Part 39

_General Appearance._--Shell generally much depressed, in a few cases rather steeply conical, in one single instance cylindrical, but not much elongated. Colour, when alive, pale, but fine purple; I presume, judging from some dried specimens, sometimes dirty white. The state of the surface varies remarkably: about half the specimens (fig. 1 _a_) which I have seen, had the outer lamina of shell quite removed, and the surface granulated, owing to the projecting and exposed tips of the upfilled parietal tubes; the radii are not developed, and often even there is no trace of the four sutures; the rather large orifice is somewhat rounded, and the two scuta, with their surfaces disintegrated, have their middle parts deeply indenting the terga. The shell, in the other and perhaps more common condition (fig. 1 _b_), has the outer lamina preserved, and is longitudinally ribbed with generally at least five or six ribs on each compartment: the radii are here very wide, and extend from tip to tip of the compartments, so that their summits are parallel to the basis; they are generally covered by a brownish epidermis, thickly clothed with little spines; the orifice is neatly diamond-shaped; the apices of the opercular valves meet at a common point: these specimens are almost always smaller and younger than the granulated specimens. Altogether the specimens in the two opposite states have, in their external appearance, nothing in common, and no one, without careful examination, would ever suspect that they were specifically identical; this, however, was proved by the intermediate forms, and, in one instance, three of the compartments had their surfaces granulated, and were entirely destitute of the radii, whilst the fourth by some chance had been preserved from corrosion, was longitudinally ribbed, and had its epidermis-covered radius fully developed. The difference in the appearance of the opercular valves, in the two states, is simply owing to the degradation of their upper parts in the granulated specimens.

The basal diameter of the largest specimen was one inch, but the height only .35 of an inch.

_Scuta_, transversely elongated, so that the basal margin is nearly twice as long as the tergal margin: articular ridge very little prominent; articular furrow wide but shallow; adductor ridge very blunt, slightly prominent, sometimes almost absent, almost parallel to the basal margin: there are no distinct crests for the rostral or lateral depressor muscles, but some small irregular pits for the latter. In one young specimen, the lines of growth were crenated, showing a tendency in the valve to become longitudinally striated, as in the allied _T. costata_. In some young and immature specimens, the basal margin was deeply sinuous.

_Terga_, small in area, not above half that of the scuta: spur extremely short, broad, placed close to the basi-scutal angle of the valve, so that there is no basal margin on that side of the spur. The lower end and sides of the spur form one uniform curve. Articular ridge barely developed. Crests for the tergal depressores sharp and prominent.

_Structure of the Shell and Radii._--The walls are very thick, and the parietal tubes small and numerous; there are sometimes from twelve to fifteen rows of tubes in the thickness of the wall. The tubes in their whole upper part are filled up solidly; and, as we have seen, are often exposed by disintegration. In very young specimens, of that size in which in _T. porosa_ there would be only a single row of parietal tubes, there were here two or three rows. The development of the radii, as we have seen, is very capricious; the sutures even sometimes being lost. The radii, when developed, are broad, square on the summit, and covered by brownish hirsute epidermis: internally they are formed of tubes like those forming the parietes; in this respect differing from all the species except the following, _T. costata_. The tubes in the radii run obliquely down towards the basis; instead of in a transverse line, directly towards the opposite compartment, as might have been expected from the structure of the radii in Balanus. The alæ have their edges finely crenated. The sheath in all the specimens which I have observed is colourless; its lower edge is not free. The corium entering the parietal tubes, and lining the opercular valves, the mouth, and the anterior cirri, is generally of an extremely dark purple colour.

The _Basis_ is entirely membranous, in which respect this species differs from all the others in the genus.

_Mouth_: all the trophi are unusually hairy or spinose. The labrum is deeply notched and apparently destitute of teeth on the crest. The palpi are club-shaped or enlarged at their extremities. The mandibles have the fourth tooth rudimentary.

