ScHARFF — On the Origin of the European Fauna. 481 



bution, must be looked upon as an ancient one. There are about three or 

 four Portuguese species, one of which, Geomalacus macuhsus, migrated 

 as far north as Ireland, and has survived there, though it appears tohave 

 become extinct in the intermediate tracts of country, which it, no doubt, 

 once inhabited. Testacella is another typically Western European genus, 

 and it is of exceptional interest from a distributional point of view, 

 owing to its subterranean habits. There are about a dozen species, of 

 which three have reached Ireland, while none occur in Central or 

 Eastern Europe. The close relationship between the South-west 

 European molluscan fauna and that of Ireland is altogether very 

 striking, but, as I have had occasion to mention, there is no need of 

 invoking a direct former land-connexion between that country and 

 Spain, as has been done by the late Prof. E. Forbes, in his classic 

 memoir, in attempting to trace the origin of the Irish flora (33«). An 

 indirect connexion between Ireland, the west of England, andErance, 

 which has so often been suggested, is sufficient to explain all the 

 minutiae of distribution. In every group of Invertebrates, the Irish 

 fauna exhibits strong affinities with France and the Spanish peninsula, 

 certainly much more so than with Germany and Eastern Europe. 

 But in all these cases it might be urged (by those naturalists, 

 especially, who adhere to the view that everything is explainable by 

 accidental introduction) that Ireland, being within easy reach of the 

 Spanish or French coasts, many of these forms were either carried by 

 migratory birds or with floating wood, etc. I will instance, therefore, 

 a case which, I think, cannot j)ossibly be attributed to any of these 

 agencies, viz. that of the blind woodlouse {Platyarthrus hoffmmiseggii). 

 The genus of Platyarthrus is confined to Western Europe and 

 jSTorthern Africa, and it has formed such a close alliance with ants, 

 that it never is found outside an ant's nest. One species inhabits 

 Scotland, Ireland, the south of England, and Western Continental 

 Europe, and is always found in the nest of the common red ant. As 

 the nests of these ants are almost invariably under stones, and ihe 

 woodlouse itself is hidden in the subterranean burrows of its host, the 

 fact of the occurrence of this species in Ireland admits of but one 

 explanation, which is that it migrated to that country when the latter 

 still formed the northern part of France. As the migration of these 

 lowly animals progresses exceedingly slowly, this land-connexion 

 must have been one of very considerable duration. How long it 

 lasted, and especially during what geological epoch it existed, will be 

 considered later on. Meanwhile, we must return to the subject of 

 the southern migration. 



