INTRODUCTION. ^jji 



privilege of consulting specimens and books so essential to the preparation of this 

 ■work, but also for the I'ricndly 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 

 S3-non3-m3- 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. 



E. R. 



