Abstract: Four Eocene mammals were reported from the Bayan Ulan locality, Nei Mongol, China, including a new rodent species— Mergenomys neimongolensis. The new species differs from the type species of the genus, M orientalis, in being larger and having the ectolophid and hypoconulid more labially positioned. Based on the fossils and stratigraphic correlations, the beds that were previously considered to be "Irdin Manha Fomation" in the Bayan Ulan section are actually two rock units: the Irdin Manha formaüon below and the Shara Murun formation above. The new materials come from the late Middle Eocene Shara Murun formation.

摘要： 记述了在内蒙古巴彦乌兰地区发现的4种始新世哺乳动物化石，其中包括1个啮齿类新种—Mergenomys neimongolensis sp. nov.。新种与在蒙古共和国发现的属型种M.orientalis的不同在于个体大，下臼齿下外脊和下次小尖相对偏于唇侧。新化石的发现以及对岩石地层的分析表明巴彦乌兰剖面上原认为的伊尔丁曼哈组应包含伊尔丁曼哈及沙拉木伦组两个地层单位。