Extensive field work in the Intendencia Meta and the Comisaria Vaup^s and Amazonas, Colombia, over a period of six years has en- abled me to observe both species of the little known crocodilian genus Paleosuchus.This genus differs from the closely related Caiman in various characteristics but most obviously in the completely ossified palpebrals (bony eyelids) and the lack of the transverse preorbital ridge.The latter characteristic has given the two species the name "smooth fronted caimans."They are to be found mainly in the Amazon and Orinoco basins (Schmidt, 1928), where they live in the general area with Caiman sclerops and Melanosuchus niger but occur in a restricted ecological niche.