Part 38

_Size._--_Tetraclita porosa_ is the largest species of the genus; I have seen specimens attached to a large pebble of granite in the British Museum, which measured two inches in basal diameter, and nearly one inch and a half in height.

_Scuta_: these are sub-triangular and generally a little elongated, but they vary slightly in relative breadth (fig. 1 _i_, 1 _l_), and likewise in the degree to which the basi-tergal angle is rounded off. The under surface is clouded with dull or pinkish-purple, or with green, or is nearly white. The articular ridge is not prominent, and the articular furrow is narrow. The adductor ridge is prominent, and runs upwards for some distance close and parallel to the articular ridge; and sometimes it extends nearly or quite up to the apex of the valve; in one single specimen the adductor ridge had an abraded appearance, and was very little developed. The crests for the rostral and lateral depressores are sharp and distinct. Along the occludent margin, the ends generally of the alternate lines of growth are enlarged into knobs, serving to lock the two valves together; but in many specimens only two or three knobs, at intervals of several lines of growth (fig. 1 _b_), are developed.

_Terga_: when the upper end of the valve is not corroded, there is a distinct beak, hollow within for a thread of corium. The scutal margin is not much inflected, and the articular ridge not very prominent. The spur is placed quite close to the basi-scutal angle of the valve, so that there is no basal margin on that side of the valve. The width of the valve and of the spur, and the acumination of the extremity of the latter, varies in a remarkable manner. In the broad and commonest variety (fig. 1 _k_), the basal margin of the valve form an angle of about 130° with the carinal side of the spur, and the basal end of the spur is broad and truncated. In the less common and narrow variety (1 _m_), the basal margin in some extreme cases forms very nearly a straight line with the carinal side of the spur; and the spur itself is bluntly pointed: in _var._ 7 it is sharply pointed.

_Structure of the parietes and radii._--In all cases the four sutures are quite distinct, from top to bottom, on the internal lamina of the shell, and generally they run through the whole thickness of the walls, and are visible externally. Often they do not quite reach the outer lamina, and then the shell externally consists of a single piece, like a patella. Sometimes the sutures can be traced running through the parietal tubes only for a short distance from the internal surface; where they cease, the two walls of the suture become fused together. When a perfect suture is split open, the radius is represented (fig. 1 _h_) by a few narrow, sinuous ridges, sending out on each side little branches or denticuli; these are received into corresponding furrows in the opposed compartment. These ridges run nearly parallel to each other, and somewhat obliquely, from the outer lamina of the shell to the basis. When the radii are developed, their edges are similarly formed, by sinuous denticulated ridges, with the interspaces between them filled up solidly. The alæ are but little prominent.

The _mouth_ does not deviate from the generic type. The _cirri_ are remarkable from the variability in the several pairs of the relative numbers of their segments, as shown in the following table. The segments do not correspond even on opposite sides of the same individual, as may be seen in the two lower lines of the table. I believe that variability to this degree is very uncommon in other cirripedes, though, as stated in the Introduction, the number of the segments always increases with the growth of the individual. The terminal segments in the longer rami of both the first and third cirrus are antenniformed,--being elongated, and of a different shape, with fewer bristles, compared with the basal segments of the same cirri. It is apparently these terminal segments which are particularly liable to vary in number. In both rami of the third cirrus, some of the segments, from the sixth to the eleventh inclusive, (counting from the bottom), more especially the eighth, ninth, and tenth, carry a few spines coarsely and doubly pectinated; but as some of the adjoining segments carry spines which may be called doubly serrated, it is not easy to draw an exact line of demarcation. Sometimes, though rarely, a few of the nearly terminal segments in the second cirrus are furnished with similar, doubly pectinated spines.

