STEKNID^ 



HYDROCHELIDON 



429 



Genua I. HYDROCHELIDON. 



Type. 

 H. nigra. 



Hydrochelidon, Boie, Ms, 1822, p. 563 



* 



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 



Pig. 136. — Tail of Hydrochelidon hybrida. x J 



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 Species. 



A. Upper tail-coverts and tail white. 

 fi. Underparts, including the axillaries, black 

 6. Undei-parts, including the axillaries, white 



B. Upper tail-ooverts and tail grey like the 



back 

 n. Underparts dark slate, axillaries white ... 

 h: Underparts white H. hybrida hieme, p. iSO. 



C. Upper tail-coverts white, tail grey H. Icucopicra, juv. p. 4.31. 



H. leucoptcra, p. 431. 



H. leiu'optera hicme, p. 431. 



H. htjbrida, p. 430. 



