# Island Life/XVI

CHAPTER XVI
CONTINENTAL ISLANDS OF RECENT ORIGIN: GREAT BRITAIN
    Characteristic Features of Recent Continental Islands—Recent Physical Changes of the British Isles—Proofs of Former Elevation—Submerged Forests—Buried River Channels—Time of Last Union with the Continent—Why Britain is poor in Species—Peculiar British Birds—Freshwater Fishes—Cause of Great Speciality in Fishes—Peculiar British Insects—Lepidoptera Confined to the British Isles—Peculiarities of the Isle of Man—Lepidoptera—Coleoptera confined to the British Isles—Trichoptera Peculiar to the British Isles—Land and Freshwater Shells—Peculiarities of the British Flora—Peculiarities of the Irish Flora—Peculiar British Mosses and Hepaticæ—Concluding Remarks on the Peculiarities of the British Fauna and Flora.
We now proceed to examine those islands which are the very reverse of the "oceanic" class, being fragments of continents or of larger islands from which they have been separated, by subsidence of the intervening land at a period which, geologically, must be considered recent. Such islands are always still connected with their parent land by a shallow sea, usually indeed not exceeding a hundred fathoms deep; they always possess mammalia and reptiles either wholly or in large proportion identical with those of the mainland; while their entire flora and fauna is characterised either by the total absence or comparative scarcity of those endemic or peculiar species and genera which are so striking a feature of almost all oceanic islands. Such islands will, of course, differ from each ​ other in size, in antiquity, and in the richness of their respective faunas, as well as in their distance from the parent land and the facilities for intercommunication with it; and these diversities of conditions will manifest themselves in the greater or less amount of speciality of their animal productions.
This speciality, when it exists, may have been brought about in two ways. A species or even a genus may on a continent have had a very limited area of distribution, and this area may be wholly or almost wholly contained in the separated portion or island, to which it will henceforth be peculiar. Even when the area occupied by a species is pretty equally divided at the time of separation between the island and the continent, it may happen that it will become extinct on the latter, while it may survive on the former, because the limited number of individuals after division may be unable to maintain themselves against the severer competition or more contrasted climate of the continent, while they may flourish, under the more favourable insular conditions. On the other hand, when a species continues to exist in both areas, it may on the island be subjected to some modifications by the altered conditions, and may thus come to present characters which differentiate it from its continental allies and constitute it a new species. We shall in the course of our survey meet with cases illustrative of both these processes.
The best examples of recent continental islands are Great Britain and Ireland, Japan, Formosa, and the larger Malay Islands, especially Borneo, Java, and Celebes; and as each of these presents special features of interest, we will give a short outline of their zoology and past history in relation to that of the continents from which they have recently been separated, commencing with our own islands, to which the present chapter will be devoted.
Recent Physical Changes in the British Isles.—Great Britain is perhaps the most typical example of a large and recent continental island now to be found upon the globe. It is joined to the Continent by a shallow bank which extends from Denmark to the Bay of Biscay, the 100 fathom line from these extreme points receding from the ​ coasts so as to include the whole of the British Isles and about fifty miles beyond them to the westward. (See Map.)
* The light tint indicates a depth of less than 100 fathoms.
* The figures show the depth in fathoms.
* The narrow channel between Norway and Denmark is 2,580 feet deep.
Beyond this line the sea deepens rapidly to the 500 and 1,000 fathom lines, the distance between 100 and 1,000 ​ fathoms being from twenty to fifty miles, except where there is a great outward curve to include the Porcupine Bank 170 miles west of Galway, and to the north-west of Caithness where a narrow ridge less than 500 fathoms below the surface joins the extensive bank under 300 fathoms, on which are situated the Faroe Islands and Iceland, and which stretches across to Greenland. In the North Channel between Ireland and Scotland, and in the Minch between the outer Hebrides and Skye, are a series of hollows in the sea-bottom from 100 to 150 fathoms deep. These correspond exactly to the points between the opposing highlands where the greatest accumulations of ice would necessarily occur during the glacial epoch, and they may well be termed submarine lakes, of exactly the same nature as those which occur in similar positions on land.
Proofs of Former Elevation—Submerged Forests.—What renders Britain particularly instructive as an example of a recent continental island is the amount of direct evidence that exists, of several distinct kinds, showing that the land has been sufficiently elevated (or the sea depressed) to unite it with the Continent,—and this at a very recent period. The first class of evidence is the existence, all round our coasts, of the remains of submarine forests often extending far below the present low-water mark. Such are the submerged forests near Torquay in Devonshire, and near Falmouth in Cornwall, both containing stumps of trees in their natural position rooted in the soil, with deposits of peat, branches, and nuts, and often with remains of insects and other land animals. These occur in very different conditions and situations, and some have been explained by changes in the height of the tide, or by pebble banks shutting out the tidal waters from estuaries; but there are numerous examples to which such hypotheses cannot apply, and which can only be explained by an actual subsidence of the land (or rise of the sea-level) since the trees grew.
We cannot give a better idea of these forests than by quoting the following account by Mr. Pengelly of a visit to one which had been exposed by a violent storm on the coast of Devonshire, at Blackpool near Dartmouth:— ​
"We were so fortunate as to reach the beach at spring-tide low-water, and to find, admirably exposed, by far the finest example of a submerged forest which I have ever seen. It occupied a rectangular area, extending from the small river or stream at the western end of the inlet, about one furlong eastward; and from the low-water line thirty yards up the strand. The lower or seaward portion of the forest area, occupying about two-thirds of its entire breadth, consisted of a brownish drab-coloured clay, which was crowded with vegetable débris, such as small twigs, leaves, and nuts. There were also numerous prostrate trunks and branches of trees, lying partly imbedded in the clay, without anything like a prevalent direction. The trunks varied from six inches to upwards of two feet in diameter. Much of the wood was found to have a reddish or bright pink hue, when fresh surfaces were exposed. Some of it, as well as many of the twigs, had almost become a sort of ligneous pulp, while other examples were firm, and gave a sharp crackling sound on being broken. Several large stumps projected above the clay in a vertical direction, and sent roots and rootlets into the soil in all directions and to considerable distances. It was obvious that the movement by which the submergence was effected had been so uniform as not to destroy the approximate horizontality of the old forest ground. One fine example was noted of a large prostrate trunk having its roots still attached, some of them sticking up above the clay, while others were buried in it. Hazelnuts were extremely abundant—some entire, others broken, and some obviously gnawed.... It has been stated that the forest area reached the spring-tide low-water line; hence as the greatest tidal range on this coast amounts to eighteen feet, we are warranted in inferring that the subsidence amounted to eighteen feet as a minimum, even if we suppose that some of the trees grew in a soil the surface of which was not above the level of high water. There is satisfactory evidence that in Torbay it was not less than forty feet, and that in Falmouth Harbour it amounted to at least sixty-seven feet."
On the coast of the Bristol Channel similar deposits occur, as well as along much of the coast of Wales and in Holyhead Harbour. It is believed by geologists that the whole Bristol Channel was, at a comparatively recent period, an extensive plain, through which flowed the River Severn; for in addition to the evidence of submerged forests there are on the coast of Glamorganshire numerous caves and fissures in the face of high sea cliffs, in one of which no less than a thousand antlers of the reindeer were found, the remains of animals which had been devoured there by bears and hyænas; facts which can only be explained by the existence of some extent of dry land stretching seaward from the present cliffs, but since submerged and washed away. This plain may have continued down to very recent times, since the whole of the Bristol Channel to beyond Lundy Island is under twenty-five fathoms deep. In the east of England we have a similar forest-bed at Cromer in Norfolk; and in the north of Holland an old land surface has been found fifty-six feet below high-water mark.
Buried River Channels.—Still more remarkable are the buried river channels which have been traced on many parts of our coasts. In order to facilitate the study of the glacial deposits of Scotland, Dr. James Croll obtained the details of about 250 bores put down in all parts of the mining districts of Scotland for the purpose of discovering minerals. These revealed the interesting fact that there are ancient valleys and river channels at depths of from 100 to 260 feet below the present sea-level. These old rivers sometimes run in quite different directions from the present lines of drainage, connecting what are now distinct valleys; and they are so completely filled up and hidden by boulder clay, drift, and sands, that there is no indication of their presence on the surface, which often consists of mounds or low hills more than 100 feet high. One of these old valleys connects the Clyde near Dumbarton with the Forth at Grangemouth, and appears to have contained two streams flowing in opposite directions from a watershed about midway at Kilsith. At ​ Grangemouth the old channel is 260 feet below the sea-level. The watershed at Kilsith is now 160 feet above the sea, the old valley bottom being 120 feet deep or forty feet above the sea. In some places the old valley was a ravine with precipitous rocky walls, which have been found in mining excavations. Sir A. Geikie, who has himself discovered many similar buried valleys, is of opinion that "they unquestionably belong to the period of the boulder clay."
We have here a clear proof that, when these rivers were formed, the land must have stood in relation to the sea at least 260 feet higher than it does now, and probably much more; and this is sufficient to join England to the continent. Supporting this evidence, we have freshwater or littoral shells found at great depths off our coasts. Mr. Godwin Austen records the dredging up of a freshwater shell (Unio pictorum) off the mouth of the English Channel between the fifty fathom and 100 fathom lines, while in the same locality gravel banks with littoral shells now lie under sixty or seventy fathoms water. More recently Mr. Gwyn Jeffreys has recorded the discovery of eight species of fossil arctic shells off the Shetland Isles in about ninety fathoms water, all being characteristic shallow water species, so that their association at this great depth is a distinct indication of considerable subsidence.
Time of Last Union with the Continent.—The period when this last union with the continent took place was comparatively recent, as shown by the identity of the shells with living species, and the fact that the buried river channels are all covered with clays and gravels of the glacial period, of such a character as to indicate that most of them were deposited above the sea-level. From these and various other indications geologists are all agreed that the last continental period, as it is called, was subsequent to the greatest development of the ice, but probably before the cold epoch had wholly passed away. But if so recent, we should naturally expect our land still ​ to show an almost perfect community with the adjacent parts of the continent in its natural productions; and such is found to be the case. All the higher and more perfectly organised animals are, with but few exceptions, identical with those of France and Germany; while the few species still considered to be peculiar may be accounted for either by an original local distribution, by preservation here owing to favourable insular conditions, or by slight modifications having been caused by these conditions resulting in a local race, sub-species, or species.
