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THE GEOGRAPHICAL DISTRIBUTION OF THE 
MOTHS OF THE SUBFAMILY BISTONINAE. 
J. W. HESLOP HARRISON, B.Sc. 
I.—INTRODUCTORY. 
This family, in the main, is one characteristic of the Hol- 
arctic region although, here and there, overflows occur into 
neighbouring areas ; independent of these overflows, we have 
possibly one or two outlying species in more or less detached 
localities. 
In the preset paper, it is proposed to deal more particularly 
with the centralised forms, but, at the same time, to account for 
the distribution of the outliers as far as possible. 
The family can readily be sub-divided into two sections, one 
of which may be regarded as the true family stock in spite of the 
fact that the genus which gives its name to the sub-family 
belongs, unfortunately, to the other section. The latter non- 
typical portion passes insensibly into the Boarmiinae with which 
sub-family all of its species are distinctly related ; it may there- 
fore be known as the Boarmioid group, as distinct from the 
other or Non-Boarmioid group, which shows no such clear rela- 
tionship. 
Characterised as the sub-family is by the presence of species 
with apterous females and of species with fully winged females, 
one might reasonably expect that this highly important charac- 
ter would be the basis of the division proposed ; such, however, 
is not the case, the divisions containing unequal but large per- 
centages of forms with apterous or subapterous females. The 
characters on which the sub-division is based are of greater or 
less value, but those which are of most importance, are those 
displayed by the male, and, to a less extent, by the female 
genitalia. : 
This separation into two groups, although rather of phylo- 
genetic importance, still has its zoogeographical value, for we 
find that, whilst the two parts overlap in most of the areas of 
their distribution, in spite of that fact, each is characteristic of, 
i.e. reaches its greatest development in, certain definite geo- 
graphical areas. 
The Non-Boarmioid fraternity, save for two outliers in the 
Nearctic regions and one or two on the Pacific coast of Siberia 
and in Japan, is centred in Europe and the Boarmioid portion, 
whilst obviously of Asiatic origin, is found, in addition, although 
in sparse numbers, in Europe, N. America and Africa. 
The genera of the first section will be treated first. 


1916 May 1. 
