78 A MANUAL OF THE BIRDS OF AUSTRALIA. 
through all the oceans, breeding on few rocky and desolate islands, and never in 
great numbers though somewhat gregariously. 
Three distinct genera can be recognised : typical Phaéthon with barred plumage 
in the adult as in the juvenile and the tail with fourteen feathers ; Scwophaéthon, 
birds as large with similar juvenile plumage but in the adult a uniform silky-white 
to pink, with sixteen tail-feathers, the central ones being very elongated and 
attenuated ; and Leptophaéthon, smaller birds, also barred as immature but uniform 
white or even orange in the adult with only twelve tail-feathers, the tail proper 
being longer proportionately than in the former genera, the long elongated central 
feathers broader. 
Osteologically, the palate has commonly been recorded as desmognathous, but 
as the young shows it to be schizognathous, the desmognathism is spurious ; similarly 
the nasals are superficially holorhinal, but again it is pseudo-holorhiny, the juvenile 
showing its development from a schizorhinal form. They have no basipterygoid 
‘processes, but there is an imperfect nasal hinge present in the adult, which is absent 
in the nestling. The lachrymals are free and there are apparently rudiments of an 
uncinate. The cervical vertebre are given as twelve or thirteen by some writers, 
fifteen by others, while the dorsals are heteroccelous. The sternum has the carina 
produced forwards but it terminates at the posterior extremity as is usual in this 
group, and unlike that of the Steganopods ; the posterior border of the sternum is 
doubly notched and the furculum does not articulate with the acrocoracoid and the 
clavicles are attached to the keel behind the extremity; the pelvis is also quite 
unlike that of a Steganopod while the humerus, ulna and manus are quite Limicoline 
and different from those of the Steganopods; the leg bones are also distinctive 
when compared with those of the Steganopods and.show generalised structure 
comparable with that of Limicoline forms. The vomer is divided posteriorly, a 
fact of which the importance is unknown but which should be noted here. There 
are two carotids present, while the digestive system does not appear to have been 
specially studied, being orthoccelous and periccelous, ceca being present. The 
leg muscle formula is AXY — or +-, as good observers have had different results, 
probably working with different species which are here referred to distinct genera ; 
a peculiar item is the lack of the tendinous loop for the biceps to pass through. In 
the wing there is no expansor secundariorum. The oil gland is present and tufted 
with six orifices, while the aftershaft is apparently lacking, and the wing aquincubital. 
The pterylosis is fairly uniform and the nestling is covered with thick down soon 
after its birth. 
As noted previously we would refer Prophaéthon shrubsolei Andrews from the 
London Clay to the Steganopod series and would not consider it a direct ancestral 
form of the present forms. 
Fammy PHAETHONTIDA. 
We have allowed three genera as differentiated above in this family whose 
limits are equivalent to those of the suborder. The diverse results recorded by 
anatomists and osteologists are very probably due to the fact that such workers 
simply use any species as “‘ typical ” of the group without investigation as to the 
accuracy of their actions. Thus Phaéthon flavirostris has been commonly used and 
differences have been noted in P. rubricauda, and these two we refer to different 
genera. We have tabulated the general osteology and anatomy of the species 
and have been compelled to refer them to the basic position in the order Lari, and 
separate them from the Steganopodous birds, from which they differ in every detail, 
externally and internally, as has been admitted by every anatomist and osteologist 
who has studied the group. 
