Affinities, Classification, Variation.

Under the Order it has been stated that the Balanidæ, are, on the cirripedial type, the highest in the class; that is, they are the most complicated, but not (to use Professor Owen’s term) by mere vegetative repetition. Amongst the Balanidæ, the first section of the genus Balanus may be taken as typical; here we have the structure of the shell extremely complicated, yet beautifully adapted for strength, and for the protection of the included body. The cementing apparatus is here, also, most complicated. I have divided the Balanidæ into two natural sub-families, the Balaninæ and Chthamalinæ, in accordance with certain differences in the structure of the shell and of the animal’s body: that this division is natural, might almost be inferred from the one fact, that all the characters by which the Chthamalinæ differ from the Balaninæ, are those by which the former approaches the family of the Lepadidæ; moreover, certain anomalous characters in the Chthamalinæ, as the supplemental whorls of compartments in Catophragmus, and the presence of caudal appendages in this same genus and in Pachylasma, reveal this same affinity. The only objection which I can see to the separation of the sixteen genera into the above two sub-families, may be drawn from the degree to which they blend together; thus, as far as the shell is concerned, Chelonobia, in one important internal point of structure, tends to assume the character of the Chthamalinæ; and on the other hand, Pachylasma, a member of the Chthamalinæ, has a shell, which if not examined during its earliest growth, would be placed without doubt amongst the Balaninæ. But it fortunately so happens, that in no one character of the body does Pachylasma approach the Balaninæ more nearly, than do the other members of its sub-family; or Chelonobia approach, in the same respects, the Chthamalinæ. It is only in Chthamalus, of which the shell clearly places it in the sub-family bearing its name, that in some of the species, the less bullate labrum,—the larger palpi,—the lower teeth of the mandibles being laterally double,—and the lower segments of the third pair of cirri being thickly clothed, like the lower segments of the second pair, with bristles—all show that these species make an approach in structure to the Balaninæ.

It will be seen that I have divided the Balaninæ into two little groups, according as whether the branchiæ consist of one or of two plicated folds of membrane, and as whether or not the scutum and tergum are articulated together. I have been greatly tempted to follow Drs. Leach and Gray, who have separated the second of these groups, containing the genera Coronula, Tubicinella, Xenobalanus, and Platylepas, into the sub-family of the Coronulinæ. Certainly these genera have a peculiar aspect in common, and agree in being parasitic and imbedded in the skin of Cetaceans, as is the case with the first three genera, or in that of turtles, manatee, and sea-snakes, as in Platylepas. Though these genera possess several peculiar characters, yet I can find none common to all four, excepting their imbedment in the skin of Vertebrata, their double branchiæ, and their non-articulated opercular valves; and these I do not think of sufficient importance to serve for the separation of a sub-family; for in Chthamalus, one species has double branchiæ, one species has no branchiæ at all, and the other species have single branchiæ; so again in Chelonobia, the scutum having only a horny articular ridge, makes an approach to Coronula and its allies. I may further specify that the folded walls, a singular character common to Coronula, Platylepas and Xenobalanus, fails in Tubicinella; the open tubes and the imperfect outer lamina of the parietes towards their bases, are characters which fail in one species of Platylepas; the muscles running to the opercular valves being thinly spread out, and partially without transverse striæ, is also a character which fails in Platylepas; the simplicity of the cement-ducts partially fails in Tubicinella; and lastly, the existence of small intermediate teeth on the mandibles, fails in Xenobalanus: hence, I repeat, I have not thought it prudent to admit the sub-family of the Coronulinæ though in many respects a very natural group.

