Chapter XXIX: Introduction (25)

_Direction of Growth: Minute Structure of Valves._--The shell grows downwards all round its basal margin. As far as the diametric growth of its upper part is concerned, there may be said to be only three valves, for the fixed scutum and tergum never become, as already stated, separated; on the three other lines of suture, the valves are added to on both sides; and thus the whole upper part of the shell, and the orifice, increases in diameter. The moveable scutum and tergum grow along their basal margins, and along the margins by which they are articulated together; but the scutum in this latter respect, less than the tergum. The summits of the moveable scutum and tergum, during continued growth, become either worn away, or they project freely; in this latter case, an internal ledge is added round the upper end of the fixed scutum and tergum, so as to keep the orifice accurately closed. In _V. nexa_ the rostrum, with its sub-central umbo, is anomalous, as already stated, owing to a broad upper internal border growing in a direction almost directly opposed to the basal growth of the moveable opercular valves.

In young specimens, on the apices of both scuta and both terga, and on the carina, but not on the rostrum, _primordial valves_ may be distinguished, resembling the valves, so called, which first appear (p. 129, Introduction) after the metamorphosis in, the Lepadidæ. In the Verrucidæ, however, they are calcareous; and the minute transverse cylinders, of which they appear to be composed, stand further apart, causing the surface of the primordial valve to be marked with little separate circles, instead of by hexagons.

The shelly matter of which the valves are composed is translucent: it is remarkably destitute of any investing membrane. The under surface is marked with rows of minute approximate pores, parallel to the lines of growth, into which the corium enters: after a portion of shell has been dissolved in acid, these threads of corium are seen to change, a short distance within, into cylinders of yellow chitine, running obliquely through the substance of the valve. These cylinders are about 1/2000th of an inch in diameter, but in parts they are spindle-shaped and twice as thick: they vary in length, about 1/100th of an inch being the average length: these cylinders at their upper ends suddenly contract into a point, more or less long, or are produced into a very fine tortuous tubulus of chitine, imbedded in the shell: I have seen in no other Cirripedes tubuli of this structure. There are other ordinary tubuli, such as occur in the valves of most Cirripedes, about 1/6000th of an inch in diameter, and which sometimes alternate with the above-described thicker cylinders. There are no external spines. From the number and length of the tubuli of both kinds, the tissue left after the action of acid is singularly complicated.

_Basis._--The basal membrane is thin, and is divided, but not very plainly, into concentric slips, marking the successive increments of growth. In the middle of it, in two young specimens, I found with great difficulty the pupal prehensile antennæ: they were of small size, measuring from the extreme edge of the main or second segment to the end of the disc, only 27/6000ths of an inch: the disc appeared narrow (as in Pollicipes and Scalpellum), with a single spine at the proximate end: the ultimate segment, placed as usual at about right angles to the disc, bore two groups of shorter and longer spines, but I could not count how many. The antennæ were enveloped in a mass of cement of a yellow colour, resembling in all its characters the cement of other Cirripedes. In only one case, I believe I saw bifurcating cement-ducts, of extreme tenuity, viz. 1/15,000th of an inch in diameter. The sheet of cement on the whole under side of the basal membrane, not rarely shows a very irregular reticulated structure. For convenience sake, it will be best to defer the discussion on the very anomalous, though slight, powers of excavation which this genus possesses, and which I must attribute to the effects of some substance secreted probably by the cement-organs. I will here only mention, that the specimens which have excavated a depression, are less firmly attached than those, which have not acted on their support; and that, in the former case, the basal membrane, for a considerable space in the middle, becomes quite detached.

_Animal's Body._--The body is much flattened and, owing to the little development of one side of the shell, lies parallel to the surface of attachment. The prosoma is but little protuberant. The articulations of the thorax are unusually straight and transverse. The _Mouth_ is also much flattened: it is placed rather distantly from the adductor scutorum muscle, owing to the production of the lower margin of the labrum. The _Labrum_ is not notched, or even hollowed out in the middle, or (excepting in _V. nexa_) bullate; its crest is surmounted by about eight (more numerous in _V. nexa_) little teeth, or by some fine bristles. The _Palpi_ are of moderate size, with their tips nearly meeting; they are slightly curved, and have bristles only on their outer sides and extremities: they are apparently capable of being lifted up and down by a muscle attached to them, just outside the rounded swelling on each side of the labrum to which they are articulated: in _V. nexa_, however, the palpi are very small and narrow, and their tips do not nearly meet. In this genus, therefore, we find the swollen state of the labrum and the size of the palpi--characters generally invariable and of high classificatory importance--variable. The mandibles have three upper main teeth, with two or three minute lower teeth, or, in _V. nexa_, with the lower part pectinated with small spines: in _V. Strömia_, I have seen traces of the second tooth being laterally double--a character of some importance. The _Maxillæ_ have a notch under the upper pair of large spines, with the lower part bearing, as usual, a double row of bristles, and forming a large step-formed projection: these organs are furnished with the usual apodeme and muscles. The _Outer Maxillæ_ are prominent, and deeply lobed on their inner surfaces, the two lobes being clothed with bristles.

