I4 The Irish Nahwalist. January 



That two species such as H. ohlongus with a holarctic 

 range and A. conspersus with a w^arm -temperate range 

 should be both locahsed in the east of Ireland suggests that 

 possibly both have reached this country comparatively 

 recently. If such a species as the former existed in the 

 British Islands during the Glacial period on the very fringe 

 of the ice -sheet, why has it been, as it were, left so far 

 behind when the ice retreated ? On the Continent and in 

 America it has succeeded in reaching much higher latitudes. 

 On the other hand it seems most improbable that a warm- 

 temperate species such as A. conspersus could have survived 

 at all in close proximity to the ice, when the flora of Devon 

 consisted of the arctic Dwarf Birch and arctic mosses even 

 at sea-level, and when the English Channel was a cold ice- 

 ridden sea.^ 



This suggests therefore that the group has reached Ireland 

 since the Glacial period, and incidentally this carries with 

 it the suggestion that the bulk of the " Irish " type is also 

 post-Glacial. The larger question I will leave to a future 

 occasion, but on the post-Glacial arrival of the south- 

 eastern species something more may be said. 



The gradual retreat of the ice -sheet, and the northward 

 extension of the temperate climate probably produced a 

 general northward movement of the fauna and flora. With 

 regard to the Britannic area the movement may well have 

 been from the east and the south-east, and the first post- 

 Glacial arrivals must have been species capable of standing 

 cold temperate conditions. The species moving westward 

 would have tended to dominate those moving from the 

 south-east, as they would have been better suited to the 

 climate, but as the ice-sheet retreated and these cold- 

 temperate species moved northward on the newly exposed 

 ground, more southern species would reach our latitudes and 

 it would be later still before any warm -temperate species 

 could extend their range limit to our islands. 



Now, A. conspersus and P. tardus are two of the warm- 

 temperate water-beetles of the British Islands. There are 



1 Clement Reid : The relation of the present Plant Population of 

 the British Isles to the Glacial Period. Section K., British 

 Association, Portsmouth, 191 1, and Irish Naturalist, vol. xx., p. 

 201. 



