69 [Vol. xxxvi. 



the Common Tern {Sterna hirundo) the chin and sides 

 of the throat are invariably dusky, whereas in the juvenile 

 Lesser Tern {Sterna minuta) these parts are always white. 

 The chief interest of this observation lies in the fact that 

 these birds represent what^ in my opinion^ are two very 

 distinct groups of Terns, easily recognisable in the adult by 

 the form of the tail. 



" The question now arises, Are tliese two characters corre- 

 lative and invariably present in all tlie members of their 

 respective groups? I have not been able to examine much 

 material, but all the specimens of Terns in down in the 

 Natural History Museum tend to support this supposition. 

 Chicks of the under-mentioned species are represented in 

 the National Collection, and, according to my classification, 

 these may be conveniently divided as follows : — 



" Group I. 



"Adult with a deeply-forked, long tail. Downy young 

 with dusky throat. 



Sterna hirundo { = fluviatilis). 



■Sterna paradisma {= macrura). 



Sterna dougalli. 

 *Sterna hirundinacea (from Falkland Islands). 

 '^Sterna aleutica (from Alaska). 



" Group II. 



^' Adult with shorter and not such a deeply-forked tail. 

 Downy young with white, or nearly white, throat. 



Sterna minuta. 



Sterna nilotica (= anglica). 



Sterna sandvicensis (= cantiaca). 



Sterna tschegrava (= caspia) . 

 ^Sterna antillurum. 

 ^Sterna melanauchen. 



* [These names have been copied direct from the old Museum 



labels.— t;. I.] 