_Cirri._--The first pair are attached, as usual, on each side of the mouth, and stand some way apart from the five posterior pairs. The second and third pairs differ considerably in structure from the three posterior pairs, which are much elongated. The _first pair_ (excepting in _V. nexa_) is short, with the two rami slightly unequal in length, and with the segments thickly clothed, as usual, with spines. The _second pair_ is remarkable from the posterior ramus being more than twice as long, and containing thrice as many segments, as the anterior ramus, which is barely as long as the shorter ramus of the first pair: the segments in the anterior ramus of the second pair (only five in number in a full-sized specimen) are broader and more protuberant in front, and more thickly clothed with spines (the terminal spines being doubly pectinated), than are the segments on the posterior ramus; on the latter, the uppermost segments have their bristles arranged in front in simple pairs, with the dorsal spines long, the lower segments being more thickly clothed with bristles, owing to the development of lateral rows. The _third pair_ resembles in every respect the second pair, except in being a little longer, and in the bristles on the posterior ramus being less crowded, more resembling the arrangement of those on the posterior cirri. In _V. nexa_, however, there is not so great an inequality in length or dissimilarity in structure in the two rami of the second cirrus, and only a very slight difference of any kind in the two rami of the third pair. _Fourth_, _fifth_, and _sixth pairs_ have numerous elongated segments, bearing four or three pairs of long slender spines in front, with a single minute bristle between each pair, and with two or three slender spines in the dorsal tuft.

There is a considerable amount of variation in the proportional length, and in the number of the segments, of the several cirri in _V. Strömia_; in some specimens the two rami of the fourth pair were unequal in length; in some, nearly all the cirri on the lower or attached side were shorter than those on the upper side.

_Caudal Appendages._--These are of most unusual length, sometimes even exceeding those of _Ibla quadrivalvis_, which surpasses, in this respect, all other cirripedes. They arise on each side and over the anus. They consist of numerous (sometimes as many as twenty-four), unequal, cylindrical, thin segments, bearing, at their upper ends, a circle of long and very slender spines. They sometimes equal two thirds or even four fifths of the length of the sixth cirrus; but their length, and the number of their segments, (sometimes imperfectly divided), varies much in different specimens of the same species, and sometimes even on opposite sides of the same individual. In some very young shells, as big as a pin's head, the caudal appendages were proportionally extremely short, and consisted of only two or three segments. No muscles enter these organs; and when the animal is taken out of its sack, they project straight out behind, instead of being curled in, like the cirri.

_Anatomical Structure._--The animal's body is attached to the two scuta by the adductor scutorum, and by the other usual muscles running towards the mouth, and surrounding the prosoma. The whole external covering or shell has no other muscles; Verruca thus differing from the Balanidæ and Lepadidæ; but the shell is attached all round, near its circumference, to the basal membrane, by a band of very short fibres, appearing like muscles, but really ligamentous, as determined for me by Professor Quekett. _Branchiæ_ are entirely absent. The _alimentary canal_ presents all the usual characters, but in the prosoma is rather abruptly bent back on itself. The orifices of the two _olfactory pouches_ are not at all prominent; they are placed directly under the outer maxillæ, (homologically in their middle segment), just above a small, medial, tongue-like apodeme. The orifices of the _acoustic sacks_ appeared to be in their usual position beneath the basal articulations of the first pair of cirri. The _vesiculæ seminales_ occupy their usual position in the prosoma; they are not much convoluted; they unite before entering the penis. The probosciformed penis is imperfectly ringed; it is thick and short, and tapers much more abruptly than is usual; it supports a few very thin hairs. The _ovarian cæca_ are spread over the basal membrane, at the bottom of the sack; hence they in fact lie almost on one side of the animal: they consist of two main trunks, proceeding out of the animal's body at the rostral end of the sack, which then branch and inosculate. In specimens of _V. Strömia_ collected by Mr. Peach for me, in Cornwall, during the first week of April, there were included two ovigerous lamellæ, placed transversely across the rostral and the carinal end of the sack: the lamellæ were .11 of an inch in length; they appeared loose and not attached, as in the Lepadidæ, to any ovigerous fræna. The ova, in their earliest age, have one end much pointed, and are 8/1000ths of an inch in length; they become blunter and increase a little in size before the larvæ burst forth. The larvæ, both during their earliest stage and after the first moult, have been excellently figured and described[137] by Mr. C. Spence Bate: they present no particular characters distinct from the larvæ of other Cirripedes. I will only further add, that the structure of the prehensile antennæ still adherent to the basal membrane, indicates that the larva in its last stage,--that is the locomotive pupa,--has a normal character.

[137] 'Annals and Mag. of Nat. Hist.,' 1851, Pl. 7, fig. 8-10.

_Affinities._--These have been sufficiently discussed under the family; I need here only remark that all the species, with the exception of _V. nexa_, are intimately allied together.

_Range--Habits--Geological History._--The genus Verruca ranges, being represented by four species, from Iceland to Cape Horn. The species that is found in Tierra del Fuego extends up the west coast to Peru. Our northern form, _V. Strömia_, (if I may trust a specimen in the British Museum, apparently ticketed in an authentic manner), occurs also in the Red Sea; and this is the only locality in the eastern hemisphere whence I have seen this genus. The species seem generally to live in rather deep water: I procured _V. lævigata_ from nineteen fathoms, on the east coast of Patagonia: _V. Strömia_ is found, according to information given me by Professor Forbes, on the British shores, between five and fifty fathoms, and on the steep shore off Mull, in ninety fathoms; but Mr. Thompson assures me that he once saw it adhering to tidal rocks and likewise to some floating bark. Generally the species are attached to living organic bodies, especially shells of Mollusca and of Cirripedes, to Gorgoniæ, and Laminariæ; less frequently to rocks. We shall immediately see that it has slight powers of excavation. This genus is geologically older than any true sessile cirripede or member of the Balanidæ: _V. Strömia_ is found in the Glacial Deposits and in the Red and Coralline Crag of England: another species (in a state not to be identified) occurs in the ancient Tertiary formations of Patagonia; and another in the Chalk of England and Belgium. The fact of this Family ascending to a Secondary epoch accords, in an interesting manner, with its affinities; inasmuch as though in appearance a sessile cirripede, it is almost equally related to the Lepadidæ and Balanidæ, and is more nearly related to the Lepadidæ than to the Balaninæ, or typical members of the Balanidæ: of the latter, none have hitherto been found in any Secondary deposit, whereas the Lepadidæ culminated during the Cretacean period.