The genera in the Balaninæ and Chthamalinæ are founded chiefly on the number of the compartments (the number being apparently due, as previously explained, to the fusion or abortion of certain of the eight typical compartments); and secondarily, on the nature and even form of the basis, and on the porosity of the walls. In Coronula and its allies, the non-articulated opercular valves and deeply folded walls come into play. As a justification for using these characters in distinguishing the genera, and even to a certain extent in separating the two sub-families, I must call to mind that the shell, with the basis, is not merely a dermal envelope, as amongst Molluscs, but actually consists of the first three segments of the head. The parts of the mouth and the cirri are of very little service in distinguishing the genera,—a singular fact, considering that most of the genera amongst the Lepadidæ could be distinguished by these organs,—though trifling details in their structure sometimes come in useful as specific characters. Balanus, with the sub-genus Acasta; Pyrgoma, with the sub-genus Creusia; Tetraclita, and Elminius, are genera of about equal value; though perhaps the two latter are rather more nearly related together than to the others. Chelonobia is more distinct; it shows some little affinity to the Chthamalinæ, and likewise to the four following genera. Coronula, Platylepas, Tubicinella, and Xenobalanus, are genera quite distinct from the foregoing, and from each other; yet, as we have just seen, palpably allied together. Amongst the Chthamalinæ, Pachylasma, Octomeris, and Catophragmus, are more closely related to each other than to the other two genera of the sub-family; yet Pachylasma, as far as the shell is concerned, leads into the Balaninæ, and Catophragmus into the Lepadidæ; Octomeris leads towards Chthamalus, and Chthamalus towards Chamæsipho.

Variation.—The discrimination of the species in most of the genera, offers very great difficulties. I cannot too strongly impress on any one intending to study this class, not to trust to external characters: he must separate and clean, and carefully examine the internal structure and form of the compartments, and more especially of the opercular valves. After considerable experience, when numerous varieties of a species have been carefully examined, the eye acquires a sort of instinctive knowledge, by which it can recognise the species, though the character cannot be defined by language; but I have found that no amount of experience with some of the commonest species, will save frequent and grave errors, as long as external characters alone are trusted to. Not only does every external character vary greatly in most of the species, but the internal parts very often vary to a surprising degree; and to add to the difficulty, groups of specimens not rarely vary in the same manner. After having given up several years to the study of this class, I must express my deliberate conviction that it is hopeless to find in any species, which has a wide range, and of which numerous specimens from different districts are presented for examination, any one part or organ,—which from differing in the different species is fitted for offering specific characters,—absolutely invariable in form or structure. I may in one respect even go further, and affirm, that, if in a species, any part or organ differs remarkably from the same part in its congeners, then if many specimens are examined, especially when collected from different districts, such part or organ will be found eminently variable. I may instance the antenniformed third pair of cirri in Chthamalus antennatus, the teeth on the posterior cirri in Acasta sulcata, the terga in Pyrgoma dentatum, the adductor ridge of the scuta in Pyrgoma cancellatum and in Creusia, and other such cases: hence it will not do to found a species on a slight, or sometimes even on a considerable difference, in any single point or organ. On the other hand, I am far from asserting, that if only half-a-dozen specimens of some rare species of Cirripede be brought from some one quarter of the world, characters beautifully defined may not be readily discovered. In determining what forms to call varieties, I have followed one common rule; namely, the discovery of such closely-allied, intermediate forms, that the application of a specific name to any one step in the series, was obviously impossible; or, when such intermediate forms have not actually been found, the knowledge that the differences of structure in question were such as, in several allied forms, certainly arose from variation,—for instance, in the case of two shells otherwise identical, one being longitudinally ribbed and the other smooth, a character which we know to vary,—but I have always used this argument from analogy with great caution. Finally, as in the large genus Balanus, there is an especial amount of variation, I have there entered in detail on this subject; and I hope that those interested in it, will refer to that discussion, which is almost verbally applicable to some other genera of the family, as Tetraclita and Chthamalus.

Rate of Growth, Exuviation, Powers of Repairing Injuries.

In my former volume I have shown that the pedunculated cirripedes grow rapidly; this is likewise the case with the Balanidæ. Mr. Stutchbury informs me that he has seen numerous specimens of Balanus tintinnabulum from 2 to 3 inches in height and from 5 to 6 inches in circumference (and this is nearly the full size which the species attains), on a vessel which had been to sea only during one year. At Coquimbo, in Chile, I have seen a specimen of B. psittacus 1.3 of an inch in basal diameter, and .8 in height, adhering to a chain that had been only six months under water. Poli, also, gives the case of some Balani (probably B. perforatus), which, in about four months, had attained a basal diameter of 1 inch, and a height of 1-1/6th of an inch. Balanus balanoides is a smaller species, and of slower growth; for the late Mr. W. Thompson, of Belfast, found that in three months from July 3d, certain marked specimens had increased from 2-1/2-3 lines to 4-1/2 lines, which is the usual maximum size attained in that locality. From other observations, Mr. Thompson believes that the extreme duration of life of this species is about two years: whether the other and apparently quicker-growing species, are shorter-lived, I have no means of judging.

