EDITOR'S PREFACE 



THE Editor's share in the preparation of the present work consists of 

 scarcely more than a careful reading and slight revision of the manu- 

 script, the planning and general execution being entirely by the Author. 

 So well, indeed, had Dr. Knowlton performed his task that there was 

 need for scarcely more than perfunctory revision ; a slight correction, 

 here and there, together with an occasional suggestion concerning a ques- 

 tionable or doubtful statement, or one involving a difference of opinion 

 between authorities, or that a particular conclusion be reconsidered, being 

 practically the extent of the Editor's censorship. 



ROBERT RIDGWAY. 

 WASHINGTON, D.C., 

 April 15, 1907. 



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