_Powers of Excavation._

My attention was called to this subject by Mr. Hancock, whose excellent researches on the boring of Mollusca are well known. _Verruca Strömia_, when attached to shells destitute of an epidermis, excavates, as he informed me, a slight depression, deepest in the middle; but when the epidermis is present no effect whatever is produced. We shall presently see that the central depression is in some degree distinct from that of the circumference. I have since found Mr. Hancock's observations strictly applicable to _V. lævigata_, _V. Spengleri_, and to an ancient tertiary species from Patagonia. From having found that the following cirripedes, viz., Lithotrya, Alcippe, and Cryptophialus, all form their deep excavations by mechanical means, and from having read the above-mentioned memoirs by Mr. Hancock on the boring of mollusca, I was strongly impressed with the idea that the action in Verruca would likewise prove mechanical: but from the following facts I have come to the conclusion that the excavation must be due to a solvent, probably poured out from the cement-ducts, which debouch on the under side of the basal membrane.

In the first place, an epidermis, as just stated, perfectly preserves the shells of the various species of mollusca and certain cirripedes, to which I have seen Verruca attached: this is well shown by comparing the effect produced on the same shell in parts covered by the epidermis and in parts whence it has been abraded; or where the shell of the Verruca had fixed itself, whilst very young, within a crack in the epidermis, and had subsequently, by its growth, turned up the edges, and had then acted on the underlying shell; whereas the specimens attached to the sound epidermis had not produced the smallest effect. Again, I have seen an epidermis-covered mussel-shell encrusted by a hard nullipora, on which _V. lævigata_ was attached; and here the calcareous nullipora, under the middle of the basal membrane, was entirely corroded away, whilst the underlying epidermis and the shell beneath it, were not in the least affected. The protection afforded by the epidermis is still more strikingly shown by contrasting shells with very sharp prominent ridges, when thus invested and when naked, to which Verrucæ have been attached: I have given a figure (Pl. 21, fig. 6) of a piece of an invested Venus, from the surface of which a _V. Spengleri_ had been just removed; on the other hand, I have seen a Peruvian Discina in which even sharper ridges, covered by epidermis, were left absolutely untouched, although projecting deeply into the shell of an attached _V. lævigata_. I have seen several specimens of this latter Verruca (which has the power of corroding naked shell as deeply as its congeners), attached to the membrane-covered variety of _Balanus lævis_, the shell of which was thus perfectly preserved: now this membrane is little more than the 1/2000th of an inch in thickness; it is not hard, and so brittle that it generally separates with the Verruca, leaving the underlying shell of the _B. lævis_ with its lines of growth glossy and perfect: it appears to me impossible that a membrane so thin and brittle could resist an action, if mechanical, which has worn away from twenty to forty times as great a thickness of hard shell; but the thinnest film of any matter on which acid does not act, as of grease in certain forms of printing, will perfectly preserve the underlying substance, and as I have ascertained by putting on a drop of acid, is the case with this membrane. I have removed several scores of shells of _V. Strömia_ from the stems of Laminariæ, and when the latter were washed and slightly dried, generally not the least effect could be seen, except that the spots where the shell had adhered were glossy from the still adherent basal membrane: yet the stems of Laminariæ are far from hard. In some cases, however, the attachment of the Verruca seemed to have produced a very slight depression on the Laminaria, but this, I think, may be safely attributed to the growth of the surrounding surface; for I have seen exactly the same effect produced by the attachment of the discs of the antennæ of a Lepas, and these discs, with their long spines, could not possibly produce any excavation; nor is Lepas or its pupa in any case a burrowing animal. Again, I have seen a few specimens of Verruca attached to Gorgoniæ, and they had not acted in the least on the horny axis. I have examined numerous specimens of _V. Strömia_ attached to three pieces of slate-rock, and to one piece of red sandstone, all from different localities, and no effect whatever had been produced; yet the slate-rock, especially in one instance, was soft. Mr. Bate, to whom I am indebted for some of these specimens, also informs me that he could discover no impressions on the slate-rocks, whence specimens of the Verruca had been removed. On the other hand, I have had two specimens of limestone, with attached Verrucæ, one coarse and very impure, and the other hard and marble-like; and in both cases there was a distinct central slight cavity, including loose gritty matter. The loose particles evidently resulted from the unequal action either of a solvent or of some mechanical power on the rock, for it is improbable in the highest degree that the shells should have fixed themselves exactly over small collections of loose particles, even if such could possibly have remained on projecting surfaces of sea-washed rocks.