In accordance with this rapid growth is the frequency of the periods of exuviation. Mr. Thompson kept twenty specimens of B. balanoides alive, and on the twelfth day he found the twenty-first cast-off integument, showing that all had moulted once, and one individual twice, within this period.[74] This frequency of exuviation, together with the durability of the cast-off integuments, explains the astonishing masses of exuviæ, which Mr. Peach assures me he annually has observed off the coast of Cornwall; they are most abundant in April and May, but he has seen quantities also in September; he could easily, as he tells me, have filled several quart-measures with them. The specimens sent to me consisted chiefly of Balanus balanoides, perforatus, and Chthamalus stellatus. The opercular membrane, with a narrow strip from between the two scuta, and another narrow strip from between the two terga, are moulted together, in connection with the more delicate membrane lining the sack, and investing the plicated branchiæ. This membrane, likewise, is continuously connected with that covering the whole body and its appendages. As I have stated under the Lepadidæ, the inner tunic of the œsophagus, of the rectum, of the olfactory pouches, and that which enters a little way into the acoustic meatus, and the apodemes of the maxillæ, are all moulted. On the cirri and jaws, new spines are formed with their upper ends enclosed within the old spines, but with their lower ends projecting inwards, beyond the bases of the old spines, and inverted like the fingers of a glove hastily pulled off. The membranes of the body, in the act of exuviation, split, I believe, only over the prosoma. How the neat separation of the opercular membrane, from all round the sheath and opercular valves, is effected, I do not fully understand; but it is, probably, analogous to the splitting of the thick carapace of the common crab. I suspect in Coronula, in which genus and its allies the opercular membrane is not periodically moulted, that the membrane lining the sack is not always thrown off at the same exact time with that of the body. In Chthamalus stellatus, in the act of moulting, the opercular membrane is the last part that separates from the new underlying membranes: I find that this species can moult when kept in a damp box out of water. The new membranes of the body, immediately after the exuviation, are not lax in any extreme degree. The exuviæ of the genus Chthamalus, and of some other genera amongst the Chthamalinæ, can at once be recognised by the divergence of the posterior four pairs of cirri: in the case of Chthamalus stellatus I have also noticed that the animal generally dies with these cirri in the same divergent position. Finally, I cannot doubt[75] that the Triton described by Linnæus was only the exuviæ of some Balanus (probably B. porcatus); Linnæus mistaking the probosciformed penis for the mouth of his imagined distinct animal.

I have seen a few specimens showing that when the shell has been broken it can be repaired; and this I believe is effected by the growth of a crest of corium between the broken edges, and the subsequent calcification of this crest. Mr. Stutchbury possesses a monstrous specimen of Chelonobia testudinaria, in which one of the lateral compartments on one side has not been developed. The cirri not rarely get cut off, but are, as it appears, soon repaired. I have observed a singular number of examples of the act of reparation in a group of the Australian Balanus vestitus. The manner in which the cirri are repaired seems to me curious: the cut-off end is closed by a rounded scale of yellowish chitine, and then the corium, in the four or five subjacent segments, separates from the external articulated membrane, which now serves only as a case or capsule. The tube of corium thus enclosed, with its contained muscles, shrinks a little, and soon can be perceived to be in process of dividing into new and smaller segments, in one instance ten in number,—which at the next exuviation would, no doubt, be invested with an external membrane, and be freely exposed. In another instance, the pedicel of a posterior cirrus had been cut off and subsequently closed; in this instance, a whole, immature, miniature cirrus, with the two rami, each having fifteen minute segments, was thus enclosed in what had been the single lower segment of the pedicel. I have seen several specimens of Balanus balanoides, as described under that species, with several of the cirri and the penis truncated; but I believe this was owing to monstrosity, which seemed particularly to affect the male organs of generation; for no reparation seemed to be in progress. In a specimen of Coronula, however, the penis appeared to have been really cut off by accident; it had been closed, by a scab, with concentric lines, like the articular rings on the penis itself; and within the case thus formed, the corium had healed, and had become pointed, but inverted; I presume that the point would, after another exuviation, have been everted, and its length thus increased.

