inch long, the fork of the carina is not developed, the lower slightly inflected portion consisting simply of an oval plate, twice as wide as the upper part. Until I had carefully examined a perfect series, showing the gradual changes in this part, I did not doubt that the young specimens formed a distinct species, and named it accordingly: the shortness of the penis first made me perceive that the specimens were immature. At this early age, I may add, the filamentary appendages were not developed. Peduncle either quite short, or as long as the capitulum, close under which it is considerably constricted all round.

Filamentary Appendages.—Two on each side; one long, tapering, placed on the prosoma (in one specimen represented by a mere knob), and the second shorter, situated on the posterior margin of the swelling beneath the first cirrus.

Mouth.—Maxillæ, with three large spines at the upper angle, and with the first step distinct, but narrow; mandibles with five teeth; in young specimens the inferior point ends in a single spine; sides of the supra-oral cavity very hairy; the membrane, forming the inner fold of the labrum, yellow and thickened in the form of a spoon.

Cirri.—In the posterior cirri there are, at the upper lateral edges of the segments on both sides, small spines; the segments in the first cirrus, and in the broad anterior ramus of the second cirrus, are hemispherically and considerably protuberant. Caudal appendages smooth.

Size.—The largest specimen had a capitulum one inch long.

The Colours (after having been long in spirit) of the valves have already been given; sack and peduncle dirty yellowish-brown, with the parts corresponding to the margins of the valves much darker brown, or almost black; segments of the cirri clouded with dark brown; body and pedicels of the cirri dirty yellowish. I have reason to believe that the colours are totally different in living specimens.

Monstrous Varieties.—Most of the specimens from lat. 50° S., on the coast of Patagonia, were more or less deformed, with the successive zones of growth overlapping each other, and forming coarse concentric ridges. The carina in several specimens was laterally distorted.

I have already remarked that this species has some affinity to L. pectinata; but it is much more closely related to L. fascicularis, the affinity being clearly shown by the thinness and translucency of the valves, their convexity, by the width and little acumination of the upper part of the carina, by the width of the fork, and by its not being deeply imbedded. In young specimens, moreover, before the fork is fully developed, there is a remarkable similarity between the two species, in the form of this lower part of the carina. Again, the narrowness and inflection of the peduncle under the capitulum in L. australis, and lastly, the lateral marginal spines on both sides of the segments of the posterior cirri, all clearly indicate this same affinity to L. fascicularis.

I believe this species is confined to the southern ocean; and perhaps there represents L. fascicularis of the northern and tropical seas. It must, judging from the number of specimens brought home by Captain Sir J. Ross, and from those previously in the British Museum, and from those collected by myself, be a very common species.

6. Lepas fascicularis. Pl. I, fig. 6.

Lepas fascicularis. Ellis and Solander. Zoophytes, 1786, Tab. xv, fig. 5.

——— ———— Montagu. Test. Brit. Suppl., 1808, pp. 5, 164.

——— cygnea. Spengler. Skrifter Naturhist. Selbskabet, Bd. i, 1790, Tab. vi, fig. 8.

——— dilata. Donovan. British Shells, 1804.

Pentalasmis fascicularis. Brown. Illust. Conch., 1844, Pl. li, fig. 2.

————— spirulicola (!) et Donovani (!) Leach. Tuckey’s Congo Expedit., p. 413, 1818.

Anatifa vitrea. Lamarck. Animaux sans Vertebres.

Dosima fascicularis. (!) J. E. Gray. Annals of Philosophy, vol. x, 1825.

Pentalepas vitrea. Lesson. Voyage de la Coquille. Mollusca, Pl. xvi, fig. 7, 1830.

Anatifa oceanica (!) Quoy et Gaimard. Voyage de l’Astrolabe, Pl. xciii.

L. valvis glabris, tenuibus, pellucidis; carinâ rectangulè flexâ, parte inferiore in discum planum oblongum expansâ.

Valves smooth, thin, transparent; carina rectangularly bent, with the lower part expanded into a flat oblong disc.

