IHia-lSiq.J r 7 



The problems connected with this interesting Woodlouse lead 

 us to others, namely, the extent of the land-connection between 

 Great Britain and Ireland. Quite a number of instances of 

 distribution tend to show that an invasion of a southern army of 

 all sorts of creatures followed closely along the shores of the 

 ancient Atlantic when Ireland was part of the Continent. Most 

 of these southern animals have long since become extinct in 

 Ireland. Certain numbers, however, still remain with us as a 

 standing testimony of these ancient geographical conditions. 



Thus another little Woodlouse, Trichoniscus vivi'dus, dis- 

 tinguished from the last by its reddish colour, its great activity 

 and independent habitat, occurs in quite an isolated district in 

 the south of Ireland, and is found nowhere else in the British 

 Islands. It does not even occur in northern France or Germany. 

 We have to travel as far south as the Pyrenees before we again 

 meet with it. It might be urged, of course, that this is one of 

 those instances of accidental dispersal, that this species has been 

 swept by winds across the sea from its usual habitat or even by 

 ocean currents. If this were an isolated occurrence we might, 

 perhaps, look favourably on such a theory, unlikely as it appears, 

 but as I remarked it is not the only instance of the kind. There 

 are a number of others. 



A well-known example is furnished by the famous Spotted 

 Slug, Geomalacus maculosus. Here again we have an instance of 

 discontinuous distribution which is suggestive of the Slug's ancient 

 origin. Anatomically also it exhibits primitive features which 

 lead us to the same belief. Its occurrence in Ireland evidently 

 represents a survival from remote, certainly pre-Glacial, times. 

 It is only found in Ireland, Spain, and Portugal. In the latter 

 country there are other species of the same genus, but only one has 

 gone further afield to colonise northern Europe. In doing so it 

 has probably kept closely to the shores of the Atlantic Ocean, and 

 we may assume that subsequently it became extinct in the inter- 

 mediate area between its southern station in Spain and the 