The above facts seem to indicate pretty plainly that the excavation of the support does not depend on its hardness, but on its containing calcareous matter, liable to be acted on by some solvent: but as this view, considering what we know of Lithotrya and of the two other burrowing genera of cirripedes to be hereafter described, appears improbable, I will add a few additional observations. I most carefully examined the shell and basal membrane of Verruca, and likewise the tissues left after the dissolution of the shell in acid, and could detect no structure at all fitted for boring; and what appears more important, there was no apparent difference in the state of the specimens which had and had not excavated a hollow; and this, I think, would certainly have been the case (as in Lithotrya) if the action had been mechanical. It is not easy to ascertain, owing to the small effect at any time produced, at how early an age Verruca begins to act on its support; but I found two sets of specimens only 1/20th of an inch in basal diameter, which had certainly commenced. The ribbed shell, (Pl. 21, fig. 6), especially the middle rib, shows, in a somewhat exaggerated degree, the _typical_ form of the excavation; it may be here seen that the excavation is of the same depth for some little distance from the circumference towards the centre, but that in the middle it suddenly becomes deeper. I have seen several specimens with a central hollow, without any, or with scarcely any, marginal depression, and likewise the reversed case. These several facts show that the central excavation cannot be due to an equable action, prolonged during the whole growth of the shell, having thus affected the middle more than the circumferential parts, for in this case the excavations would have sloped into each other. In specimens which have not at all acted on their support, the whole basal membrane is firmly attached, as in all ordinary cirripedes, to the supporting surface; but in those which have acted, the middle portion of the basal membrane is quite unattached, and the circumferential portion is, I think, less firmly attached than is usual; but between these two portions, there is a circular zone strongly cemented to the supporting surface, and which alone keeps the shell in its place. Now, on the mechanical theory, to account for the circumferential hollow, the basal edges of the shell together with the circumference of the basal membrane must be subjected to movement, but the shell is united to the basal membrane by corium and by transparent structureless chitine (both of which may be left out of question) and by a circle of short fibres, which adhere at their lower ends to the firmly cemented circular zone, and by their upper ends to the shell; and these fibres have been very carefully examined by Professor Quekett, and pronounced to be not muscular, but exclusively ligamentous, and therefore incapable of moving the edge of the shell. The basal membrane over the central hollow is, as stated, quite loose: its lower surface, formed by a reticulated layer of horny cement-tissue, shows no signs of abrasion, and the membrane is so brittle and tender, that in specimens which have been once dried and then well soaked, it almost invariably cracks when the shell is removed, owing to its mere adhesion to the delicate inner tunics of the sack; yet on the mechanical theory, the wearing of the central hollow must have been caused by the action of this middle portion of the basal membrane,[138] which, it may be repeated, is destitute of muscles. From the presence of the prehensile pupal antennæ, enveloped in cement, nearly in the centre of the basal membrane, it is certain that this spot was originally attached to the supporting surface, and has since been detached from it; as, moreover, the central hollow goes on increasing in diameter with the growth of the shell, it is certain that the inner edge of the firmly attached circular zone of basal membrane must likewise continually go on becoming detached: it may, then, be asked by what force can the basal membrane, seeing that it is united to its own shell above only by fibres of ligament near the circumference, be continually torn away from the underlying support, to which it is strongly cemented? On the other hand, on the theory of a solvent slowly poured out from the cement-ducts, its separation from its support is simply explained. It might be supposed that the calcareous matter, when dissolved, would not be able to escape from the central hollow, owing to the basal membrane being so firmly cemented all round it; but the attachment is by a reticulated layer of cement; and I infer that it must be permeated by open passages, from the fact of the hollow being often filled, in dried specimens, by a bubble of air, instead of the basal membrane being pressed closely down into the hollow, as would have been the case had the hollow been hermetically sealed up. I have seen a few instances in which the bottom of the central hollow was occupied, (as was remarked to me by Mr. Hancock), by a little chalky and gritty matter; and in the case of one of the specimens of calcareous rock, before alluded to, by coarse grains and oxide of iron; this seems quite compatible with a solvent acting more readily on certain parts of the rock or shell than on other and less soluble parts or particles.

[138] Mr. Hancock suggests to me that the basal membrane, on the
mechanical theory, need not itself move; the motion of epithelial
scales, were they transferred into cutting agents, might be
supposed to be sufficient. But of such scales, though I used very
high powers, I could see no trace; and their presence on the under
side of the layer of cement seems hardly possible. Moreover,
according to Von Siebold ('Anatomie Comparée,' tom. 1, p. 412),
ciliary action has not been observed in any Crustacean, or indeed
any Articulate animal. This same statement is likewise made in
Annals and Mag. of Nat. Hist. 1854, p. 136, by Dr. T. Williams.

The greatest depth of the central hollow, in any specimen seen by me, even measuring from the top of a rib in the case of a ribbed shell, to the deepest point, was only 1/50th of an inch; but considering how much depressed the shell of Verruca is, I have no doubt that this small gain of space is of service to the animal: we must suppose the loose middle portion of the basal membrane is stretched slightly, or splits and is repaired, so as to fit the hollow. With respect to the even much slighter circumferential excavation, it barely equals in depth the thickness of the extreme edges of the walls; it must, I presume, give strength to the shell when _laterally_ pushed; but it certainly appeared to me that the individuals which had excavated a depression for themselves, could be pried vertically up much more easily than those which had not acted on their support. Finally, we must suppose that the hypothetical solvent is poured out of the cement-ducts at the extreme circumference of the basal membrane, which is almost loose and destitute of cement, so as to slightly corrode outwards and downwards the calcareous support; the action here then stops, and this rim of basal membrane becomes, after a new rim has been formed and as the shell grows outwards, firmly cemented down to the now slightly excavated surface of attachment; but during all the time the solvent goes on acting in the middle, and continues, during the whole growth of the shell, to encroach on and dissolve the supporting surface from under the inner edges of the previously cemented down, circular zone of basal membrane. I have discussed this subject at considerable length, as it appears to me an interesting one. In this case we have the action of ciliæ[139] and of respiratory currents, to which in the case of Mollusca so much has been attributed, entirely eliminated. It is, also, an interesting fact, that within the same Order we should have some Cirripedes boring by simply mechanical means, and others by a chemical solvent.[140]

[139] See the previous note to p. 516.

[140] The solvent may be carbonic acid gas, as suggested by Mr. C.
S. Bate in the case of Mollusca ('Report of British Association,'
1849, p. 73), but here, under the basal membrane, we cannot have
the respiratory currents, or the ciliary action (see note, supra),
as likewise suggested by Mr. Bate.

