The number of well-ascertained recent Scottish Mammals recognized in the following pages is fifty-one, the proportions of the different orders, as compared with the faunas of England and Ireland, being shown in the following Table:- *

DISTRIBUTION OF BRITISH MAMMALS. ENGLAND. SCOTLAND. IRELAND.

The fifteen English species not hitherto recorded as having occurred north of the Tweed are the following:

1. Rhinolophus hipposideros.

2. Rh. ferrum-equinum.

3. Vesperugo serotinus.

4. V. noctula.

5. V. leisleri.

6. Vespertilio nattereri.

7. V. bechsteini.

8. V. mystacinus.

9. Synotus barbastellus.

10. Phoca hispida.

11. Balaenoptera laticeps.

12. Grampus griseus.

13. Delphinus delphis.

14. D. albirostris.

15. Muscardinus avellanarius.

The six Scottish species not yet included in the English fauna

are

1. Trichechus rosmarus.

2. Ziphius cavirostris.

3. Mesoplodon bidens.

4. Delphinapterus leucas.

5. Delphinus acutus.

6. Lepus variabilis.

The four species found in Ireland, but not in Scotland, are all Bats, namely

1. Rhinolophus hipposideros.

2. Vesperugo leisleri.

3. Vespertilio nattereri.
4. V. mystacinus.

* In these Tables I have rejected several species of so-called British Bats and Cetaceans as

not being well ascertained. Cf. Bell's British Quadrupeds, 2nd ed. (1874).

Whereas no less than nineteen Mammals are on the Scottish list, whose presence is not yet authenticated in the sister isle:_*

1. Sorex tetragonurus.

2. Crossopus fodiens.

3. Talpa europaea.
4. Felis catus.

5. Mustela vulgaris.
6. M. putorius.

7. Trichechus rosmarus.

8. Megaptera longimana. 9. Balaenoptera sibbaldi. 10. Hyperoodon laticeps.

11. Ziphius cavirostris.
12. Monodon monoceros.
13. Delphinapterus leucas.
14. Capreolus capraca.
15. Mus minutus.
16. Arvicola agrestis.
17. A. glareolus.
18. A. amphibius.
19. Lepus europaeus.

From the above Tables it is clear that the principal distinctions between the Mammal-faunas of England and Scotland are to be found in the aerial order of Chiroptera and among the marine Fissipedes and Cetaceans, while that of Ireland differs in the absence of no less than twelve species of land animals. My friend Professor A. Leith Adams has recently shown that both the recent and the extinct Hibernian Mammals agree with those of Scotland rather than of England, and has given strong reasons for believing that Ireland received this part of its fauna from the south of Scotland, after its separation from Wales and western England. It therefore becomes a point of some interest to compare the fauna of the Scottish Islands with those of the mainland and of Ireland. In such an investigation it is most convenient to restrict our attention to the indigenous terrestrial Mammals, dismissing entirely the Bats, Seals, and Cetaceans, and also the introduced and cosmopolitan Rats and House-Mouse, which may almost be regarded as domestic animals. Taking the Scottish Islands in four principal groups-(I.) the Inner Islands (Skye, Mull, Islay, &c.); (II.) the Outer Hebrides (the Lews, Harris, the Uists, Benbecula, &c.); (III.) Orkney; and (IV.) Shetland-we find the distribution of Mammals, as far as I have been able to ascertain the facts, to be as shown in the following Table, which represents the known range of twenty-four species of land quadrupeds:—

*On the somewhat vexed subject of Irish Mammals I have followed the list given by Professor Leith Adams, on the authority of Mr. A. G. More, Proc. R. Dublin Society, 1878, pp. 40, 41, The complete absence from Ireland of some species, as the Common Shrew Weasel, Harvest Mouse, &c., has been disputed by some writers.

↑ Proc. R. Irish Academy, 2nd Ser., III., pp. 99-100; Proc. R. Dublin Soc., 1878, p. 42.

The facts indicated by the above Table are, at first sight, somewhat contradictory. As Ireland possesses the greatest number of species in common with the mainland of Scotland, it might well be supposed to have been in connection with it up to a later date than even the Inner Islands. On the other hand we have the presence of other forms, as of the Field Vole in the Hebrides, and of the same species with the Water Shrew and Water Vole in Orkney, which are conspicuous by their absence from the Irish fauna. It appears to me, however, that this apparent contradiction may be explained, if we remember the more northern position of the Scottish Islands and the nature of the country lying between them and the south-western source from which our Mammalian fauna was undoubtedly derived.

A consideration of the relative depths of the channels which respectively divide Ireland and the Islands from the mainland of Scotland would lead us to the conclusion that the severance of the former took place first, and that the Orkneys remained longest uninsulated. An upheaval of about 240-270 feet would bring the latter again into communication with Caithness, while it would require a rise of about 300-320 feet to reunite the Hebrides with Skye, and of from 700 to 900 feet to restore land communication between the various parts of south-western Scotland and northeastern Ireland. Nor does the distribution of Mammal life seem to me to contradict such a hypothesis. The absence from the known fossil fauna of Scotland and Ireland of most of the characteristic postpliocene English animals shows that the northward migration of these forms was slow, gradually advancing as the glacial conditions of the northern parts of our islands decreased in intensity. Thus it is not difficult to suppose that the Hedgehog, Ermine, Badger, Squirrel, and Mountain Hare, may have found their way through southern Scotland into Ireland long before they were able to penetrate into the still sub-arctic regions of the Highlands. Subsequently, when the continued depression of the land had isolated Ireland, and the improvement of the climate had continued, the Shrews and Voles may well have found their way northwards along the comparatively genial coasts, before the larger beasts of prey could find a sufficient stock of game. When they reached Orkney, however, they appear to have found it a veritable Ultima Thule, for the absence from Shetland of any land animal (except the half-aquatic Otter) seems to indicate that

those islands were already separated before the arrival of any form of Mammalian life.

Such a hypothesis of the dispersal of English Mammals through Scotland and Ireland appears to me to be the only one which explains the peculiarities of their present distribution, and is likewise in accord with the facts of physical geography. Should it be accepted, the recent and extinct Mammals of Scotland may be arranged in five categories, in the order of the dates of their immigration. This I have attempted to show in the following list, in which the extinct species are marked with an asterisk:— LIST OF EXTINCT AND RECENT SCOTTISH MAMMALS, ARRANGED IN THE

PROBABLE ORDER OF THEIR ARRIVAL FROM THE SOUTHWARD.

I.-Before deposit of boulder-clay :

*1. Elephas primigenius.

:

II. Before separation of Ireland :—

3. Erinaceus europaeus.

4. Sorex minutus.

*5. Canis lupus.
6. C. vulpes.
*(Ursus fossilis.)*
7. Martes sylvestris.
8. Mustela erminea.

9. Meles taxus.

*2. Rangifer tarandus.

*11. Equus cabullus.
*12. Sus scrofa.

*13. Megaceros giganteus.
14. Cervus elaphus.

15. Sciurus vulgaris.

16. Mus sylvestris.
17. Lepus variabilis.
18. L. cuniculus.

I now proceed to the consideration of the details of the distribution of the species, taking first the recent, and second the fossil and extinct forms.

LONDON, 1880.

* Remains of the Cave Bear have not yet been found in Scotland, but its former existence is rendered probable by their presence in Irish deposits.-Cf. A. Leith Adams, loc. cit.