Hydroprogne Kaup, Skizz Entwick. Gescb. Nat. Syst.. p. 91 (1829).
Type by mon., Sterna caspia Pall.
The genus Hydroprogne is distinguished from the next genus, Gelochelidon, by its comparatively short tarsi, still shorter tail and by its long, stoat bill; it is the largest of all the Terns, recognizable at once by its great size and very large red bill. There is but one species divisible into several races which extends over Europe, Asia and Africa to Australia.