Genus— T HALASSEUS. 
Thalasseus Boie, Isis 1822, p. 563 . . . . Type 
T, sandvicensis. 
Actochelidon Kaup, Skizz Entwick-Gesch. Nat. 
Syst., p. 31, 1829 . . . . . . . . Type T. sandvicensis. 
Felecano'pus Wagler, Isis 1832, p. 277 . . Type T. bergii pelecanoides. 
(Also spelt Pelanopus Gray, Handl. Gen. Sp. Birds Brit. Mus., 
pt. ni., p. 120, 1871.) 
Large Terns with long slender bills, long tails, long wings and short legs, and 
decided occipital crest in their breeding-plumage. The diagnostic features 
of this genus are the long, slender bills, long tails, and small feet. The 
metatarsus is about half the length of the culmen, which is longer than the 
head, while the tail is just about half the length of the wing. 
It might be here noted that when Wagler {Isis, 1832, p. 1,225) introduced 
his genus Laropis for Sterna anglica Mont., he wrote : “ Her Fr. Boie bring t 
diese Schwalbe, welche nach Xema zu stehen kommt, zu seiner Sippe 
Thalasseus {Isis, 1822, p. 563), fur welche er als Typus Sterna cantiaca angibt, 
die jedoch einen ganylich anders gebildeten Schnabel als St. anglica hat ” ; 
and regarding Thalasseus added, “ Eine zweite species dieser Sippe ist 
Th. velox, Biipple Sterna velox {Zool. Atl., t. 13).” 
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