Distribution of Moths of the Sub-family Bistonine. 356 
once more when the climate became unfavourable 01 the ground 
submerged. The former supposition is the least likely, for 
then we should naturally expect to find European colonies of 
the insec_, and this we fail to ao. Let us observe, however, 
that this view means that, in the case of other insects which 
transgressed the point at which Miocene and Pliocene European 
and Asiatic continents were severed, we do find colonies so 
isolated. Such, indeed, is the case in very many insects as 
well as in other groups. Typical instances in the Lepidoptera 
are Ennomos antumnaria, limited to Europe and Eastern Asia, 
Deileptenia abietaria to Central Europe and Japan, Hybernia 
leucophearia to Central Europe, the Amur district and Japan. 
From these consideracions, we conclude either that Nvyssv- 
odes originated in its present habitats or more probably, when 
due attention is given to the Boreal nature of the group, at 
points north of them, in Miocene times. This view is confirmed 
by the fact that the tines of advance of all the primitive members 
of the Brstoninae, and of the whole Boarmiad family, as well 
as those of the carly groups, e.g., the Attacid genus Ac/zas, 
radiate from the centres. And many of these insects are 
demonstrably of Miocene origin, for their present habitats 
coincide with those of many Miocene relicts, like the Sensitive 
Fern (Onoclea sensibilis), the former existence of which in high 
Arctic latitudes, is proved by abundant fossil remains in 
mid-Tertiary strata. Adopting, then, the conclusion that 
Nyssiodes came into being in the ancient Asiatic continent to 
the north of Wrangel Island, we see tnat it must have spread 
westward but, most certainly, not via Western Asia, for over 
that area rolled a mighty inland sea. Most likely, the advance 
was dve west or even north-west. Reaching the northern 
European area, it yielded us the genera Poecilopsis and Nyssva 
very early. Almost immediately, local subsidences of the land 
cut it off frem its derivatives and drove it gradually south 
eastward over the huge peninsula which then, and even into 
Pleistocene* times, stretched north wescward from what is now 
Cape Chelyuskin and the New Siberian Islands. Gaining the 
valley of the River Lena, and utilising it and the foothills of 
the then relatively lower Yablonoi Mountains as a causeway, 
it continued its slow and methodical retreat, finally obtaining 
access to the headwaters of the River Amur at some place not 
far from the pass used by the Trans-Siberian railway. Here, 
safety was attained, and now it was not a question of retreat, 
but of organising new ground. At this period, the whole of 
its present northern stations, as well as the shores of the Yellow 
Sea were invaded, and from Corea, across the low isthmus 
which connected that country to Japan, the latter district was 


* As the fossiliferous deposits of the islands show. 
1016 Wout, . 