In the _Cirri_, the second and third pairs are remarkably short and blunt. In one specimen the two rami of the first cirrus had respectively six and sixteen segments; those of the second, six and seven; those of the third, seven and seven; and those of the sixth cirrus twenty rather elongated segments, with a small tuft of spines between each main pair of spines.

_Affinities._--This species differs from all, in its membranous basis, and in its transversely elongated scuta. It resembles _T. costata_, and differs from all the other species, in its radii (when developed) being square on the summit, and in being formed of tubes,--in the smallness and number of the parietal tubes,--in the absence of crests on the under side of the scuta for the rostral and lateral depressor muscles,--in the shortness and rounded form of the spur to the terga,--and, lastly, in the club-shaped palpi and small size or absence of the fourth tooth in the mandibles. _T. purpurascens_ differs from _T. costata_ in those points, namely, in its membranous basis and transversely elongated scuta, in which it differs from all the other species, and, moreover, in its scuta not being plainly striated longitudinally, in having more ribs on the external surface of the parietes of its shell, and in having only three pairs of main spines on the three posterior cirri.

5. TETRACLITA COSTATA. Pl. 11, fig. 2 _a_-2 _c_.

_Shell depressed, whitish, generally with ten very prominent longitudinal ribs: radii broad, with their summits parallel to the basis: basis calcareous: scutum externally striated longitudinally: tergum with the spur short and rounded._

_Hab._--Philippine Archipelago, Mus. Cuming. Attached to various shells, within the tidal limit.

_General Appearance._--Shell whitish, probably tinged, when alive, with reddish-purple; depressed; surface perfectly preserved, smooth, but having longitudinal very prominent ribs, almost invariably ten in number; namely, three on both the rostrum and carina, and two on the two lateral compartments, with ten corresponding projections round the basal margin. Orifice passing from rounded-trigonal to diamond-shaped. The radii are very broad and square at the summit, and extend from tip to tip of the compartments. Basal diameter of largest specimen under half an inch, generally from .3 to .4 of an inch.

_Scuta_, of the usual sub-triangular shape, and not transversely elongated, as in _T. purpurascens_. External surface striated longitudinally; in many specimens there is a medial depression, or a row of very small pits, such as occur on the scuta of _Balanus trigonus_ and _lævis_. The adductor ridge is moderately developed, and runs nearly parallel to the occludent margin; there are no crests for the rostral and lateral depressor muscles.

_Terga_: these in area equal two thirds of the scuta: the spur is short and rounded, and placed as described under _T. purpurascens_; but the articular ridge seems to be more prominent than in that species.

_Structure of the Shell and Radii._--The parietal tubes are small, and very numerous, as in _T. purpurascens_. The radii are wide, square on the summits, but not so conspicuously covered by hirsute epidermis as in that species. Internally, the tubes forming the radii are smaller, and run more transversely than in _T. purpurascens_, that is in the normal course, as in Balanus. The edges of the alæ are nearly or quite smooth. The _Basis_ is as distinctly calcareous, as in the other species of the genus.

_Mouth_: the trophi are not so hairy as in _T. purpurascens_; the labrum seems destitute of teeth; the palpi are club-shaped at their ends; the mandibles have only three teeth. The second and third cirri are not so short and blunt relatively to the others as in _T. purpurascens_. In the posterior cirri, the elongated segments carry four main pairs of spines, between which there is no intermediate tuft of fine spines.

The _Affinities_ of this species have been fully pointed out under the last and closely related species. In external appearance, _T. costata_ can at first hardly be distinguished from those young and pale-coloured varieties of _T. purpurascens_, which have their external surface not corroded, and their radii well developed.

6. TETRACLITA VITIATA. Pl. 11, fig. 3 _a_-3 _e_.

_Shell white, generally tinged in the upper part with pink; surface irregular: parietal tubes very irregular: radii moderately wide, with their summits oblique: alæ with very thick crenated sutural edges: tergum with the spur not joined to the basi-scutal angle; spur with its extremity equably rounded._

_Hab._--Philippine Archipelago; Barrier Reef, (Raine's Islet), Australia; Mus. Cuming and Stutchbury. Attached to massive corals, to coral-rock, to a Tridacna, and to _Tetraclita cœrulescens_.

