Heminautilus

Heminautilus is an extinct genus of nautiloids from the nautilacean family Cymatoceratidae that lived during the early Cretaceous (Kummel 1964). Nautiloids are a subclass of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species.

Heminautilus has a discoidal compressed involute shell with flanks converging on a narrow flattened outer margin, the venter. Whorls are higher than wide. The suture is sinuous with a ventral lobe, subtriangular saddles on the ventral shoulders, broad lateral lobes, and narrow rounded saddles on the umbilical shoulders. The siphuncle is subcentral (Kummel 1964).