PRINCIPLES AND PRACTICE OF CLASSIFICATION. 81 



ornithiilcigical system is still in a triinsitinu statf, and the classification implied by the way 

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

 provisional. In the original edition of tlie " Key,'' the classification was vitiated at the outsi't 

 by physiological considerations,' and in some other respects was open to decided improvement, as 

 1 trust the present edition shows. The general aiTangement is, however, much the «&me. Tlie 

 table given on a succeeding page (p. 23i) will afford the student a coup d'ceil 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 principal groups, higlier than families, whicli are absent from tlie 

 Nortli American Fauna, are : the whole of tire Ratita, or Struthious birds ; tlie Dromceor/natlue, 

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

 Penguins of the Southern Hemisphere, Sphenisci : and several small superfamily groups be- 

 longing in tlie vicinity of the Gallinaceous and Columbine birds. 



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

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

 between struthious or Katite and Carinate Birds. Tlie arrangement offered on p. 23i has 

 perhajis some claims to consideration. The subclass Carinatfe, which includes all other exist- 

 ing birils, 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 directly into a large number — perhaps about twenty — 

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

 take Carinatie as a subclass of the class At'es. The attempt to force birds into a few — five nr 

 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 estaljlislied of these ordinal groups. " Picarue " is one of the most 

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



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

 structure of l)irds, 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 iirder to use the present volume easily and successfully. 

 Here, however, I will insert a tabular illustration of a sequence of zoological groups, from 

 big]] est to lowest, under whicli a bird may fall : — 



Kingdom, AnimaUa: Animals. 



Branch, Vertebrata : Back-boned Animals. 



Province, Sauropsida : Lizard-like Vertebrates. 

 Class, Aves : Bird.s. 



Subclass, Carinatce: Birds with keeled breast-bone. 

 Order, Passeres : Perching Birds. 



Suborder, Oscines : Singing Birds. 



Family, TurdidcE : Thrush-like Birds. 



Subfamily, Tiirdiiire: True Thrushes. 

 Genus, Tardus : Typical Thrushes. 



Subgenus, Hylociclda : Wood Thrushes. 



Species, ustulattis : Olive-backed Thrush. 

 Subspecies, alicice : Alice's Thrush. 



' In priraarily dividing birds into --ires aerea;. Arcs terrestres, and Aves aquatlca', after LilJjeborg, T slionld 

 do myself til t: 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.). 



