Valves smooth; scuta dest.i.tute 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; a.s.sociated 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 ac.u.minated; the occludent margins of the two scuta stand rather separate from each other, showing a wide s.p.a.ce 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 ac.u.minated. The degree of prominence and outline of the double occludent margin varies very much.
_Carina_, separated by a rather wide s.p.a.ce from the scuta and terga; of very varying shape, the upper part not much ac.u.minated, 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; p.r.o.ngs 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 s.p.a.ce with similar but smaller little spheres, and still higher up still minuter ones; others occur on different parts of the capitulum; these s.p.a.ces 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 ac.u.minated; maxillae 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. c.u.ming, 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, pa.s.sing into the finest scarlet, and varying slightly in tint in different specimens. s.p.a.ce 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 a.s.sumes 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. c.u.ming, 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 inters.p.a.ce 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. _Linnaeus._ Syst. Naturae, 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.
x.x.xviii, p. 300.
PENTALASMIS ANSERIFERUS. _Brown._ Ill.u.s.t. Conch., 1844, Pl. li, fig. 1.
[27] Professor Macgillivray does not consider the species, which he has described under _L. nauta_, and which I cannot doubt is the same with the present species, as the _L. anserifera_ of Linnaeus; but I find it so named in all old collections, and it seems to agree very well with Linnaeus"s description. There has been much groundless confusion about this species; I have no hesitation in giving _A. striata_, of Brugiere, as a synonym, though I have received from Paris the _Lepas pectinata_ of this volume, named as the _A. striata_; and on the other hand, Poli has incorrectly called a common variety of _L. pectinata_ by the name of _L. anserifera_.
_L. valvis approximatis leviter sulcatis (tergis praecipue); scuto dextro dente forti interno umbonali, laevo aut dente exiguo, aut mera crista instructo; margine occludente arcuato, prominente: pedunculi parte superiore aurantiaca._
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 s.p.a.ce 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, Janthinae, Spirulae; often a.s.sociated 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 s.p.a.ce 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 p.r.o.ngs diverge at an angle of 90, or rather more, and are wider than the widest upper part of the valve; rim between the p.r.o.ngs 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 ac.u.minated, the fork about twice as wide as the widest upper part, and the p.r.o.ngs 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 k.n.o.bs. 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 inters.p.a.ces, 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 sh.e.l.l 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.
c.u.ming"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 Janthinae and Spirulae 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 p.r.o.ngs of the fork diverging at an angle of from 135 to 180; by the thinness of its valves; by the coa.r.s.eness 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.
---- spirulae (!) (var.) _Leach._ Tuckey"s Congo Expedit. Appendix, 1818.
---- RADULA (var.) et SULCATUS. _Brown._ Ill.u.s.t. of Conchology, Pl. li, figs. 3-6, 1844.
---- INVERSUS. _Chenu._ Ill.u.s.t. Conchy., Pl. i, fig. 14.