XVI PREFACE, 



service for comparison witli closely allied species of the United States, as have also specimens from 

 Mr. P. L. Sclater, of London, Mr. J. P. Verreaux, of Paris, .and Messrs. J. H. Grurney and 

 Alfred Newton, of Norwich, England. 



The types of eastern birds have been furnished by the collection of the author deposited in 

 the Smithsonian Institution. This consists of a full collection of birds of Central Pennsylvania, 

 with sex, date, and measurements before skinning. It also embraces a large number of Mr. 

 Audubon's typical specimens used in the preparation of his "Birds of America," including 

 many of those from the Columbia river and Rocky mountains, furnished him by Mr. J. K. 

 Townsend. 



In addition to the collections just mentioned, with others not enumerated, all in charge of 

 the Smithsonian Institution, and amounting to over 12,000 specimens, types have been supplied 

 for the occasion by Mr. Cassin, Mr. Lawrence, Mr. John Gr. Bell, Dr. Michener, and others. 

 The ornithological gallery of the Philadelphia Academy of Natural Sciences, believed to be the 

 richest in the world, has also furnished the means of making many essential comparisons. 



The measurements of the specimens have usually been made in hundredths of the English 



inch^, mostly with the dividers. All the measurements in the list of specimens are as made 



before the bird was skinned, each collector being responsible for the accuracy of his work. The 



comparative tables of measurements show, in many cases, the change of dimensions produced in 



the dried skin. 



S. F. B. 

 Washington, October 20, 1853. 



1 The EDgliBh inch is about equal to 11. 26 French lines, .9383 French Inches, or to 25. 40 millimetres. 



