’ INTRODUCTION. xiil 
privilege of consulting specimens and books so essential to the preparation of this 
work, but also for the friendly advice and valuable suggestions which have ren- 
dered comparatively easy the performance of a task which under less favorable 
auspices would have been far more difficult of accomplishment. For valuable 
aid, always most cordially rendered, the author is much indebted to Dr. Leonhard 
Stejneger, whose well-known thorough bibliographical knowledge and excellent 
judgment have greatly facilitated the settlement of many vexatious questions of 
synonymy and difficult problems of relationship. To the authorities of the several 
public museums and the owners of the private collections already mentioned, the 
author is glad to have this opportunity of publicly expressing his sense of obliga- 
tion for many courtesies, including, besides unrestricted access to the collections in 
question, the loan of valuable and unique type specimens. 
R. RB. 
