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 Stercorariidae 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 the nasals schizorhinal , 

 but in the Stercorariidce there is a distinct tendency towards pseudo-holorhiny, 

 while there are no basipterygoid processes or occipital f ontanelles (which are, however, 

 present in juveniles) and well-marked supraorbital grooves. The lachrymals are 

 firmly united with pref rentals while the furcula shows a hypocleidium. The cervical 

 vertebrae number fifteen, the dorsals opisthocoelous, 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, caeca 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. 



FAMILY STERNID^E. 



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 caeca 

 are rudimentaiy but in Leucanous the caeca are long. The digestive system is 

 periccelous in the Terns but not definitely stated in detail for the Noddies. 



Genus CHLIDONIAS. 



CMidonias Rafinesque, Kentucky Gazette, Vol. 36 (new ser., Vol. I.). No. 8, Feb. 21st. 1822 



[3]. Type (by monotypy) : Sterna melanops Rfsque. = Sterna eurinamensis 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 Linne. 



Viralva Stephens, in Shaw's Gen. Zool., Vol. XIII., pt. i., p. 166, Feb. 18th, 1826 (ex Leach 



MS.). Type (by subsequent designation, Coues, Proc. Acad. Nat. Sci. Philad., p. 554, 1862) : 



Sterna nigra Linne*. 



Ptlode* Kaup, Skizz. Entwick.-Gesch, Nat. Syst., p. 107, (pref. April) 1829. Type (by 



monotypy) : Sterna leucopareia Temminck. 



