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Genus— H YDROPROGNE. 
Hydroprogne Kaup, Skizz Entwick-Gesch. Nat. Syst., 
p. 91, 1829 Type 
Sylochelidon Brehm, Vogel Deutschl., p. 767, 1831 . . Type 
Helopus Wagler, Isis 1832, p. 1224 . . . . . . Type 
Heroprogne Buller, Suppl. Birds New Zeal., Vol. I., 
p. 157, 1905 Type 
Thalasseus, Auct. not Boie, 1822. 
H. tschegrava. 
H. tschegrava. 
H. tschegrava. 
H. tschegrava. 
Largest Terns, with long stout biUs, long wings, short legs, and short tails. 
The diagnostic features of this genus are the large size and the long, stout 
bills and short tail. The metatarsus is much shorter than the culmen, 
which is longer than the head. The tail is forked and only about a third 
of the wing. 
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