_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 Paecilasma, 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 antennae, 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 inters.p.a.ces 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 branchiae; 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 maxillae 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 maxillae (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 dest.i.tute of spines.
The prosoma is well developed. The stomach is surrounded in the upper part by a circle of large branching caeca. 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 lamellae contain a vast number of ova; they are united to rather large fraena, 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 sh.o.r.es, the _L. australis_, apparently inhabits the whole circ.u.mference 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 Paecilasma 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 Paecilasma. 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 Paecilasma 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 Paecilasma.
1. LEPAS ANATIFERA. Tab. I. fig. 1. (_var._)
L. ANATIFERA. _Linnaeus._ Systema Naturae, 1767.
ANATIFA vel ANATIFERA vel PENTALASMIS laevis[24], plerumque auctorum.
---- ENGONATA (!).[25] _Conrad._ Journal Acad. Nat. Sc.
Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 15.
---- DENTATA (var.) _Brugiere._ Encyclop. Meth. (des Vers), 1789.
PENTALASMIS DENTATUS (var.) _Brown._ Ill.u.s.t. Conch., Pl. lii, fig.
5.
ANATIFA ..... _Martin St. Ange._ Mem. sur l"organisation des Cirripedes, 1835.
[24] As this, though the commonest species, has never been defined, I give only a few synonyms and references, it being quite impossible to distinguish, in any published description, this species from _A. Hillii_ of Leach; this latter species I recognise under this name only from having authentic specimens from the British Museum, as Leach overlooked every one of the real diagnostic characters.
[25] I have used, in conformity with botanists, the mark of interjection, to show that I have seen an authentic specimen.
_L. valvis aut laevibus aut delicate striatis: e duobus scutis, dextro solum dente interno umbonali instructo; pedunculi parte superiore fusca._
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, Ba.s.s"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 inters.p.a.ce between the carina and the scuta and terga is not wide. The carina exteriorly, is either convex and smooth, or furnished with k.n.o.bs 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 ac.u.minated; 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 p.r.o.ngs 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.
[26] Mr. W. Thompson found that 15 specimens, out of about 200, attached to a vessel which came from New Orleans into Belfast, had their carinas barbed.
_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. Maxillae (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. Inters.p.a.ces 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. c.u.ming, 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 Laminariae, has been cast upon the coast of England and Scotland.
2. LEPAS HILLII. (Pl. I, fig. 2).
ANATIFA vel PENTALASMIS LaeVIS (!) plerumque auctorum.
PENTALASMIS HILLII (!). _Leach._ Tuckey"s Congo Expedit. p. 413, 1818.
---- CHELONIae (!) 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 laevibus; scutorum dentibus internis umbonalibus nullis; carina a caeteris valvis, furca etiam a scutorum basali margine, paululum distante; pedunculi parte superiore aut pallida aut aurantiaca._