Filaments, five on each side; segments of the three posterior cirri with triangular brushes of spines.

Var. (Donovani, of Leach.) Carina with the upper part flat, spear-shaped, externally with a narrow central ridge.

Var. (Villosa. Pl. I, figs. 6 b, c.) Valves placed rather distant from each other; carina extremely narrow, with the upper part of nearly the same width throughout; terga with the lower part much acuminated; body of animal finely villose.

Coasts of Great Britain and France; Baltic Sea, according to Montagu Southern United States (from Agassiz); tropical Atlantic Ocean; East-Indian Archipelago, off Borneo and Celebes; Pacific Ocean, between the Sandwich and Mariana Archipelagos; New Zealand: attached to fuci, Spirulæ Janthinæ, Velellas, often to feathers and cork; often associated with the young of L. anserifera, (var. dilatata,) and L. pectinata.

General Appearance.—Capitulum highly variable in all its characters; thick and broad in proportion to its length, but the breadth is variable,—in some specimens, the capitulum being longer by one-fifth of its total length than broad; in others, one-fifth broader than long. Valves generally approximate; in some varieties, however, from the narrowness of the carina and terga, the valves stand far apart, there being an interval between the carina and scuta of nearly half the breadth of the latter. Valves excessively thin, brittle, transparent, colourless, smooth, but generally sinuous along the zones of growth, which are conspicuous: valves generally covered throughout by thin chitine membrane, which is thickly clothed, especially in the interspaces between the valves, with minute spines, barely visible to the naked eye. Scuta with the lower part of the tergo-carinal margin extremely protuberant; occludent margin, more or less, but slightly reflexed, with a depressed line running from the umbo to the apex; basal margin much reflexed, but to a variable extent and at a varying angle, even up to a right angle,—an external rim or collar being thus formed. There are no distinct internal teeth, but the basal margin under the umbones, is more or less distinctly produced into a rounded disc or projection, which is generally not so much outwardly reflexed as the rest of the basal margin: there is no distinct internal basal rim. The primordial valves are generally visible, but they do not lie, as in all other species, close to the basal margin, but a little above it,—the lower reflexed portion having been subsequently developed. Terga flat, with the occludent margin slightly arched, and not, as in the foregoing species, formed of two sides; apex bent towards the carina; width of the lower half highly variable, owing to the varying extent to which the scutal margin is hollowed out; in some specimens, the whole lower half beneath the apex of the scuta is of nearly the same width throughout; in other specimens this lower part is spear-shaped. The widest part of the tergum either equals in width, or is only two-thirds of the width of the widest part of the carina beneath its umbo. Carina (Pl. I, fig. 6 a) highly variable in shape, with the part above the umbo either spear-shaped and slightly concave within, or nearly flat and furnished with a central external ridge; or the upper part (fig. 6 c) is of equal and extreme narrowness throughout, and deeply concave within, appearing as if only the central ridge had been developed. The part below the umbo, (answering to the fork in the foregoing species,) is about one-third of the length of the whole valve, and generally twice as wide as the upper part, but in the variety with the upper part of the carina equally narrow throughout, the lower part is thrice as wide as the upper; the disc, or lower part, is generally slightly concave within, exteriorly either with or without a central ridge; basal margin rounded; lateral margin more or less curved, according to the form of the upper part. The disc is not more deeply imbedded in membrane than is the upper part of the valve. The heel or umbo is either angular and prominent, or rounded. In very young specimens the carina is simply bowed, instead of being rectangularly bent.