Why Britain is Poor in Species.—The former union of our islands with the continent, is not, however, the only recent change they have undergone. There have been partial submergences to the depth of from one hundred to perhaps three hundred feet over a large part of our country; while during the period of maximum glaciation the whole area north of the Thames was buried in snow and ice. Even the south of England must have suffered the rigour of an almost arctic climate, since Mr. Clement Reid has shown that floating ice brought granite blocks from the Channel Islands to the coast of Sussex. Such conditions must have almost exterminated our preexisting fauna and flora, and it was only during the subsequent union of Britain with the continent that the bulk of existing animals and plants could have entered our islands. We know that just before and during the glacial period we possessed a fauna almost or quite identical with that of adjacent parts of the continent and equally rich in species. The glaciation and submergence destroyed much of this fauna; and the permanent change of climate on the passing away of the glacial conditions appears to have led to the extinction or migration of many species in the adjacent continental areas, where they were succeeded by the assemblage of animals now occupying Central Europe. When England became continental, these entered our country; but sufficient time does not seem to have elapsed for the migration to have been completed before subsidence again occurred, cutting off the further influx of purely terrestrial animals, and leaving us without the number of species which our favourable climate and varied surface entitle us to. ​
To this cause we must impute our comparative poverty in mammalia and reptiles—more marked in the latter than the former, owing to their lower vital activity and smaller powers of dispersal. Germany, for example, possesses nearly ninety species of land mammalia, and even Scandinavia about sixty, while Britain has only forty, and Ireland only twenty-two. The depth of the Irish Sea being somewhat greater than that of the German Ocean, the connecting land would there probably be of small extent and of less duration, thus offering an additional barrier to migration, whence has arisen the comparative zoological poverty of Ireland. This poverty attains its maximum in the reptiles, as shown by the following figures:—
| Belgium | has | 22 | species | of reptiles and | amphibia. |
| Britain | ,, | 13 | ,, | ,, | ,, |
| Ireland | ,, | 4 | ,, | ,, | ,, |
Where the power of flight existed, and thus the period of migration was prolonged, the difference is less marked; so that Ireland has seven bats to twelve in Britain, and about 110 as against 130 land-birds.
Plants, which have considerable facilities for passing over the sea, are somewhat intermediate in proportionate numbers, there being about 970 flowering plants and ferns in Ireland to 1,425 in Great Britain,—or almost exactly two-thirds, a proportion intermediate between that presented by the birds and the mammalia.
Peculiar British Birds.—Among our native mammalia, reptiles, and amphibia, it is the opinion of the best authorities that we possess neither a distinct species nor distinguishable variety. In birds, however, the case is different, since some of our species, in particular our coal-tit and long-tailed tit, present well-marked differences of colour as compared with continental specimens; and in Mr. Dresser's work on the Birds of Europe they are considered to be distinct species, while Professor Newton, in his new edition of Yarrell's British Birds, does not consider the difference to be sufficiently great or sufficiently constant to warrant this, and therefore classes ​ them as insular races of the continental species. We have, however, one undoubted case of a bird peculiar to the British Isles, in the red grouse (Lagopus scoticus), which abounds in Scotland, Ireland, the north of England, and Wales, and is very distinct from any continental species, although closely allied to the willow grouse of Scandinavia. This latter species resembles it considerably in its summer plumage, but becomes pure white in winter; whereas our species retains its dark plumage throughout the year, becoming even darker in winter than in summer. We have here therefore a most interesting example of an insular form in our own country; but it is difficult to determine how it originated. On the one hand, it may be an old continental species which during the glacial epoch found a refuge here when driven from its native haunts by the advancing ice; or, on the other hand, it may be a descendant of the Northern willow grouse, which has lost its power of turning white in winter owing to its long residence in the lowlands of an island where there is little permanent snow, and where assimilation in colour to the heather among which it lurks is at all times its best protection. In either case it is equally interesting, as the one large and handsome bird which is peculiar to our islands notwithstanding their recent separation from the continent.
The following is a list of the birds now held to be peculiar to the British Isles:—
| 1. Parus ater, sub. sp. britannicus | Closely allied to P. ater of the continent; a local race or sub-species. |
| 2. Acredula caudata, sub. sp. rosea | Allied to A. caudata of the continent. |
| 3. Lagopus scoticus | Allied to L. albus of Scandinavia, a distinct species. |
Freshwater Fishes.—Although the productions of fresh waters have generally, as Mr. Darwin has shown, a wide range, fishes appear to form an exception, many of them being extremely limited in distribution. Some are confined to particular river valleys or even to single rivers, others inhabit the lakes of a limited district only, while some are ​ confined to single lakes, often of small area, and these latter offer examples of the most restricted distribution of any organisms whatever. Cases of this kind are found in our own islands, and deserve our especial attention. It has long been known that some of our lakes possessed peculiar species of trout and charr, but how far these were unknown on the continent, and how many of those in different parts of our islands were really distinct, had not been ascertained till Dr. Günther, so well known for his extensive knowledge of the species of fishes, obtained numerous specimens from every part of the country, and by comparison with all known continental species determined their specific differences. The striking and unexpected result has thus been attained, that no less than fifteen well-marked species of freshwater fishes are altogether peculiar to the British Islands. The following is the list, with their English names and localities:—
Freshwater Fishes peculiar to the British Isles.
| Latin Name. | English Name. | Locality. |
| 1. Salmo brachypoma | Short-headed salmon | Firth of Forth, Tweed, Ouse. |
| 2.   ,,  gallivensis | Galway sea-trout | Galway, West Ireland. |
| 3.   ,,  orcadensis | Loch Stennis trout | Lakes of Orkney. |
| 4.   ,,  ferox | Great lake trout | Larger lakes of Scotland, Ireland, the N. of England, and Wales. |
| 5.   ,,  stomachicus | Gillaroo trout | Lakes of Ireland. |
| 6.   ,,  nigripinnis | Black-finned trout | Mountain lochs of Wales and Scotland. |
| 7.   ,,  levenensis | Loch Leven Trout | Loch Leven, Loch Lomond, Windermere. |
| 8.   ,,  perisii | Welsh charr | Llanberris lakes, N. Wales. |
| 9.   ,,  willughbii | Windermere charr | Lake Windermere and others in N. of England, and Lake Bruiach in Scotland. |
| 10.   ,,  killinensis | Lock Killin charr | Killin lake in Inverness-shire. |
| 11.   ,,  colii | Cole's charr | Lough Eske and Lough Dan, Ireland. |
| 12.   ,,  grayi | Gray's charr | Lough Melvin, Leitrim, N.W. Ireland. |
| ​ 13. Coregonus clupeoides | The gwyniad, or schelly | Loch Lomond, Ulleswater, Derwentwater, Haweswater, and Bala lake. |
| 14.     ,,    vandesius | The vendace | Loch Maben, Dumfriesshire. |
| 15.     ,,    pollan | The pollan | Lough Neagh and Lough Earne, N. of Ireland. |
These fifteen peculiar fishes differ from each other and from all British and continental species, not in colour only, but in such important structural characters as the number and size of the scales, form and size of the fins, and the form or proportions of the head, body, or tail. Some of them, like S. killinensis and the Coregoni are in fact, as Dr. Günther assures me, just as good and distinct species as any other recognised species of fish. It may indeed be objected that, until all the small lakes of Scandinavia are explored, and their fishes compared with ours, we cannot be sure that we have any peculiar species. But this objection has very little weight if we consider how our own species vary from lake to lake and from island to island, so that the Orkney species is not found in Scotland, and only one of the peculiar British species extends to Ireland, which has no less than five species altogether peculiar to it. If the species of our own two islands are thus distinct, what reason have we for believing that they will be otherwise than distinct from those of Scandinavia? At all events, with the amount of evidence we already possess of the very restricted ranges of many of our species, we must certainly hold them to be peculiar till they have been proved to be otherwise.
The great speciality of the Irish fishes is very interesting, because it is just what we should expect on the theory of evolution. In Ireland the two main causes of specific change—isolation and altered conditions—are each more powerful than in Britain. Whatever difficulty continental fishes may have in passing over to Britain, that difficulty will certainly be increased by the second sea passage to Ireland; and the latter country has been longer isolated, for the Irish Sea with its northern and southern channels is considerably deeper than the German Ocean and the ​ Eastern half of the English Channel, so that, when the last subsidence occurred, Ireland would have been an island for some length of time while England and Scotland still formed part of the continent. Again, whatever differences have been produced by the exceptional climate of our islands will have been greater in Ireland, where insular conditions are at a maximum, the abundance of moisture and the equability of temperature being far more pronounced than in any other part of Europe.
Among the remarkable instances of limited distribution afforded by these fishes, we have the Loch Stennis trout confined to the little group of lakes in the mainland of Orkney, occupying altogether an area of about ten miles by three; the Welsh charr confined to the Llanberris lakes, about three miles in length; Gray's charr confined to Lough Melvin, about seven miles long; while the Loch Killin charr, known only from a small mountain lake in Inverness-shire, and the vendace, from the equally small lakes at Loch Maben in Scotland, are two examples of restricted distribution which can hardly be surpassed.
Cause of Great Speciality in Fishes.—The reason why fishes alone should exhibit such remarkable local modifications in lakes and islands is sufficiently obvious. It is due to the extreme rarity of their transmission from one lake to another. Just as we found to be the case in Oceanic Islands, where the means of transmission were ample hardly any modification of species occurred, while where these means were deficient and individuals once transported remained isolated during a long succession of ages, their forms and characters became so much changed as to bring about what we term distinct species or even distinct genera,—so these lake fishes have become modified because the means by which they are enabled to migrate so rarely occur. It is quite in accordance with this view that some of the smaller lakes contain no fishes, because none have ever been conveyed to them. Others contain several; and some fishes which have peculiarities of constitution or habits which render their transmission somewhat less difficult occur in several lakes over a wide area of country, though only one appears to be common to the British and Irish lakes. ​
The manner in which fishes are enabled to migrate from lake to lake is unknown, but many suggestions have been made. It is a fact that whirlwinds and waterspouts sometimes carry living fish in considerable numbers and drop them on the land. Here is one mode which might certainly have acted now and then in the course of thousands of years, and the eggs of fishes may have been carried with even greater ease. Again we may well suppose that some of these fish have once inhabited the streams that enter or flow out of the lakes as well as the lakes themselves; and this opens a wide field for conjecture as to modes of migration, because we know that rivers have sometimes changed their courses to such an extent as to form a union with distinct river basins. This has been effected either by floods rising over low watersheds, by elevations of the land changing lines of drainage, or by ice blocking up valleys and compelling the streams to flow over watersheds to find an outlet. This is known to have occurred during the glacial epoch, and is especially manifest in the case of the Parallel Roads of Glenroy, and it probably affords the true solution of many of the cases in which existing species of fish inhabit distinct river basins whether in streams or lakes. If a fish thus wandered out of one river-basin into another, it might then retire up the streams to some of the lakes, where alone it might find conditions favourable to it. By a combination of the modes of migration here indicated it is not difficult to understand how so many species are now common to the lakes of Wales, Cumberland, and Scotland, while others less able to adapt themselves to different conditions have survived only in one or two lakes in a single district; or these last may have been originally identical with other forms, but have become modified by the particular conditions of the lake in which they have found themselves isolated.
