Hoeloceras
Hoeloceras is an extinct orthoconic nautiloid cephalopod from the upper Ordovician, generally included in the Actinocerida.
Nautiloids are a subclass of shelled cephalopods that were once diverse and numerous but are now represented by only a couple of genera, Nautilus and Allonautilus.
Hoeloceras, which has a straight shell with a broadly curved to almost flattened venter on the underside and a more highly arched dorsum on the upper, meeting acutely on either side, was named by Walter Sweet in 1958 who first recognized it in Ordovician sediments near Oslo, Norway, and included it in the Actinocerida.
Teichert identified Hoeloceras as a synonym of Lambeoceras, as the acutely angled dorso-ventral seam suggests. Flower referred to Hoeloceras as a "flatfish", in common with Lambeoceras and Gonioceras, but reassigned it to the Reudemannoceratidae noting that neither annuli or parispatium - diagnostic of the Actinocerida - had been observed.
Since then specimens identified as Hoeloceras, and retained in the Actinocerida, have been discovered in China and Korea, where, in Korea, it is associated with the actinocerids, Armenoceras, Ormoceras, and Selkirkoceras.