ABSTRACT: Poseidonamicus is one of the most intensively studied genera among marine fossil ostracods due to its common occurrence in the world deep oceans and its distinctive morphological features. Many studies using Poseidonamicus have contributed to our understanding in a wide range of research topics, from evolutionary developmental biology to paleoenvironmental reconstruction. However, taxonomic confusion with Poseidonamicus species remains widespread because of subtle interspecific differences within this genus and limited taxonomic work on deep-sea faunas. The objectives of this paper are to update taxonomic information about Poseidonamicus species in the Pliocene–Quaternary North Atlantic, and to summarize paleobiogeographical distribution of all known Poseidonamicus species.We describe one new species, Poseidonamicus parasculptus n. sp., and present high-resolution scanning electron microscope images of North Atlantic Poseidonamicus major for the first time. Our distributional compilation shows that many Poseidonamicus species are confined to either the Indo-Pacific, theAtlantic, or the Southern Oceans. This information may provide identification guidance for future regional studies.