Distribution of Moths of the Sub-Famuly Bistoninae. 165 
vachelae (Hulst), is a specialised form, derived from Lycia, but 
not closely related thereto, and having three distinct congeners, 
Poecilopsis pomonaria (Hb.) P. lapponaria (B.) and P. tsabellae 
(Harr.) in Europe. Two choices are then left as the home of the 
genus. If the present geographical distribution is to be the 
standpoint from which to decide then, from the occurrence of 
Lycia hirtarva in Algiers and in the Abruzzi, and from the great 
development of the whole section in Europe, with the presence 
of the third species Amorphogynia necessaria (Z.) in Asia Minor, 
we seem irresistibly forced to the conclusion that the group is 
European. Ifthe great number of distinct species occurring in, 
or near, a given area can be used, as seems logical, to determine 
the point of origin of the group, then the genus Lycza and its 
satellites originated in Pliocene or earlier times in the Northern 
and more mountainous portions of the Balkan Peninsula. This 
conclusion, however, takes no account of climatic oscillations in 
the past and it seems clear that all that has been proved, is that 
the Balkan area has once been a centre of dispersal of the various 
genera comprised in the group. From phylogenetical grounds, 
and from the Boreal (as distinct from Arctic) nature of the group, 
in addition to a consideration of the paucity of its representatives 
in America, their true home was in all probability in the old 
Arctic continent at some point much nearer Europe than Amer- 
ica, or in areas from which the various species, except for outliers 
in the Arctic Archipelago, could more readily retreat, when the 
southward march began, to Europe. From this centre of origin, 
the single species, which then represented L. ursaria eral HA 
hirtaria, worked its way westward and south eastward, but, as it 
marched, climatic conditions were deteriorating in its northern 
home and the species was forced slowly southward, part pressing 
south to our continent and the remainder passing to America. 
Coincident with, or just subsequent to it, in late Pliocene times, 
extensive subsidences occurred both in the North Atlantic and in 
the more easterly portions of “ Arctica ” and finally, the Ameri- 
can branch of Lycia pal@ohirtaria (if one may coin a name for 
the theoretical original species) was effectually severed from 
that invading the European area. 
Conditions, however, did not ameliorate ; in both continents, 
matters moved inexorably to their climax in the Glacial Period 
and further geographical divergence of the two contingents oc- 
curred until, in America, the species which had never penetr ated 
far to the west of Greenland and Labrador, was wedged between 
the Appalachian Mountain system and the coast, any possible 
movement north of the Great Lakes and thence southward, 
being squashed by the early development of the Keewatin Ice 
Sheet. In this home of refuge, this division slowly developed in 
Pleistocene times into Lycia ursaria. Similarly, the European 
migratory stream would pass southward but, undeterred by the 
1916 May 1. 
