Part 36

_Diagnosis._--Finally, this species, if it be, as I believe, distinct, differs from _A. spongites_ only in the internal surface of the parietes being more strongly ribbed and brighter coloured,--in the edge of the basal cup being more plainly crenated,--in the articular ridge of the scutum being of a different shape,--in the spur of the tergum being often broader,--in the segments of the posterior cirri having only three pairs of main spines,--and, lastly, in the occasional presence of the hook-like teeth on the anterior ramus of the fourth cirrus.

3. ACASTA CYATHUS. Pl. 9, fig. 3 _a_-3 _c_.

_Carino-lateral parietes about one fourth of width of lateral parietes: radii wider than the parietes: basis nearly flat, small: tergum with the spur truncated, half as wide as valve._

_Hab._--Madeira, Mus. Lowe, and Bowerbank. West Indies, Mus. Stutchbury. Hab. unknown, Mus. Brit.

I feel more confidence in this case, than in that of _A. sulcata_, that we here have a distinct species, though at one time I treated it only as a marked variety of _A. spongites_. I rely chiefly on the great proportional width of the radii of all the compartments, and on the width of the carino-lateral compartments, compared with the lateral compartments, and on the general shape of the shell, which differs considerably from that of the two previous forms: in consequence of Acasta being attached to and imbedded in a yielding substance, such as sponge, I believe external form to be of more value as a specific character in this genus, than in most sessile cirripedes. I have examined specimens taken out of the yielding _Spongia officinalis_ and out of an unusually compact sponge, and they resembled each other in every respect.

_General Appearance._--Colour pale pink, or that of flesh: basis remarkably flat and rather small, with the walls above bulging out a little. The radii are very wide, being wider than the parietes to which they belong: the orifice is generally rather large. The parietes of the carino-lateral compartments vary from one third to one fourth of the width of the parietes of the lateral compartments. Basal diameter of largest specimen .35 of an inch. Internally, the parietes are generally more strongly ribbed than in _A. spongites_.

The _Opercular Valves_ are large, owing to the form of the shell. The _Scuta_ present no particular character, and are not distinguishable from those of _A. sulcata_; but the adductor ridge is perhaps rather more developed. The _Terga_ (Pl. 9, fig. 3 _c_) are nearly as large as the scuta, and this is an unusual circumstance; the spur is more than half as wide as the valve; it is placed not quite close to the basi-scutal angle; on the carinal side, the basal margin of the valve slopes a little towards the spur. I may mention, that in several specimens from Madeira, the scuta and terga, on one side, had grown to a monstrous thickness.

_Cirri_: these resemble, in every respect, those of _A. spongites_, with the remarkable exception that on the anterior ramus of the fourth cirrus, several segments were furnished with the beautiful downward curved, mandible-like teeth, as in _A. sulcata_; but differently from in that species, there were none on the upper segment of the pedicel. I should have thought this an excellent specific character, had not these teeth been so extremely variable in _A. sulcata_.

Finally, I think this species is more nearly related to _A. sulcata_ than to _A. spongites_.

4. ACASTA UNDULATA. Pl. 9, fig. 4.

_Shell, apparently, as in A. spongites, but larger: scutum marked by longitudinal ridges, often in pairs, with the intermediate furrows rather wide: spur of tergum nearly half as wide as valve._

_Fossil_ in Coralline Crag (Sutton), Mus. S. Wood.

I owe to Mr. Wood the inspection of a fine suite of separate valves. Owing to the shell never having been found entire, its general shape is not known, and, what is of more consequence, the relative proportional width of the parietes of the carino-lateral compartment is unknown. I have (but with doubt) given it a distinct specific name, owing to the peculiar character of the furrows on the scuta, and to the large size of the whole shell. In its other characters it comes nearest to _A. spongites_, excepting in the spur of the tergum, which resembles that of _A. sulcata_.

