Quadrum gartneri Prins & Perch-Nielsen in Manivit et al., 1977
Polycyclolith features a two-storey wall, each storey consisting of four to nine segments, with or without free length. The inner ends of the segments converge at the centre, leaving no central opening for diaphragm development. The walls are moderately to firmly twisted along their joining surface. The segments may vary in size or be equal in dimension. The number of segments, which decreases over time, defines the species within Quadrum.
Quadrum is distinguished from Lithastrinus and Uniplanarius by the absence of a diaphragm.
Manivit, H., Perch-Nielsen, K., Prins, B. & Verbeek, J. W. 1977. Mid Cretaceous calcareous nannofossil biostratigraphy. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen B80(3): 169-181.