i902. Kank. — Irish Natural History. 59 



there any other hypothesis which would bring them into line 

 with other Mysis habitats ? 



For if we are forced to conclude our Mysis to be an 

 extremely ancient inhabitant of fresh water, in spite of its 

 close resemblance to M. oculata^ we must provide a theory for 

 its introduction with our other fresh-water fauna, overland 

 from lake to lake by some Continental land connection. 

 Let us see, therefore, what evidence is afforded by the other 

 contents of these lakes. Firstly, we are struck by the fact 

 that the Pollan, or " Fresh-water Herring," inhabits both 

 Loughs Erne and Neagh. The genus Coregonus, or '' Charr," 

 to which this species belongs, is characterised as a group by 

 its alpine habitats. Various species are known to inhabit 

 lakes in the North of Ireland and Great Britain, Scandinavia, 

 North Germany, Finland and Russia, as well as North America. 

 We may therefore infer that part of the fauna of Loughs 

 Neagh and Erne came from northern latitudes, or at least 

 from alpine regions. Now, in my examinations of Lough 

 Erne I happened upon a minute crustacean, slides of which 

 have been exhibited under the microscope to this Club, which 

 was identified by Professor Lilljeborg, of Upsala, as Bosmifia 

 mixta V. humilis, and is new to the British Islands, and another 

 closely allied, Bosmina coregoni. The former, so far as is 

 known, only occurs in Scandinavia, and the Alps of Central 

 Europe. I took it myself this year in a lake in the Bavarian 

 highlands. The latter has one Scotch habitat. Loch Maben, 

 where also is a species of Corego?ms or Charr, the Vendace, 

 also confined to that Dumfriesshire lake and the neighbouring 

 waters, whose chief food is said to consist oi Bosnmia coregoni. 



Here, again, we have an indication that some of the 

 organisms of Lough Erne may have passed over to us from 

 Scotland before Ireland was insulated from it. Further, I 

 found another species of Entomostracan of a much larger size 

 inhabiting the open waters of the lake, which has not yet 

 been detected in any British waters ; though an allied species 

 is known in Irish waters, certain lakes of Scotland and the 

 north of England, as well as Central Europe. Its name is 

 Bythotrephes cederstromii, and it appears to be subarctic in 

 its European distribution, not yet having been recorded from 

 Germany. Here, then, we have three fresh-water Scandinavian 