_Numbers of the segments in the rami of the Cirri, in different specimens._

+------------------+--------------+--------------+--------------+-------+ | |First cirrus. |Second cirrus.|Third cirrus. |Sixth | | | | | |cirrus.| | |--------------+--------------+--------------+-------| | |Shorter|Longer|Shorter|Longer|Shorter|Longer|Either | | |ramus. |ramus.|ramus. |ramus.|ramus. |ramus.|ramus. | |------------------+-------+------+-------+------+-------+------+-------| |Specimen from | | | | | | | | |Pernambuco, Brazil| 9 | 19 | 10 | 11 | 15 | 27 | 26 | |(_var._ 1) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |Another specimen | | | | | | | | |from the same | 12 | 23 | 12 | 14 | 14 | 19 | 23 | |cluster | | | | | | | | |(_var._ 1) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From the Galapagos| | | | | | | | |Archipelago, | 10 | 16 | 10 | 11? | 11 | 16 | 25 | |(_var._ 1) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From the | | | | | | | | |Philippine | 10 | ? | 10 | 10 | 11 | 19 | 18 | |Archipelago, | | | | | | | | |(_var._ 4) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From California | 15 | 24 | - | - | - | - | 22 | |(_var._ 5) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From the bottom | | | | | | | | |of a ship | - | - | 9 | 9 | 10 | 17 | 14 | |(_var._ 7), | | | | | | | | |young | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From South America| | | | | | | | |(_var._ 1) | 11 | 18 | 11 | 12 | 13 | 21 | 22 | |British Museum | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |Another specimen | | | | | | | | |from the | 16 | 25 | 13 | 18 | 15 | 23 | 27 | |same cluster with | | | | | | | | |the last specimen | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |Same individual, | | | | | | | | |but the cirri | 15 | 28 | 15 | 21 | 16 | 23 | - | |from the opposite | | | | | | | | |side of the body | | | | | | | | +------------------+-------+------+-------+------+-------+------+-------+

_Varieties._--Under the generic description, I have stated that after having spent some time in examining a very large suite of specimens of _T. porosa_, I concluded that at least four of the varieties were true species. It so happened that all the specimens which I first examined of the _var._ (4) _rubescens_, had the narrow sloping terga, and scuta with only two or three great teeth on their occludent margins; but ultimately, in a group thus characterised, I found one or two individuals with terga precisely of the shape of those in _var._ (1) _communis_. Again, in a group of dull purple specimens of _var. communis_, a few had the narrow sloping terga, and scuta with teeth on their occludent margins, intermediate in size and number between the varieties with only one or two great teeth, and those with every alternate growth-ridge enlarged into a tooth. Hence _var. rubescens_ completely broke down as a species.

With respect to _var._ (5) _elegans_ (a M.S. specific name of Leach) I inferred at first, from external appearance alone, that it was distinct; the outer lamina of the shell and even the epidermis is preserved; the surface is strongly ribbed, and the whole shell, excepting the sheath, is nearly white; the terga are narrow, with a sloping basal margin as in _var._ (4) _rubescens_. Whole groups of specimens are thus characterised. But as _var. communis_ is often white, and as the surface, when the outer lamina is preserved, is generally, as we shall presently see, ribbed longitudinally, the differences in _var. elegans_ are quite unimportant.

The (6th) _var._ differs from _var. communis_ only in the narrow radii having been developed, and consequently in the orifice being pentagonal, and in the outer, longitudinally ribbed lamina of the shell having been preserved. In the same group of specimens, I have seen every intermediate stage between this and the common form. It must not, however, be supposed that the young of _var. communis_ always pass through these stages, for such is not the case. In the genus _Balanus_ it has been seen, how capricious in some species is the development of the radii.

Of the other varieties, enumerated at the beginning, no further mention is required, excepting with respect to _var._ (7), the most singular of all. I have seen only three specimens, sent to me by Dr. Aug. Gould, of Boston, United States, and these from the appearance of their bases I have no doubt had been attached to a ship,--the only instance which I have met with, in the present species. The shell is steeply conical, with the orifice so small as to be reduced to a mere pore; the radii are extremely narrow and white; the shell is thin, with the surface smooth, but ribbed longitudinally and regularly; the outer lamina of the shell and the epidermis are perfectly preserved; the upper part of the shell is reddish purple, which dies away towards the base: careful examination of the apex shows that at the first growth the young shell was blueish-green. The terga are narrow, with a sloping basal margin, as in _var. rubescens_, but with the point of the spur sharper. I have formerly remarked that the shape of the terga seems influenced by the size of the orifice. The lower edge of the sheath depends freely: I have seen no other instance of this latter structure, so common, but so variable, in _Balanus_, in the present species, except to a partial extent in one distorted specimen, in Mr. Stutchbury's collection, adhering to _Balanus tintinnabulum_, and probably taken from a ship's bottom. I may add that this distorted specimen was remarkable from its radii being wider than in any other instance,--from its smooth uncoloured surface without longitudinal ribs,--and from the perfect preservation of the epidermis over its entire surface. Although Dr. Gould's specimens, in external aspect, are absolutely and entirely different from the common varieties of _T. porosa_, there are so many intermediate forms, and the differences are so little important that I feel no hesitation in attributing them to variation, consequent on the individuals having been exposed to unusual conditions, attached to the bottom of a ship.

