XVI PREFACE. 
service for comparison with 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. Gurney 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 G. 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 Iinglish 
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. 
Sp ey ded, 
Wasuinaton, October 20, 1853. 
2 The English inch is about equal to 11. 26 French lines, .9383 French inches, or to 25, 40 millimetres. 
