Abstract: New rodent fossils found in the Oligo-Miocene sediments in Kyushu, West Japan, are identified to the following four taxa: l) Castoridae gen. et sp. indet. A; 2) Steneofiber sp. from the Late Oligocene Sasebo Group; 3) Castoridae gen. et sp. indet. B; 4) Diatonys shantungensis from the Early to Middle Miocene Nojima Group. Studies of two specimens identified to the family Castoridae gen. et sp. indet. A and B indicate that they are large beavers with the skull of nearly same size as Trogontherium that holds enamel of longitudinally grooved incisors. Resemblance in size and features of the incisor enamel indicates that these specimens could be of the same genus. Furthermore, it is known that Steneofiber is a cosmopolitan genus, however, it has not been found in the Late Oligocene in East Asia. The occurrence of Diatonys shantungensis, on the other hand, strongly suggests that the late Early Miocene mammals from Japan and the East China• belong to the same province in East Asian margin.

摘要： 日本九州渐新-中新世沉积物中新发现的啮齿类，有四种类型:1.河狸科未定属种A; 2.晚渐新世Sasebo(佐世保)群的Steneofiber sp.; 3.河狸科未定属种B; 4.早-中中新世Nojima(野岛)群的山东硅藻鼠(Diatomys shantungensis )。河狸科的两个未定属种的标本属于大型河狸，头骨大小接近于巨河狸((Trogontherium )，门齿珐琅质具有明显的纵沟。个体大小和门齿珐琅质特征方面的相似性表明这些标本可能为同一个属。Steneofiber是一个遍布北半球的属，以