PREFACE. v 
The author is greatly indebted to Dr. Charles W. Richmond, 
Associate Curator of the Division of Birds, U. S. National Museum, 
for indispensable aid in the matter of nomenclatural questions—now 
so complicated and difficult a branch of zoological science that only 
specialists in that line of research are competent authorities—for 
assistance in correcting proofs, and help in various ways; and to Mr. 
J. H. Riley, Aid in the Division of Birds, for compilation of a consid- 
erable proportion of the synonymatic references, measurements of 
many specimens, and preparation of the Keys to the species of the 
genus Blasipus (pp. 652, 653) and immature stages of the species of 
Larus (pp. 583, 584). 
Measurements of specimens for use in the preparation of the pres- 
ent volume were made by Mr. Riley and Miss Celestine B. Hodges, 
and the original drawings of the outline figures illustrating the generic 
characters (pls. I-XX XIV), except those previously published, were 
made by Mr. E. R. Kalmbach, of Washington. 
It may be added that printing of the present volume has been 
greatly retarded by exigencies resulting from prosecution of the 
World War, now happily ended. 
Rosert Rmeway. 
DECEMBER 3, 1918. 
