Jonathan Kingdon, 45 years ago, first pointed out the special nature of the East African coastal and montane forests, that a number of mammals are endemic to these forests, and that they are not just an eastern extension of the Central African rainforest belt. Other authors, and Kingdon himself, subsequently enhanced and modified this concept (which applies also to other animals and to plants) although, in the main, the montane forms have been designated to the ‘Eastern Arc’ region or subregion and the coastal ones to the ‘Swahilian’ region or subregion. In this paper, I review the mammals of these two sets of forests, and find that they are not in fact so different from each other. As such, I formally propose to unite them, using the name under which Kingdon informally designated them, the ‘Zanj Subregion’.