PBINCIPLES AND PFACTICE OF CLASSIFICATION. 81 



<)rnitlu)lc)gical system is still in a transition state, and tlie classification implied by the way 

 North American birds are arranged in the present work must be regarded as tentative and 

 provisional. In the original edition of the '* Key," the dassificatitm was vitiated at the outset 

 by pliysiological considerations,* and in some other respects was open to decided improvement, as 

 I trust the present edition shows. The general arrangement is, however, much the same. The 

 table given on a succeeding page (p. 234) will afiVu-d the student a cottp d'oeil of the groups, from 

 subclass to subfamily, which I have been led to adopt; it represents, as far as it goes, a classifi- 

 cation of birds at large. The piincipal groups, higher than families^ which are absent from the 

 Ntirth American Fauna, are : the whole of the Ratitce, or Struthious birds ; the DromceognatJicp, 

 probably an order, embracing the South American Tinamous ; the order or suborder of the 

 Penguins of the Southern Hemisphere, Sjihenisci : and several small supeifamily groui)s be- 

 longing in the vicinity of tiie Gallinaceous and Columbine birds. 



As to the primary divisions of Aves, it seems certain that these must be made with special 

 reference to the extraordinary extinct forms from the Cretaceous, and to the radical difference 

 between struthious or Ratite and Carinate Birds. The arrangement offered on p. 234 has 

 perhaps some claims to consideration. The subclass Carinatce, which includes all other exist- 

 ing birds, seems certainly not to be primarily divisible into a few orders, such as were in vogue 

 but a few years ago; but to be split du-ectly into a large number — perhaps about twenty — 

 groups of approximately equivalent value, to be conventionally designated as orders, if we 

 take Carinatse as a subclass of tiie class Aves. The attempt to force birds into a few — five or 

 six — leading divisions cannot be justified if we are to regard the taxonomic significance of a 

 number of remarkable forms, the peculiarities of which are now well known. Passeres seems 

 to be one of the most firmly established of these ordinal groups. " Picarice" is one of the most 

 unsatisfactory of all, and I have no doubt it will be abolished. 



With this glance at some taxonomic principles and practices, I pass to an outline of the 

 structure of birds, some knowledge of which is indispensable to any appreciation of orni- 

 thological definitions and descriptions. It is necessary to be brief, and I shall confine myself 

 mainly to the consideration of those points, and the explanation of those technical terms, which 

 the student needs to understand in order to use the present volume easily and successfully. 

 Here, however, I will insert a tabular illustration of a sequence of zoological groups, fi-om 

 highest to lowest, under which a bird may fall : — 



Kingdom, Animalia: Animals. 



Branch, Vertebrata : Back-boned Animals. 



Province, Sauropsida : Lizard-like Vertebrates. 

 Class, Aves : Birds. 



Subclass, Carinai(S: Birds with keeled bi'east-bone. 

 Order, Passeres : Perching Birds. 



Suborder, Oseines: Singing Birds. 



Family, Turdidee : Thi-ush-like Birds. 



Subfamily, TtirdincB: True Thrushes. 

 Genus, Turdus : Typical 'Jhrushes. 

 > Subgenus, Hylodchla: Wood Thrushes. 



Species, ustulatus : Olive-backed Thrush. 

 Subspecies, cdicia; : Alice's Thrush. 



1 In primarily dividing birds into Aves aerece, Aves terrestres, and Aves aquatlcm, after Lilljeborg, I should 

 •do myself the justice to say, however, that the fact that these divisions did not rest upon morphological characters 

 •of any consequence was expressly stated (pp. 8 and 276 of the orig. ed.). 



