In the consideration of the Permo-Carboniferous history of Eastern Asia,the Yuehmenkou series stands out as an unit of wide extent both stratigraphicallyand palaeontologically. The name Yuehmenkou series was first given by Dr.Norin in 1922 as a whole coal-bearing formation of Central Shausi, which wasdivided into two parts--a lower, the Taiyuan series, and an upper, the Shansiseries. The type-locality of this formation is the Yuehmenkou, in the WesternHills of Taiyuan. The Taiyuan series is composed mainly of shale, variegatedclay, sandstone, important coal seams and a few interstratified marine lime-stones. The same may be said to be the case in the Shansi series, but thereseems to be only one layer of marine limestone, the Tungtayao Limestone, lo-cally developed at the lower part of this series. The preliminary study of thepalaeozoological remains contained in the marine beds of this formation, leadsProf. Grabau and Dr. Norin to consider its lower part, i. e., the Taiyuan seriesas representing the transition from Viseen to Moscovian, without being as yettrue Moscovian, and its upper, i. e., the Shansi series to be of Permo-Car-boniferous age.