LETTER OF TRANSMITTAL. 
Museum or ComparaTiIvE Zoo.ocy, 
Cambridge, Mass., March 15, 1877. 
Sir: transmit herewith for publication my memoir on the North Ameri- 
can Sciuride. As only two genera of the Sciwride 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 Sciuride”. 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 fo 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 Zodlogy at Cambridge, Mass., without access to which my me- 
moir would have been far more incomplete than it isat 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 specinens of the 
American Sciuride. 
I am, Sir, very respectfully, yours, 
J. A. ALLEN. 
Dr. I’. V. Haypen, 
United States Geologist, etc., ete, Washington, D. C. 
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