1. VERRUCA STRÖMIA. Pl. 21, fig. 1 _a_-1 _f_.

LEPAS STRÖMIA. _O. Müller._ Zoolog. Dan. Prod., No. 3025, 1776.

---- ---- _Ib._ Zoolog. Dan., vol. 3, Tab. 94, 1789.

---- STRIATA. _Pennant._ British Zoology, vol. 4, Tab. 38, fig. 7,
1777.

DIE WARZENFORMIGE MEEREICHEL. _Spengler._ Schriften der Berlin.
Gesell., 1 B., Tab. 5, fig. 1-3, 1780.

LEPAS VERRUCA. _Spengler._ Skrifter af Naturhist. Selskabet, 1 B.,
1790.

---- ---- ET STRÖMIA. _Gmelin._ Syst. Nat., 1789.

BALANUS VERRUCA. _Bruguière._ Encyclop. Meth., 1789; _Clisia
verrucosa_, Deshayes, in Tab.

---- INTERTEXTUS. _Pulteney._ Catalogue of Shells of Dorsetshire,
1799.

LEPAS STRIATUS. _Montagu._ Test. Brit., 1803.

---- VERRUCA. _Wood's_ General Conchology, Pl. 9, fig. 5, 1815.

VERRUCA STRÖMII. _Schumacher._ Essai d'un Nouveau Syst. Class., 1817.

CREUSIA STRÖMIA ET VERRUCA. _Lamarck._ Animaux sans Vertèbres, 1818.

OCHTHOSIA STROEMIA. _Ranzani._ Memoire di Storia Nat., 1820.

CLISIA STRIATA. _Leach._ Encyclop. Brit. Suppl., vol. 3 (sine
descript.), 1824.

CLITIA VERRUCA. _G. B. Sowerby._ Genera of Recent and Fossil Shells,
Plate.

VERRUCA STRÖMII. _J. E. Gray._ Annals of Philosophy (new series),
vol. 10, Aug., 1825.

_Moveable scutum, with the lower articular ridge not half as broad as the short upper articular ridge: shell generally ribbed longitudinally._

_Var., with the shell not longitudinally ribbed._

_Hab._--Shores of Great Britain and Ireland, Shetland Islands;
and, according to various authors, Denmark, Iceland, and shores of
northern Europe. Red Sea, Brit. Mus. Attached to shells, laminariæ,
rocks, crabs, and floating bark, from low tidal mark to fifty or
ninety fathoms.

_Fossil_ in Glacial deposits of Scotland, Mus. Lyell; Red Crag
(Walton, Essex), Coralline Crag (Sutton), Mus. S. V. Wood.

I have given so full a description of the genus that little remains to be said under the species. Generally the whole shell is covered (independently of the interfolding, oblique, articulating plates) by narrow, longitudinal ridges or folds; and by this character alone the ordinary variety of _V. Strömia_ can be distinguished (as far as I have seen) from all the other species. The shell is white or dirty yellowish-brown. The scutum has the lower articular ridge on its tergal margin very narrow (but somewhat variable in width), appearing like a mere slight shoulder, against which the longitudinal axial ridge of the tergum abuts: it is not half as wide as the short, upper articular ridge. On the under side there is a very slight depression for the adductor scutorum muscle. There is considerable variation in the degree to which the transverse ledge on the under side of the fixed tergum projects, and therefore in the depth of the hollow thus formed. The specimens with the right-side, and those with the left-side opercular valves moveable, are apparently about equally numerous.

The specimen in the British Museum, from the Red Sea, was attached to a Gorgonia, and was in the same box with a Pyrgoma--circumstances favouring the correctness of the locality--but I am much surprised from the general distribution of the species, that _V. Strömia_ should occur in so distant and isolated an area. After careful examination, I can discover no constant difference between the Red Sea and British specimens.

The specimens from the Crag have not their moveable opercular valves, which offer much more important diagnostic characters than the shell; but as far as the latter is concerned, no difference whatever can be perceived from _V. Strömia_.

2. VERRUCA LÆVIGATA. Pl. 21, fig. 3 _a_, 3 _b_.

VERRUCA LÆVIGATA. _G. B. Sowerby._ Genera of Recent and Fossil
Shells, Plate.

_Moveable scutum, with the lower articular ridge broader than the short upper articular ridge; moveable tergum broader than high, with the upper articular ridge produced into a point._

_Hab._--Tierra del Fuego; Eastern Patagonia, nineteen fathoms; Chile;
Peru; Mus. Brit., Cuming, Stutchbury, Darwin: attached to shells, and
often to _Balanus lævis_ and _psittacus_.

I can point out no difference in the shell between this species and _V. Strömia_, excepting that its walls seem invariably to be smooth, which is rarely the case with _V. Strömia_; perhaps also the oblique interfolding articular plates between the several compartments are here more prominent. It appears that specimens with the left side uppermost, and therefore with the left opercular valves moveable, are considerably more common than those with the right valves moveable. The moveable scutum and tergum are articulated together by much more prominent articular ridges than in _V. Strömia_, and the two valves together are broader in proportion to their height,--the height being measured from the apex to the basal margin. In the scutum the lower articular ridge is considerably broader than the short upper ridge. In the tergum, the basi-carinal corner is more rectangular, and the whole valve is nearly square: owing to the deep furrow receiving the lower articular ridge of the scutum, the axial ridge of the tergum is proportionally narrower but more prominent than in _V. Strömia_; the uppermost ridge (formed by the occludent margin of the valve) projects, especially when viewed on the under side (fig. 3 _b_), as a moderately sharp point.

