LETTER OF TRANSMITTAL. 
[Covering Lagomyida, Castoroidida, and Castorid@. } 
CamBripcE, Mass., November 8, 1876. 
Sir: I transmit herewith for publication my articles on the families 
Castoroidide, Castoride, amd Lagomyide. The first (Castoroidide) is repre- 
sented, so far as at present known, by the single extinct species Custoroides 
ohioensis ; the second (Castoridz) by one living species (Castor fiber) and 
several extinct ones; the third (Lagomyide) by the single living species 
Lagomys princeps. 
The materials on which these reports are based are contained mainly in 
the National Museum at Washington. Iam, however, indebted to the Museum 
of Comparative Zodlogy for important additional materials, and have been 
further greatly aided by specimens kindly loaned me by the Boston Society ot 
Natural History. I have also been kindly permitted to examine the speci- 
mens of the extinct species of Castoride described by Dr. Leidy, contained 
in the Museum of the Academy of Natural Sciences of Philadelphia. The 
forms described by Professor Cope I know as yet only from his published 
descriptions and figures. 
I am, Sir, very respectfully, yours, 
J. A. ALLEN. 
Dr. F. V. Haypen, 
United States Geologist, etc., etc., Washington, D. C. 
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