Key to the Species 
Summer-plumage. 
A. Back black ; under wing-coverts black, 
and tail whitish. . . . . . . . H. leucoptera grisea, p. 312. 
B. Back, wings and tail uniform grey. 
a'. Throat greyish, belly dark slate . . H. leucopareia fluviatilis, p. 316. 
h'. Throat and belly lighter . . . . H. leucopareia rogersi, p. 323. 
W inter-plumage. 
G. Bill slender ; wing shorter ; distinct black 
spot in front of eye and dark patch on 
the ear-coverts, with forehead and front 
of top of head pure white . . . . H. leucoptera grisea, p. 312. 
D. Bill heavier ; wing longer ; no dark patch 
on ear-coverts, and when fore-part of 
head is pure white, back part is also 
almost pure white leucopareia fluviatilis * p. 316. 
\H. leucopareia rogersifl^ p. 323. 
* I have not material whereby I can differentiate the subspecies in the winter-plumage. 
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