Thalasseus Boie, Isis, 1822, p. 563.
Type, Sterna cantiaca Gmelin=S. sandvicensis Lathom,
This genus is distinguishable from all our Indian Terns by its very long bill, which is slightly curved throughout. The tail is nearly as long as in true Sterna and equal to about half the length of the wing; the feet are small and fully webbed; the tarsus is equal to about half the length of the culmen.
The genus has a wide range over the greater part of the Northern Hemisphere and ranges to Australia.
Key to Species.
A. Bill black, tipped yellow T. sandvicensis, p. 119.
B. Bill yellow.
a. No white forehead in breeding plumage. Wing under 300 mm………T. bengalensis, p. 124.
b. A white forehead in breeding plumage.Wing over 300 mm………T. bergii, p. 120.