LETTER OF TRANSMITTAL. 



Museum of Comparative Zoology, 



Cambridge, Mass., March 15, 1877. 



Sir: I transmit herewith for publication my memoir on the North Ameri- 

 can SciuridcB. As only two genera of the Sciurida of the New World are 

 represented south of the southern boundary of the United States, and one of 

 these by only a single species not found north of that line, I have thought it 

 best to include all of the New World forms in the present memoir, thereby 

 making it a "Monograph of the American Sciuridse". The extralimital species 

 belong, with a single exception, to the genus Sciurus, which has its centre of 

 development in Mexico and Central America. It has, however, represent- 

 atives throughout the greater part of both Americas. 



As in the case of previous monographs of this series which I have 

 had the pleasure of transmitting to you for publication, the present memoir 

 is based mainly on the material contained in the National Museum at Wash- 

 ington, including all that has been collected either by yourself personally or 

 under your immediate direction and auspices. In addition to this, I have 

 been able to use a large amount of material contained in the Museum of 

 Comparative Zoology at Cambridge, Mass., without access to which my me- 

 moir would have been far more incomplete than it is at present. In this con- 

 nection, I beg leave to express my gratitude to the officers of both these 

 institutions for their kindness in allowing me the freest access to these mag- 

 nificent collections, embracing upward of two thousand specimens of the 

 American Sciurida'. 



I am, Sir, very respectfully, yours, 



J. A. ALLEN. 



Dr. F. V. Hayden, 



United States Geologist, etc., etc , Washington, D. C. 



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