2. TETRACLITA SERRATA. Pl. 10, fig. 2 _a_-2 _d_.

_Shell dark greenish-gray, with narrow, longitudinal, serrated ribs: radii absent: scutum with the adductor and articular ridges forming a cavity, which runs up to the apex of the valve._

_Hab._--Cape of Good Hope; Algoa Bay; attached to sandstone and to Patellæ; Mus. Brit., Cuming, and Stutchbury.[108]

[108] I have seen three separate lots of this species all from the Cape of Good Hope; one lot was collected by Dr. Krauss, at Algoa Bay, and I strongly suspect is the species described by him in his 'Südafrikanischen Mollusken' as _Conia porosa_. If the species, figured by Chemnitz, and mentioned in a note (p. 329), under _T. porosa_, be the present species, the specimens probably did not come from Tranquebar, on which point Chemnitz speaks only from memory. I have seen one specimen ticketed New South Wales, it is possible, considering the case of _T. rosea_, that this may be correct, but I should like to have further confirmation before giving it as a habitat.

_General Appearance._--Colour dark greenish gray; form steeply conical; surface covered, especially in the lower half of the shell, by numerous, narrow, sharp, longitudinal ridges, but slightly prominent, and serrated or transversely divided into small teeth: when the shell has been much disintegrated, the upper part of the surface consists of the exposed, smooth, rather large, upfilled parietal tubes. I have seen no instance of the development of the radii; sometimes even the sutures are with great difficulty distinguishable, though I believe they always reach the outer surface; sometimes the sutures are wide from the disintegration of the edges of the compartments. Orifice rounded or oval.

_Scuta._--The scuta and carinal half of the terga are blueish-green. In the scuta neither the articular ridge or furrow are much developed: the adductor ridge is prominent, and is united to the articular ridge, about half way up the latter, thus forming a rather large, triangular cavity, which runs up to the apex of the valve.

The _Terga_ are beaked. The spur, measured across the upper part, is half as wide as the valve; it is bluntly pointed; it is placed quite close to the basi-scutal angle of the valve, so that there is no basal margin on that side; it curves towards the scutum, its extremity extending beyond the basi-scutal angle.

_Structure of the Shell and Radii._--The parietal tubes are rather large, especially those adjoining the inner lamina of the walls. The shell is of singularly little specific gravity, which is due to the parietal tubes not being filled up with shelly matter nearly to so great an extent as in the other species; even in the uppermost part the tubes are not solidly filled up, only their external sides are thickly coated with greenish-black shell, which by corrosion becomes grayish. The radii, as stated, are not developed: the shell breaks with singular facility along the sutures, and the radii are then seen to be most feebly represented by a few very small branching ridges. The alæ have their edges plainly crenated. The sheath is dark green, with the lower edge free.

The _Mouth_ presents no particular characters. With regard to the _Cirri_, I am doubtful whether any confidence can be placed in the numbers of the segments being constant; but I may state that the second cirrus contained thirteen and sixteen segments in its two rami; the third cirrus only fourteen in both rami; and the sixth cirrus twenty-six segments in both rami. Whereas in every specimen of _T. porosa_, the longer ramus of the third cirrus contained more segments than either ramus of the second. About half the segments, namely, those in the middle of both rami of the third cirrus, are furnished with coarsely and doubly pectinated spines, like those in _T. porosa_.

_Affinities._--Upon the whole, this species is more nearly allied to _T. porosa_ than to any other. In the cavity formed by the union of the adductor and articular ridges, it is allied to _T. cœrulescens_. This species differs from all, in its little specific gravity, consequent on the parietal tubes being only slightly filled up, and in the peculiarly serrated, narrow, approximate ridges on the external surface of the walls. The character derived from the adductor ridge, just alluded to, is remarkable. In the shape of the terga, in the absence of radii, and in the structure of the body, this species approaches closely to _T. porosa_.

3. TETRACLITA ROSEA. Pl. 10, fig. 3 _a_-3 _d_.

CONIA ROSEA.[109] _Krauss_ (!). Die Südafrikanischen Mollusken, Tab. 6, fig. 28, 1848.

BALANUS CUMINGII. _Chenu._ Illust. Conch., Tab. 4, fig. 5.

[109] I am greatly indebted to Professor Krauss for having sent me, for examination, the unique specimen collected by himself in Algoa Bay. There can be no doubt of the identity of the African and Australian specimens. It is a singular circumstance that the same species should occur in these two distant places, and, as far as at present known, not in the intermediate, more tropical coasts.

_Shell dirty white, tinged with pink; parietes formed by a single row of large tubes: radii generally narrow: tergum with the spur rather short and broad._

_Hab._--New South Wales, Moreton Bay in lat. 27°, Port Jackson, and Twofold Bay; South Africa, Algoa Bay. Attached, in Australia, to littoral rocks and shells; often associated with _T. purpurascens_, _Chthamalus antennatus_, and _Catophragmus polymerus_; Mus. Brit., Cuming, Krauss, Darwin, Stutchbury.

