WHITE-TAILED HAWK. 
19 
of Vieillot, whose authority, it is true, could in this case be of 
little weight, as he had not seen the species, but like many others 
had merely given it a name; his sole knowledge of it being 
derived from the work of d’Azara. We have now yielded only 
to the decision of Temminck, (who has lately introduced the 
young into his Planches Coloriees;) but not without much reluctance, 
especially as that distinguished ornithologist has evidently not 
been at the trouble of comparing the two species. Otherwise, he 
would certainly not have omitted noticing their affinities and 
differential characters; since in the history of species so closely 
allied as these two, the differential characters are of more 
importance and utility than the most laboured descriptions. 
This comparison we have carefully instituted between our Ame¬ 
rican specimens, and others from Africa and Java. They agreed 
perfectly, especially with that from Java, in every, the minutest 
character, even feather by feather, much better than birds of prey 
of the same species, and from the same country, do generally. 
They are even more alike than different specimens from the old 
continent of the Black-winged itself, since that species is said to 
vary considerably in the black markings, which extend more or 
less on the wings in different individuals. Nevertheless, a constant, 
though trivial, differential character, added to the difference of 
locality, has induced us to follow Temminck’s course, in which 
we should never have ventured to take the lead. This character 
consists in the tail being in Falco dispar constantly irregular, while 
in F. melanopteras, it is even; or to explain it more clearly, the 
outer tail-feather is rather the longest in the African, and more 
than half an inch shorter than the next in the American species. 
This essential character is much more conspicuous in Temminck’s 
plate than in ours, owing to the tail being spread. In the Black¬ 
winged also, the lower wing-coverts are destitute of the black 
patch so conspicuous in the American bird; a female from Java, 
