Figure 15.  Thin section of white limestone facies showing a slightly oblique, slightly off-axial section through Grzybowskia jasoni n.sp. and two specimens of the small species Discocyclina oceanica Nuttall. The involute nature of the Grzybowskia test is clear. The first two whorls are virtually indistinguishable from Palaeonummulites, but by the third to fourth whorl the rapidily increasing spire height and increasing numbers of septa distinguish this specimen as an involute heterostegine. Figure is 2.5 mm high.