PREFACE TO THIRD EDITION. 9 
of the ordinal and subordinal groups of birds. It was at first the 
intention of the Committee to modernize the sequence of these groups. 
The fact, however, that present systems of classification in ornithology 
are admittedly tentative, and differ widely among themselves, it seemed 
best, from the standpoint of convenience, to continue the old Check- 
List system unchanged, since the users of the Check-List are familiar 
with the present order of arrangement and would regret the annoyance 
that a radical change from it would cause. In deference to this 
known wide-spread preference the old order of arrangement has been 
continued. In the opinion of the Committee, a slight modification’ 
of the system proposed by Dr. Hans Gadow in 1892-93? would best 
reflect our present knowledge of the classification of birds, an abstract 
of which is here added. This system is at present extensively em- 
ployed, it being that followed by Evans in the volume ‘Birds’ of the 
‘Cambridge Natural History Series’ (London, 1899), and by Knowl- 
ton in his recently published ‘Birds of the World’ (New York, 1909). 
It is also the basis of the system adopted by Ridgway in his ‘Birds of 
North and Middle America.’ The subjoined abstract of the Gadow 
system is from Bronn’s ‘Thier-reichs’. The Check-List equivalents 
are added in brackets, for convenience of comparison. 
ABSTRACT OF GADOW’S CLASSIFICATION OF BIRDS. 
Cuass AVES? 
Subclass I. ARCHA:ORNITHES. 
Subclass II. NrornitTHEs. 
Division I. Neornithes Ratite. 
Ratite. 
Struthiones. 
Rhee. 
1 It is believed, for example, that the groups Columbe, Striges, and Psittaci should be 
accorded ordinal rank; and in general the Committee would prefer the Check-List eval- 
uation of the groups therein recognized as orders and suborders. 
2 On the Classification of Birds. By Hans Gadow, M. A., Ph. D., F. Z. S., Strickland 
Curator and Lecturer on Advanced Morphology of Vertebrata in the University of 
Cambridge.— Proc. Zodél. Soc. London, 1892, pp. 229-256. 
Dr. H. G. Bronn’s Klassen und Ordnungen des Thier-reichs, wissenschaftlich darges- 
telt in Wort und Bild. Sechster Band. Vierte Abtheilung. Végel. Von Hans Gadow, 
Ph. D., M.A., F.R.S. .... II, Systematischer Theil, Leipzig, 1893.— Roy. 8vo, pp. 
vii + 304. 
3 Subclass I, and Divisions 1 and 2, and Order 1 of Division 3, consist wholly of extinct 
types, and are not included in the classification, adopted in the Check-List, given above 
in the ‘Table of Contents’, 