Peduncle,—short, narrow, being abruptly inflected all round under the basal edges of the capitulum; lower part of very variable shape, being often suddenly contracted into a mere thread (fig. 6 b), which sometimes widens again at the extreme end. The external membrane is very thin, and is penetrated by the usual fine tubuli leading to the corium; its surface is wrinkled and destitute of spines, or with extremely few. The peduncle is often completely surrounded by a yellowish ball, (of which I have seen specimens from the coast of England, and from off Borneo,) sometimes half as wide as the capitulum, composed of very tender, vesicular, structureless membrane, and of a pulpy substance: perhaps the yellow colour may be owing to long immersion in spirits. Some authors have supposed that the ball was the ovisac of the animal; and for the first few minutes, deceived by the numerous included spores of, as I believe, Bacillariæ, I thought that this was the case; others have supposed that it consisted of some encrusting algæ or other foreign organism; but it is, in reality, a most singular development of the cement-tissue, which ordinarily serves to attach Cirripedes by their bases to some extraneous object, but here surrounding that object and the peduncle, gives buoyancy, by its vesicular structure, to the whole. The membrane of the ball falls to pieces in caustic potash, differently from the chitine membrane of the enclosed peduncle, and this shows that there is some difference in composition from ordinary cement. The ball, when cut in two, exhibits an obscure concentric structure. The whole is excreted by the two cement-ducts, through two rows of orifices, one on each side of the surrounded portion of the peduncle; and I actually traced, in one case, the yellow pulpy substance coming out of the cement-ducts. The upper apertures are in gradation larger than those below them, and they stand a little further apart from each other; these are figured as seen from the outside, much magnified, at Pl. I, fig. 6 d. I did not succeed in finding the cement-glands, but I followed the ducts, of rather large size, running for a considerable distance as usual along and within the longitudinal muscles of the peduncle. Nearly opposite the uppermost aperture, on each side, the duct passes out through the corium, and becomes laterally attached to the outer membrane of the peduncle, at which point an aperture is formed (as in other cases, by some unknown process), thus giving exit to the contents of the duct. Beneath this upper aperture the duct runs down the peduncle, between the corium and the outer membrane, till it comes to the next aperture, to which it is also attached, and so on to all the lower ones; but I believe no cement tissue continues to pass out through these lower apertures. Beneath the lowest aperture the two ducts run into the two prehensile antennæ of the larva, which, as usual, terminate the peduncle. The antennæ are attached to some small foreign body in the centre of the vesicular ball, by the usual tough, light brown, transparent cement. The two upper apertures are nearly on a level with the outside surface of the ball; and it was evident that as the animal grows, new apertures are formed higher and higher up on the sides of the peduncle, and that out of these, fresh vesicular membrane proceeds, and grows over the old ball in a continuous layer. It appears that the growth of the vesicular ball is not regular,—that it is not always formed,—and that when formed the whole, or the lower part, sometimes disintegrates and is washed away. As that portion of the peduncle which is enclosed ceases to grow, and has its muscles absorbed, retaining only the underlying corium, whereas the upper unenclosed portion, and likewise, (as it appears) lower portions once enclosed but since denuded, continue to increase in diameter, the peduncle, when the vesicular ball is removed, often has the most irregular outline, contracting suddenly into a mere thread, and then occasionally expanding again at the basal point.

Frequently two or three specimens have their peduncles imbedded in one common ball, of which there is a fine specimen in the College of Surgeons (Pl. I, fig. 6), the ball being about one inch and a quarter in diameter, with a slice cut off. In this specimen, it is seen that the vesicular membrane proceeding from several individuals, unites to form one more or less symmetrical whole, and that the original common object of attachment is entirely hidden. Dr. Coates[29] gives a curious account of the infinite number of specimens, through which he sailed during several days, in the Southern Atlantic Ocean: the balls appeared like bird’s eggs, and were mistaken for some fucus, which was supposed to have encrusted the scales of the Velellæ, to which the Cirripede had originally become attached. Several individuals had their peduncles imbedded in the same ball, “which floated like a cork on the water.” As this species grows into an unusually bulky animal, we here see a beautiful and unique contrivance, in the cement forming a vesicular membranous mass, serving as a buoy to float the individuals, which, when young and light, were supported on the small objects to which they originally had been cemented in the usual manner.

Filamentary Appendages.—Five on each side, of which four lie in pairs at the base of the first cirrus (of these, only three are sometimes developed), and one on the flank of the prosoma.

