276 Distribution of Moths of the Sub-family Bistoninae. 
Larix sibirica.—N. E. Russia, Ural Mountains, Siberia to 
Kamschatka. 
Larix dahurica,—Siberia extending far past the Arctic circle. 
Larix griffithi.cNepaul, Bhotan, Sikkim. 
Lanx leptolepis.—Japan. 
Larix lyalliimRocky Mountains. 
Larix americana with its forms pendula and microcarpa.— 
Canada and United States. 
Larix occidentalis.—N. W. America. 
From the above details it will be seen that, if we accept 
the usual test of taking the area in which a genus reaches its 
greatest development as its centre of origin, then the genus 
Larix has spread from some point in South-central or South- 
eastern Siberia. This is confirmed by the fact that the 
European larch is only a form of a widespread polymorphic 
species having local races in the form of L. stbivica, L. occi- 
dentalis and L.decidua from which we see that it extends from 
East-central Europe to N. W. America. But, let it be noted, 
it is of such recent occurrence in Europe that it has not had 
time to spread, as a wild plant, further than the Central 
European Mountains, failing to reach Scandinavia, which, 
for an Alpine plant of Eastern origin, is a very remarkable 
thing. Further, its only occurrence fossil is in certain Inter- 
glacial deposits at Lauenburg in Prussian Saxony and, if 
that were the maximum western range then, it would be 
very seriously limited before the close of the Ice Age. 
Hence, we must conclude that in all probability the larch 
permanently occupied the areas it now holds in Post-glacial 
times. Add to this the fact that P. isabellae is not found 
accompanying the larch either in Russia or in Asia and we 
must draw the conclusion that P. tsabellae has arisen from 
P. pomonaria since the larch reached Silesia, Austro-Hungary 
and Switzerland and, consequently, is of Post-glacial origin. 
This is strongly confirmed by the fact that in spite of the great 
differences in specific characters between P. pomonaria and 
P. isabellae the physiological divergence is so slight that they 
hybridise freely and, what is still more emphatic, the hybrids 
themselves are fertile. 
From all of these facts, it is clear that P. zsabellae must 
have had its origin in a spot where, very early, its food plant 
larch came into contact with P. pomonaria ; this spot, too, 
must be one whence P. isabellae could advance easily to its 
present habitats. Such a locality is the Sudeten Gebirge in 
Silesia or, rather, the angle between them and the Carpathians. 
From this abode, the species has evidently spread, using the 
Mountains of Moravia and the Little Carpathians as its path, 
to the present stations in the Noric and Rhaetian Alps and 
subsequently to the Eastern Alps of Switzerland and Bavaria. 
Naturalist,. 