In the _mouth_, the lower teeth of the mandibles are more distinct than in _V. Strömia_; the lower part of the edge of the maxilla is very prominent. In the second and third pairs of cirri the terminal spines on the shorter rami are coarsely pectinated; on the sixth pair there are only three pairs of main spines on each segment; but these several points, according to the analogy of other species, I should expect to be variable.

This species is alluded to by Bruguière, in the 'Encyclopédie Méthodique,' but was confounded by him with the _V. Strömia_ of Europe.

3. VERRUCA SPENGLERI. Pl. 21, fig. 2.

_Moveable scutum, with a sharp, straight, medial adductor ridge: fixed scutum not larger than the fixed tergum._

_Hab._--Madeira, Mus. Lowe; attached to shells.

It would appear that the present species does not attain quite so large a size as the more northern _V. Strömia_; the walls are not longitudinally ribbed as is usual with this latter species. The proportional sizes of the compartments seem to be somewhat different; the fixed scutum is either equal to or even smaller than the fixed tergum, instead of being larger, as in _V. Strömia_; but in young individuals the proportions are reversed. In several specimens the fixed scutum and tergum together were larger than the carina. The rounded adductor plate of the fixed scutum is extremely large. The lines of growth, especially on the moveable opercular valves, are rather more plainly crenated than in _V. Strömia_. In the moveable scutum the lower articular ridge on the tergal margin varies a little in size, and is sometimes larger than in _V. Strömia_ (but never so large as in _V. lævigata_), and is placed more in the middle of the tergal margin: but by far the most important character by which this species can be distinguished from all the others, is the presence, on the under side of the moveable scutum, of a straight, prominent adductor ridge, which runs up to and even under the apex of the valve, for it is there slightly hollowed out. In the moveable tergum, owing to the medial position of the lower articular ridge of the scutum, the middle of the scutal margin is more hollowed out, and the axial ridge narrower, than in _V. Strömia_.

In the animal's body the only difference which I could perceive was that the shorter rami of the second and third pairs of cirri were not so short, compared either to the other cirri or to the longer rami of these same cirri. In the second cirrus, in a moderately-sized specimen, the segments were six and thirteen in number in the two rami, and in the third cirrus, seven and fifteen.

Had it not been for the specimen in the British Museum of _V. Strömia_, from the Red Sea, I should have concluded, from geographical considerations, that _V. Spengleri_ probably was the species found in the Mediterranean, and noticed by Spengler ('Schriften der Berl. Gesell.,' 1 B., 1780), as a small variety of the northern _V. Strömia_; and likewise that it was the _Creusia echinoides_ of Risso ('Hist. Nat. Product. de l'Europe,' tom. 4, p. 382, 1826), which is certainly a Verruca, but not described with sufficient minuteness to be recognised.

4. VERRUCA NEXA. Pl. 21, fig. 5.

_Shell reddish: moveable scutum, with three strongly prominent longitudinal ridges, besides the articular ridges: fixed scutum larger than the carina, with no distinct adductor plate._

_Hab._--West Indies, Mus. Brit.; attached to a Gorgonia.

This species differs considerably from all the others in the genus. The shell is brownish-red, tinted yellow: it is not at all depressed like the former species, but the walls are almost perpendicular or even overhang their bases, and the summit of the shell consequently is broad. This form may be in part, but only in part, due to the attachment on the thin branches of the Gorgonia. The umbones of the compartments are remarkably prominent and sharp. Although the parietes are nearly smooth, yet from being so steep, they are little seen, and owing to the very prominent but rounded ribs by which the compartments and opercular valves are articulated together, the whole shell has a strongly ribbed appearance. The diameter of the largest specimen was .2 of an inch.

The _rostrum_ (A, fig. 5) is patelliformed, with the umbo of growth sub-central, but rather above the middle point; hence this valve, differently from the carina, and differently from the rostrum of the other species, grows not only at its basal margin, and on both sides where opposed to the carina and fixed scutum, but also along its upper margin where opposed to the basal edges of the moveable scutum and tergum: owing to the perpendicularity of this valve, the upper part forms a ledge almost parallel to the orifice of the shell. The carina (B) is of unusually small size, being about only half the size of the rostrum, and scarcely exceeding in size the fixed tergum. The _fixed scutum_ (S′) is large, larger even than the carina; it is oblong, and its shape is more simple than in the other species; this is chiefly owing to the rostrum articulating with the whole of that margin (_b_) which answers to the basal margin of the moveable valve; whereas in the other species (fig. 1 _b_) it curls beyond this margin, and articulates with the very protuberant, so-called, parietal portion of the valve. Three or four rounded prominent longitudinal ribs, exactly like the homologous ribs on the moveable scutum, run from the apex of the fixed scutum to the basal margin, and their extremities form the teeth by which it articulates, as just stated, with the rostrum. Its upper articular ridge (′) is more prominent, and placed much lower down in the suture between it and the fixed tergum, than in the foregoing species. The ledge (_o_) by which the orifice is kept neatly closed, is here more distinct than in _V. Strömia_: this ledge is necessary, as well as in the case of the fixed tergum, owing to the altered shape of the summits of the moveable scutum and tergum, due to their corrosion and to their coming to project freely. But the most remarkable character of the fixed scutum is, that on the under side there is no great adductor plate, but a rounded hollow with its lower edge only slightly prominent; the absence of the adductor plate, which is present in all the other species of the genus, is no doubt due to the under side of this valve being inclined even outwards, and so standing in some degree opposed to the moveable valve; thus affording on its under surface a place for the attachment of the lower end of the adductor scutorum muscle; whereas in the other species this muscle could not possibly have been attached, without the aid of an adductor plate, to the under side of the much depressed and sloping fixed valve. The _fixed tergum_ (T′) is a little more simple in form than the corresponding valve in the other species; the two arms, answering to the occludent and carinal margins of the moveable tergum, are more nearly equal in length: the internal transverse ledge, separating these rims or margins from the parietal portion of the valve, is but little developed.

