THE BIRDS OF AUSTRALIA. 
When the remaining Gannets come to be examined, these aU agree in 
having bare faces as described under the genus Piscatrix, and to the genus- 
lumper might constitute a single genus. They differ sufficiently, however, to 
be considered separable and 1 call the differences generic. For criticism of 
tbe plumage changes, combined with study of the varied proportions, show 
that this group is a very ancient one, a conclusion confirmed by study of 
their osteology, and that slight superficial distinction is of great phylogenetic 
value. 
I notice that the females exceed the males in size generally throughout 
the family. 
The birds pass through a brown coloration, uniform at first, then white 
on the belly and then white above. In the genus Sulita, distinct plumage 
changes differ from those of the remainder of the family ; and in the genus 
Sulttf which name falls upon my Hemisula — ^a name I provided for the species 
Pelecanus leucogaster Boddaert, — ^the brown coloration is retained in the 
adult, the breast and the remainder of the under-parts only becoming white. 
In addition to this retention of an immature phase of plumage, the only case 
in the family, Sula is characterised by its short tail and longer legs when 
contrasted with Piscatrix, which has also, while developing its tail-length, 
added a couple of tail-feathers to the two that Piscatrix has additional to 
the twelve of Sulita. 
Sula has the culmen more than twice the length of the metatarsus, 
while the tail is about twice the length of the culmen and also about half 
the length of the wing. The fact that this would tend to show is that 
Piscatrix has developed in exactly the opposite direction from Sula, though 
both have been derived from the same source. Both are small Gannets with 
long wings. 
The last form I would recognise is that typified by Sula dactylatra Lesson. 
This agrees in general coloration and structural features with Piscatrix, but 
the birds are large with a wing-length nearly equal to that of Sulita. The 
bill is very large proportionately, while the tail is comparatively short. 
The bill is more than half the length of the tail, which is decidedly less 
than half the length of the wing, while the tarsus is more than half the length 
of the bill. 
I have carefully considered the above and there can be no other conclusion 
than that the four groups should be recognised, and I maintain that these are 
of generic value. If such differences were proportionately observed in the 
Passeriformes, the birds showing them would be placed in different families. 
When a couple of tail feathers appear in a bird intervening between 
birds geographically as far apart as the poles, yet agreeing exactly, that 
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