The compartments appear to have been rather smooth externally. The radii are not wide, as in _A. cyathus_; and the basis is cup-formed. Internally, the parietes are feebly ribbed, as in _A. spongites_. Judging from the dimensions of the separated valves, this species must have equalled and perhaps exceeded the size of the largest living species, namely, _A. glans_, from Australia. Hence we may infer, that the basal diameter probably exceeded .55 of an inch: I may add, that the largest European specimens of _A. spongites_, from Naples and Portugal, are only .3 of an inch in basal diameter.

_Scuta._--These seem to resemble the scuta of _A. spongites_ in all respects, except in the longitudinal ridges standing much further apart, and, consequently, in the furrows being much wider: each ridge is generally double. Although there is a good deal of variability in the character of these ridges in _A. undulata_, and likewise in _A. spongites_, I have not seen any form intermediate between them. It must, however, be confessed, that this is an extremely variable character in many sessile cirripedes. In the _Terga_, the spur is about half the width of the whole valve, and therefore rather wider than in _A. spongites_.

5. ACASTA GLANS. Pl. 9, fig. 5 _a_-5 _c_.

ACASTA GLANS. _Lamarck._ Animaux sans Vertèbres, 1818.

_Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge rarely crenated, but furnished with six inwardly prominent teeth: scutum strongly striated longitudinally._

_Var._ (_a_) _with the edge of the basal cup finely crenated_.

_Hab._--New South Wales, Southern Australia; Mus. Brit., Stutchbury, &c.

This fine species seems to be extremely common, imbedded in an open porose sponge on the eastern and southern shores of Australia. It is very distinct from the other species, with the exception of the following _A. lævigata_, which, with some hesitation, I have allowed to remain specifically separated.

_General Appearance._--Excepting in its larger size, this species differs in external appearance but little from _A. spongites_; its colour is pale dirty reddish. The surface is generally studded with small calcareous points. The parietes of the carino-lateral compartments are about one fourth of the width of the parietes of the lateral compartments, and therefore proportionally of the same width as in _A. cyathus_. The largest specimen which I have seen, was .55 of an inch in basal diameter.

_Scuta._--These are slightly narrower, thicker, and more convex than in _A. spongites_: they are strongly striated in longitudinal lines. The articular ridge is very feebly developed. _Terga_: in full-grown specimens, the spur is half the width of the whole valve, and is truncated; its basal edge being parallel to the basal margin of the valve. The articular ridge and crests for the depressor muscles are very feebly developed.

_Internal structure of the parietes._--The inner surface of the parietes is quite smooth, without even a trace of ribs or teeth. But the most important character is that the internal lateral margins on both sides of each compartment, from the sheath to the basis, project inwards and form a rim; so that when the shell is viewed from within (Pl. 9, fig. 5 _b_, representing the lateral and carino-lateral compartments, and part of the carina), the six sutures are seen to be strengthened by six double columns.

_Basis._--This is moderately cup-formed. The edge, in order to meet the basal points of the inwardly projecting lateral margins of the six compartments, has six knob-like teeth. These are placed at unequal distances, for two on each side stand near each other, owing to the narrowness of the carino-lateral compartments. The degree of their development varies extremely; when most developed, as in the specimen figured (Pl. 9, fig. 5 _a_), each tooth is bifid and a little hollowed out, so as to receive the points of the two inwardly projecting margins which form each suture. Ridges, more or less prominent, running from each of the six marginal teeth, extend towards the centre of the cup. These six teeth cannot be seen from the outside. The edge of the cup is rarely crenated; but I have seen two instances in which this was the case.

_Cirri._--In the first pair, the rami are not quite so unequal as in _A. spongites_; the longer ramus being about twice as long as the shorter. In the third pair, there are some very minute, thick, upwardly-pointing spines, which I did not notice in _A. spongites_. In the fourth pair, the spines are a little more crowded, with longer dorsal tufts, than in the sixth pair; and they are mingled with some very minute, thick, upwardly pointing spines. In young individuals, there are only three pairs of main spines on the segments of the sixth pair, instead of four pairs.