Mouth.—Palpi much acuminated. Mandibles with five teeth; the first not far remote from the second; inferior point rather broad and finely pectinated. Maxillæ with two large, unequal, upper spines, and four regular steps.

Cirri.—Posterior cirri, with the upper parts of the segments slightly protuberant; in young specimens, the spines can be seen to consist of five pairs, placed in two converging lines in the upper half of each segment, with numerous minute, latero-marginal, and intermediate little bristles: in large specimens, all these latter have so increased in number, that the normal five pair cannot be distinguished, and the front of each segment is covered by a triangular thick brush of bristles, all pointing in the same direction, thus giving a very unusual character to the posterior cirri: the dorsal tuft on each segment consists of six or seven large spines, with from one to three dozen fine ones. First cirrus and anterior ramus of second cirrus with broad brushes of bristles. The pedicels of all the cirri are thickly covered with bristles. Caudal appendages smooth, with rounded summits.

Penis very hairy: vesiculæ seminales purple, much convoluted, lying within the prosoma; testes dendritic, scarcely enlarged at their terminal points, purplish; ovigerous fræna large with sinuous margins, the glandular beads being arranged in groups.

Size.—The largest specimen (from the coast of Devonshire) had a capitulum 1.6 of an inch long, and 1.2 broad, and of unusual thickness.

Colours, after having been in spirits: front surfaces of the segments of the cirri and of the pedicels purple. In some specimens from off Borneo, parts of the sack and the interspaces between the two scuta, were of a fine purple. Montagu states, that the whole shell and body of animal, when fresh, are pale blue, with the cirri spotted with brown.

General Remarks.—The extreme variability of this species is remarkable. In the College of Surgeons, there is a group of specimens collected by Mr. Bennett, I believe, in the Atlantic, in which the extreme narrowness of the carina and of the terga (Pl. I, fig. 6, b, c) (with consequent wide spaces of membrane left between these valves), led me, at first, to entertain no doubt, that it was quite a distinct species, which was strengthened by finding that the whole surface of the cirri were villose, with very minute spines; hence I called this variety, villosa. On the closest examination, however, I could detect no other differences, and the narrowness of the carina and terga varied very considerably: moreover, in one of the specimens, which was about intermediate in the form of its valves between this variety and the common form, the surfaces of the cirri were not in the least degree villose. Again, in some other specimens, the terga were as narrow as in Mr. Bennett’s, whilst the carina had its usual outline.

In a var. (called by Leach, P. Donovani,) from the Atlantic, under the Equator, the carina is remarkable from the extreme flatness of the upper part, and from the presence of an exterior, narrow, central ridge. In one specimen from Jersey, in the British Museum, the carina made an extremely near approach to this same form.

Affinities.—This species is certainly much the most distinct of any in the genus, and Mr. Gray has proposed to separate it under the name of Dosima; but considering the close similarity of the whole organisation of the internal parts, together with the transitional characters afforded by L. australis, I think the grounds for this separation are not quite sufficient. I have remarked, under L. australis, on the affinity between that and the present species. In the carina terminating in a disc (though here not imbedded), there is some slight affinity to Pæcilasma eburnea and crassa, and markedly so in the arrangement of the bristles on the posterior cirri. In the valves being covered with villose membrane, and to a certain extent in the form of the carina and of the occludent margin of the terga, and especially in the two rows of cement-orifices in the peduncle, there is some affinity to Scalpellum.

Pæcilasma. Nov. Genus.[30] Plate II.

Anatifa. J. E. Gray. Proc. Zoolog. Soc., 1848, p. 44.

Trilasmis. Hinds. Voyage of the Sulphur. Mollusca, 1844.

Valvæ, 3, 5, aut 7, approximatæ: carina solùm ad basales apices tergorum extensa, termino basali aut truncato aut in discum profunde infossum producto: scuta pænè ovalia, umbonibus ad angulum rostralem positis.

