STEKNID^ HYDKOCHELIDON 



Genus I. HYDROCHELIDON. 



429 



Type. 

 Hydrochelidon, Bole, Isis, 1822, p. 563 H. nigra. 



Bill nearly straight and somewhat compressed, about as long as 

 the head, culmen slightly curved, both mandibles equal; wings long 

 and pointed, extending far beyond the tail, the first primary the 

 longest ; tail short, less than half the length of the wing, but very 



FIG. 13G. Tail of Hydrochelidon hybrida. x 1 



slightly forked ; legs feeble, webs much indented, so that the toes 

 appear to be only half webbed ; lower surface of the body always 

 black or dark grey in the breeding plumage. 



This is a genus of marsh-haunting Terns spread over the greater 

 part of the world ; only four species are generally recognised, two of 

 which are migrants to South Africa from the northern Hemisphere. 



Key of the Specie. s. 



A. Upper tail-coverts and tail white. 



<t. Underparts, including the axillaries, black H. Icucoptera, p. 431. 



/;. Underparts, including the axillaries, white H. IcHcojtteni Ji icme, p. 431. 



B. Upper tail-coverts and tail grey like the 



back 



a. Underparts dark slate, axillaries white ... H. liybrida, p. 430. 



1). Underparts white H. hybrid a hieme, p. 430. 



C. Upper tail-coverts white, tail grey H. Icucoptera, juv. p. 431. 



