In the Zoological Garden of Dresden, since the year 1887, there has been a living specimen of a Cercopithecus, brought hither from Central West-Africa by Dr. Ludwig Wolf. This specimen so obviously represents an undescribed species of monkey, that I need not hesitate any longer in describing it shortly, though this can be done but imperfectly during its life-time. The following remarks, therefore, must be looked upon as preliminary only, to be completed after the animal’s death. This new species belongs to the Mona-group, which was divided by Prof. Schlegel (Cat. Mus. Pays-Bas, Singes, 1876, p. 80) into those with white over the root of the tail and those-without it.