THE NORTH-AMERICAN ARBOREAL SQUIRRELS. 
J. A. ALLEN. 
No attempt at a critical revision of the American arboreal 
squirrels has been made since 1878, but during the last two 
years several noteworthy contributions to this end have 
appeared, covering practically the Sciuri occurring north of 
Panama; but those of South America still await revision. The 
latest and by far the most important of these contributions is 
Mr. E. W. Nelson’s recently published “ Revision of the Squir- 
rels of Mexico and Central America,” ! which marks an epoch 
in the history of the subject. Mr. Nelson is not only a well- 
trained naturalist, but has several marked advantages over 
previous monographers in having at his command not only 
a far greater amount of material, but material incomparably 
better in character, and also an intimate acquaintance with the 
physiographic conditions of the region to which his studies 
relate, and with the animals themselves in life, gained through 
eight years’ field experience in Mexico and Central America. 
He has not only thoroughly explored, in company with his 
assistant, Mr. E. A. Goldman, under the auspices of the United 
States Biological Survey of the Department of Agriculture, 
western Guatemala, but has traversed Mexico from sea to sea, 
and from north to south, on several different lines. Of the 919 
specimens on which his monograph is based, more than 600 
were collected by himself and assistant. During the prepara- 
tion of his paper he was “able to examine representatives — 
and in most cases types or topotypes— of nearly all the known 
species and subspecies found in Mexico and Central America.” 
The investigation, under such favorable conditions, of the large 
amount of excellent material at his disposal has led him to 
recognize 30 species and 13 subspecies as occurring between 
1 Proc. of the Washington Acad. of Sci., vol. i, pp. 15-106, Pls. I and II. Pub- 
lished May 9, 1899. 
635 
