This is an account of a zoo-geographic reconnaissance through the Brazilian hinterland. The official and proper title of the expedition is that given it by the Brazilian Government: Expedicao Scientifica Roosevelt- Rondon. When I started from the United States, it was to make an expedition, primarily concerned with mammalogy and ornithology, for the American Museum of Natural History of New York. This was undertaken under the auspices of Messrs. Osborn and Chapman, acting on behalf of the Museum.