Genus-STERN A. 
Sterna Linne, Syst. Nat., ed. X, p. 137, 1758 . . . . Type S. hirundo. 
Chelido “ Billberg, Synopsis Faunae Scand., Vol. I., 
pars 2, p. 193, 1828 ” Type 8. himndo. 
Thalassma Kaup, Skizz Entwick-Gesch. Nat. Syst., p. 97, 
1829 . . . . . . . . . . . . . . Type 8. dougallii. 
(Also spelt Thalassia Bonaparte, Comptes Rendus Sci., 
Paris, Vol. XLIII., p. 645, 1856 ; Thalassea^ id., ih., 
Vol. XLII., p. 772, 1856.) 
Hydrocecropis Boie, Isis 1844, p. 178 Type 8. hirundo. 
(Substitute-name for 8terna Linne.) 
Medium-sized Terns with slender bills, short legs, long wings and very long 
tails. The bill is longer than the head and twice the length of the tarsus, 
which is shorter than the middle toe and claw. The tail is long and forked, 
the length of the streamers more than half the length of the wing. Toes 
completely webbed. 
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