Derivation of britIsh coleoptera. 173 



west of Ireland. The characteristics of this fauna are 

 very enigmatical ; some species occur only in England, 

 some few only in Ireland, and some are common to both. 

 From Scotland the group is quite absent. 



Now, from what is now known of the distribution of the 

 British Coleoptera, we could go through the entire list 

 and allocate, with more or less precision, nearly every 

 species to one or other of these groups. And the questions 

 suggested by so doing would be something like these — 

 Do such groups really represent separate waves or streams 

 of immigration ? Are they of different age, and if so, in 

 what relation as regards time do they stand to one another? 

 Did separate areas originate them, or only separate 

 epochs ? 



Now, to answer, as some have done, firstly, that all life 

 was destroyed over these islands either by the severity of 

 glacial conditions or by submergence, and secondly, that 

 during the slow subsequent amelioration of the climate 

 these streams of migration arrived in the order in which 

 I have mentioned them, and that sometime during this 

 process, but subsequent to the dispersal of the first group, 

 the connection between Great Britain and Ireland broke 

 down, may appear a simple explanation, but however well 

 it may fit some of the fauna or flora, certainly it does 

 not exhaustively explain all the facts of their distribu- 

 tion. It does not explain the vestiges of a distinctively 

 Iberian fauna, still less those of a North American one in 

 Ireland. 



To make this clearer, let us consider these groups a 

 little more in detail. Our first or Celtic division's maxi- 

 mum development is in the north, from Orkney and 

 Shetland, over all the Highlands and all the western isles 

 of Scotland, and all the mountains north and west of Ireland 