Peculiar British Insects.—We now come to the class of insects, and here we have much more difficulty in determining what are the actual facts, because new species are still being yearly discovered and considerable portions of Europe are but imperfectly explored. It often happens that an insect is discovered in our islands, and for some ​ years Britain is its only recorded locality; but at length it is found on some part of the continent, and not unfrequently has been all the time known there, but disguised by another name, or by being classed as a variety of some other species. This has occurred so often that our best entomologists have come to take it for granted that all our supposed peculiar British species are really natives of the continent and will one day be found there; and owing to this feeling little trouble has been taken to bring together the names of such as from time to time remain known from this country only. The view of the probable identity of our entire insect-fauna with that of the continent has been held by such well-known authorities as the late Mr. E. C. Rye and Dr. D. Sharp for the beetles, and by Mr. H. T. Stainton for butterflies and moths; but as we have already seen that among two orders of vertebrates—birds and fishes—there are undoubtedly peculiar British species, it seems to me that all the probabilities are in favour of there being a much larger number of peculiar species of insects. In every other island where some of the vertebrates are peculiar—as in the Azores, the Canaries, the Andaman Islands, and Ceylon—the insects show an equal if not a higher proportion of speciality, and there seems no reason whatever why the same law should not apply to us. Our climate is undoubtedly very distinct from that of any part of the continent, and in Scotland, Ireland, and Wales we possess extensive tracts of wild mountainous country where a moist uniform climate, an alpine or northern vegetation, and a considerable amount of isolation, offer all the conditions requisite for the preservation of some species which may have become extinct elsewhere, and for the slight modification of others since our last separation from the continent. I think, therefore, that it will be very interesting to take stock, as it were, of our recorded peculiarities in the insect world, for it is only by so doing that we can hope to arrive at any correct solution of the question on which there is at present so much difference of opinion. For the list of Coleoptera with the accompanying notes I was originally indebted to the late Mr. E. C. Rye; and Dr. Sharp also gave me valuable information as to the recent ​ occurrence of some of the supposed peculiar species on the continent. The list has now been revised by the Rev. Canon Fowler, author of the best modern work on the British Coleoptera, who has kindly furnished some valuable notes.
For the Lepidoptera I first noted all the species and varieties marked as British only in Staudinger's Catalogue of European Lepidoptera. This list was carefully corrected by Mr. Stainton, who weeded out all the species known by him to have been since discovered, and furnished me with valuable information on the distribution and habits of the species. This information often has a direct bearing on the probability of the insect being peculiar to Britain, and in some cases may be said to explain why it should be so. For example, the larvæ of some of our peculiar species of Tineina feed during the winter, which they are enabled to do owing to our mild and insular climate, but which the severer continental winters render impossible. A curious example of the effect this habit may have on distribution is afforded by one of our commonest British species, Elachista rufocinerea, the larva of which mines in the leaves of Holcus mollis and other grasses from December to March. This species, though common everywhere with us, extending to Scotland and Ireland, is quite unknown in similar latitudes on the continent, but appears again in Italy, the South of France, and Dalmatia, where the mild winters enable it to live in its accustomed manner.
Such cases as this afford an excellent illustration of those changes of distribution, dependent probably on recent changes of climate, which may have led to the restriction of certain species to our islands. For should any change of climate lead to the extinction of the species in South Europe, where it is far less abundant than with us, we should have a common and wide-spread species entirely restricted to our islands. Other species feed in the larva state on our common gorse, a plant found only in limited portions of Western and Southern Europe; and the presence of this plant in a mild and insular climate such as ours may well be supposed to have led to the preservation of some of the numerous species which are or have been dependent on it. Since the first edition was ​ published many new British species have been discovered, while some of the supposed peculiar species have been found on the continent. Information as to these has been kindly furnished by Mr. W. Warren, Mr. C. G. Barrett, Lord Walsingham, and other students of British Lepidoptera, and the first-named gentleman has also looked over the proofs.
Mr. McLachlan has kindly furnished me with some valuable information on certain species of Trichoptera or Caddis flies which seem to be peculiar to our islands; and this completes the list of orders which have been studied with sufficient care to afford materials for such a comparison. We will now give the list of peculiar British Insects, beginning with the Lepidoptera and adding such notes as have been supplied by the gentlemen already referred to.
List of the Species or Varieties of Lepidoptera which, so far as at present known, are confined to the British Islands. (The figures show the dates when the species was first described. Species added since the first edition are marked with an asterisk.)
Diurni.
    1. Polyommatus dispar. "The large copper." This fine insect, once common in the fens, but now extinct owing to extensive drainage, is generally admitted to be peculiar to our island, at all events as a variety or local form. Its continental ally differs constantly in being smaller and in having smaller spots; but the difference, though constant, is so slight that it is now classed as a variety under the name of rutilus. Our insect may therefore be stated to be a well-marked local form of a continental species.
    2. Lycæna astrarche, var. artaxerxes. This very distinct form is confined to Scotland and the north of England. The species of which it is considered a variety (more generally known to English entomologists as P. agestis) is found in the southern half of England, and almost everywhere on the continent.
Bombyces.
    3. Lithosia complana, var. sericea. North of England (1861).
    4. Hepialus humuli, var. hethlandica. Shetland Islands (1865). A remarkable form, in which the male is usually yellow and buff instead of pure white, as in the common form, but exceedingly variable in tint and markings.
    5. Epichnopteryx reticella. Sheerness, Gravesend, and other localities along the Thames (1847); Hayling Island, Sussex.
    6. E. pulla, var. radiella. Near London, rare (1830?); the species in Central and Southern Europe. (Doubtfully peculiar in Mr. Stainton's opinion.) ​
Noctuæ.
    7. Acronycta euphorbiæ, var. myricæ. Scotland only (1852). A melanic form of a continental species.
    8. Agrotis subrosea. Cambridgeshire and Huntingdonshire fens, perhaps extinct (1835). The var. subcærulea is found in Finland and Livonia.
    9. Agrotis candelarum var. ashworthii. South and West (1855). Distinct and not uncommon.
    10. Luperina luteago, var. barretti. Ireland (1864).
    11. Aporophyla australis, var. pascuea. South of England (1830). A variety of a species otherwise confined to South Europe.
    12. Hydræcia nictitans, var. paludris.
Geometræ.
    13. Boarmia gemmaria, var. perfumaria. Near London and elsewhere. A large dark variety of a common species.
    14. *B. repandata, var. sodorensium. Outer Hebrides.
    15. *Emmelesia albulata, var. hebridium. Outer Hebrides.
    16. *E. albulata, var. thules. Shetland Islands.
    17. *Melanippe montanata, var. shetlandica. Shetland Islands.
    18. *M. sociata, var. obscurata. Outer Hebrides. A dark form.
    19. Cidaria albulata, var. griseata. East of England (1835). A variety of a species otherwise confined to Central and Southern Europe.
    20. Eupithecia constrictata.. Widely spread, but local (1835). Larva on thyme.
    21. *E. satyrata, var. curzoni. N. Scotland.
    22. *E. nanata var. curzoni. Shetland Islands.
Pyralidina.
    23. Aglossa pinguinalis, var. streatfieldi. Mendip Hills (1830). A remarkable variety of the common "tabby."
    24. *Scoparia cembræ, var. scotica. Scotland (1872).
    25. *Myelois ceratoniæ, var. pryerella. North London (1871).
    26. *Howœosoma nimbella, var. saxicola. England, Scotland, Isle of Man (1871).
    27. *Epischnia bankesiella. Isle of Portland (1888).
Tortricina.
    28. Aphelia nigrovittana. Scotland (1852). A local form of the generally distributed A. lanceolana.
    29. Grapholita parvulana. Isle of Wight (1858). Rare. A distinct species.
    30. Conchylis erigerana. South-east of England (1866).
    31. *Brachytænia woodiana. Herefordshire (1882).
    32. *Eupœcilia angustana, var. thuleana. Shetland Islands.
    33. *Tortrix donelana. Connemara, Ireland (1890).
Tineina.
    34. Tinea cochylidella. Sanderstead, near Croydon (1854). Unique!
    35. Acrolepia betulætella. Yorkshire and Durham (1840). Rare.
    36. Argyresthia semifusca. North and West of England (1829). Rather scarce. A distinct species.
    37. Gelechia divisella. A fen insect (1856). Rare. ​
    38. G. celerella. West of England (1854). A doubtful species.
    39. *G. tetragonella. Yorkshire. Norfolk. Salt marshes.
    40. *G. sparsiciliella. Pembroke.
    41. *G. plantaginella. A salt-marsh species.
    42. G. Ocellatella (Barrett nec Stainton). Bred from Beta maritima. Very distinct.
    43. Bryotropha politella. Moors of North of England. Norfolk (1854).
    44. *B. portlandicella. Isle of Portland (1890).
    45. Lita fraternella. Widely scattered (1834). Larva feeds on shoots of Stellaria uliginosa in spring.
    46. L. blandulella. Kent.
    47. Anacampsis sircomella. North and West England (1854). Perhaps a melanic variety of the more widely spread A. tæniolella.
    48. A. immaculatella. West Wickham (1834). Unique! A distinct species.
    49. *Œcophora woodiella?
    50. Glyphipteryx cladiella. Eastern Counties (1859). Abundant.
    51. G. schœnicolella. In several localities (1859).
    52. Gracilaria stramineella. (1850). On birch. Perhaps a local form of G. elongella, found on alder.
    53. Ornix loganella. Scotland (1848). Abundant, and a distinct species.
    54. O. devoniella. In Devonshire (1854). Unique!
    55. Coleophora saturatella. South of England (1850). Abundant on broom.
    56. C. inflatæ. South and East of England. On Silene inflata. ? continental.
    57. C. squamosella. Surrey (1856). Very rare, but an obscure species.
    58. C. salinella. On Sea-coast (1859). Abundant.
    59. *C. potentillæ. South of England.
    60. *C. adjunctella. Essex salt marshes. ? Lancashire (1882).
    61. *C. limoniella. Isle of Wight. Feeds on Statice limonium.
    62. Elachista flavicomella. Dublin (1856). Excessively rare, two specimens only known.
    63. *E. scirpi. Wales and Sussex. Salt marshes.