All four valves forming the shell are remarkable from having, when full-grown, but not whilst young, their basal edges abruptly inflected inwards, thus forming a ledge all round the basal membrane, as in _Chthamalus intertextus_ and _Hembeli_.

_Moveable Scutum._--This is slightly larger in proportion to the tergum than in the foregoing species: it is chiefly remarkable from the presence of three prominent longitudinal ridges on the main part of the valve, like the two articular ridges on the tergal margin; of these latter, the lower one extends down to about the middle of the tergal margin. The _moveable tergum_ is rhomboidal, with the whole carinal portion marked only by lines of growth: it is only remarkable by the upper of the three articular ridges on the scutal margin being unusually distinct from the occludent margin.

With respect to the animal's body, its several peculiarities have already been pointed out under the genus. The _labrum_ is decidedly bullate, triangular in section, with a row of minute bead-like teeth on the crest; the palpi are very narrow and short, and do not nearly touch each other: this variation in the structure of the labrum and in the size of the palpi, is very remarkable, considering how important, in a classificatory point of view, these parts are in all other Cirripedes. In the _mandibles_ there are either two or three main teeth, with the whole lower part of the organ pectinated with sharp spines. _Cirri_: the first pair is not short; in the individual examined, the two rami had eleven and twelve segments. In the second pair, the shorter ramus was two thirds of the length of the longer ramus, the segments being in number ten and fifteen; in the arrangement of the spines this second pair resembles its homologue in the three other species. In the third pair, the two rami are very nearly equal in length, having sixteen and eighteen segments; and the segments of the anterior ramus are only a little thicker and more thickly clothed with spines than those of the posterior ramus. The remaining cirri and the caudal appendages are as in the other species.

5. VERRUCA PRISCA. Pl. 21, fig. 4.

VERRUCA PRISCA. _Bosquet._ Monographie des Crustacés fossiles du
Terrain Crét. de Limbourg, Tab. 1, fig. 1-6; 1853.

_Shell smooth: moveable scutum, with the lower articular ridge somewhat broader than the upper articular ridge._

Fossil--'Système Senonien et Maestrichtien,' Belgium, Mus. Bosquet;
in Chalk, Norwich, Mus. J. de C. Sowerby.

M. Bosquet has admirably figured and described the several separated valves belonging to this species, and I owe to his great kindness an examination of some of them. In Mr. J. de C. Sowerby's collection, also, there is a single specimen, attached to a Mollusc, with the four valves of the shell united together, but without the two moveable opercular valves; it cannot be positively asserted that this is the same species with that of M. Bosquet, but such probably is the case. This is the species to which I alluded in the Introduction to my 'Monograph on Fossil Lepadidæ.' It is an interesting species, from being the only known Secondary one, but in itself it is a very poorly characterised form, and I can point out no important character in the shell by which it can be recognised. The rostrum and carina, which are of nearly equal sizes, are locked together by the usual interfolding plates, and likewise to the fixed scutum and tergum; but these latter plates seem to have been less developed in M. Bosquet's specimen than in the English. The fixed scutum has a large adductor plate, which seems to have been chipped in M. Bosquet's specimen; this valve and the fixed tergum in all essential respects resemble the same valves in _V. Strömia_. The surface of the shell is very smooth.

The _moveable scutum_ has its occludent margin considerably arched: the lower articular ridge is broader than the upper ridge, in which respects it resembles the same valve in _V. lævigata_, but the whole valve is not so broad as in that species. There is no adductor ridge on the under surface. The _moveable tergum_ has its upper articular ridge narrow, and slightly produced into a point on the scutal margin: in this latter respect this species also resembles _V. lævigata_, but the whole valve is not so broad in proportion to its height.

3. Family LEPADIDÆ.

_Cirripedia having a flexible peduncle, provided with muscles: scuta and terga, when present, not furnished with depressor muscles: other valves, when present, not united into an immoveable ring._