Valves, 3, 5, or 7, approximate: carina extending only to the basal points of the terga; with its lower end either truncated or produced into a deeply imbedded disc. Scuta nearly oval, with their umbones at the rostral angle.

Mandibles with four teeth; maxillæ notched, with the lower part of edge prominent; anterior ramus of the second cirrus not thicker than the posterior ramus; caudal appendages uniarticulate, spinose.

Generally attached to Crustacea.

I have already given my reasons for instituting and separating this genus from Lepas; as far as the capitulum is concerned, the differences between these genera certainly appear trivial; they consist in the carina not extending up between the terga, and in the lower end being either truncated, or produced into an imbedded disc: the terga have a single occludent margin. The included animal’s body differs in more important respects; for both mandibles and maxillæ are very distinct; the cirri of some of the species also differ; and the caudal appendages are here always spinose: there are no filamentary appendages: and lastly, the habits are different.

The genus may be divided into two sections, firstly, P. Kæmpferi and P. aurantia, which have their carinæ basally truncated, the basal angles of their terga cut off, and the anterior rami of their second cirri shorter than the posterior rami; and, secondly, P. crassa, P. fissa, and P. eburnea, which in these several respects are otherwise characterised. The P. eburnea, however, differs rather more from P. crassa and P. fissa, than these two do from each other; but certainly not enough to allow of the retention of Mr. Hinds’ genus of Trilasmis. P. crassa, in an especial degree, connects together all the forms.

General Appearance.—Capitulum oval, more or less produced, flat or gibbous; formed of three, five, or seven approximate valves; the lesser number arising from the abortion of the terga, and the greater number from the scuta being divided into two segments. Valves moderately thick, either white or reddish, smooth or striated, and sometimes partly covered by membrane, bearing minute spines. Scuta oval, of varying proportions; the basal margin is generally narrow, and blends into the carina-tergal margin; the internal basal rim generally is well developed, sometimes with, and sometimes without internal teeth beneath the umbones. In P. eburnea, and sometimes in P. crassa, there is a line of apparent fissure, and in P. fissa of actual disseverment, running from the umbo to the apex of each scutum, nearly in the line in which a ridge extends in Lepas: the primordial valves of the scuta in these three species, are seated at the basal angles of the lateral and larger segments. The positions of the primordial valves, and the direction of growth in the calcified valves, are, in all the species, the same as in Lepas. In several of the species attached to Crustacea, the two scuta are unequally convex, which is caused, as was pointed out to me by Mr. Gray, by that valve which lies close and nearly parallel to the body of the crab, being least developed. The Terga are either quite absent, or rudimentary as in P. crassa, or pretty well developed as in the other species: the occludent margin is single, and not double as generally in Lepas; the basal angle is either pointed or truncated. The Carina varies considerably in shape, but never extends up between the terga, nor ends downwards in a fork; in the first two species it is truncated; in the others, it terminates in a deeply-imbedded oblong disc, which in P. eburnea seems almost entirely (but of course not quite) to separate the inside of the capitulum from the peduncle; a similar separation is effected in P. fissa, where the imbedded disc is small, by two large teeth on the internal basal rims of the two scuta. The carina is always narrow, and either solid internally or very slightly concave.

Peduncle, is very short and narrow; the membrane is generally ringed with thicker, yellower portions, and often bears very minute spines.

Size.—All the species are small, with a capitulum not exceeding half an inch in length.

Filamentary Appendages.—None.

Mouth.—Labrum generally considerably bullate in the upper part, with a row of teeth on the crest. The mandibles have four teeth, with the inferior point narrow and spine-like, or rudimentary and absent. The maxillæ have, under the two or three upper great spines, a deep notch itself bearing spines; beneath this, the lower part is straight and considerably prominent, Pl. X, fig. 15. Outer maxillæ are covered on their inner sides continuously with spines.