    64. E. consortella. Scotland (1854). A doubtful species.
    65. E. megerlella. Widely distributed (1854). Common. Larva feeds in grass during winter and early spring.
    66. E. obliquella. Near London (1854). Unique!
    67. E. triseriatella. South of England (1854). Very local; an obscure species.
    68. *Tinagma betulæ. East Dorset (1891).
    69. Lithocolletis nigrescentella. Northumberland (1850). Rare; a dark form of L. Bremiella, which is widely distributed.
    70. *L. anderidæ. Sussex. Dorset (1886).
    71. L. irradiella. North Britain (1854). A northern form of the more southern and wide-spread L. lautella.
    72. L. triguttella. Sanderstead, near Croydon (1848). Unique! very peculiar.
    73. L. ulicicolella. In a few wide-spread localities (1854). A peculiar form.
    74. L. caledoniella. North Britain (1854). A local variety of the more widespread L. corylifoliella. ​
    75. L. dunningiella. North of England (1852). A somewhat doubtful species.
    76. Bucculatrix demaryella. Widely distributed (1848). Rather common.
    77. Trifurcula squamatella. South of England (1854). A doubtful species.
    78. Nepticula ignobiliella. Widely scattered (1854). On hawthorn, not common. ? on continent.
    79. N. poterii. South of England (1858). Bred from Larvæ in Poterium sanguisorba.
    80. N. quinquella. South of England (1848). On oak leaves, very local. ? continental.
    81. N. apicella. Local (1854). Probably confused with allied species on the continent.
    82. N. headleyella. Local (1854). A rare species.
    83. *N. hodgkinsoni. Lancashire.
    84. *N. woolhopiella. Herefordshire.
    85. *N. serella. Westmoreland and S. England.
    86. *N. auromarginella. Dorset (1890).
    87. *Micropteryx sangii. (1891).
    88. *M. salopiella.
Pterophorina.
    89. Agdistis bennetti. East coast. I. of Wight (1840). Common on Statice limonium.
We have here a list of eighty-nine species, which, according to the best authorities, are, in the present state of our knowledge, peculiar to Britain. It is a curious fact that no less than fifty of these have been described more than twenty-five years; and as during all that time they have not been recognised on the continent, notwithstanding that good coloured figures exist of almost all of them, it seems highly probable that many of them are really confined to our island. At the same time we must not apply this argument too rigidly, for the very day before my visit to Mr. Stainton he had received a letter from Professor Zeller announcing the discovery on the continent of a species of our last family, Pterophorina, which for more than forty years had been considered to be exclusively British. This insect, Platyptilia similidactyla (Pterophorus isodactylus, Stainton's Manual), had been taken rarely in the extreme north and south of our islands—Teignmouth and Orkney, a fact which seemed somewhat indicative of its being a straggler. Again, seven of the species are unique, that is, have only been captured once; and it may be supposed that, as they are so rare as to have been found only once in England, they may be all ​ equally rare and not yet found on the continent. But this is hardly in accordance with the laws of distribution. Widely scattered species are generally abundant in some localities; while, when a species is on the point of extinction, it must for a time be very rare in the single locality where it last maintains itself. It is then more probable that some of these unique species represent such as are almost extinct, than that they have a wide range and are equally rare everywhere; and the peculiarity of our insular climate, combined with our varied soil and vegetation, offer conditions which may favour the survival of some species with us after they have become extinct on the continent.
Of the sixty-nine species recorded in my first edition fourteen have been since discovered on the continent, while no less than twenty-two species and eleven varieties have been added to the list. As we can hardly suppose continental entomologists to be less thorough collectors than ourselves, it ought to be more and more difficult to find any insects which are unknown on the continent if all ours really exist there; and the fact that the list of apparently peculiar British species is an increasing one renders it probable that many of them are not only apparently but really so. Both general considerations dependent on the known laws of distribution, and the peculiar habits, conspicuous appearance, and restricted range, of many of our species, alike indicate that some considerable proportion of them will remain permanently as peculiar British species.
We will now pass on to the Coleoptera, or beetles, an order which has been of late years energetically collected and carefully studied by British entomologists.
List of the Species and Varieties of Beetles which, so far as at present known, are confined to the British Islands. Those added since the first edition are marked with an asterisk.
Carabidæ.
    1. *Bembidium saxatile, var. vectensis (Fowler). Isle of Wight.
    2. Dromius vectensis (Rye). Common in the Isle of Wight, also in Kent, and at Weymouth and Seaton. Closely allied to D. sigma.
    3. Harpalus latus, var. metallescens (Rye). Unique, but very marked! South coast. "Perhaps a sport or a hybrid" (Fowler).
    4. Acupalpus derelictus (Dawson). Unique! North Kent. Canon Fowler thinks it may be a variety of A. dorsalis. ​
Dyticidæ.
    5. *Acilius sulcatus, var. scoticus (Curtis). Scotland. A melanic variety.
Helophoridæ.
    6. Ochthebius poweri (Rye). Very marked. S. coast. A few specimens only.
    7. *O. æneus (Steph).
Brachyelytra.
    8. Ocyusa hibernica (Rye). Ireland, mountain tops, and at Braemar.
    9. *Oxypoda tarda (Sharp).
    10.    ,,   pectita (Sharp). Scotland.
    11.    ,,   verecunda (Sharp). Scotland, also London districts.
    12. Homalota diversa (Sharp).
    13.    ,,    fulvipennis (Rye).
    14.    ,,    oblongiuscula (Sharp). Scotland, also England and Ireland.
    15.    ,,    princeps (Sharp). A coast insect.
    16.    ,,    curtipennis (Sharp). Scotland and near Birmingham.
    17. H. levana, var. setigera (Sharp).
    18. Stenus oscillator (Rye). Unique! South coast. May be a hybrid.
    19. Trogophlæus spinicollis (Rye). Mersey estuary, unique! Most distinguishable, nothing like it in Europe. Perhaps imported from another continent.
    20. Eudectus whitei (Sharp). Scotch hills. A variety of E. Giraudi of Germany (the only European species) fide Kraatz (Sharp).
    21. Homalium rugulipenne (Rye). Exceedingly marked form. Northern and western coasts; rare.
    22. *Mycetoporus monticola (Fowler). Cheviots and Inverness-shire.
Scydmænidæ.
    23. *Scydmænus poweri (Fowler) S. England. A recent discovery.
    24. *S. planifrons (Fowler).          ,,          ,,
Pselaphidæ.
    25. Bryaxis cotus (De Sauley). Scotland.
    26. Bythinus glabratus (Rye). Sussex coast; also Isle of Wight; a few specimens; very distinguishable; myrmecophilous (lives in ants' nests).
Trichopterygidæ.
    27. Ptinella maria          (Matthews) Derbyshire.
    28. Trichopteryx saræ      (   ,,   ) Notts.
    29.     ,,      poweri     (   ,,   ) Oxon.
    30.     ,,      edithia     (   ,,   ) Kent.
    31.     ,,     *angusta    (   ,,   ) Leicestershire.
    32.     ,,      kirbii      (   ,,   ) Norfolk.
    33.     ,,      fratercula (   ,,   )
    34.     ,,      waterhousii (   ,,   )
    35.     ,,      championis (   ,,   ) Wicken Fen.
    36.     ,,      jansoni    (   ,,   ) Leicestershire.
    37.     ,,      suffocata (Haliday). Ireland, Co. Cork.
    38.     ,,      carbonaria (Matthews). Notts.
​ 39. Ptilium halidayi (Matthews). Sherwood Forest.
    40.   ,,   caledonicum (Sharp). Scotland; very marked form.
    41.   ,,   insigne (Matthews). London district.
    42. *Orthoperus mundus (Matthews). Oxfordshire.
    43. *O. punctulatus (Matthews). Lincolnshire.
Anisotomidæ.
    44. Agathidium rhinoceros (Sharp). Old fir-woods in Perthshire; local, many specimens; a very marked species.
    45. Anisotoma similata (Rye). South of England. Two specimens.
    46.     ,,    lunicollis (Rye). North-east and South of England, a very marked form; several specimens.
Phalacridæ.
    47. Phalacrus brisouti (Rye). South of England. Rare. "Perhaps a small form of P. coruscus" (Fowler).
Cryptophagidæ.
    48. Atomaria divisa (Rye). Unique! South of England.
Lathridiidæ.
    49. Melanopthalma transversalis, var. wollastoni (Waterhouse). South coast, and Lincolnshire.
Byrrhidæ.
    50. Syncalypta hirsuta (Sharp). South of England, local. "Closely allied to S. setigera" (Fowler).
Mordellidæ.
    51. *Anaspis septentrionalis. Scotland (1891). (Champion.)
    52. *   ,,  garneysi (Fowler). London District. (1890.)
Telephoridæ.
    53. Telephorus darwinianus (Sharp). Scotland, sea-coast. A stunted form of abnormal habits. Perhaps a variety of T. lituratus.
Cyphonidæ.
    54. Cyphon punctipennis (Sharp). Scotland.
Anthicidæ.
    55. Anthicus salinus (Crotch). South coast.
    56.    ,,    scoticus (Rye). Loch Leven; very distinct; many specimens.
Cioidæ.
    57. *Cis bilamellatus (Wood). West Wickham, Kent. "Perhaps imported. Has the appearance of an exotic Cis" (Fowler).
Tomicidæ.
    58. *Pityopthorus lichtensteinii, var. scoticus (Blandford). Scotland.
Curculionidæ.
    59. Ceuthorhynchus contractus, var. pallipes (Crotch). Lundy Island; several specimens. A curious variety only known from this island.
    60. Liosomus troglodytes (Rye). A very queer form. Two or three specimens. South of England.
    61. *Orcheites ilicis, var. nigripes (Fowler). London District. (1890.)
    62. Apion ryei (Blackburn). Shetland Islands. Several specimens. Perhaps a var. of A. fagi.
Chrysomelidæ.
    63. Chrysomela staphylea, var. sharpi (Fowler). Solway district.
Halticidæ.
    64. Longitarsus agilis (Rye). South of England; many specimens.
    65.     ,,     distinguenda (Rye). South of England; many specimens.
    66. Psylliodes luridipennis (Kutschera). Lundy Island. A very curious form, not uncommon in this small island, to which it appears to be confined. "An extreme and local variety of P. chrysocephala" (Fowler).
Coccinellidæ.
