1897] THE PROBLEMS OF BRITISH FAUNA 383 
archipelago ; central and southern Wales an island; while the south 
and midlands of England were joined to France by an isthmus. The 
sea covered nearly the whole of eastern England; and stretched across 
north Wales, and over eastern and central Ireland. Zoological 
evidence for this transgression of the northern sea over eastern 
Ireland is found in the distribution of the arctic marine crustacean 
Mysis relicta, which forms part of the ‘relic fauna’ not only of the 
Swedish lakes, but also of Lough Neagh. The sea separating 
southern and central England from Scotland, as well as from 
Ireland, checked the northern as well as the western progress of 
the ‘ Siberian’ mammals. None of these animals are found fossil in 
Scottish Pleistocene deposits, though the recession of the glacial sea 
has in recent times opened a way to the north, of which the sur- 
viving species have availed themselves. But meanwhile the isthmus 
between Scotland and Ireland had become broken through. 
Having thus put forward a summary of Dr Scharff’s views as to 
the ages and paths of migration of the various sections of the British 
fauna, I venture, with some diffidence, to offer a few observations 
and suggestions. I entirely agree with Dr Scharff in considering the 
South-western as the oldest section of our fauna, and I have no 
doubt that it came into our area long before the Glacial Period. 
The North American plants and animals seem to me to be more 
ancient than Dr Scharff is inclined to admit. He classes them 
with the general Northern fauna, but I believe that their very 
restricted and discontinuous ranges along the extreme western margin 
of Europe mark them as decidedly older than those northern animals 
and plants which have a general circumpolar distribution. 
Study of the distribution of British insects shows that there is a 
Southern fauna! distinct from the South-western, in that its members 
occur generally in southern Britain, as well as in Ireland and 
western Britain, and have a wide continental range. It is clearly 
newer than the South-western fauna, yet the fact that it is confined 
in Ireland to the south and west suggests that it is of considerable 
geological age. Along the west coast of Ireland the insects of this 
group often range some distance to the north, and their general 
British distribution around the west and south of our islands renders 
it likely that they held the country west and south of the area where 
the Glacial deposits were being formed, and have, since the retroces- 
sion of the agent which produced those deposits, been unable to 
spread far eastwards in Ireland or northwards in Great Britain. This 
fauna may safely be regarded as comparable to Forbes’ Norman and 
Kentish floras, and older than the Arctic fauna. As yet, however, 
I am not prepared to accept so great an antiquity for the bulk of 
1 Examples of this group are the ground-beetles, Carabus cancellatus and Panagaeus 
cruz-major, the butterflies Gonepteryx rhamni, and Leptida sinapis, and themoths Zeuzera 
pyrina and Stauropus fagi. 
