484 Proceedings of the Royal Irish Academy. 



fish found cliiefly in Lough. Neagh. It occurs also, but less commonly, 

 in Lough Erne, Lough Derg, and Lough Corrib, and is quite peculiar to 

 Ireland. Two allied species of Coregonus live in the South of Scot- 

 land, the North of England, and in Wales, viz. C. vandesius and C, 

 clupeoides, the former being very closely related to the Irish pollan. 



Coregonus vandesius^ known as the vendace in England, was 

 formerly believed to be peculiar to some very small lakes situated in 

 the neighbourhood of Lochmaben in Dumfrieshire, in the south-west 

 of Scotland. More recently, however, it has also been obtained in 

 Derwentwater and Bassenthwaite water in Cumberland. Beyond this 

 very restricted range, the vendace is unknown in any other locality in 

 the British Islands. 



Coregomis clupeoides, often called the freshwater herring or 

 " gwyniad," has a wider distribution than either of the two species 

 just mentioned, though like them its range is confined to the British 

 Islands. In Scotland it has been obtained in the south-west in Loch 

 Lomond. In England it is only known from the lake districts of 

 Cumberland, Westmoreland, and Lancashire. It occurs chiefly in the 

 UUswater and Haweswater, but it has also been taken in the Ked 

 Tarn, a small mountain lake, upwards of 2600 feet above sea-level, 

 near the summit of Helvellyn. In Wales it has only been found in the 

 Bala Lake. The three species are therefore confined to some lakes of 

 northern and western Ireland, southern Scotland, northern England 

 and Wales, almost all of which lakes communicate directly with the 

 Irish Sea. The two most closely related species, viz. C. vandesius and 

 C. pollan have a more restricted range than the third species C. 

 clupeoides. Its range extends as far south as Wales, but it should be 

 noted that it is not found in any of the Welsh lakes which do not 

 communicate directly with the central portion of the Irish Sea. 



The distribution, indeed, in the British Islands of these three 

 species of freshwater fish is so very peculiar that one cannot help 

 being struck by it, and under the present conditions of land and water 

 it seems to me diflicult to conceive how it could have come about. 

 Once, however, we admit that in later tertiary times there must have 

 existed a land communication between Great Britain and Ireland, the 

 cause of the local range of these species becomes more evident. It may 

 be observed that we need not here bring to aid an elevation of vast 

 tracts of country, but merely suppose that the mountain ranges of 

 northern and south-eastern Ireland, i.e. those of Antrim and Wicklow, 

 were still continuous — as they must have been at a more remote 

 period — with those on the opposite side of the Channel, and that the 