    67. Scymnus lividus (Bold). Northumberland. A doubtful species.
Of the sixty-seven species and varieties of beetles in the preceding list, a considerable number no doubt owe their presence there to the fact that they have not yet been discovered or recognised on the continent. This is almost certainly the case with many of those which have been separated from other species by very minute and obscure characters, and especially with the excessively minute Trichopterygidæ described by Mr. Matthews. There are others, however, to which this mode of getting rid of them will not apply, as they are so marked as to be at once recognised by any competent entomologist, and often so plentiful that they can be easily obtained when searched for. The peculiar species of Apion in the Shetland Islands is interesting, and may be connected with the very peculiar climatal conditions there prevailing, which have led in some cases to a change of habits, so that a species of weevil (Otiorhynchus maurus) always found on mountain sides in Scotland here occurs on the sea-shore. Still more curious is the occurrence of two distinct forms (a species and a well-marked variety) on the small granitic Lundy Island in the Bristol Channel. This island is about three miles long and twelve from the coast of Devonshire, consisting mainly of granite with a little of the Devonian formation, and the presence here of peculiar insects can only be due to isolation with special conditions, and immunity from enemies or competing forms. When we consider the similar islands off ​ the coast of Scotland and Ireland, with the Isle of Man and the Scilly Islands, none of which have been yet thoroughly explored for beetles, it is probable that many similar examples of peculiar isolated forms remain to be discovered.
Looking, then, at what seem to me the probabilities of the case from the standpoint of evolution and natural selection, and giving due weight to the facts of local distribution as they are actually presented to us, I am forced to differ from the opinion held by our best entomological authorities, and to believe that some at least, perhaps many, of the species which, in the present state of our knowledge, appear to be peculiar to our islands, are, not only apparently, but really, so peculiar.
I am indebted to Mr. Robert McLachlan for the following information on certain Trichopterous Neuroptera (or caddis-flies) which appear to be confined to our islands. The peculiar aquatic habits of the larvæ of these insects, some living in ponds or rivers, others in lakes, and others again only in clear mountain streams, render it not improbable that some of them should have become isolated and preserved in our islands, or that they should be modified owing to such isolation.
Trichoptera peculiar to the British Isles.
    1. Philopotamus insularis. (? A variety of P. montanus.)—This can hardly be termed a British species or variety, because, so far as at present known, it is peculiar to the Island of Guernsey. It agrees structurally with P. montanus, a species found both in Britain and on the continent, but it differs in its strikingly yellow colour, and less pronounced markings. All the specimens from Guernsey are alike, and resident entomologists assured Mr. McLachlan that no other kind is known. Strange to say, some examples from Jersey differ considerably, resembling the common European and British form. Even should this peculiar variety be at some future time found on the continent it would still be a remarkable fact that the form of insect inhabiting two small islands only twenty miles apart should constantly differ; but as Jersey is between Guernsey and the coast, it seems just possible that the more insular conditions, and perhaps some peculiarity of the soil and water in the former island, have really led to the production or preservation of a well-marked variety of insect. In the first edition of this work two other species were named as then, peculiar to Britain—Setodes argentipunctella and Rhyacophila munda, but both have now been taken on the continent.
    2. Mesophylax impunctatus, var. zetlandicus.—A variety of a South and Central European species, one specimen of which has been found in Dumfriesshire. The variety is distinguished by its small size and dark colour.
Land and Freshwater Shells.—In the first edition of this work four species were noted as being, so far as was then known, exclusively British. Two of these, Cyclas pisidioides (now called Sphærium pisidioides) and Geomalacus maculosus, have been discovered on the continent, but the other two remain still apparently confined to these islands; and to these another has been added by the discovery of a new species of Hydrobia in the estuary of the Thames. The peculiar species now stands as follows:—
    1. Limnea involuta.—A pond snail with a small polished amber-coloured shell found only in a small alpine lake and its inflowing stream on Cromagloun mountain near the lakes of Killarney. It was discovered in 1838, and has frequently been obtained since in the same locality. It is sometimes classed as a variety of Limnea peregra, and is at all events closely allied to that species.
    2. Hydrobia jenkinsii.—A small shell of the family Rissoidæ inhabiting the Thames estuary both in Essex and Kent. It was discovered only a few years ago, and was first described in 1889.
    3. Assiminea grayana.—A small estuarine pulmonobranch found on the banks of the Thames between Greenwich and Gravesend, on mud at the roots of aquatic plants. It has been discovered more than sixty years.
But besides the above-named species there are a considerable number of well-marked varieties of shells which seem to be peculiar to our islands. A list of these has been kindly furnished me by Mr. Theo. D. A. Cockerell, who has paid much attention to the subject; and after omitting all those whose peculiarities are very slight or whose absence from the continent is doubtful, there remain a series of forms some of which are in all probability really endemic with us. This is the more probable from the fact that an introduced colony of Helix nemoralis at Lexington, Virginia, presents numerous varieties among which are several which do not occur in Europe. The following list is therefore given in the hope that it may be useful in calling attention to those varieties which are not yet positively known to occur elsewhere than in our islands, and ​ thus lead, ultimately, to a more accurate knowledge of the facts. It is only by obtaining a full knowledge of varieties, their distribution and their comparative stability, that we can ever hope to detect the exact process by which nature works in the formation of species.
List of the Species and Varieties of Land and Freshwater Shells which, so far as at present known, are believed to be Peculiar to the British Isles or not found on the Continent.
Limacidæ.
    1. Limax marginatus, var. maculatus. Ireland; frequent, very distinct.
    2.  ,,     ,,     ,, decipiens. Ireland and England.
    3.  ,,   flavus, var. suffusus. England; Melanic form.
    4.  ,,     ,,   ,, griseus. England; Melanic form.
    5. Agriolimax agrestis, var. niger. Yorkshire. Melanic. Azores.
    6.    ,,      ,,    ,, griseus. England. Melanic.
    7. Amalia gagates, var. rava. W. of England.
    8.   ,,  sowerbyi, var. rustica. England.
    9.   ,,     ,,    ,, nigrescens. Surrey and Middlesex.
    10.  ,,     ,,    ,, bicolor. Ealing.
    11. Hyalina crystallina, var. complanata. Near Bristol.
    12.   ,,  fulva, var. alderi.
    13. Vitrina pellucida, var. depressiuscula. S. England, Wales.
Helicidæ.
    14. Arion ater, var. albo-lateralis. England, Wales, Isle of Man; very distinct.
    15.  ,,  hortensis, var. fallax. England. Common at Boxhill.
    16. Geomalacus maculosus. Kerry and Cork. Three varieties have been described, one of which occurs in Portugal.
    17. Helix aspersa, var. lutescens. England. Not rare perhaps in France.
    18.  ,,  nemoralis, var. hibernica. Ireland.
    19.  ,,  rufescens, var. manchesteriensis. England.
    20.  ,,  hispida, var. subglobosa. England.
    21.  ,,    ,,    ,, depilata. England.
    22.  ,,    ,,    ,, minor. England, Ireland.
    23.  ,,  granulata, var. cornea. Lulworth, Dorset.
    24.  ,,  virgata, var. subaperta. Bath.
    25.  ,,    ,,    ,, subglobosa. England, Wales, Bantry Bay.
    26.  ,,    ,,    ,, carinata. Wareham, Dorset.
    27.  ,,  caperata, var. major. England, Wales, Scotland. Distinct.
    28.  ,,     ,,    ,, nana. England.
    29.  ,,     ,,    ,, subscalaris. Wales, Ireland.
    30.  ,,     ,,    ,, alternata. England, Kent.
    31.  ,,  acuta, var. nigrescens. England.
Pupidæ.
    32. Pupa anglica, var. pallida. Not rare.
    33.  ,,  lilljeborgi, var. bidentata. Ireland.
​ 34. ,, pygmea, var. pallida. Dorset and Devon.
    35. Clausilia rugosa, var. parvula. Ireland.
Stenogyridæ.
    36. Cochlicopa lubrica, var. hyalina. Wales, Scotland.
    37. Cœcilianella acicula, var. anglica. England.
Succineidæ.
    38. Succinea putris, var. solidula. Wiltshire.
    39.   ,,   virescens, var. aurea. Ireland.
    40.   ,,   pfeifferi,  ,, rufescens. England, Ireland.
    41.   ,,      ,,     ,, minor. England.
Limnæidæ.
    42. Planorbis fontanus, var. minor. England.
    43.   ,,   carinatus, ,, disciformis. England.
    44.   ,,   contortus, ,, excavatus. Ireland.
    45.   ,,      ,,    ,, minor.
    46. Physa fontinalus, var. oblonga. England, Wales, Ireland.
    47. Limnæa involuta. Ireland.
    48. Limnæa glutinosa, var. mucronata.
    49.   ,,   peregra, var. burnetti. Scotland. Very distinct.
    50.   ,,     ,,   ,, lacustris. Perhaps in C. Verde Islands.
    51.   ,,     ,,   ,, maritima. Great Britain.
    52.   ,,     ,,   ,, lineata. England.
    53.   ,,     ,,   ,, stagnaliformis. England.
    54.   ,,   stagnalis, var. elagantula. Curious. In a pond at Chislehurst.
    55.   ,,   palustris, var. conica. England, Ireland.
    56.   ,,      ,,    ,, tincta. England, Wales.
    57.   ,,      ,,    ,, albida. England.
    58.   ,,   truncatula, var. elegans. England, Ireland. Distinct.
    59.   ,,      ,,    ,, fusca. Wales.
    60. Ancylus lacustris, var. compressus. England.
Paludinidæ.
    61. Paludina vivipara, var. efasciata. England. Not uncommon.
    62.   ,,     ,,    ,, atropurpurea. Pontypool.
Rissoidæ.
    63. Hydrobia jenkinsii. Thames Estuary.
    64.    ,,    ventrosa, var. minor.
    65.    ,,      ,,    ,, decollata.
    66.    ,,      ,,    ,, ovata.
    67.    ,,      ,,    ,, elongata.
    68.    ,,      ,,    ,, pellucida.
Cyrenidæ.
    69. Sphærium corneum, var. compressum.
    70.    ,,      ,,    ,, minor.
    71.    ,,      ,,    ,, stagnicola.
    72.    ,,   ovale, var. pallidum. England.
    73.    ,,   lacustre, var. rotundum. Wales.
    74. Pisidium pusillum, var. grandis.
    75.   ,,     ,,    ,, circulare. Wales.
    76.   ,,  nitidum, var. globosum.
Unionidæ.
    77. Unio tumidus, var. richensis. Regent's Park. Peculiar form.
    78.  ,, pictorum, var. latior. England.
    79.  ,,   ,,     ,, compressus. England.
    80.  ,, margaritifer, var. olivaceus.
    81. Anodonta cygnæa, var. incrassata. England.
    82.    ,,     ,,    ,, pallida. England, Ireland.
Estuarine or Marine Pulmonotranchs.
