During my stay in Spain a rock was found in the surroundings of Ronda, wherein Cycloclypeus was met with by the side of other foraminifera. The scarcity of our knowledge about the occurrence of this genus in Europe and in the Mediterranean Basin, induced me to collect in different parts of Spain, more material wherein Cycloclypeus might occur, especially Oligocene and Miocene rocks. The inducement became even stronger, when a publication by Tan Sin Hok about the genus Cycloclypeus Carpenter, demonstrated the value this genus has for stratigraphy. The results obtained during the examination of the samples, induced me to deviate from my original intention, of giving a survey of the development of the foraminifera-containing Oligocene in some parts of Spain and to try and follow the way indicated by the provisional results. To do so it proved to be desirable to involve other material in this examination.