mm 



LETTER OF TRANSMITTAL. 



Office op United States Geological amd 

 Geoobapbical Subvey of the Tebbitories, 



Washington, D. C, December 1, 1876. 

 Sir : I have the honor to transmit herewith, fur publication as one of 

 the series of "Monographs of North American Rodentia", a memoir on tho 

 family T'aplodontida;. 



To the single species which constitutes this family, unusual interest 

 attaches, in the facts that its structure has remained very imperfectly known 

 up to the present time, and that its systematic position consequently has been 

 a matter of dispute. The anatomy of the species is herewith presented at 

 considerable length, from original dissections ; and a notice of its history and 

 habits follows the description of its structure. 



Like my other menxirs of this series, the present is based upon the 

 material contained in the ^ 'ional Museum, for the opportunity of examining 

 which I am indebted to the liberal policy of the Smithsonian Institution. 

 I am. Sir, &c., 



ELLIOTT COUES, 

 Assistant S'urgeon United States Army, 

 Secretary and Naturalist of the Survey, 

 Vroi F. V. Haydem, 



United States Geologist-in-charge. 



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