Fig. 18.—The Spotted Slug (Geomalacus maculosus).

Much more characteristic of South-western Europe, however, than these land-shells are some of the slugs. The peculiar genus Geomalacus is almost entirely confined to Portugal. One species, which I have had several occasions to refer to in illustration of the term "discontinuous distribution," ranges far beyond the confines of that country. This is Geomalacus maculosus ([Fig. 18]), first discovered in the south-west of Ireland, and more recently also in Portugal. Although careful search has been made for it in other parts of the British Islands, this slug has only been found in the portion of Ireland just indicated. Within the last few years I have taken it, up to a height of over a thousand feet, on the promontory north of the Kenmare River, also from sea-level up to a considerable height near Glengariff, and more recently Messrs. Praeger and Welch discovered it in abundance near the town of Kenmare. But beyond this rather circumscribed area in the counties of Cork and Kerry it does not occur (vide [Fig. 19]). Several Portuguese species of this interesting genus have since been added to science by Dr. Simroth and others. Dr. Simroth, too, has promulgated the view that the genus Arion—to which our common brown garden slug belongs—is of Lusitanian origin. Indeed, the number of species of Arion diminishes as we leave that province, though one extends beyond the borders of Europe into Siberia. The same number of species, viz. five, occur in Germany and in England. Testacella—a slug-like mollusc—which lives underground on earthworms, and of which genus three species, viz. T. maugei, T. haliotidea, T. scutulum, are known to inhabit the British Islands, is another Lusitanian animal. All the species are confined to Western Europe and North Africa; they do not even reach Germany or Switzerland.

Fig. 19.—Map of the British Islands on which the geographical distribution of Geomalacus maculosus is indicated in black.

I have had occasion to mention once before an extremely interesting genus of blind Woodlouse, viz., Platyarthrus. Like Testacella, it lives underground, and also resembles it in its general range. Its distribution is therefore of particular interest. It is difficult to conceive that Platyarthrus, from its peculiar mode of life could have crossed any formidable barrier, such as even a narrow straits of sea. Its occurrence in Spain and North Africa indicates, therefore, that the Straits of Gibraltar did not exist at the time when it undertook the migration southward, just as the English Channel and the Irish Sea could not have been there when it wandered to England and Ireland. The species which occurs in the south of England has a wide range in Ireland, and reaches in Scotland its most northern European limit of distribution. Platyarthrus is only one of the Lusitanian genera of woodlice. In Ireland—chiefly on the west coast—we also find a brilliantly coloured Woodlouse, which is absent from Great Britain, viz. Metoponorthus cingendus. It reappears again on the Continent in the south of France. Its range is therefore suggestive of a Lusitanian origin; and indeed, when we examine the general distribution of the genus Metoponorthus, we find that out of the forty-four known species, fully one-half are confined to Western Europe and North Africa.

My friend and colleague, Mr. Carpenter, informs me that among the Irish Spiders he is acquainted with, the following are to be looked upon as Lusitanian species:—

Of the Coleoptera, the genera Trichis, Glycia, and Singilis, all belonging to the Running Beetles (Carabidæ), are almost confined to the Spanish peninsula.