29 18 Proceedings of the Royal Irish Academy. 



temperature may be of some importance in suiting these " westerns " better 

 than it suits the bulk of the fauna and flora. The tendency of mountain 

 species to descend on the coasts has long been known and the mountain 

 climate for a large part of the fauna and for the flora resembles the coast 

 climate in its limited annual range of temperature. The summer heat in 

 mountain districts is not excessive and direct insolation is controlled by the 

 prevalence of clouds, while in the winter the smaller animals and the plants 

 are protected from excessive cold by a covering of snow and, in the ease of 

 water species, the temperature will, of course, nut fall below freezing-point. 



That our " arctics " can however withstand greater variations of tempera- 

 ture is seen from the fact that some of them still survive in other parts of 

 our islands. For instance, Caelambus v-lineatus and ix-lineatus and Agabus 

 congener are found in Hampshire, and the latter has also occurred in West 

 Kent and Berkshire, in situations approaching sea- level. The first-mentioned 

 species also occurs not only all over Ireland but is the commonest species in 

 some of the hot mill-dams in the neighbourhood of Belfast, where the 

 temperature runs as high as 25° C (77° F). In the ease of plants many of 

 them live well in our gardens in all parts of the country provided they are 

 protected from excessive cold during the winter. 



The localisation of these " arctics " seems therefore to be due chiefly to 

 the fact that the conditions which they endure in mountain districts and 

 on our western coasts are less inconvenient to them than to the bulk of the 

 fauna and flora and their position is therefore due to competition. They are 

 really species which have been squeezed out of the better places by stronger 

 competitors and, in our latitudes, they are now penned into the only situa- 

 tions where they have an advantage over those species which happen to 

 require a greater annual range of temperature for their existence. 



The so-called " Lusitanians " may be a similar group to the arctics, but 

 requiring rather more warmth than these. They may represent a few sur- 

 vivors of the pre- Glacial temperate group which had been driven out of the 

 better places and owe their survival in Ireland to the fact that they had been 

 penned in along the western coast. 



On the other hand, if the squeezing-out process took place in pre-Glacial 

 times it may equally well be taking place now, so that genuine pre-Glacials 

 may, in the west, be mixed with post-Glaeials. In another paper ("The 

 Aquatic Coleoptera of the south-east of Ireland," Irish Nat., January, 1912) 

 I have suggested that those water-beetles which show a south-eastern Irish 

 distribution are the latest arrivals in the country. The range of these species 

 is almost entirely confined to the coastal counties, but several have spread 

 westward as far as Kerry and one or two even as far as Clare. Peloliua 



