26 THE ENTOMOLOGIST. 
very properly separated from autumnaria, years ago, by Guenée: 
under the name magnaria. 
We have thus the history of a small group of three insects 
to unravel, two of which—JL. autumnaria and E. quercinaria— 
present but little trouble, for one is most certainly derived from 
the other. Which is the original form and which the derived 
matters little. What is of importance is the history of the con- 
nection between the American subsignaria and the European 
quercinaria, which, of the two European forms, seems the most 
primitive. Where have these two forms come into contact? 
And when? We are not here dealing with the usual circum- 
polar or Holarctic distribution of the bulk of insects and plants 
peculiar to both areas, as we have one species restricted to 
Eastern America and the other to West-Central Europe. In 
the case of the majority of Holarctic forms, there is abundant 
evidence that the passage was from Siberia eastward across the 
Behring Straits to America and westward to Europe. And to 
emphasise this, one may point to the closer resemblance of 
forms found in America west of the Rocky Mountains to Pale- 
arctic species than of those found in Eastern America. Thus 
we have here a connection that definitely implies that, when the 
two species originated, either from one another or from a 
common parent, there existed a land-bridge between North 
America and Europe. Granting this, there are three possibili- 
ties open—either the group is American, and passed thence to 
Europe, or it is European, and passed to America; or the third 
course is possible—that it originated in high Arctic latitudes in 
Miocene or Pliocene times, whence it was driven, subsequent to. 
the fall in the average annual temperature of the Northern 
Hemisphere during the latter epoch, one stream passing south- 
ward in America, and the other passing in a similar direction to. 
Europe. The last hypothesis seems the most likely, and in this 
case we have before us two forms which have diverged and 
become genuine species because of long geographical isolation. 
This would place the origin of the group long anterior to the 
advent of the Glacial epoch, so that there is no need to utilise 
the presence of a land-bridge during early Pleistocene times to 
explain the present case, even were it possible for insects so 
constitutionally southern in character as the present pair to 
avail themselves of such a connection. Not that I disbelieve 
the existence of such a passage; I am of opinion that there 
was a constant stream of forms along this bridge during the 
vaunted rigours of the Ice Age, and some of these forms reached 
our islands, and, with others resulting from previous American 
immigration, existed there during the whole of Pleistocene times. 
No other explanation than that of survival will account for the 
presence of Pwcilopsis lapponaria in Scotland, of the North 
American spider, Hypselistes florens, in Cleveland, and of the 
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