Geographical Range and Habits.

With respect to range, the results arrived at have no particular interest, for the species are not sufficiently numerous; and, what is still more adverse, the genera, with unimportant exceptions, range over the world; so that there is no scale of differences, and it cannot be said that these two regions differ in their genera, and these two only in their species. In all the following remarks, I have trusted exclusively to my own specific identification; and have rejected all assigned localities which appeared from any cause to be doubtful. Sessile cirripedes are found in every sea, from lat. 74° 18′ north to Cape Horn. The area included between the north point of the Philippine Archipelago and the south point of Australia, extending on the right hand to New Zealand, and on the left to Sumatra,—an area, which, though including two distinct Cirripedial regions, is small compared with the surface of the globe, yet includes a greater number of species, especially of peculiar species, than the whole rest of the known world. This is, probably, in chief part due to the broken nature of the land, affording diversified habitats, and to much of the coast being rocky. Cirripedes, from requiring to be attached, cannot live where the shores and adjoining bottom are sandy or muddy or formed of moving shingle; hence, no doubt, it arises, that there is such a remarkable contrast in the great number of the species inhabiting the bold rocky western coast of South America, and the few species living on the sloping, and often sandy or muddy or shingly, eastern shores of this continent. Hence, also, I believe, it is that not many species have been brought from India. Coral-reefs are not favorable to Cirripedes, consequently but few are known to inhabit the islands of the Pacific Ocean. Where Cirripedes can live, though the species in no district are numerous, the individuals abound in infinite numbers: I have walked over the coast-rocks of the Falkland and Chonos Islands, of Chile and Van Diemen’s Land, fairly encrusted over wide spaces with a continuous layer of Cirripedes, consisting of only two or three species; in the same manner as may be observed on many parts of the shores of Great Britain, and, I believe, of North America.

With respect to the effects of temperature on the range of Cirripedes, no genus (having more than one species) is confined to the torrid zones. Pyrgoma, from being always attached to corals, is, of course, ordinarily found in the hotter seas; but one species ranges from the Cape de Verde Islands in the torrid zone to the southern shores of England and Ireland. Tetraclita is not found in the colder seas, but is numerous in species and in individuals, on the southern shores of Australia and at the Cape of Good Hope. I may here add, that the two genera with the most confined ranges, are Chamæsipho and Elminius; the former has only two species, one inhabiting Australia, and the other the East Indian Archipelago; Elminius has four species, confined to the southern hemisphere, and inhabiting Australia, New Zealand, and South America. To return to the effects of temperature; in Mr. Dana’s great work on Crustacea, an excellent chart is given, in which the isocrymal lines, or those exhibiting the mean temperature of the waters along their course, for the coldest thirty consecutive days in any season of the year, are given; and which lines Mr. Dana has shown are the most influential in governing the distribution of marine animals. At the isocryme of 68°, Mr. Dana divides the torrid and sub-torrid zones from the several temperate zones; and at 44°, the temperate from the sub-frigid and frigid zones; but as no Cirripedes are exclusively confined to these frigid zones, we may here disregard them. From Mr. Dana’s[76] table of the areas of the torrid and temperate ocean-zones, on both sides of the equator, it seems that they are nearly as 337 to 278, in relative area; and consequently, he remarks, that the marine species in any class, if distributed equally over the two, would be one fifth more numerous in the torrid than in the temperate zones. Now of Cirripedes, taking all the orders, there are at present known 147 species; of these, 7 have doubtful habitats, leaving 140 for comparison. Of these 140, nearly one quarter, or 37, inhabit both the torrid and temperate zones, as above defined; 46 are found exclusively in the torrid, and 57 exclusively in the temperate zones; so that the temperate zones, though less in area, and having, proportionally, even a considerably lesser length of coastline, nevertheless have a preponderance in the number of species. But it should be borne in mind, that there are two great temperate districts, separated from each other by one great torrid district; and, inasmuch as the number of species in any region seems to depend in some degree on the isolation of the sub-regions, we might have expected (the other conditions now being, and the past conditions having been alike), that the two great temperate areas would have contained more species, perhaps doubly more, than the single great torrid area.

