The larger foraminifera，Operculina，has recently been discovered in the Miocene Tottori Group．The biostratigraphical and paleozoogeographical significance of this occurrence are as follows；
（1）The features of the specimen are identical with those of Operculanate japonica． The horizon of Operculina complanata japonica corresponds commonly to the N．8 and rarely to the base of the N．9．The occurrence of Operculina has brought an addition of fossils indicating geologic age in the Tottori Group．
（2） The Tottori area has been assigned to in the Operculina-Miogypsina zoogeographic province on the Japan Sea coast side in the late Early Miocene to early Middle Miocene．This assumption is consistent with the new occurrence of Operculina．