_General Appearance._--Shell conical, moderately steep: white, generally with a tinge of pinkish-purple in the upper part, owing to the exposure of the tips of the upfilled parietal tubes. The lower part of the surface is generally well preserved, and is formed by very irregular, branching, longitudinal, slightly prominent, ridges. Radii of moderate width, with their summits oblique. Orifice rather large, rounded trigonal.

_Scuta_, rather narrow, with the upper part acuminated: the external surface generally much disintegrated, and marked with some irregular blotches of dark red. Articular ridge not prominent; articular furrow rather deep: adductor ridge, distinct from the articular ridge, pretty well developed, as are the crests for the rostral and lateral depressor muscles. In young and well preserved scuta, there is an external, medial, hyaline band, corresponding with the hollow under the adductor ridge, and caused by the thinness of the valve along this line.

_Terga_: externally, the carinal half is longitudinally and very feebly striated. Internally, the articular furrow is very wide, but shallow, and of unusual length, owing to the preservation of the upper part of the valve; the articular ridge is not prominent. The spur does not actually join, as in all the foregoing species, the basi-scutal angle, but is separated from it by a short piece of basal margin; its two sides are more nearly parallel than is usual, and the end is regularly rounded. It is always rather narrow, though the width varies considerably (fig. 3 _d_, 3 _e_). It extends in the same straight line with the middle of the articular furrow. The terga, though not possessing any striking characters, differ considerably in appearance from those of the other species.

_Structure of the Shell and Radii._--The parietal tubes are remarkable from their irregular shapes, and unequal sizes (fig. 3 _b_),--hardly two resembling each other. Sometimes a single elongated tube will reach across the whole thickness of the walls. The septa between the tubes are rather thick and rugged. The tubes are generally darkly coloured from the adhering corium; they are solidly upfilled, but only in the uppermost part, by dark chocolate-red shelly matter. The radii are formed by irregularly branching ridges, with the interspaces filled up solidly. The square edges of the alæ are much thicker than in any other species, and are furnished with transverse ridges, which are sometimes slightly branched. The inner lamina of the walls near the basis, in most of the specimens, is irregularly and longitudinally ribbed, the ribs being longitudinally striated. The sheath and the upper part of the inner lamina of the parietes are clouded with chocolate-red.

The animal's _Mouth_ and _Cirri_ were ill-preserved; but I was able to make out that the labrum had some strong teeth, and that the mandibles were furnished with five teeth, a greater number than in any other species. The palpi had parallel sides as usual. In the sixth cirrus, the segments had four pairs of main spines, instead of the usual number of three.

_Affinities._--This species does not appear to be particularly related to any other one: perhaps it is rather nearer to the two following than to the foregoing species. The irregular parietal tubes, thick-edged alæ, form of terga, five teeth to the mandibles, and four pairs of spines to the segments of the posterior cirri, are its chief characteristics.

7. TETRACLITA CŒRULESCENS. Pl. 11, fig. 4 _a_-4 _d_.

LEPAS CŒRULESCENS. _Spengler._ Skrivter af Selskabet, 1 Bind., 1790.[111]

[111] The longitudinally folded walls, as described by Spengler, the blue colour, the habitat, namely, associated with _B. tintinnabulum_ from the East Indies, and more especially the expression "Valvulæ operculi cardine dentato mobilis," apparently referring to the highly prominent articular ridge of the scutum, leave little doubt on my mind that I have rightly named the present species.

_Shell with the upper part tinged greenish-blue, longitudinally ribbed: radii moderately wide, with their summits oblique: scutum with a small adductor and extremely prominent articular ridge, united together and so forming a small sub-cylindrical cavity: tergum with the spur not joined to the basi-scutal angle._

_Hab._--Philippine Archipelago, attached to _Balanus tintinnabulum_; attached to a ship's bottom, and to _Balanus tintinnabulum_, both from the Pacific Ocean; attached to a massive coral, and associated with _T. vitiata_, and therefore from the tropical eastern seas; Mus. Brit., Cuming, Stutchbury.