6. ACASTA LÆVIGATA. Pl. 9 fig. 6 _a_, 6 _b_.

ACASTA LÆVIGATA. _J. E. Gray_ (!). Annals of Philosophy, (new series), vol. 10, Aug. 1825.

_Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge strongly crenated, and furnished with six inwardly prominent teeth: scutum feebly striated longitudinally, or smooth._

_Var._ (_a_), _epidermis coloured dull orange_.--Red Sea.

_Hab._--Red Sea, Philippine Archipelago; Mus. Brit., Cuming, &c.

This species, of which I have examined many specimens from the above two and other unknown localities, agrees in all essential points of structure with _A. glans_, and consequently I for some time classed them together; but the characters, though usually of small value, by which this form differs from _A. glans_ being apparently constant, I have with some doubt allowed it to remain specifically distinct. These characters are, firstly, the much smaller size of the whole shell in _A. lævigata_; secondly, the edge of its basal cup being always crenated, which seems to be a rare accident in _A. glans_; thirdly, though of secondary importance, the scutum being here less plainly striated; and, lastly, the spur of the tergum being of less breadth, and of a more rounded outline; on the other hand, it must be confessed, that when small specimens of _A. glans_ are taken, there is hardly any difference in the spurs of the terga.

_General Appearance and Structure of Shell._--The surface of the shell is often very smooth, but is sometimes studded with some small sharp calcareous points. The colour is white, or pale reddish-brown; but in the specimens from the Red Sea, the tint is more orange, with the upper part of the shell white. The orifice of the shell is unusually small. The largest specimen which I have seen was only .25 of an inch in basal diameter, and therefore less than half the size of _A. glans_. The internal surfaces of the _parietes_ are smooth, with the two lateral margins inflected, as in _A. glans_. The edge of the basal cup has six knob-like teeth, like those in _A. glans_, but smaller; and, in addition, it is finely crenated.

_Scuta_: these differ only in being less plainly striated in longitudinal lines; indeed, some specimens show hardly a trace of this structure. _Terga_; these valves, in some varieties (Pl. 9, fig. 6 _b_) can hardly be distinguished from those of equal size from young individuals of _A. glans_; other varieties have the spur (Pl. 9, fig. 6 _a_) not truncated, but broadly pointed, and therefore of considerably different shape.

Neither in the mouth, nor cirri could I detect any difference with _A. glans_.

7. ACASTA FENESTRATA. Pl. 9, fig. 7 _a_-7 _c_.

_Shell reddish, with six large, membrane-covered apertures between the sutures, above the basal cup: carino-lateral parietes half as broad as lateral parietes; internally, parietes and edge of basis smooth; tergum with the articular ridge short and prominent; spur pointed._

_Hab._--Philippine Archipelago, Mus. Cuming.

_General Appearance._--Shell rather elongated or tubular; with the upper part reddish, and the surface roughened with very minute points. The basal cup is generally as deep as the shell is high, ending downwards in a blunt point, often curved to one side. The summits of the radii, as usual, are oblique. The parietes of the carino-lateral compartments are about half as wide as the parietes of the lateral compartments, and are therefore of greater proportional width than in the foregoing or any other species of the genus. The large membrane-covered openings, or, as they may be called, windows, presently to be described, between the lower halves of the compartments, is much the most remarkable character of this species. The largest specimen which I have seen was only .23 in diameter, and .6 of an inch in height, measured from the basal point of the cup to the tips of the compartments.

_Scuta._--These barely exhibit a trace of longitudinal striæ. The valve is rather thick and convex. The basi-tergal angle is much rounded off. Internally, the articular ridge is thick and rather prominent. _Terga_: the valve is furrowed in the line of the spur: the spur is pointed and rather long; it is distinctly separated from the basi-scutal angle of the valve, and the basal margin on the two sides of the spur forms a straight line. The articular ridge is prominent, and short.