    83. Assiminea grayana. Thames Estuary.
Peculiarities of the British Flora.—Thinking it probable that there must also be some peculiar British plants, but not finding any enumeration of such in the British Floras of Babington, Hooker, or Bentham, I applied to the greatest living authority on the distribution of British plants—the late Mr. H. C. Watson, who very kindly gave me the information I required, and I cannot do better than quote his words: "It may be stated pretty confidently that there is no 'species' (generally accepted among botanists as a good species) peculiar to the British Isles. True, during the past hundred years, nominally new species have been named and described on British specimens only, from time to time. But these have gradually come to be identified with species described elsewhere under other names—or they have been reduced in rank by succeeding botanists, and placed or replaced as varieties of more widely distributed species. In his British Rubi Professor Babington includes as good species, some half-dozen which he has, apparently, not identified with any foreign species or variety. None of these are accepted as 'true species,' nor even as 'sub-species' in the Students' Flora, where the brambles are described by Baker, a botanist well acquainted with the plants of Britain. And as all these nominal species of Rubi are of late creation, they have truly never been subjected to real or critical tests as 'species.'"
In my first edition I was only able to name four species, sub-species, or varieties of flowering plants which were believed to be unknown on the continent. But much attention has of late years been paid to the critical examination of British plants in comparison with continental specimens, and I am now enabled to give a much more ​ extensive list of the species or forms which at present seem to be peculiar. For the following list I am primarily indebted to Mr. Arthur Bennett of Croydon. Sir Joseph Hooker has been so kind as to examine it carefully and to give me his conclusions on the relative value of the differences of the several forms, and Mr. Baker, of Kew, has also assisted with his extensive knowledge of British plants.
    List of Species, Sub-species, and Varieties of Flowering Plants found in Great Britain or Ireland, but not at present known in Continental Europe. By Arthur Bennett, F.L.S. The most distinct and best determined forms are marked with an asterisk.
    1. *Caltha radicans (Forst.). "A much disputed species, or form of C. palustris. It is a relatively rare plant." (J. D. H.) "Certainly distinct from the Scandinavian form." (Ar. Bennett.)
    2. *Arabis petræa (Lam.) var. grandifolia (Druce). Scotch mountains. "The larger flowers alone distinguish this." (J. D. H.)
    3. Arabis ciliata (R. Br.). In Nyman's Conspectus Floræ Europææ this species is given as found in England and Ireland only. "A very much disputed form of a plant of very wide distribution in Europe and North America." (J. D. H.)
    4. Brassica monensis (Huds.). "This and the continental B. cheiranthus (also found in Cornwall) are barely distinguishable from one another." (J. D. H.)
    5. Diplotaxis muralis (D. C.) var. Babingtonii (Syme). South of England. "A biennial or perennial form; considered to be a denizen by Watson." (J. D. H.)
    6. *Helianthemum guttatum (Mill), var. Breweri (Planch). Anglesea. "Very doubtful local plant. H. guttatum (true) has lately been found in the same locality." (J. D. H.)
    7. *Polygala vulgaris (L.), var. grandiflora (Bab). Sligo, Ireland. "A very distinct variety." (J. D. H.)
    8. Viola lutea (Huds.), var. amœna (Symons). "V. lutea itself is considered to be a form of V. tricolor, and V. amœna the better coloured of the two forms of V. lutea." (J. D. H.)
    9. *Cerastium arcticum (Lange), var. Edmonstonii (Beeby). Shetland Is. "But C. arcticum is referable to the very variable C. alpinum." (J. D. H.) "Near to the European C. latifolium." (Ar. Bennett.)
    10. *Geranium sanguineum (L.), var. Lancastriense (With.). Lancashire. "A prostrate local form growing out of its native soil in sand by the sea." (J. D. H.) Mr. Bennett writes: "I have grown G. sanguineum and its prostrate variety in sand, and neither became Lancastriense."
    11. Genista tinctoria (L.), var. humifusa (Dickson). Cornwall. "A decumbent hairy form confined to the Lizard." (J. D. H.)
    12. Cytisus scoparius (Link.), var. prostratus (Bailey). Cornwall. "A prostrate form." (J. D. H.)
    13. Anthyllis vulneraria (L.), var. ovata (Bab.). Shetland Is. "A slight variety." (J. D. H.)
    14. *Trifolium repens (L.), var. Townsendii (Bab.). Scilly Isles. "A ​ well-marked form by its rose-purple flowers. Confined to the Scilly Isles." (J. D. H.)
    15. *Rosa involuta (Sm.), var. Wilsoni. (Borrer.) Wales. "There are a multitude of forms or varieties of R. involuta, and R. wilsoni is one of the best-marked, found on the Menai Straits and Derry." (J. D. H.)
    16. Rosa involuta var. gracilis (Woods). "This is considered by many as one of the commonest forms of R. involuta." (J. D. H.)
    17. Rosa involuta var. Nicholsoni (Crepin). "Another slight variety of R. involuta." (J. D. H.)
    18. Rosa involuta var. Woodsiana (Groves). "A Wimbledon Common variety of R. villosa." (J. D. H.)
    19. Rosa involuta var. Grovesii (Baker). "Mr. Baker thinks this of no account." (J. D. H.)
    20. Rubus echinatus (Lind.). "A variety of the widely spread R. Radula, itself a form of R. fruticosus." (J. D. H.)
    21. *Rubus longithyrsiger (Lees). "Mr. Baker informs me that this is a very distinct plant never yet found on the continent." (J. D. H.)
    22. Pyrus aria (Sm.) var. rupicola (Syme). "A very local form, confined to Gt. Britain, and owing its characters to its starved position." (Baker.)
    23. Callitriche obtusangula (Le Gall), var. Lachii (Warren). Cheshire. "This is intermediate between two sub-species of C. verna." (J. D. H.)
    24. *Œnanthe fluviatilis (Coleman). South of England. "The fluitant form of Æ. Phellandrium." (J. D. H.)
    25. Anthemis arvensis (L.), var. anglica (Spreng). N. Coast of England. "A maritime form with more fleshy leaves formerly found near Durham. It has other very trifling characters." (J. D. H.)
    26. Arctium intermedium (Bab.). "There are two sub-species of A. lappa, majus and minus, each with varieties, and this is one of the intermediates." (J. D. H.)
    27. Hieracium holosericium (Backh.). Scotch Alps.
    28. H. gracilentum (Backh.).          ,,
    29. H. lingulatum (Backh.).           ,,   A var. of this in Scandinavia.
    30. H. senescens (Backh.).           ,,
    31. H. chrysanthenum (Backh.).       ,,
    32. H. iricum (Fr.). Teesdale and Scotland.
    33. H. gibsoni (Backh.). Yorkshire and Westmoreland.
    34. Hieracium nitidum (Backh.). Lower glens of the Scotch Alps. Mr. Bennett writes:—"The following Hieracia have been named by Mr. F. J. Hanbury as endemic forms. One can only safely say they are certainly not known in Scandinavia, as they have all been submitted to Dr. Lindeberg. But usually Scotch species are not represented in Central Europe to any great extent, though several do occur. Still these new forms ought to be critically compared with all Dr. Peters' new species."
    35. H. Langewellense (Hanb.). Caithness.
    36. H. pollinarium (Hanb.). Sutherland.
    37. H. scoticum (Hanb.). Sutherland and Caithness.
    38. H. Backhousei (Hanb.). Aberdeen, Banff, Inverness.
    39. H. caledonicum (Hanb.). Caithness and Sutherland.
    40. H. Farrense (Hanb.). Sutherland and Shetland Is.
    41. H. proximum (Hanb.). Caithness. With regard to all these ​ Hieracia Sir Joseph Hooker and Mr. Baker say:—"No case can be made of these. They are local forms with the shadowest of shady characters." Mr. Bennett writes: "H. iricum and H. Gibsoni are the best marked forms."
    42. *Campanula rotundifolia (L.), var. speciosa (A. G. More). W. Ireland. "Very well distinguished by its large flowers and small calyx lobes, approaching the Swiss C. Scheuzeri." (J. D. H.)
    43. Statice reticulata (Sm.). "Baker agrees with me that this is also a Mediterranean species." (J. D. H.)
    44. Erythræa capitata (Willd.), var. sphærocephala (Towns.). Isle of Wight. "A form of E. centaurium utterly anomalous in its genus in the insertion of the stamens. A monster rather than a species." (J. D. H.)
    45. *Erythræa latifolia (Sm.). On the sandy dunes near Liverpool. "A local form." (J. D. H.)
    46. Myosotis collina (Hoffim.), var. Mittenii (Baker). Sussex.
    47. Veronica officinalis (L.), var. hirsuta (Hopk.). Ayr, Scotland.
    48. Veronica arvensis (L.), var. eximia (Towns.). Hampshire.
    49. Mentha alopecuroides (Hull). Nearest to M. dulcissima (Dum.).
    50. Mentha pratensis (Sole). Only once found.
    51. Chenopodium rubrum (L.), var. pseudobotryoides (H. C. Watson).
    52. Salix ferruginea (Forbes). England, Scotland. "Probably a hybrid between S. viminalis and S. cinerea." (J. D. H.)
    53. Salix Grahami (Borr.). Sutherland, Perth. "A hybrid?" (J. D. H.)
    54. Salix Sadleri (Syme). Aberdeen. "A hybrid?" (J. D. H.)
    55. *Spiranthes Romanzoviana (Cham.). Ireland (N. America).
    56. *Sisyrinchium angustifolium (Mill.). Ireland. (Arctic and Temp. N. America.)
    57. Allium Babingtonii (Borrer). West England, West Ireland. "A form of A. ampeloprasum, itself a naturalised species." (J. D. H.)
    58. *Potamogeton lanceolatus (Sm.). Anglesea, Cambridgeshire, Ireland. Mr. Bennett writes:—"Endemic! I have taken a good amount of trouble to ascertain this. Nearly 400 specimens I have distributed all over the world with requests for information as to anything like it. The response is everywhere the same, 'nothing.' The nearest to it occurs in the Duchy of Lauenberg but is referable to P. heterophyllus."
    59. Potamogeton Griffithii (Ar. Bennett). Carnarvon. "Nearest to this is a probable hybrid from N. America, but not identical." (Ar. Bennett.)
    60. Potamogeton pusillus (L.), sub-sp. Sturrockii (Ar. Benn.). Perth.
    61. Potamogeton pusillus (L.), var. rigidus (Ar. Benn.). Orkneys, Shetlands.
    62. Ruppia rostellata (Koch.), var. nana (Bosw.). Orkneys.
    63. *Eriocaulon septangulare (With.). Hebrides, Ireland. N. America.