The proportional numbers, above given, are not very widely different, whether we take separately the Balanidæ, the Lepadidæ, or all together. Mr. Dana has shown[77] at length, that generally amongst the Crustacea, the species which he considers of highest rank, belong to the extra-torrid zones: there seems to me in all such cases to be some degree of vagueness in the attempt to determine which are highest or lowest, but I have already elsewhere stated that Balanus is, probably, the most eminently Cirripedial form, and exhibits in the strongest manner all the characters by which Cirripedes differ from other Crustacea; as this genus is the largest, containing 36 species, of which the habitats are known, I may state that of these, exactly one third, or 12, inhabit both zones; 9 exclusively inhabiting the torrid, and 15 exclusively the temperate zones. According to the proportions of the whole class, the numbers should have been 9 torrid, to only 11.11 temperate; so that evidently the genus Balanus (in one sense typical) inclines towards the temperate regions more strongly than does either the family or the sub-class to which it belongs.

With respect to the relation between the size acquired by the different species of sessile cirripedes, and the temperature of the localities inhabited by them, the genera Chthamalus, Tetraclita, and Balanus, alone can serve for comparison: in Chthamalus much the largest species is found in the temperate zone: on the other hand, the two largest species of Tetraclita are from the torrid zone, though one of them also sometimes ranges into the temperate seas: in Balanus, the largest species, and six other species having a basal diameter sometimes over two inches, inhabit the temperate regions; and two out of these seven species, flourish even in the Arctic seas; whereas, within the torrid zone, there are only three species with a diameter sometimes exceeding two inches, but two of these frequently become very large and massive; so that Balanus, judging from the size of the species, as well as from their range, does not require for its highest development the temperature of the torrid zones.

The greater number of the species of the Balanidæ have wide ranges, as might be inferred from the fact of between one third and one fourth of the total number inhabiting both the torrid and temperate zones; but it should not be overlooked, that those species, as Balanus tintinnabulum, amphitrite, improvisus, and, in a lesser degree, B. trigonus and Tetraclita radiata, which seem to range over nearly the whole world (excepting the colder seas), are species which are habitually attached to ships, and which could hardly fail to be widely transported. Indeed, it appears to me surprising, that such species as Balanus psittacus and eburneus, which often become attached to vessels, should still be confined, the one to Southern, and the other to Northern America. But some other Cirripedes, which I have never seen attached to vessels, have likewise immense ranges: thus Tetraclita porosa is found in every tropical and warmer sea, and Chthamalus stellatus ranges round the world in the northern hemisphere, and, along the eastern side of America, far south of the equator: Balanus spongicola, and Acasta spongites, extend from the shores of Britain to the Cape of Good Hope: Balanus lævis ranges from Tierra del Fuego to California. I may further remark, that the only two other species of Balanus, and the one Chthamalus, inhabiting Tierra del Fuego, are, also, found on the shores of Peru. But to show the powers of endurance in some species, I may specify the case of Balanus improvisus, which flourishes on the coast of Nova Scotia, amongst the West Indian Islands, in Southern Patagonia, and near Guayaquil. Even more striking is the case of B. crenatus, of which I have seen specimens from latitude 74° 48′ north, from the West Indies, and the Cape of Good Hope! In these two latter localities, however, it seems to be rare, and may have been first transported to them from the shores of Europe, on the bottoms of vessels, to which it sometimes adheres.

The several species of Balanidæ live attached either to coast-rocks, or to objects at various depths, down to, as in the case of Balanus crenatus, 50 fathoms. Balanus balanoides sometimes adheres to rocks or wood so high up, that it is not covered by water during the neap tides. Mr. Thompson has informed me, that he once accidentally kept some specimens of this species out of water for seven days in a warm room, and that they were then quite lively. This species, is very easily killed by brackish water, as are some other species, whilst B. improvisus and eburneus can flourish in it; and at the Falkland Islands, I saw Elminius Kingii attached to rocks at the mouth of a fresh-water brook, so as to be covered by pure water during the ebb of each tide. Sessile cirripedes adhere to all sorts of objects, floating and fixed, animal and vegetable, living and dead, organic and inorganic. Chthamalus is, perhaps, more commonly attached to rocks than are the other genera. Living Mollusca are, I think, the most frequent objects of attachment: Mr. Cuming has remarked to me, that shells covered by an epidermis, as Patella, Haliotis, and Mytilus, are the greatest favorites. Acasta is always imbedded in sponges, or in the sponge-like bark of Isis; Pyrgoma and Creusia in corals; Chelonobia is attached to turtles, and one species to crabs or very smooth shells; Coronula, Tubicinella, and Xenobalanus, are imbedded in the skin of Cetaceans; and Platylepas in that of manatee, turtles, or sea-snakes.

