476 Proceedings of the Royal Irish Academy. 



Continental Europe, -u-Hlst the Eriocaulon {Eriocaidon septanguJare) 

 occurs on the north and west coasts of Ireland, and on some of the 

 islands off the west coast of Scotland.^ All these species of plants, as 

 I mentioned, are commonly distributed in IS'orth America. 



Among animals no doubt a good many similar examples occur, 

 though probably few of such very restricted range. I have already 

 referred to the common stickleback ( G^«rs#ero«^eM« aculeatus),Mv\a.ch.\s, 

 found in Greenland, J^orth America, and Europe, but is quite absent 

 from Asia, though an allied species inhabits Kamtchatka. The nine- 

 spiued stickleback {Gasterosteiis pungitius) is confined to Western 

 Europe and Xorth America, whilst an allied species {G. sinensis) lives 

 in China, and has probably penetrated there from the Xew "^orld 

 across the old Behring Straits land-connexion. Europe has many 

 land and freshwater mollusca in common with Xorth America, also 

 many butterflies, moths and beetles, but the Asiatic distribution of the 

 insects generally is not sufficiently well known to permit us to 

 definitely assert their absence in Asia. The freshwater sponges of 

 Central and Northern Europe have been fairly well worked, and it 

 must be sui-prising to many to hear that we possess in Ireland three 

 Korth American species which have not hitherto been discovered 

 elsewhere in Europe or Asia. These three, viz. Ephjdatia craterifar- 

 mis, Heteromeyenia Ryderi, and Tubella pennsylvanica, were recently 

 described by Dr. Hanitsch (37, p. 125) in the "Irish ]S'aturalist.'* 

 They all inhabit lakes on the west coast of Ireland. 



The spider {Porrhomma rnyops), which was discovered by Mr. 

 Carpenter in Mitchelstown Cave in Ireland (16 c), is, as he remarks, 

 probably identical with a Noilh American species, and in Europe is 

 confined to the west. I think all these instances of a close relation- 

 ship between the European — and chiefly Western European — and the 

 iNorth American fauna and flora are to be explained by a former land- 

 connexion between these two continents in the manner described 

 on p. 462 (see map, p. 461). 



Many eminent geologists have held that the Glacial Period was 

 produced by a rising of the land in the Arctic regions. Sir Charles 

 Lyell was an adherent to that theory. Professor Dana suggested that 

 an elevation of the Arctic land sufficient to exclude the Gulf Stream, 

 might have been the source of cold during the Glacial Period (20, p. 



' Two additional Ifortli American plants, viz. Juncus tenuis and Polygonnm 

 sagxtlifolium, have recently been discovered in the west of Ireland by Dr. Scully, 

 and one {Sisyrinchium californicum) by Mr. Marshall on the coast of Wexford 

 ("Irish Nat.," 1896). 



