PLATYCERCUS. 
species. In the North-east we have the xanthochroism present in a species 
which is also simultaneously working with a cyanistic tendency. 
This genus is peculiarly Australian, no species being extralimital though 
it ranges quite up to Cape York and to Port Essington. The form of P. elegans 
found on Norfolk Island I believe to be a recent introduction to that locality, 
as it varies little from the normal Sydney form while the whole of the members 
show great variation according to locality and also individual variation. More- 
over, though we have here undoubtedly six distinct species their ranges rarely 
overlap, but are separate. 
There is, however, a seventh species, eximius which though still showing the 
same colour scheme, has developed in a much more beautiful manner and peculiarly 
this species lives on the East, ranging into Tasmania, occupying the same 
localities as elegans , flaveolus and caledonicus . In this the head and breast 
are scarlet, the lower breast golden yellow, the abdomen green, the under tail- 
coverts scarlet : the cheeks are white : the black back is scallopped with 
golden green, the rump yellowish green, the two middle tail feathers green, 
the others blue and the shoulder patch blue. This very distinct species has 
undoubtedly developed from the same stock but probably much more quickly, 
and has then migrated into Tasmania as in this case the Tasmanian birds are 
more highly coloured still, not subdued as in the case of caledonicus. 
Further the immature of eximius are more dull coloured and more nearly 
approach the ancestral form. 
It is somewhat difficult to trace the evolution of the group, but from 
the facts we can suppose that the ancestral green phase overran Australia 
down the East Coast into Tasmania before the last was separated from the 
mainland. A xanthochroistic tendency was in the group as all show this rather 
strongly on the East Coast : the bird, which arrived in the West probably 
via the South, did not develop this peculiarity, but quite recently and very 
slowly has grown erythristic and this erythrism is not yet absolutely fixed. 
The Tasmanian species was soon isolated, and it retained the normal coloration 
developing more brightly not becoming entirely yellow but keeping that 
colour subdued, though the tendency is easily observed. The Victorian form 
went on developing the yellow coloration quite purely and this became fixed, 
but the form having a stronger ally was not able to extend its range much. 
This stronger ally was the New South Wales form, which developing in an 
erythristic style very vividly, also extended its range Northwards and South- 
wards, probably at the expense of its weaker, certainly more weakly-coloured, 
relations. In the North-east a form also governed by the xanthochroistic 
tendency evolved into a pallid form which, however, by a strange freak, 
simultaneously acquired a cyanistic phase. This cyanism in the group had 
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