    64. Scirpus uniglumis (Link), var. Watsoni (Bab.). Scotland, England. "This is a variety of a sub-species of the common S. palustris." (J. D. H.)
    65. Luzula pilosa (Willd.), var. Borreri (Bromf).
    66. *Carex involuta (Bab.). Cheshire. "A distinct enough plant but probably a hybrid between C. vesicaria and C. ampullacea, found in one place only." (J. D. H.)
    67. Carex glauca (Murr.), var. stictocarpa (Sm.). Scotland.
    ​ 68. Carex precox (Jacq.), var. capitata (Ar. Benn.). Ireland. "A remarkable plant (monstrosity?) simulating C. capitata (L.)." (Ar. Bennett.)
    69. *Carex Grahami (Boott). "A mountain form of C. vesicaria." (J. D. H.)
    70. *Spartina Townsendi (Groves). Hampshire. "A distinct but very local form of S. stricta, found in one place only." (J. D. H.)
    71. Agrostis nigra (With.).
    72. Deschampsia flexuosa (Trin.), var. Voirlichensis (J. C. Melvill). Perth.
    73. *Deyeuxia neglecta (Kunth), var. Hookeri (Syme). Ireland. "A distinct variety confined to Lough Neagh." (J. D. H.)
    74. Glyceria maritima (Willd.), var. riparia (Towns.). Hampshire.
    75. Poa Balfouri (Bab.). Scotland. "An alpine sub-variety of a variety of the protean P. nemoralis." (J. D. H.)
In his comments on this extensive list of supposed peculiar British plants, Sir Joseph Hooker arrives at the following conclusions:—
    1. There are four unquestionably distinct species which do not occur in continental Europe: viz.—
    One absolutely endemic species, Potamogeton lanceolatus.
    Three American species, Sisyrinchium angustifolium, Spiranthes romanzoviana, Eriocaulon septangulare.
    2. There are sixteen endemic varieties of British species, viz.—
    Eleven of more or less variable species, Caltha palustris, var. radicans; Polygala vulgaris, var. grandiflora; Cerastium arcticum, var. edmonstonii; Trifolium repens, var. Townsendii; Rosa involuta, var. wilsoni; Rubus fruticosus, sub-sp. longithyrsiger; Campanula rotundifolia, var. speciosa; Erythræa centaurium, sub-sp. latifolia; Carex involuta, (? Hyb.); Carex vesicaria, var. Grahami; Deyeuxia neglecta, var. Hookeri.
    Five of comparatively well limited species. Arabis petræa, var. grandifolia; Helianthemum guttatum, var. Breweri; Geranium sanguineum, var. Lancastriense; Œnanthe Phellandrium, var. fluviatilis; Spartium stricta, var. Townsendi.
The above twenty species are marked in the list with an asterisk. Of the remaining fifty-five, Sir Joseph Hooker says, "that for various reasons it would not be safe to rely on them as evidence. In most cases the varietal form is so very trifling a departure from the type that this may be safely set down to a local cause, and is probably not constant. In others the plant is doubtfully endemic; in still others a hybrid."
Even should it ultimately prove that of the whole number of the fifty-five doubtful forms none are established as peculiar British varieties, the number admitted after so ​ rigorous an examination is about what we should expect in comparison with the limited amount of speciality we have seen to exist in other groups. The three American species which inhabit the extreme west and north-west of the British Isles, but are not found on the continent of Europe are especially interesting, because they demonstrate the existence of some peculiar conditions such as would help to explain the presence of the other peculiar species. Whether we suppose these American forms to have migrated from America to Europe before the glacial epoch, or to be the remnants of a vegetation once spread over the north temperate zone, we can only explain their presence with us and not further east by something favourable either in our insular climate or in the limited competition due to our comparative poverty in species.
About half of the peculiar forms are found in the extreme west or north of Britain or in Ireland, where peculiar insular conditions are at a maximum; and the influence of these conditions is further shown by the number of species of West or South European plants which occur in the same districts.
We may here notice the interesting fact that Ireland possesses no less than twenty species or sub-species of flowering plants not found in Britain, and some of these may be altogether peculiar. As a whole they show the effect of the pre-eminently mild and insular climate of Ireland in extending the range of some south European species. The following list of these plants, for which I am indebted to Mr. A. G. More, with a few remarks on their distribution, will be found interesting:—
List of Irish Flowering Plants which are not found in Britain.
    1. Polygala vulgaris (var. grandiflora). Sligo.
    2. Campanula rotundifolia (var. speciosa). W. Ireland.
    3. Arenaria ciliata. W. Ireland (also Auvergne, Pyrenees, Crete).
    4. Saxifraga umbrosa. W. Ireland (also Pyrenees, N. Spain, Portugal).
    5.    ,,   geum. S. W. Ireland (also Pyrenees).
    6.    ,,   hirsuta. S. W. Ireland (also Pyrenees).
    7. Inula salicina. W. Ireland (Scandinavia, Middle and South Europe).
    8. Erica mediterranea. W. Ireland (W. France, Spain, Portugal).
    9.  ,, mackaiana (tetralix sub.-sp.) W. Ireland (Spain).
    10. Arbutus unedo. S. W. Ireland (W. of France, Spain, Portugal and shores of Mediterranean).
    11. Dabeocia polifolia. W. Ireland (W. of France, Spain and Portugal).
    ​ 12. Pinguicula grandiflora. S. W. Ireland (Spain, Pyrenees, Alps of France and Switzerland).
    13. Neotinea intacta. W. Ireland (S. France, Portugal, Spain, and shores of Mediterranean).
    14. Spiranthes romanzoviana. S. W. Ireland (North America).
    15. Sisyrinchium angustifolium. W. Ireland (North America, Arctic and Temp.).
    16. Potamogeton lonchites. Ireland, Mr. Arthur Bennett informs me that this is certainly not British or European, but may possibly be identical with P. fluitans var. Americanus of the U. States.
    17. Potamogeton kirkii (natans sub.-sp.). W. Ireland. (Arctic Europe?)
    18. Eriocaulon septangulare. W. Ireland, Skye, Hebrides (North America).
    19. Carex buxbaumii. N. E. Ireland, on an island in Lough Neagh (Arctic and Alpine Europe, North America).
    20. Deyeuxia neglecta (var. Hookeri). On the shores and islands of Lough Neagh. (And in Germany, Arctic Europe, and North America.)
We find here nine south-west European species which probably had a wider range in mild preglacial times, and have been preserved in the south and west of Ireland owing to its milder climate. It must be remembered that during the height of the glacial epoch Ireland was continental, so that these plants may have followed the retreating ice to their present stations and survived the subsequent depression. This seems more probable than that so many species should have reached Ireland for the first time during the last union with the continent subsequent to the glacial epoch. The Arctic, Alpine, and American plants may all be examples of species which once had a wider range, and which, owing to the more favourable conditions, have continued to exist in Ireland while becoming extinct in the adjacent parts of Britain and Western Europe.
As contrasted with the extreme scarcity of peculiar species among the flowering plants, it is the more interesting and unexpected to find a considerable number of peculiar mosses and Hepaticæ, some of which present us with phenomena of distribution of a very remarkable character. For the following lists and the information as to the distribution of the genera and species I am indebted to Mr. William Mitten, one of the first authorities on these beautiful little plants. That of the mosses has been corrected for this edition by Dr. R. Braithwaite, and several species of hepaticæ have been added by Mr. Mitten. ​
List of the Species of Mosses and Hepaticæ which are peculiar to the British Isles (or not found in Europe).
(Those belonging to non-European genera in Italics.)
Mosses. :
| 1. | Systegium Mittenii | South England. |
| 2. | Campylopus Shawii | North Britain. |
| 3. | ,,    setifolius | Ireland, Wales, and Hebrides. |
| 4. | Seligeria calcicola | South England. |
| 5. | Pottia viridifolia | South England. |
| 6. | Leptodontium recurvifolium | Ireland and Scotland. |
| 7. | Tortula Hybernica | Ireland. |
| 8. | Streptopogon gemmascens | Sussex. |
| 9. | Bryum barbatum | Scotland. |
| 10. | Bartramidula Wilsoni | Ireland, Wales, and Scotland. |
| 11. | Daltonia splachnoides | Ireland, Antilles, and Mexico. |
| 12. | Hookeria laetevirens | Ireland, Cornwall, and Madeira. |
| 13. | Hypnum micans | Ireland. |
| 14. | Myurium Hebridarium | Hebrides and Atlantic Islands. |
| 15. | Hedwigia ciliata var. striata | Wales and Scotland. |
| Hepaticæ. |||
| 1. | Frullania germana | Ireland. |
| 2. | ,,  Hutchinsiæ | Ireland, Scotland, Wales, Devon, Tropical regions. |
| 3. | Lejeunia flava | Ireland, Atlantic Islands, S. America, Africa, &c. |
| 4. | ,,  microscopica | Ireland, Wales, Cumberland, Madeira. |
| 5. | ,,  Holtii | Ireland (Killarney). |
| 6. | ,,  diversiloba | Ireland (Killarney), Mexico? |
| 7. | ,,  patens | Ireland. |
| 8. | Radula tenax | Ireland. |
| 9. | ,,  Holtii | Ireland. |
| 10. | ,,  voluta | Ireland, Wales, Cumberland, Mexico? |
| 11. | ,,  Carringtonii | Ireland. |
| 12. | Lepidozia Pearsoni | Wales. |
| 13. | Adilocolia decipiens | Ireland, Wales, Africa, and S. America. |
| 14. | Cephalozia aeraria | Wales. |
| 15. | Lophocolia spicata | Ireland, Cornwall, Anglesea. |
| 16. | Martinellia nimbosa | Ireland (Brandon Mountain). |
| 17. | Plagiochila spinulosa | Wales, Ireland, and Scotland, Atlantic Islands. |
| 18. | ,,   ambagiosa | Ireland, India. |
| 19. | Jamesoniella Carringtonii | Scotland. |
| 20. | Gymnocolea Nevicensis | Scotland. |
| 21. | Jungermannia Doniana | Scotland. |
| 22. | Cesia crenulata | Ireland, Wales. |
| 23. | Chasmatocolea cuneifolia | Ireland. |
| 24. | Aerobolbus Wilsoni | Ireland, S. America, New Zealand. |
| 25. | Petalophyllum Ralfsii | Ireland, Cornwall, Devon. |
Many of the above are minute or obscure plants, and are closely allied to other European species with which they may have been confounded. We cannot therefore lay any stress on these individually as being absent from the continent of Europe so much of which is imperfectly explored, though it is probable that several of them are really confined to Britain. But there are a few—indicated by italics—which are in a very different category; for they belong to genera which are altogether unknown in any other part of Europe, and their nearest allies are to be found in the tropics or in the southern hemisphere. The four non-European genera of mosses to which we refer all have their maximum of development in the Andes, while the three non-European Hepaticæ appear to have their maximum in the temperate regions of the southern hemisphere. Mr. Mitten has kindly furnished me with the following particulars of the distribution of these genera:—
    Bartramidula. Asia, Africa, S. America and Australia, but not Europe or N. America.