Cirri.—The first pair is sometimes seated very distant from the second. The arrangement of the spines on the posterior cirri varies, to an unusual degree within the limits of the same genus. We have either the ordinary structure of anterior pairs, with single fine intermediate spines (as in P. Kæmpferi and aurantia), or we have the pairs increased by one or two additional longitudinal lateral rows, as in P. eburnea; or we have the front spines forming a single transverse row, as in P. crassa and P. fissa, Pl. X, fig. 29, a. The segments in none of the species are protuberant; the anterior ramus of the second cirrus does not seem to be thicker than the posterior ramus, as is usually the case. The rami of the second, and of most of the other cirri, are unequal in length,—the anterior ramus, contrary to the ordinary rule, being longer in P. eburnea, P. fissa, and P. crassa, than the posterior ramus by several segments; I have hitherto observed this inequality only in the sessile genus Chthamalus.

The Caudal Appendages are small, uniarticulate, and always furnished with bristles.

Distribution.—Four out of the five species live attached to Crustacea in the European and Eastern warmer temperate and tropical oceans; the fifth species was found attached to the dead spines of an Echinus, off New Guinea. It is probable that several more species will be hereafter discovered.

1. Pæcilasma Kæmpferi. Pl. II, Fig. 1.

P. valvis 5; carinæ basi truncatâ et cristatâ: scutorum dentibus internis umbonalibus fortibus: tergorum acumine basali truncato, margini occludenti pæne parallelo.

Valves 5; carina with a truncated and crested base; scuta with strong internal umbonal teeth; terga with the basal point truncated, almost parallel to the occludent margin.

Maxillæ with short thick spines in the notch under the two upper great spines; caudal appendages with scattered bristles on their summits, and along their whole outer margins.

Japan; attached, in great numbers, to the upper and under sides of the Inachus Kæmpferi of De Haan, a slow-moving brachyourous crab, probably from deep water. British Museum.

General Appearance.—Capitulum rather compressed, narrow, and produced. Valves white, tinged with orange, smooth, moderately thin, occasionally with faint traces of striæ radiating from the umbones. Scuta, apex pointed, with a very slight ridge running to the umbo; basal margin equalling two thirds of the length of the terga, with an internal basal rim; on the under side of each valve, beneath the umbo, there is a strong tooth. Out of the numerous specimens, all excepting one had their scuta unequally convex, with their occludent margins unequally curved, that of the more convex valve at the umbo, curling beyond the medial line. The basal end of the carina is, likewise, slightly curved laterally, and always turns towards the more convex valve. This inequality, as Mr. Gray pointed out to me, depends on the position of the specimens; the flatter side lying close to the carapace of the crab. Terga, flat, oblong, nearly rectangular; occludent margin straight; basal angle, truncated, almost parallel to the occludent margin; in width, three or four times as wide as the carina. Carina, (fig. 1, a) short, narrow, slightly curved, upper part broadest, with the apex rounded, only just passing up between the basal broad ends of the terga; externally carinated, internally very slightly concave; basal end abruptly truncated, crested, not deeply imbedded in the membrane of the peduncle.

Peduncle, barely as long as the capitulum, apparently (for specimens dry and much shrunk) narrow, surrounded by rings or folds of thicker yellowish membrane, of which the upper ones retain moderately long spines; low down these rings become confluent; whole surface finely dotted, dots largest on the rings.

Mouth.—Labrum highly bullate in the upper part, with a row of teeth on the crest; mandibles with four teeth, the fourth close to the inferior apex, which is very little developed, sometimes making the fourth tooth appear simply bifid. Maxillæ with two large spines on the upper angle, beneath which there is a large depression, bearing one rather long and thick, and four short and thick, spines; inferior upraised part with a double row of longer and thinner spines.

Cirri.—Posterior cirri with segments bearing five pairs of spines, of which the lowest pair is very minute; intermediate spines minute; spines of the dorsal tuft thin, of nearly equal size; segments not at all protuberant, elongated. First cirrus, standing far separated from the second (as in Scalpellum), with its nearly equal rami rather above half as long as those of the second cirrus. Second cirrus with anterior ramus not thicker, and scarcely more thickly clothed with spines, than the posterior ramus, but shorter than it by three or four segments; the spines not forming a very thick brush on the anterior ramus. Both rami of third cirrus with a longitudinal row of minute spines, parallel to the main pairs. Between the bases of the pedicels of the first pair of cirri, there are two closely approximate, conical flattened protuberances, like the single one to be described in Ibla.

