Like the Macroura, also the Brachyura collected by Dr. Büttikofer in Central Borneo ought to be considered as a valuable contribution to the Carcinological Fauna of this Island. Fifteen species were collected, all but one freshwater forms, inhabitants of the Kapoeas-basin and of the Upper Mahakkam, and of these 14 Land- and Freshwaterspecies no less than eleven or twelve proved to be new to Science! As far as I am aware, only three freshwater crabs were hitherto known to inhabit the large Island of Borneo, viz. Parathelphusa tridentata H. M. E., Potamon borneense v. Mart, and Pot. loxophthalmum de M. Now, however, this number has increased quintuple! Firstly a remarkable new species of Menippe ought to be mentioned, that was captured at Sanggau on the Middle Kapoeas. It is closely allied to the rare Menippe Panope Herbst from Tranquebar, a species not yet found back since Herbst, as far as I know, and that perhaps once may prove to be also a freshwater crab, whereas the other representatives of Menippe and Myomenippe are marine forms. A new description and a figure of the equally little-known Myomenippe Fornasinii, made after a type-specimen from the Paris Natural History Museum, is added, though this species was not collected. A pretty small Sesarma proved also to be new, unfortunately the locality was not defined, but very likely it has been collected at Sintang. The other 11 or 12 species are all Thelphusidae. Parathelphusa tridentata H. M. E. is represented by 15 specimens; this species is, already since 1868, known to inhabit Borneo by von Martens. This author described in the same year also a new Potamon from Borneo, Potamon borneense, a new variety of which was now collected, probably at Sintang. For this species and for two other new ones a new subgenus Perithelphusa is established.