6 [Proc. B.N.F.C., 



After this high level period we may suppose that the land 

 gradually sank. The southern fauna could now no longer pass 

 into Ireland except by a very circuitous route by way of Scotland, 

 because the large lake or bay almost entirely barred the way. A 

 steadily advancing submergence of the land would have slowly 

 narrowed the only land-bridge to Ireland still available in 

 the north. At this stage the Irish Hare, which has its nearest 

 relatives in Scotland, Scandinavia, and Greenland, may have 

 found its way to Ireland. The great herds of Reindeer, and also 

 the Lemmings and the Arctic Fox may all have come into the 

 country at that time. We have no means of ascertaining precisely 

 at which particular stage of geological history this invasion took 

 place, but we possess some evidence that the course of events was 

 somewhat like what I have just described. The evidence I have 

 in my mind is based on the geographical distribution of certain 

 fresh-water Fishes. In Lough Neagh, close to Belfast — in the 

 largest lake in the British Islands — there lives a Fish somewhat 

 like a Herring in shape, locally known as the Pollan. It is not 

 peculiar to Lough Neagh, for it has also been observed in Lough 

 Krne, Lough Derg, and Lough Ree — all situated rather more 

 westward. But this Pollan is not known beyond the confines of 

 Ireland. It feeds largely on a fresh-water Shrimp, My sis relict a, 

 which is likewise unknown in Great Britain. The latter only 

 inhabits a few lakes on the Continent which are supposed to 

 have been covered by the sea within recent geological times, and 

 it is closely related to a marine Shrimp which lives in the Arctic 

 Ocean. How are we to explain the occurrence of the Pollan in 

 Lough Neagh and the other lakes referred to ? Let us examine 

 for this purpose the near relations of this remarkable Fish. The 

 nearest relations of the Pollan are found in the Lake District of 

 Fngland, in a lake in the south-west of Scotland, and in a small 

 tarn in Wales. All the Pollan-like fish in the British Islands in 

 fact live within a small circular area, although the species are now 

 separated from one another by the Irish Sea. The three or four 



