82 A MANUAL OF THE BIRDS OF AUSTRALIA. 
tails and stouter legs and always fully webbed feet. They vary in size, from 
species as small as a Tern to very large birds, the majority being larger than the 
majority of Terns and Noddies. The Stercorariide is a family consisting of few 
species of different facies but absolutely close relationship. The bill is somewhat 
Gull-like but easily distinguished by having a cere-like covering over the nostrils ; 
the largest species are heavily built, but strong flyers, and have long wings and long 
square tail and powerful legs and fully webbed toes, while the least species is delicately 
built with long wings and long tail with very elongated central feathers and compara- 
tively delicate legs and feet similar in formation to the others, as is also the bill 
but more gracefully formed. 
Osteologically, in the skull the palate is schizognathous and thenasals schizorhinal, 
but in the Stercorariide there is a distinct tendency towards pseudo-holorhiny, 
while there are no basipterygoid processes or occipital fontanelles (which are, however, 
present in juveniles) and well-marked supraorbital grooves. The lachrymals are 
firmly united with prefrontals while the furcula shows a hypocleidium. The cervical 
vertebree number fifteen, the dorsals opisthoccelous, and the sternum is strongly 
keeled, the posterior border generally doubly notched. Both carotid arteries are 
present and the syrinx is typically tracheo-bronchial with one pair of intrinsic muscles, 
while the digestive system is periccelous and orthoccelous, ceca present and variable 
in size. The leg muscle formula is also variable, the biceps slip present but the 
expansor secundariorum present or absent. The oil gland is always present and 
tufted, an aftershaft present and the wing aquincubital. The pterylosis of a few 
species has been studied. The young are hatched covered with down, and we suggest 
there is more of value in the study of the downy nestlings than has been allowed, 
and that they provide good clues to the phylogeny of the groups. The Terns have 
downy young showing colour patterns of more than one distinct style, and this indi- 
cates the heterogeneous nature of the commonly admitted groupings. Thus the 
nestlings of some of the Terns recall those of the Gulls very clearly and we find 
that these species show internal items of resemblance. 
Fossils have been described as referable to the present suborder, but little of 
real value has yet been discovered, the characters used for identification being 
variable ones. 
Famity STERNIDA. 
We have included here, the Terns and Noddies, but are doubtful as to the 
association of these two groups. We have noted above the superficial distinctions 
and may here add a few of the internal characters. The leg muscle formula of the 
Terns is always ABXY-+ (an instance of the loss of the accessory femoro-caudal 
has been recorded in connection with a ternlet), while in the Noddies some species 
agree, while Leucanous has lost the accessory femoro-caudal. The expansor secund- 
ariorum is absent in the Terns, but it is present in some of the Noddies. The ceca 
are rudimentary but in Leucanous the ceca are long. The digestive system is 
periccelous in the Terns but not definitely stated in detail for the Noddies. 
Genus CHLIDONIAS. 
Chlidonias Rafinesque, Kentucky Gazette, Vol. 36 (new ser., Vol. I.), No. 8, Feb. 21st, 1822 
[3]. Type (by monotypy): Sterna melanops Risque. = Sterna surinamensis Gmelin (cf. 
Rhoads, Auk, Vol. XXIX., p. 197, April 1912). 
Hydrochelidon Boie, Isis, heft 5, col. 563, May 1822. Type (by subsequent designation, 
Gray, p. 100, 1841): Sterna nigra Linné. 
Viralva Stephens, in Shaw’s Gen. Zool., Vol. XIII., pt. 1., p. 166, Feb. 18th, 1826 (ex Leach 
MS.). Type (by subsequent designation, Coues, Proc. Acad. Nat. Sci. Philad., p. 554, 1862) : 
Sterna nigra Linné. 
Pelodes Kaup, Skizz. Entwick.-Gesch, Nat. Syst., p. 107, (pref. April) 1829. Type (by 
monotypy): Sterna leucopareia Temminck. 
