THE brain-case found by Mr. W. C. Pei at Chou Kou Tien on Dec. 2, 1929, is the most significant and illuminating relic of primitive man ever recovered. Prof. H. Fairfield Osborn, writing in Science of Feb. 22, 1929, raises the possibility that Piltdown man may be so old as the Pliocene. He claims that the dark-coloured fragments of the skull of Eoanthropus are intermingled with similarly coloured fragments of proboscidian molars of unquestionably Upper Pliocene age, and that it is not certain that Eoanthropus belongs to the Lower Pleistocene. In the case of Sinanihropus, there is no such uncertainty as to the contemporary fauna, for the human remains were left on the floor of a cave and a vast number of the animals which roamed the region of Chou Kou Tien in these remote times left their bones in the same cave. As all these fossils belong to the same geological epoch, the Lower Pleistocene, there can be no doubt of the age of Sinanihropus.