PREFACE. V 



The author is greatly hulebted to 13r. 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 sN'nonymatic references, measurements of 

 man}' 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. 588, 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 (pis. I-XXXIV), 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. 



Robert Ridgway. 

 December 3, 1918. 



