Uutela, A., Tynni, R. 1991.
Ordovician acritarchs from the Rapla borehole, Estonia.Geological Survey of Finland. Bulletin353,
1-135.
Smelror, M. 1991.
Palynomorphs from the Cyrtograptus centrifugus graptolite zone (Early Wenlock, Silurian), Bornholm.Bulletin of the Geological Society of Denmark39,
2,83-89. DOI:10.37570/bgsd-1991-39-02