This Family has been fully treated of in my former volume, published by the Ray Society,[141] and I should here only have alluded to its existence, had it not been for the genus Alcippe, which differs in so many important characters from the other members of the Lepadidæ, that formerly I did not even suspect that it could belong to this Family, and therefore deferred its examination. The genus Alcippe was discovered, well described and illustrated, in 1849, by Mr. Hancock; to whose very great kindness I am indebted for permission to dissect and examine his entire stock of this truly remarkable Cirripede. In the classification of the whole class I have not felt so much doubt, as whether I ought to institute a family for the reception of this genus. Alcippe differs from all other Cirripedes (putting on one side for the instant, the males and complemental males of Ibla and Scalpellum) in the very singular fact of being destitute of a rectum and anus;--in the three segments of the thorax, which usually support the second, third, and fourth pairs of cirri, being without any appendages;--in the fifth and sixth pairs of cirri having their inner or posterior rami metamorphosed into very singular roughened cushions or buttons, which apparently serve to triturate the food;--in the caudal appendages being muscular, and being used conjointly with the cirri;--and lastly, in the pupa having a lesser number of segments in its abdomen and caudal appendages than in (as far as I have seen) any other Cirripede. It will be thought that these characters are amply sufficient to justify the placing Alcippe in a separate family, more especially when the close general resemblance in the animal's body in most of the other members of the Balanidæ, Verrucidæ, and Lepadidæ, is borne in mind. On the other hand, the males and complemental males of Scalpellum and Ibla must indisputably be considered as members of the Lepadidæ; yet the male of _Scalpellum vulgare_ and _ornatum_ has no stomach, anus, or mouth, which is a far more abnormal structure than the absence only of the anus in Alcippe: the cirri, also, in these same males, differ from the ordinary cirripedial type decidedly more than in Alcippe. Again, in the male of Ibla, all the cirri, excepting the fifth and sixth pairs, are aborted, and these two pairs are usually only uniramous; here, then, we have a decided resemblance to Alcippe. Hence, if we might assume that the female Alcippe had partially assumed characters confined to the males of the other genera, it would assuredly stand amongst the Lepadidæ. Independently of this comparison with the foregoing males, the affinities of Alcippe are so special to several genera amongst the Lepadidæ, that it seems unnatural to force it out of the position which it well occupies between Ibla and Anelasma, and place it in another family by itself: thus, in being bisexual, and in the general character of its very curious males, Alcippe shows an affinity to Ibla and Scalpellum; and to the former of these genera it is related in several particulars, such as in the body being lodged within the peduncle, and in the structure of the larval antennæ, &c.: to Anelasma and Alepas it is allied in the general character, and to a certain extent in the muscles, of the capitulum; Anelasma, also, has all its cirri to a certain degree rudimentary, and _Alepas cornuta_ has the inner rami of the fifth and sixth pairs of cirri,--namely, the very same rami which are so curiously modified in Alcippe,--small, destitute of muscles, and functionless for their proper purpose: to Anelasma and Lithotrya it is allied in the peculiarity of the lower end of the peduncle becoming elongated by growth, and in being imbedded; and to Lithotrya by its powers of excavation and manner of attachment. Now, I believe it generally holds good that when a form is really distinct from another group, its affinities are general, or only in a slight degree special to the members of that group. Nor, indeed, can it be asserted that Alcippe differs much more, somewhat more it certainly does, from the other genera, than does Anelasma, with its more singular mouth, spineless rudimentary cirri, and fimbriated peduncle; and I have never regretted having included this genus amongst the Lepadidæ. Hence, after much consideration, I have resolved to consider Alcippe as one of the Lepadidæ, though so curiously modified,[142] and having characters confined to the males of the other genera. Perhaps I have been in some degree influenced by the difficulty of finding external characters by which to separate Alcippe as a family from the other Lepadidæ.

[141] The fossil species have been described in a separate
Monograph published by the Palæontographical Society. Since
its publication, M. Bosquet has produced an excellent memoir,
containing descriptions, with the most beautiful illustrations, of
several new Cretacean species of Pollicipes and Scalpellum. The
memoir is entitled a 'Monographie des Crustacés Fossiles du Terrain
Crétacé, du D. de Limbourg.'

[142] Adrien de Jussieu, in his 'Memoir on the Malpighiaceæ,'
'Archives du Museum,' tom. 3, p. 86, when speaking of the
characters afforded by the degraded flowers, which in certain
genera are borne together with ordinary flowers, makes the
following observations bearing on the question here discussed,
viz., whether or not to include Alcippe amongst the Lepadidæ.
"Ces exemples peut-être aideront à comprendre comment à des
genres d'une organisation assez compliquée, viennent quelquefois
s'en rattacher d'autres d'une organisation beaucoup trop simple
en apparence, membres appauvris et dégradés d'une même famille,
qui lui appartiennent sans la représenter; comment le type,
s'y présente comme effacé, ne conservant plus pour se laisser
reconnaître que quelque trait isolé, mais caractéristique, dont la
valeur, essentiellement ordinale, peut être ainsi constatée." Under
the point of view, so strongly and admirably insisted on lately by
Milne Edwards ('Annales des Sciences Nat.,' 3d series, tom. 17), of
describing types without regarding whether the different members
blend together on their confines, perhaps Alcippe should be raised
to the rank of a Family: I feel quite unable to decide how properly
to act.

But we shall presently find, when we come to Cryptophialus, that all the above difficulties, great as they are, are greatly enhanced, for Cryptophialus is certainly allied in a very direct and curious manner (in decided opposition to the remarks just made on special affinities) to Alcippe, and yet in all the more important parts of its organisation, and in its metamorphosis, it differs so fundamentally, that I have felt myself obliged to form not merely a Family, but a distinct Order for its reception.

_Genus_--ALCIPPE. Pl. 22, 23.

ALCIPPE. _Hancock._ Annals and Mag. of Nat. Hist., vol. 4, 1849, Pl.
8, 9.

_Fem.--Capitulum without valves, with the orifice spinose: peduncle with the basal end added to during growth; its rostral surface depressed and covered by a horny disc: capitulum and peduncle imbedded in a cavity excavated in the shells of molluscs._

_Labrum very large, with a row of long hairs on each side: palpi rudimentary: mandible one-toothed: second, third, and fourth cirri absent: fifth and sixth cirri with the posterior ramus represented by a button-like body: caudal appendages four jointed, muscular: anus none._

_Males,--several, adhering to the upper end of the horny disc of the female: capitulum naked, transparent, elongated, with a small orifice at the end: peduncle lobed, with the lower end extending far beyond the pupal antennæ: eye, testis, and vesicula seminalis single; probosciformed penis very long: mouth, stomach, thorax, abdomen, and cirri none._

ALCIPPE LAMPAS, _Hancock_ ut suprà.

_Hab._--North-eastern shores of England, fifteen to twenty fathoms,
imbedded in dead shells of _Fusus antiquus_ and _Buccinum undatum_
(A. Hancock); south-eastern shores, off the Eddystone, Lighthouse (C.
S. Bate).

FEMALE. Pl. 22.

I may premise that after the sketch of the leading peculiarities of Alcippe, and after the discussion on its affinities, just given under the Family, I think it would be superfluous to institute a full generic description, separately from the following detailed account of this most anomalous cirripede.