Key to the Species, 
A. Vermiculated more or less on upper-back ; 
bill very stout. 
Tail only white in very aged birds. 
a'. Smaller ; wing-coverts dark, primaries 
also dark , . . . . . . . D. exulans rothschildi, p. 246. 
h'. Larger ; wing-coverts nearly white, 
and primaries with white patch on 
inner webs . . . . . . . , D. exulans chionoptera, p. 255, 
5. No vermiculations on upper-back ; bill 
proportionately slender ; tail always 
pure white . . . . . . . . D. epomophora epomophora, p. 258. 
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