Introduction. 
The family Geometridae contains altogether an enormous number of species, occurring for the most part 
in such individual abundance that in most regions nearly as many Heterocera of this family are met with as 
of all the rest put together. In dull weather sometimes almost exclusively Geometridae are found, and in collect¬ 
ing with light they usually represent 50 per cent, of the captures, and this in nearly all faunas and climates. 
Only as visitors to sugar are they greatly in the minority, probably because they are almost all attached 
to flowers and have little taste for decaying matter, fermented liquids, exudations from trees and the like. 
The main character of the group is the arrangement of the larval legs. Almost invariably the prolegs of 
the middle segments are wanting, one pair being developed before the anal claspers. For the Palaearctic Fauna 
(and, so far as was earlier known, also for the others) this criterion passed without exception until latterly the 
group Brephinae, consisting of only 8 palaearctic and nearctic species and not occurring in the other faunas, 
was transferred to the Geometrids. 
While we refer the reader to the Introduction which L. B. Pkout gives in Vol. 4 (p. 1 — 5) for the palae¬ 
arctic Geometrids, it may here be further remarked that different authors have had a different conception of 
the division into subfamilies. The Geometrinae are sometimes regarded as synonymous with Boarmiinae, but 
by others again as designating the group that contains the striking green geometers which are hardly wanting 
in any temperate locality. Further, the genera related to Orthostixis have -— as already mentioned in Vol. 4 -— 
been separated out from the Oenochrominae as Orthostixinae. To this have been referred in particular a number 
of very remarkable Indian genera, which as a matter of fact will not fit accurately into any group; thus the 
sometimes wholly purple-red Eumelea, the bright yellow, black-bordered Celerena, Alex with its oblique stripe 
straight through both wings, the snow-white,, black-dotted Naxa, the falcate-winged Ozola and some other 
genera. We here place all these in the Oenochrominae, while recognizing that the latter represents a rather 
vague division and still requires thorough investigation, especially in respect of the early stages, which are 
at present little known. 
As regards specially the Indo-Australian geometric! fauna, it is subject to the law which applies also 
to the other families, that the forms deviate the more widely from their palaearctic relatives the more tropical 
is their habitat, and not according to their geographical remoteness from palaearctic localities. That is to 
say, for example, there are found at the most distant points of the Australian region, e. g. on New Zealand, 
a relatively much greater number of geometers which resemble the palaearctic species than, for instance, on 
the much less remote Sumatra, on Ceylon or even in Hindostan, from which latter our region is not separa¬ 
ted by any sea. 
In the Indo-Australian Region we may also look for those territories in which the prevalence of Geo- 
metrids relatively to the total of species is the most manifest. In Australia, at least in the south, the Geome¬ 
tridae pretty well balance all the rest of the Macco-Heterocera, and on New Zealand there are even 1 % 
times as many geometers as other moths, if one disregards the Microlepidoptera. Whereas in the Palaearctic 
Region there is only one species of Geometrid to three of Heterocera, in the extreme south of the Indo- 
Australian Region we may count three Geometrids to two other species of Heterocera; in S.W. Australia 
the proportion declines to 1 : 1, and northwards, in India proper, where there are approximately 1200 Geome¬ 
tridae against some 3000 other Heterocera, we already see a transition to the proportion which prevails in the 
greater part of the Palaearctic Region. 
Numerically one of the principal constituents of the moth fauna of the whole world, the Geometrids 
further become especially familiar to us through two other circumstances. In theTirst^place we find among 
them many of the commonest insects, but in addition they are, as already mentioned in Vol. 4, particularly 