_Structure of the Parietes, Radii, and Basis._--The parietes are internally quite smooth down to its basis. The edges of the radii are also smooth, as is the edge of the basal cup. The alæ project less than usual. The radii are of moderate breadth, they extend downwards only a little below the sheath, namely, about half way down the shell, where they terminate, as usual, in a point. The increase in width, during growth, of the radii, and their not extending down to the basis, would necessarily cause a gap between the opposed edges of the walls, in the portion beneath the radii; but besides this, the edges of the walls themselves, beneath the radii, and on the opposed side beneath the alæ, are hollowed out, but on the latter side or beneath the alæ sometimes in a lesser degree. The result of this is, that the compartments, in their lower halves, are separated from each other by membrane-covered windows or apertures, arched at their upper ends, and of considerable size, namely, about as wide as the parietes of the carino-lateral compartments. I have only further to remark, that during the downward growth of the parietes, the apertures increase in size, but at the same time become closed up at their upper ends; and the arched layers of shell added at these upper ends, assume a very different aspect from the rest of the parietal surface,--appearing like two wedges, with their points upwards, let in, on one side of the suture, between the ordinary parietal surface and the radius, and, on the other side of the suture, between the ordinary parietal surface and the recipient furrow of the radius.

The _animal's body_ was in a bad state of preservation; but, as far as I could make out, the cirri resembled those of _A. glans_.

_Affinities._--This species differs from _A. glans_ in not having the internal margins of the compartments projecting inwards. It differs from all the ordinary varieties of _A. spongites_, in the smoothness of the basal edges of the parietes and of the edge of the cup; in the greater width of the carino-lateral compartment, though this is a variable point in _A. spongites_; slightly in the shape of the scuta and terga; and, lastly, in the large, membrane-covered openings between the compartments.

8. ACASTA PURPURATA. Pl. 9, fig. 8 _a_-8 _c_.

_Shell dull blueish-purple, with six small, membrane-covered apertures between the sutures, close above the basis: tergum with the articular ridge very short and prominent; spur very broad and rounded._

_Hab._--Sumatra; Philippine Archipelago; imbedded in the bark of an Isis; Mus. Cuming, Stutchbury, Brit.

This species is perfectly distinct from the others, as shown by its general appearance, its habits, and the structure of its opercular valves: it is allied to _A. fenestrata_, in having membrane-covered apertures between the compartments, and in some respects in its opercular valves: it is also allied to _A. sulcata_ and _cyathus_ in the parietes being often internally ribbed, in the basal cup having a crenated edge, and in the anterior ramus of the fourth cirrus being furnished with the minute hook-like spines.

_General Appearance._--Sub-globular, slightly compressed, with a rather small orifice; smooth, but sometimes furnished with sharp shelly points; dull purple, more or less dark, with the upper parts of the walls often white. The radii are rather narrow, and generally white, with their summits only slightly oblique, but variable in this latter respect. The parietes of the carino-lateral compartments are narrow, being only one sixth of the width of the parietes of the lateral compartments. In some specimens there are membrane-covered apertures of considerable size, in others mere narrow clefts, between the basal halves of the compartments. The basal cup is moderately deep. The largest specimen was only .16 of an inch in basal diameter.

_Scuta_, rather broad, externally convex, not longitudinally striated: articular ridge prominent, short, not extending down above one third of the length of the valve. Depression for the adductor muscle deep. On the internal surface, near to the rostral angle, a rather large purple spot of corium adhered to the valve. _Terga_, broad, externally rather convex: scutal margin protuberant: carinal margin slightly inflected, or furnished internally with a rim: articular ridge prominent, very short, not extending down above one fourth of the valve. Spur very broad, rounded, confluent with the basi-scutal angle of the valve.

_Internal Structure of the Parietes, Radii, and Basis._--The parietes, internally, are either quite smooth, or more commonly ribbed, with the basal edge in consequence crenated; the ribs are either placed at an unusual distance from each other, and consequently are few in number, or are pretty close together. The edge of the basal cup is either quite smooth, or closely crenated, or distantly toothed, in conformity with the state of the internal surface of the parietes. The radii have nearly smooth edges, with their summits more or less oblique. They sometimes extend down only three fourths, or only two thirds, of the length of the shell, and the margins of the parietes under the radii being a little hollowed out, the sutures are converted into clefts or apertures (of course covered by membrane) like, but not so large as, those in _A. fenestrata_. The margins of the parietes are hollowed out only on the side of the radius, and not on both sides of the sutures, as is most usual in _A. fenestrata_. In some specimens the radii extended down close to the basal cup, and only very minute clefts were left between the opposed edges of the parietes.

