PREFACE. 
v 
Columba leucocephala, of the present volumes, may be cited as 
examples of the latter description. 
But in our opinion the most interesting, and towards which 
we most earnestly desire to direct the attention of American 
naturalists and collectors, are those species once noticed by 
former authors, but from not having been since observed, now 
become in a manner obsolete, though still without being declared 
nominal. Such was for a period the case with Garrulus stelleri of 
this volume, and is yet with Sylvia velata and others established 
by Vieillot, of whose existence as distinct species there can 
hardly be any reasonable doubt. In order more clearly to 
explain our meaning, it may be proper to enter into the following 
calculations. 
In Linne’s last edition of his Systema Naturae, a work professing 
to contain, like all others, all the then known birds of the United 
States, which had been chiefly taken from the original sources 
of Catesby and Edwards, only one hundred and eighty-three are 
assigned to North America. It is true that he was acquainted 
with several other North American birds which also inhabit 
other countries, those common to Europe especially; but as 
many of the one hundred and eighty-three are merely nominal, 
we may allow them to counterbalance those omitted. Of the 
entire number, one hundred and three are land birds, all which 
we have verified either as real or nominal, four excepted, of 
which Ficus hirundinaceus alone (a real species) may have escaped 
Wilson and ourselves, though we do not believe it. Of the three 
remaining, two, Lanius canadensis and Loocia canadensis , are now 
well known to be South American birds given as North American 
through mistake; and the third, Sylvia trochilus of Europe, may 
have been reckoned as American on account of the resemblance 
between it and the female of some American Warbler, probably 
Sylvia trichas. 
