AUSTRALIAN CASPIAN TERN. 
of which are white ; remainder of the plumage pure white ; irides black ; bill scarlet, 
staiued with yellow on the sides and tip, and with greenish-yellow near the extremity. 
Total length 20J inches ; bill 4, wing 16|-, tail 6J, tarsi 2. 
Hab. Southern coasts of Australia. 
Rbmabk. — The above is the description of the plumage of the breeding-season ; at 
other times the head instead of being wholly black is mottled with black and white. 
Afterwards this name fell into disuse, and Saunders, in the Cat. Birds 
Brit. Mus., lumped the form without question. 
In his Review of the Terns of North America, Coues {Proc. Acad. Nat. Sci. 
PJiilad. 1862, p. 538), from a comparison with two European birds, concluded 
that the North American birds were larger in all their dimensions, and thereupon 
introduced for them the name of TJialasseus im'pcrator. Recently it appears 
that American ornithologists do not admit any distinction at all for their form. 
It would seem that in this group the Americans have followed the Cat. Birds 
Brit. Mus.y though they admit subspecies, while Saunders, the author of the 
monograph in the Catalogue, did not. I consider that these birds do show 
differences worthy of subspecific rank, but the series at hand do not permit 
the diagnosis of the Palsearctic forms.* The North American form is 
however quite worthy of recognition, as I find that the bill, wing, and tarsus 
are constantly longer than those of the Palsearctic birds ; Austrahan birds are 
larger still, the bill noticeably so. Probably the West African breeding-birds 
are also separable. 
I would recognise the Palaearctic form as 
Hydro'progne tschegrava tschegrava (Lepechin) 
(about the Caspian Seas, breeding). 
As an absolute synonym must be quoted Sterna caspia Pallas ; if the West 
European bird is separable. Sterna 7negar}iynchos Meyer and Wolf is available. 
Sterna schillingii Brehm and Sylochelidon balthica Brehm being synonyms ; if 
the West African birds prove distinct, Swainson’s T. inelanotis may be used. 
Hydroprogne tschegrava hnperator (Coues) (North America, breeding). 
I conclude this name should be used for the North American breeding bird. 
Hydroprogne tschegrava strenua (Gould) (Australia, breeding). 
The Austrahan birds are absolutely larger and should never have been lumped. 
It is interesting to note that in this respect it agrees with Oelochelidon nilotica 
7)iacrotarsa Gould, which is also larger than the Palaearctic form of the species. 
I have also noticed that Sclater {Birds South Africa, Vol. IV., p. 435) 
records a breeding form in South Africa. I have not specimens, but the locality 
suggests a race quite distinct from any of the preceding. 
* I note Buturlin (Nasa ochota, St. Petersburg, 4, 1910, 5, p. 64) has proposed Sterna tschegrava leptorhyncha 
for birds from Ussuri-Gibiet (Zool. Record, 1910). I have not seen this paper. 
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