1912. Browne. — Aquatic Coleoptera of S.E. Ireland. 15 



others, as for instance : — Haliplus cinereus, Aubfe ; Cnemi- 

 dotus imprcssus, F ; Laccophilus variegatus, Germ. ; 

 Hydrovatus clypealis, Sharp ; Agabus hrunneus, F., etc. Only 

 the first two species occur in Ireland, the rest being 

 found in the Britannic area only in the extreme south and 

 south-east of England. 



In other groups of the fauna and in the flora there are 

 species whose present " metropolis " is in the south and 

 south-west of Europe which within the Britannic area occur 

 only in the extreme south and south-east. The Dartford 

 Warbler among birds, a native of Spain, Provence, Italy, &c., 

 is found only in the eastern counties of England. Suaeda 

 fruticosa, Forsk, Frankenia laevis, L., Salicornia radicans, 

 L., &c., are examples of " Lusitanian " plants confined to 

 or centered in the southern and south-eastern counties ; 

 other examples occur among the land-beetles, butterflies, 

 land and fresh-water shells, and no doubt in other groups. 



Now these southern English species seem to be merely 

 another and later group of the general fauna and flora of 

 the British Islands, species which, having got a precarious 

 footing are struggling to extend their range under less suitable 

 climatic conditions than they enjoy in southern Europe, but 

 under conditions which, we may assume, will become more 

 suitable in the course of ages — so long as the polar ice-cap 

 continues to shrink ! 



I make no attempt to discuss the question of the means by 

 which these species have reached our area, whether by 

 crossing a land-bridge or through chance dispersal by winds 

 and ocean currents. There seems everv reason to believe 

 that their in-coming has been since the climax of the 

 Glacial period, and that we can still, to some extent, re- 

 cognise earlier and later arrivals. 



If land-bridges are essential for the expansion to our area 

 of the continental fauna and flora, then, no doubt, the 

 British Isles will develop, in the course of time, a peculiar 

 type markedly different from that found on the mainland of 

 Europe ; if, on the other hand, chance dispersal by winds 

 and ocean currents is an important factor in the peopling of 

 islands, then only a few of the animal groups are completely 