In the _animal's body_ the only noticeable character was, that on the anterior ramus of the fourth pair of cirri, some of the segments were furnished with very broad and thick, small, downwardly curved, teeth or hooks, like those described in certain varieties of _A. sulcata_; but they are here stronger and thicker. The segments in the three posterior pairs of cirri are not so much elongated, as in the other species.

9. ACASTA SPORILLUS. Pl. 9, fig. 9 _a_-9 _d_.

_Shell purplish-brown, with the parietes internally strongly ribbed and reticulated: carino-lateral compartments extremely narrow, not extending down to the basis._

_Hab._--Sooloo Islands, East Indian Archipelago; Mus. Dana.

I am indebted to Mr. Dana, the distinguished naturalist of the United States Antarctic Expedition, for two specimens of this interesting species, which, in the singular reticulated structure of the inner surface of the walls, and in the almost rudimentary condition of the carino-lateral compartments, not extending down to the basal cup, is very distinct from the foregoing species. I have used Mr. Dana's very appropriate MS. name of _sporillus_. The specimens were dredged up, lying quite loose and unattached at the bottom of the Sooloo sea; the one which I opened, must have long lain dead; but Mr. Dana assures me that some were living, and he has sent me drawings of parts of the mouth and cirri: I am much surprised at this circumstance; for analogy would have made me believe that this species must have been imbedded in some sponge-like body, such as the bark of a zoophyte, and that it could not have lived unattached. I may add that a small fragment of a brown leathery substance adhered to the upper end of one of the two specimens, and this seems to indicate attachment.

_General Appearance._--Shell shaped like a pointed acorn; slightly flattened; orifice extremely small; surface very finely punctured, covered by a purplish-brown epidermis, with transverse stripes of different shades, and with the apex dark; according to Mr. Dana, when fresh, the colour was purplish-carmine. Radii narrow, white. The carino-lateral compartments are extremely narrow; the wall-portion (fig. 9 _b_) forming a mere linear rib, terminating downwards in a sharp point, which does not reach the basal cup: hence this compartment evidently tends to become rudimentary. The basal cup is moderately deep and pointed. Basal diameter .16; height, from the bottom of the cup to the top of the shell, .24 of an inch.

_Scuta_: narrow, with the upper part produced; not striated longitudinally; coloured by a pale purple, longitudinal band. Internally, there is scarcely a trace of an articular ridge, which, in the other species, is always more or less developed. _Terga_ with the spur bluntly pointed; nearly the whole basal margin, on the carinal side, slopes towards the spur.

_Internal Structure of the Parietes, Radii, and Basal Cup._--The parietes are strongly ribbed internally; and these ribs are connected by very narrow, less prominent, transverse, slightly branched ridges, giving a reticulated structure to the inner surface. Between several of the main longitudinal ribs, in the lower part of the shell, new ribs may be seen in process of formation, and these tend to convert the reticulated structure into a double row of minute cells. I have not met with an exactly similar structure in any other cirripede; but I have no doubt that the little transverse ridges are homologous with the transverse calcareous septa in the parietal pores of many Balani, in the same manner as the internal longitudinal ribs, in this and other species of Acasta, are homologous with the longitudinal septa forming the above pores. The edge of the basal cup is pectinated with teeth, which lock into the teeth formed by the ends of the internal parietal ribs. The radii are narrow, and have smooth edges. The alæ project beyond the parietes to a remarkably small extent. The sheath is free, or hollow beneath. I have already described the almost rudimentary condition of the carino-lateral compartments; this is best exhibited in an internal view of the two compartments, as given in Pl. 9, fig. 9 _b_.