Caudal Appendages, about one third of the length of the pedicel of the sixth cirrus, with some moderately long and strong spines at the end, and down the whole outer sides.

Ova, much pointed. Penis, hairy.

Size.—Capitulum in largest specimens half an inch long.

2. Pæcilasma aurantia. Pl. II, Fig. 2.

P. valvis 5; carinæ basi truncatâ: scutis ovatis, margine basali perbrevi, dentibus parvis, internis, umbonalibus instructo: tergorum acumine basali perobliquè truncato.

Valves 5; carina with a truncated base; scuta oval, with the basal margin very short, furnished with small internal umbonal teeth; terga, with the basal point very obliquely truncated.

Maxillæ with fine spines in the notch under the three great upper spines; caudal appendages with scattered bristles on their summits, and along only the upper part of their outer margins.

Madeira; found by the Rev. R. T. Lowe, attached to the rare Homola Cuvierii, probably a deep-water crab. British Museum.

General Appearance.—This species so closely resembles P. Kæmpferi, that it is superfluous to describe it in detail; and I will indicate only the points of difference. When the valves have been well preserved, they are of fine pale orange colour, and hence the name above given, which was proposed by the Rev. R. T. Lowe.

Scuta, with the internal umbonal teeth small; basal internal marginal rim very prominent, furrowed within; basal margin short, (only equalling half the length of terga), owing to the great curvature of the lower part of the carino-tergal margin; hence, the outline of the scuta is almost pointed oval. I saw no appearance of inequality in the two sides.

Terga, rather smaller in proportion to the scuta, than in P. Kæmpferi, with the basal end very obliquely truncated, so as to appear at first simply pointed, not parallel to the occludent margin; apex considerably more pointed and produced than in the foregoing species.

Carina, almost of equal narrowness throughout, barely concave within; lower end triangular, abruptly truncated, and not crested.

Primordial valves very plain, with the usual hexagonal structure: those of the terga, rounded at both ends, instead of being square, as in the mature calcified valves.

Peduncle short, narrow, not half as long as the capitulum; paved with minute equal beads, as in the genus Dichelaspis.

Mouth.—Mandibles with the fourth tooth very small; inferior angle rudimentary. Maxillæ, with three great upper spines, beneath which there is a deep notch bearing some delicate spines; inferior upraised part, as in P. Kæmpferi.

Cirri.—Rami of first cirrus hardly more than one third as long as the rami of the second cirrus, which latter rami are unequal in length by only two segments; the posterior ramus being the longer one.

Caudal Appendages, with only two or three lateral bristles, besides those on the summit.

Size.—Capitulum, three to four tenths of an inch long.

General Remarks.—This species has the closest general resemblance to P. Kæmpferi, and is evidently a representative of it. On close examination, however, almost every part differs slightly; the chief points being the narrowness of the basal margin of the scuta; the obliqueness of the truncated basal end of the terga and the sharpness of the upper end; the rudimentary state of the inferior angle of the mandibles; the character of the spines on the maxillæ; the proportional lengths of the cirri, and the fewness of the spines on the outer sides of the caudal appendages. The fact of Madeira having this Pæcilasma, a representative both in structure and habits of a Japan species, is interesting, inasmuch, as I am informed by Mr. Lowe, that some of the Madeira fishes are analogues of those of Japan.

3. Pæcilasma crassa. Pl. II, Fig. 3.

Anatifa crassa. J. E. Gray. Proc. Zoolog. Soc., 1848, p. 44, Annulosa, Tab. iii, figs. 5, 6.

P. valvis 5; carinæ termino basali in discum parvum infossum producto: scutis convexis, dentibus internis umbonalibus nullis: tergis pæne rudimentalibus, vix carinâ latioribus.