_General Appearance._--Shell conical, sometimes depressed; surface with rather broad, smooth, longitudinal ridges; whitish, with the upper part greenish-blue, sometimes very feebly tinted with pink; radii white, or mottled with blueish-green, or with pink. When the outer lamina of shell has been corroded, the upfilled parietal tubes, of a dull blueish-gray colour, are exposed. The radii are moderately wide, with their summits very oblique. In basal diameter, one specimen was 1.8, and another 1.5 of an inch.

_Scuta_, externally furrowed very slightly in a longitudinal direction, causing the lines of growth to become a little sinuous. The valve is strong and thick; and the epidermis, when preserved, is hirsute with spines. The articular ridge is extraordinarily prominent; it projects, as measured from the external surface of the valve, to an amount equalling half the width of the valve in its widest part. The adductor ridge is very short, and is united to the bottom of the articular ridge, thus forming a small, nearly cylindrical tube, which runs up to near the apex of the valve. The inflected occludent margin is broad and coarsely toothed. The crests for both depressor muscles are not very prominent. When the scuta and terga are articulated together, owing to the great projection of the articular ridge of the scutum, its upper part is separated from the tergum (fig. 4 _b_), by a remarkably wide and deep, fissure-like hollow. The scutum, in some distorted specimens from a ship's bottom, was narrow in proportion to its ordinary breadth.

_Terga._--These are large. Externally, there is a broad, longitudinal depression, bounded on each side by a ridge. The carinal half is feebly striated longitudinally. A large upper portion (fig. 4 _b_) projects freely, and stands, when the two valves are articulated together, above the apex of the scutum, but does not form a beak as in _T. porosa_. Internally, the tergal margin is widely inflected; the articular furrow is very deep, but the articular ridge is not prominent. The spur is not very broad; it is separated from the basi-scutal angle by a small space of basal margin, which forms a straight line with the basal margin on the opposite side of the spur. The end of the spur is truncated, and is parallel to the basal margin.

_Structure of the Shell and Radii._--The walls are thick: the parietal tubes are rather large and regular; they become solidly filled up in their upper parts. The sutural edges of the radii are formed by unusually narrow, sinuous ridges, sending off delicate denticuli on each side: the interspaces between these ridges are solidly filled up. The crenated edges of the alæ are rather thick. Neither the _mouth_ nor the _cirri_ offer any noticeable character; but I may observe, that, in the mandibles, the third and fourth teeth are close together; and that, in the three posterior cirri, the tufts of small spines between the main pairs are small.

_Affinities._--This species is very distinct from the others, with the exception of the following _T. radiata_, to which it is in several respects allied. The under side of the scutum, with its great articular ridge, and the cylindrical tube formed by the union of the latter with the short adductor ridge, affords the most noticeable character.

8. TETRACLITA RADIATA. Pl. 11, fig. 5 _a_-5 _d_.

CONIA RADIATA.[112] _De Blainville._ Dict. Sc. Nat., 1816-1830, Pl. 164, fig. 5, 5 _a_, (sine descript.)

---- LYONSII. _G. B. Sowerby._ Genera of Recent and Fossil Shells, Plate, 1823, (sine descript.)

[112] The synonymy of this species is complicated. De Blainville gives no description under the article Conia, published in 1818, or in the vol. published in 1822; but I believe, from the figures of the opercular valves, that I have correctly identified this species with his _C. radiata_. Mr. Sowerby gives no description of _C. Lyonsii_, or any figure of the opercular valves, but his drawing of the shell is much better than de Blainville's, and I believe it is the same species. Whether de Blainville's or Sowerby's plate appeared first I cannot ascertain. In the second edition of Lamarck, _Conia radiata_ of Blainville is given as a synonym to _Balanus radiatus_ of that work; but this is quite erroneous. I may add that if de Blainville's name does not apply to the present species, it must to _T. cœrulescens_, and as the latter is the older name it will be permanent. In this case, _T. radiata_ might be allowed to stand as my own name, considering that Mr. Sowerby's figure is imperfect and is not accompanied by any description. At first I thought that the present species might be the _Lepas mitra_ of Spengler, ('Skrivter af Naturhist. Selskabet,' 1790, Tab. 6, fig. 5), but the parietes are not described as porose; and the folds on the walls are too broad; on the other hand, his description of the opercular valves makes me think this may be the same species.

