Mammalogist, ornithologist, geographer and anthropologist. One of the founders of the American Society of Mammalogists, and of the American Ornithologists' Union; the first head of the Section of Ornithology, later the Biological survey; and member of the Board of Geographical Names. He made large collections of North American mammals and birds during his various expeditions, all of which were deposited in the U. S. National Museum. He is most famous for his studies on life zones and was author of most of the first ten numbers of North American Fauna. These letters addressed to Witmer Stone cover the various aspects of his work as outlined above.