ScHARFF — Origin of Irish Land and Freshwater Fauna. 483 



Britain chiefly the southern and western counties. There are, on the 

 other hand, a number of species in England which inhabit mainly the 

 south-eastern counties, but some of them have spread over most of 

 England and parts of Scotland. Not one of them, however, has reached 

 Ireland. 



We may look upon the western British land and freshwater 

 moUusca as the earlier immigrants which were able to reach Ireland 

 by means of the land connection during Pliocene times. The eastern 

 species, on the other hand, came probably along with the Siberian 

 mammals during Pleistocene times, and, like them, they were not able 

 to reach Ireland, as the southern connectionbetweenit and Ireland had 

 already been severed. 



Dr. "Wallace^ believes that a submersion of the British Islands 

 during the latter part of the Glacial Period destroyed the greater part 

 of the life of our country, and subsequently, that is to say quite 

 recently, an elevation and reunion -^'ith the continent took place. He 

 further remarks that "the depth of the Irish Sea being somewhat 

 greater than that of the German Ocean, the connecting land would 

 there probably be of small extent and of less duration, thus offering an 

 additional barrier to migration, whence has arisen the comparative 

 zoological poverty of Ireland." But although we have evidence in 

 Ireland of a submersion or of a marine transgression, we have none of 

 an extinction of the native fauna and subsequent immigration. If a 

 land connection existed which allowed such slowly-spreading specie 

 as the badger to cross to Ireland, why did the roebuck, the English 

 hare, the wild cat, and others find it impossible to do so, when they are 

 evidently all supposed to have come to England about the same time ? 

 The slowly-moving moUusca would have had but a poor chance to 

 reach Ireland when the connecting land was not of sufficient duration 

 to allow all the English mammals and reptiles to cross over. But the 

 Irish molluscan fauna is not an impoverished one, the number of 

 species almost equaling that of England. 



As I mentioned before, the Irish freshwater fishes also throw some 

 light on the extent of the land connection. A few of the species may 

 have originated in this country, but most of them have no doubt 

 migrated from Great Britain. The peculiar range of some species 

 seems to indicate that the present area of the Irish Sea was to a large 

 extent occupied by a freshwater lake. 



Let us take for example the pollan ( Coregonus pollan) a freshwater 



1 Wallace, A. K., Island Life, p. 339, 2nd ed. 1892. 



2 K 2 



