LETTER TO THE SECRETARY. vie 
can Mammalogy. Being exhaustive of the subject, it necessarily becomes the 
permanent basis of future work on this group, and remains an enduring wit- 
ness to the industry, ability, and scientific acquirements of the authors. 
A word of explanation of the plan of the work will not be out of 
place. The Report consists of eleven separate and distinct memoirs, each 
_ treating of a single family. The Muride, Zapodide, Haplodontide, Geomyida, 
and Saccomyidz are by Dr. Coues; the Leporide, Lagomyide, Hystricide, 
Castoroidide, Castoride, and Sciuride are by Prof. Allen. The authors, 
while working together in entire accord, have prepared their respective por- 
tions independently of each other, and neither is to be accredited with the 
work of the other, or to be held responsible therefor. Prof. Allen has alone 
treated of the fossil species of the order. The general superintendence of 
the volume during its passage through the press has devolved upon Dr. Coues. 
The memoirs have been accepted for publication and put to press in the 
order in which they have been transmitted to this office. Their sequence in 
the volume, therefore, is not according to the natural classification, which will 
be found upon a subsequent page. 
The Bibliography of North American Mammals (Appendix B), with 
which the work concludes, has been contributed by Prof: Theodore Gill and 
Dr. Coues conjointly. Though regarded by the authors as incomplete, it is, 
nevertheless, by far the most extensive and elaborate exposition of the 
subject extant. 
The thanks of the Survey are due to the Public Printer, the foreman of 
printing, and the proof-readers and compositors of the Government Printing 
Office, for the pains they have taken to render the typography of the volume 
so creditable to all concerned. In this connection, I take pleasure in men- 
tioning particularly Mr. William Young, who may be justly regarded as one 
of the most accomplished proof-readers of the country, and w hose zealous 
discharge of his duties and long experience in scientific publications have 
rendered his services invaluable. 
I have the honor to be, very respectfully, your obedient servant, 
F. V. HAYDEN, 
United States Geologist. 
Hon. Caru Scuurz, 
Secretary of the Interior, Washingten, D. C. 
