LETTER OF TRANSMITTAL. 



United States Engineer Office, 

 Geographical Explorations and Surveys 



West of the One hundredth Meridian, 



Washington, D. C, February 5, 1875. 



General: I have the honor to transmit herewith a report based upon 

 the results of the examinations of the collections in zoology, made by the 

 several field parties of the survey during the years 1871 to 1874, inclusive. 



In the examination and identification of these collections, several gen- 

 tlemen, eminent in this branch of scientific investigation, have cheerfully 

 rendered valuable assistance, and their reports, together with those by 

 members of the survey, constitute the subject-matter of this volume. 



The general collation of the data and supervision for publication has 

 been intrusted to Acting Assistant Siu'geon H. C. Yarrow, United States 

 Army, in addition to his duties as medical officer during and since 1872, in 

 which he has manifested commendable energy. 



Skilled assistance in this branch was had for the first time in the expe- 

 dition of 1871; the services of Acting Assistant Surgeon W. J. Iloffiuan, 

 United States Army, by detail through the Medical Department, and of 

 Mr. Ferdinand Bischoff, having been secured. 



In 1872, Acting Assistant Surgeon H. C. Yarrow, United States Army, 

 with the assistance of Mr. H. W. Henshaw, and incidentally of other mem- 

 bers of the expedition, accomphshed most satisfactory results. 



In 1873, the force was further augmented by the services of Acting 

 Assistant Surgeons J. T. Rothrock and C G. Newberry, United States 

 Ai-my, and Mr. John Wolf, collector. 



The field operations of the survey require the services of medical offi- 

 cers in their professional capacity, yet not to such an extent as to preclude 

 their availability for labor in other directions, hence their assignment to 

 investigations in the important branches of zoology. 