    Streptopogon is a comparatively small genus, with seven species in the Andes, one in the Himalayas, and three in the south temperate zone, besides our English species.
    Daltonia is a large genus of inconspicuous mosses, having seventeen species in the Andes, two in Brazil, two in Mexico, one in the Galapagos, six in India and Ceylon, five in Java, two in Africa, and three in the Antarctic Islands, and one in Ireland.
    Hookeria (restricting that term to the species referable to Cyclodictyon) is still a large genus of handsome and remarkable mosses, having twenty-six species in the Andes, eleven in Brazil, eight in the Antilles, one in Mexico, two in the Pacific Islands, one in New Zealand, one in Java, one in India, and five in Africa—besides our British species, which is found also in Madeira and the Azores but in no part of Europe proper.
These last two are very remarkable cases of distribution, since Mr. Mitten assures me that the plants are so markedly different from all other mosses that they would scarcely be overlooked in Europe.
The distribution of the non-European genera of Hepaticæ is as follows:—
    Chasmatocolia. South America and Ireland.
    Acrobolbus. A small genus found only in New Zealand and the adjacent islands, besides Ireland.
    ​ Petalophyllum. A small genus confined to Australia and New Zealand in the southern hemisphere, Algeria, and Ireland in the northern. We have also one of the Hepaticæ—Mastigophora Woodsii—found in Ireland and the Himalayas, but unknown in any part of continental Europe. The genus is most developed in New Zealand.
These are certainly very interesting facts, but they are by no means so exceptional in this group of plants as to throw any doubt upon their accuracy. The Atlantic islands present very similar phenomena in the Rhamphidium purpuratum, whose nearest allies are in the West Indies and South America; and in three species of Sciaromium, whose only allies are in New Zealand, Tasmania, and the Andes of Bogota. An analogous and equally curious fact is the occurrence in the Drontheim mountains in Central Norway, of a little group of four or five peculiar species of mosses of the genus Mnium, which are found nowhere else; although the genus extends over Europe, India, and the southern hemisphere, but always represented by a very few wide-ranging species except in this one mountain group!
Such facts show us the wonderful delicacy of the balance of conditions which determine the existence of particular species in any locality. The spores of mosses and Hepaticæ are so minute that they must be continually carried through the air to great distances, and we can hardly doubt that, so far as its powers of diffusion are concerned, any species which fruits freely might soon spread itself over the whole world. That they do not do so must depend on peculiarities of habit and constitution, which fit the different species for restricted stations and special climatic conditions; and according as the adaptation is more general, or the degree of specialisation extreme, species will have wide or restricted ranges. Although their fossil remains have been rarely detected, we can hardly doubt that mosses have as high an antiquity as ferns or Lycopods; and coupling this antiquity with their great powers of dispersal we may understand how many of the genera have come to occupy a number of detached areas scattered over the whole earth, but ​ always such as afford the peculiar conditions of climate and soil best suited to them. The repeated changes of temperature and other climatic conditions, which, as we have seen, occurred through all the later geological epochs, combined with those slower changes caused by geographical mutations, must have greatly affected the distribution of such ubiquitous yet delicately organised plants as mosses. Throughout countless ages they must have been in a constant state of comparatively rapid migration, driven to and fro by every physical and organic change, often subject to modification of structure or habit, but always seizing upon every available spot in which they could even temporarily maintain themselves.
Here then we have a group in which there is no question of the means of dispersal; and where the difficulties that present themselves are not how the species reached the remote localities in which they are now found, but rather why they have not established themselves in ​ many other stations which, so far as we can judge, seem equally suitable to them. Yet it is a curious fact, that the phenomena of distribution actually presented by this group do not essentially differ from those presented by the higher flowering plants which have apparently far less diffusive power, as we shall find when we come to treat of the floras of oceanic islands; and we believe that the explanation of this is, that the life of species, and especially of genera, is often so prolonged as to extend over whole cycles of such terrestrial mutations as we have just referred to; and that thus the majority of plants are afforded means of dispersal which are usually sufficient to carry them into all suitable localities on the globe. Hence it follows that their actual existence in such localities depends mainly upon vigour of constitution and adaptation to conditions just as it does in the case of the lower and more rapidly diffused groups, and only partially on superior facilities for diffusion. This important principle will be used further on to afford a solution of some of the most difficult problems in the distribution of plant life.
Concluding Remarks on the Peculiarities of the British Fauna and Flora.—The facts, now I believe for the first time brought together, respecting the peculiarities of the British fauna and flora, are sufficient to show that there is considerable scope for the study of geographical distribution even in so apparently unpromising a field as one of the most recent of continental islands. Looking at the general bearing of these facts, they prove, that the idea so generally entertained as to the biological identity of the British Isles with the adjacent continent is not altogether correct. Among birds we have undoubted peculiarities in at least three instances; peculiar fishes are much more numerous, and in this case the fact that the Irish species ​ are almost all different from the British, and those of the Orkneys distinct from those of Scotland, renders it almost certain that the great majority of the fifteen peculiar British fishes are really peculiar and will never be found on the European Continent. The mosses and Hepaticæ also have been sufficiently collected in Europe to render it pretty certain that the more remarkable of the peculiar British forms are not found there; why therefore, it may be well asked, should there not be a proportionate number of peculiar British insects? It is true that numerous species have been first discovered in Britain, and, subsequently, on the continent; but we have many species which have been known for twenty, thirty, or forty years, some of which are not rare with us, and yet have never been found on the continent. We have also the curious fact of our outlying islands, such as the Shetland Isles, the Isle of Man, and the little Lundy Island, possessing each some peculiar forms which, certainly, do not exist on our principal island which has been so very thoroughly worked. Analogy, therefore, would lead us to conclude that many other species or varieties would exist on our islands and not on the continent; and when we find that a very large number (150) in three orders only, are so recorded, we may I think be sure that some considerable portion of these (though how many we cannot say) are really endemic British species.
The general laws of distribution also lead us to expect such phenomena. Very rare and very local species are such as are becoming extinct; and it is among insects, which are so excessively varied and abundant, which present so many isolated forms, and which, even on continents, afford numerous examples of very rare species confined to restricted areas, that we should have the best chance of meeting with every degree of rarity down to the point of almost complete extinction. But we know that in all parts of the world islands are the refuge of species or groups which have become extinct elsewhere; and it is therefore in the highest degree probable that some species which have ceased to exist on the continent should be preserved in some part or other of our islands, especially ​ as these present favourable climatic conditions such as do not exist elsewhere.
There is therefore a considerable amount of harmony in the various facts adduced in this chapter, as well as a complete accordance with what the laws of distribution in islands would lead us to expect. In proportion to the species of birds and fresh-water fishes, the number of insect-forms is enormously great, so that the numerous species or varieties here recorded as not yet known on the continent are not to be wondered at; while it would, I think, be almost an anomaly if, with peculiar birds and fishes there were not a fair proportion of peculiar insects. Our entomologists should, therefore, give up the assumption, that all our insects do exist on the continent, and will some time or other be found there, as not in accordance either with the evidence or the probabilities of the case; and when this is done, and the interesting peculiarities of some of our smaller islands are remembered, the study of our native animals and plants, in relation to those of other countries, will acquire a new interest. The British Isles are said to consist of more than a thousand islands and islets. How many of these have ever been searched for insects? With the case of Lundy Island before us, who shall say that there is not yet scope for extensive and interesting investigations into the British fauna and flora?
131 ↑ Geological Magazine, 1870, p. 155.
132 ↑ Transactions of the Edinburgh Geological Society, Vol. I. p. 330.
133 ↑ Quarterly Journal of Geological Society, 1850, p. 96.
134 ↑ British Association Report, Dundee, 1867, p. 431.
135 ↑ The list of names was furnished to me by Dr. Günther, and I have added the localities from the papers containing the original descriptions, and from Dr. Haughton's British Freshwater Fishes.
136 ↑ See "The Virginia Colony of Helix nemoralis," T. D. A. Cockerell, in The Nautilus, Vol. III. No. 7, p. 73.
137 ↑ I am indebted to Mr. Mitten for this curious fact.
138 ↑ The following remarks by Dr. Richard Spruce, who has made a special study of mosses and especially of hepaticæ, are of interest. "From what precedes, I conclude that no existing agency is capable of transporting the germs of our hepatics of tropical type from the torrid zone to Britain, and I venture to suppose that their existence at Killarney dates from the remote period when the vegetation of the whole northern hemisphere partook of a tropical character. If I am challenged to account for their survival through the last glacial period, I reply that, granting even the existence of a universal ice-cap down to the latitude of 40° in America and 50° in Europe, it is not to be assumed that the whole extent, even of land, was perennially entombed 'in thrilling regions of thick-ribbed ice.' Towards the southern margin of the ice the climate was probably very similar to that of Greenland and the northern part of Norway at the present day. The summer sun would have great power, and on the borders of sheltered fjords the frozen snow would disappear completely, if only for a very short period, and I ask only for a month or two, not doubting the capacity of our hepatics to survive in a dormant state under the snow for at least ten months in the year. I have gathered mosses in the Pyrenees where the snow had barely left them on August 2nd; by September 25th they were re-covered with snow, and would not be again uncovered till the following year. The mosses of Killarney might even enjoy a longer summer than this; for the gulf-stream laves both sides of the south-western angle of Ireland, and its tepid waters would exert great melting power on the ice-bound coast, preventing at the same time any formation of ice in the sea itself." This passage is the conclusion of a very interesting discussion on the distribution of hepaticæ in a paper on "A New Hepatic from Killarney," in the Journal of Botany, vol. 25, (Feb. 1887), pp. 33-82, in which many curious facts are given as to the habits and distribution of these curious and beautiful little plants.
139 ↑ While these pages are passing through the press I am informed by my friend Mr. W. H. Beeby that in the Shetland Isles, where he has been collecting for five summers, he has found several plants new to the British flora, and a few altogether undescribed. Among these latter is a very distinct species of Hieracium (H. Zetlandicum), which is quite unknown in Scandinavia, and is almost certainly peculiar to the British Islands. Here we have another proof that entirely new species are still to be discovered in the remoter portions of our country.