If we attempt, with our present not very imperfect materials, to divide the globe into provinces, according to the amount of difference in their Cirripedial inhabitants, including all orders and families, and disregarding entirely, as I think we ought, all probabilities or conclusions deduced from the distribution of other tribes of animals, we find that the globe may be divided into the four following great provinces and one sub-province. I should premise, that in the following remarks and tables,[78] the species of Lepas, Conchoderma, Chelonobia, Coronula, Platylepas, and Tubicinella, are excluded, owing to their being attached to floating or swimming objects, and being consequently widely and irregularly distributed.

The first, or North Atlantic province, is that of Europe and the eastern shores of North America, from the arctic regions to lat. 30°: the island of Madeira, part of the north-west coast of Africa, and the whole Mediterranean being included. In this province (the above-named genera being excluded) we have 31 species, of which 22 are not found in any other distant quarter of the globe. As some few of these species range into the West Indies, I have not, on this account, excluded them from the 22 peculiar forms. Had I included the West Indies[79] in my first province, the total number of species would have been 42, of which 28 would have been peculiar. The coast of Brazil, even as far south as the Rio Plata, might, also, have been included, for I have not seen from it a single species not included in the above 42 West Indian species. So also, by adding a single species, might the west coast of equatorial Africa. The two coasts of South America and Africa, which face each other within the torrid zone, seem to be remarkably barren in Cirripedes. Europe has several more species than the United States, which is inhabited by only ten species, including even the probably imported Balanus tintinnabulum and amphitrite. Of these ten United States species only two are not found in Europe; and both these two range into the West Indies, and as far as the northern shores of South America, and therefore cannot be considered as peculiar to the United States.

I have formed my single sub-province for the southern extremity of Africa; for although I know of only 11 species from this comparatively short and uniform line of coast, yet I was not able to group these eleven in any of the main provinces: 5 of the species are peculiar, 1 Australian, 3 European and West Indian, and 2 almost universally distributed.

The second province includes the west coast of North and South America, from Tierra del Fuego to Behring’s Straits: on this enormously long line of coast, only 22 species are known to exist, but of these no less than 15 are peculiar. Of these 15, four are not found south of the torrid equatorial region, and eight are not known to occur north of this same region; so that this long line of coast might have been divided into two sub-provinces, of which the southern would have been the most peculiar; but as eight species are found both north and south of the equatorial region, I have not made this sub-division. Two of the species occurring on the western coast of North America, seem to represent species found on its eastern coast, and in Europe; thus, Balanus glandula takes the places of B. crenatus, and B. cariosus that of B. balanoides. Not a single species, excepting a few which are also widely distributed over other parts of the world, is known to be common to the east and west coasts of the two Americas.

The third province is that of the East Indian Archipelago, and includes the Philippines, Borneo, New Guinea, Sumatra, Java, Malacca, and the eastern coast of India. Here we find 37 species, of which 24 are peculiar. I may remark, that I have received no species from Madagascar or the eastern coast of Africa; few from India, or from the coast of China; and I suspect, that on most of these coasts, only few exist. Probably our third province will hereafter be found to include the whole Indian Ocean.

The fourth province is that of Australia, including New Zealand: it has 30 species, of which 21 are peculiar. Had the temperate Australian coasts (i. e., those south of the isocryme of 68°) been alone considered, the number of the species would have been probably 25, of which 20 would have been peculiar,—that is, if we admit within the 20, several species which range from the temperate into the torrid zone, but do not extend beyond the Australian shores. Owing to the widely-extended ranges of most Cirripedes, no Arctic or Antarctic provinces can be said to exist.