_General Appearance._--Shell steeply conical, often rather convex; dirty or brownish white, feebly tinted with pink; external surface generally much disintegrated, and having in the upper part a pillared appearance, owing to the exposure of the upfilled, large, square, parietal tubes, and, in the lower part, a striated (and sometimes serrated) appearance, from the exposure of the parallel, approximate plates, with which the outer lamina of the shell is internally strengthened. In only a few young specimens, the whole outer lamina of the shell was well preserved; and in these the surface was very smooth, and even glossy, giving to the specimens a quite different aspect; even in partially corroded specimens, the lower part of the shell sometimes is quite smooth. Generally, the radii are developed; in most specimens they are narrow, but sometimes of moderate width; their summits are oblique, and their edges often notched or toothed. The recipient furrow, in each opposed compartment, is often almost as wide as the radius itself, and is equally notched. In some much corroded specimens there were no radii. Basal diameter of largest specimen, 1.1 of an inch.

_Scuta_, generally thick, sometimes very thick, with the external surface usually much corroded: articular furrow rather wide; articular ridge not very prominent; adductor ridge prominent. The rostral depressor muscle is attached in a small oblong pit, sometimes including little crests; and the lateral depressor muscle is attached to what may be described either as three or four parallel furrows or crests.

_Terga_, with the spur placed close to the basi-scutal angle, so that there is no basal margin on that side; spur short, with its lower end truncated and rounded; broad, even exceeding, when measured across the upper part, half the width of the valve. Articular furrow wide. Apex not beaked.

_Structure of Walls and Radii._--This species differs from all the others of the genus in having only a single row (fig. 3 _d_) of parietal tubes; these are large, quadrangular, but elongated in the ray of the circle. They are not filled up, even at the very top of the shell, but they become thickly lined all round with compact shelly matter. When the surface of the shell is disintegrated, these upfilled tubes greatly affect, as already stated, the external appearance. The outer lamina near the basis is internally strengthened by longitudinal, sharp, approximate ridges or plates, which, also, often affect, after corrosion, the external appearance. The _radii_ have their sutural edges formed by a set of narrow, branching ridges or septa; the ends of which, seen externally, often give a notched outline to this edge; the recipient furrows in the opposed compartments are deep, and their edges likewise are often notched: the interspaces between the branching ridges are filled up solidly. The _alæ_ have their edges coarsely crenated. The lower edge of the sheath is not free.

The _mouth_ and _cirri_ present no particular characters: the third cirrus has both its rami elongated, with the terminal segment tapering. In the three posterior pairs of cirri, the tufts of little spines between the main pairs are rather large.

_Affinities._--This species has no particular affinity with any other. The circumstance of there being only a single row of parietal tubes is not so important a difference as might at first be thought, inasmuch as in the other species, during their quite early youth, the walls are formed of only a single row of tubes or pores.

4. TETRACLITA PURPURASCENS. Pl. 11, fig. 1 _a_-1 _d_.

LEPAS PURPURASCENS.[110] _Wood's_ General Conchology, p. 55, Pl. 9, fig. 42, 1815.

BALANUS PLICATUS. _Lamarck._ Animaux sans Vertèbres, 1818.

---- ---- ET PUNCTURATUS. _Chenu._ Illust. Conch., Tab. 4, fig. 3 et 12.

CONIA DEPRESSA (!). _J. E. Gray._ Appendix, Dieffenbach's Travels in New Zealand, 1843 (sine descript. vel figurâ).

[110] The descriptions given by Wood and Lamarck are fuller and more accurate than is usual in the case of Cirripedes, and I have no doubt regarding these two names. The _Conia depressa_ of Dr. J. E. Gray is, as I know from having seen the original specimens, the young of this same species; the name is unaccompanied by any description or figure.

_Shell depressed, pale purple or dirty white, with the surface longitudinally ribbed, or corroded and granulated: radii or even sutures none, or radii well developed and broad, with their summits parallel to the basis: basis membranous: scutum transversely elongated: tergum small, with the spur extremely short and rounded._

_Hab._--Sydney, New South Wales; Flinder's Lagoon, Sir C. Hardy's Island, Barrier Reef; King George's Sound, Western Australia; Van Diemen's Land; New Zealand, adhering to _Pollicipes spinosus_; Mus. Brit., Cuming, Stutchbury, Darwin, &c. China (?) attached to _Pollicipes mitella_, Mus. Brit. and Stutchbury. Generally attached to tidal rocks, sometimes to shells. Very common.