What is "hexameroceras"

Hexameroceras is a nautiloid genus belonging to the Oncocerida that lived during the middle and late Silurian some 422-416 Ma. Its fossils have been found in North America in Indiana, New York, Ohio, and Wisconsin, and in Europe in the Czech Republic.

Hexameroceras is similar to Tetrameroceras but has 3 pairs of dorsolateral sinuses (lateral embayments in the aperture) and narrow mid-dorsal projection or salinet. The shell, as for the family, is breviconic, i.e. short, curved toward the apex, straight toward the aperture. The siphuncle is ventral, nummuloidal (beeded) and contains inwardly radial actinosiphonate deposits.