_Shell white, with numerous approximate longitudinal ribs: radii broad, with their summits slightly oblique, internally porose: tergum with the articular ridge extraordinarily prominent, with the spur not joined to the basi-scutal angle._

_Hab._--West Indies, adhering to _Balanus eburneus_ and to _Lepas anserifera_. New South Wales, adhering to _Tetraclita porosa_. Attached to _Balanus tintinnabulum_, on a ship's bottom from Sumatra; not rarely attached to _Balanus tintinnabulum_ on ships' bottoms; Mus. Brit., Stutchbury, and Cuming.

_General Appearance._--Shell white, rather steeply conical, with numerous, approximate, rather narrow, longitudinal, rounded ribs on the walls: in a specimen half an inch in diameter, there were from eight to twelve ribs on each compartment. The outer lamina of shell seems always well preserved. Orifice rounded, trigonal. Radii white, smooth, broad, with their summits only slightly oblique. I have seen one specimen 1.2 in basal diameter, but quarter of an inch is a common size, and very young specimens are unusually frequent in collections.

_Scuta_ broad, externally not striated longitudinally. The articular ridge is prominent, and the furrow deep, but not in so great a degree as in _T. cœrulescens_. The adductor ridge is only slightly prominent; it extends upwards only a little way above the lower end of the articular ridge, and does not form with the latter a cavity. There are no crests for the rostral depressor muscle, but there is a little pit, formed by the folding over of the occludent margin.

_Terga._--These valves, when articulated with the scuta (fig. 5 _b_), project above them to an extraordinary degree, and are separated from them by a deep, fissure-like hollow, caused by the remarkable prominence of the articular ridge of the terga. The upper part of the tergum is not beaked, and does not project freely much above the sack. The valve is large; externally there is a rounded longitudinal furrow. The tergal margin is broadly inflected. The articular furrow is deep, and the articular ridge far more prominent than in any other sessile cirripede, for it projects, as measured from the outside surface, more than half the width of the valve; and consequently the valve, when viewed vertically from above, almost appears as if formed by the union of three plates, viz., the articular ridge, and the outside surface on each side of the spur. The spur is of moderate width, with the corners rounded: it is placed near, but not close to the basi-scutal angle, so that there is on this side a small portion of basal margin, forming nearly a straight line with the margin on the carinal side. In some young specimens, about the tenth of an inch in diameter, from the West Indies and from New South Wales, the spur (the position of which I found varied a little in some other specimens) was placed nearly in the middle of the valve, and very nearly at right angles to the basal margin; it is possible that these may be a distinct species, but without larger specimens to judge from, I think it more probable that this difference in the tergum is due to variation and youth.

_Structure of Shell and Radii._--The parietal tubes are commonly elongated in the ray of the circle: the septa are rather thick, and strongly crenated at their basal edges. The inner lamina of the walls is strongly ribbed longitudinally. The broad radii have their sutural edges formed by ridges, with numerous and closely approximate denticuli: the interspaces between the main ridges are not soon filled up, and at the bottom, each interspace usually terminates in a pore or tube; so that the radii are not solid, as in most of the foregoing species, but porose. The alæ have their edges crenated.

_Basis_, calcareous, of unusual thickness; the inner, or upper surface, is striated from the centre in rays, corresponding with the ribs on the inner lamina of the walls. This striated or furrowed structure in the basis, shows a tendency to its becoming tubular or porose, as may be inferred from analogous cases in Balanus.

_Animal's body_ unknown.