Altogether--and this was strongly urged by Edward Forbes--the Lusitanian element is the oldest of the components of our fauna, and it must have poured into the British Islands for many geological periods almost without cessation. The same author, in his classic essay, refers especially to the Lusitanian flora, two prominent members of which are the British plants, _Arbutus unedo_ (Fig. 20, p. 305) and _Euphorbia hiberna_ (Fig. 21, p. 306). The former has a wide range in the Mediterranean region, and occurs in the British Islands only in the south-west of Ireland. The Spurge, on the other hand, is also found in the south-west of England, besides Ireland and Southern Europe. SUMMARY OF CHAPTER VII. The term "Lusitanian" is in this chapter employed in the wide sense, as indicating the South-west of Europe and North-western Africa. From this centre, and probably also from a now sunken land which lay to the west of it, issued a fauna and flora of which we have abundant evidence in our own islands, especially in Ireland. Edward Forbes held that the Lusitanian element of the British flora was of miocene age, and that it survived the Glacial period in this country. At the time when the Straits of Gibraltar did not exist, and when there was free land communication between Asia Minor, Greece, and Tunis, many Oriental species migrated westward by this ancient Mediterranean route as far as Spain. They would then have invaded the more central parts of Europe from the south-west, without however being of Lusitanian origin. Of the true Lusitanian mammals a typical example is the Rabbit. Then we have a few birds and several interesting reptiles and amphibians. The genus to which the Brimstone Butterfly belongs is also of south-western origin. A number of Mollusca are mentioned which from their range likewise indicate a Lusitanian origin. Most of our British Slugs and many of our larger Snails belong to this group. All these are merely a small remnant of what we received from South-western Europe during the Miocene and Pliocene Epochs. But they spread into many parts of Europe, and a few even crossed into Asia. The antiquity of the Lusitanian element in our fauna is especially indicated by the frequent recurrence of "discontinuous distribution" among the species belonging to that section. CHAPTER VIII. THE ALPINE FAUNA.