1. Amler, M.R.W., D. Heidelberger, and H. Schöning. 2002. Gastropoden aus paläozoischen Geschieben des Kies-Sand-Rückens in der Laerheide (Landkreis Osnabrück). Osnabrücker Naturwissenschaftliche Mitteilungen 28: 7–25.
2. Barrande, J. 1850. Graptolites de Bohême. Théophile Haase Fils, Prague (published by the author).
3. Bates, D.E.B., A. Kozlowska-Dawidziuk, J. Maletz, N.H. Kirk, and A.C. Lenz. 2006. The retiolitid graptolite genus Plectograptus: new observations and new species. Acta Palaeontologica Polonica 51: 525–540.
4. Berry, W.B.N. 1964. The middle Ordovician of the Oslo Region, Norway, No. 16. Graptolites of the Ogygiocaris Series. Norsk Geologisk Tidskrift 44 (1): 61–169.
5. Bjerreskov, M. 1975. Llandoverian and Wenlockian graptolites from Bornholm. Fossils and Strata 8: 1–94.