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itis.gov
Integrated Taxonomic Information System (ITIS): Procolobus (TSN 572832)itis.gov. Viitattu 26.7.2014. (englanniksi)
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Oates, J.F., Gonedelé Bi, S., Ikemeh, R., Koné, I., McGraw, S., Nobimè, G., Osei, D. & Wiafe, E.: Procolobus verusIUCN Red List of Threatened Species. Version 2020-1. 2020. International Union for Conservation of Nature, IUCN, Iucnredlist.org. Viitattu 27.3.2020. (englanniksi)