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 Phaethvn with barred plumage 

 in the adult as in the juvenile and the tail with fourteen feathers ; Scceophaethon, 

 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 Leptophaethon, 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 

 tmcinate. The cervical vertebrae 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 f urculum 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 Limicoliiu- 

 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, caeca being present. The 

 leg muscle formula is AXY - or -f, 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 secundarioruni. The oil gland is present and tufted 

 with six orifices, while the afters haft 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 Prophaethon shrubsolei Andrews from the 

 London Clay to the Steganopod series and would not consider it a direct ancestral 

 form of the present forms. 



FAMILY PHAETHONTHXE. 



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 Phaethon 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. 