To recapitulate the above results, bearing in mind that, although the total number of known existing Cirripedes is 147, yet that the habitats of seven are unknown, and that eighteen are excluded owing to their being attached to floating or swimming objects, so that there are only 122 species referred to in the following table:

	Total number of species.	Species confined to the province.
(1.) First, or North Atlantic Province, to lat. 30° N. (If the West Indies had been included the numbers would have been 42 and 28)	31	22
(2.) Sub-province of South Africa	11	5
(3.) Second province, or West Coast of North and South America	22	15
(4.) Third province, or East Indian Archipelago	37	24
(5.) Fourth, or Australian province	30	21

The least prolific of these provinces contains 22 species, or between 1/5th and 1/6th of the total number of species, and the most prolific between 1/3rd and 1/4th of this same number. In each of these provinces, it is remarkable that the peculiar species are very nearly two thirds of the whole of its inhabitants. These facts, I think, show that the above provinces are natural divisions of the world, as far as their Cirripedial inhabitants are concerned.

As Cirripedes belong to the great class of Crustacea, and as the distribution of the latter has lately been fully discussed by Mr. Dana, it may be worth while briefly to compare my results with his; more especially as they are so very different. I should premise, as perhaps accounting to a certain extent for this difference, that, owing to the wide range of many species, and the almost universal extension of the same genera, my provinces are founded merely on a certain proportion of the species, namely, two thirds, being peculiar or confined to a region of considerable dimensions: whereas, in the case of ordinary Crustaceans, the greater number of the species are distinct even in the sub-provinces, and the provinces are founded mainly on generic differences. Mr. Dana divides the surface of the globe into three great sections, or provinces, the Africo-Europæan, the extent of which is shown by its title; the Occidental, which includes both the east and west coast of both Americas; and the Oriental, including the Indian and Pacific Oceans, with the East Indian Archipelago, and Australia. Thus Mr. Dana entirely separates the Eastern shores of North America from Europe; whereas, as far as their Cirripedial inhabitants are concerned, they are most intimately allied, and form my first or North Atlantic province; and to this, as I have shown, even the West Indies, the coast of Brazil, and equatorial West Africa might have been added. It follows, from this similarity in the Cirripedes on the two sides of the Atlantic, and from their dissimilarity with those on the shores of the Pacific, that the east and west coasts of the two Americas form two quite distinct Cirripedial provinces; though, in the northern half, some connection is shown by a few representative species: on the other hand, Mr. Dana unites both sides of the whole American continent, into his single Occidental province. The South-African province is not brought out by Mr. Dana so prominently, as I have found necessary. Mr. Dana joins the East Indian Archipelago and Australia into his single Oriental province, and makes New Zealand, as a sub-province, apparently as distinct from Australia, as Australia is from the East Indian Archipelago: whereas I find that the Cirripedes of New Zealand clearly belong to Australia; and that the Australian Cirripedes, especially if the temperate shores be alone considered, are as distinct from those of the East Indian Archipelago, as from those of any other quarter of the whole world. I believe that the provinces deduced from the distribution of Cirripedes, accord better with the Molluscan provinces, than with those given by Mr. Dana for the rest of the great class of Crustaceans.

In the following tables, an asterisk means that the species is not found in any other distinct region of the globe. When found in one of the five provinces, a corresponding number, within brackets, is appended, to show in which province or sub-province it has been found.

(1.) FIRST OR NORTH ATLANTIC PROVINCE: Europe and the Eastern United States, from the Arctic Regions to 30° north latitude.

Here we have 31 species, of which 22 are not found in any other great region of the world.

(2.) SUB-PROVINCE: Africa, South of lat. 30°.

In this small region we have only 11 species, of which five are peculiar: Balanus Capensis and Tetraclita serrata, seem to be representatives of B. psittacus of S. America and of T. porosa of that and several other regions.

(3.) SECOND PROVINCE: West Coast of South and North America, from Tierra del Fuego to Behring’s Straits.

Here we have on this long line of coast, 22 species, of which 15 are peculiar.

(4.) THIRD PROVINCE: Indian Archipelago (including the Philippines, Malacca, Borneo, Sumatra, Java, and New Guinea, and eastern coast of India).

Here we have 37 species, of which 24 are peculiar to this province.

(5.) FOURTH PROVINCE: Australia (including New Zealand).

Here we have 30 species, of which 21 are peculiar.