Wikipedia
Octamerella
Octamerella is an extinct genus of prehistoric nautiloid from the oncocerid family Hemiphragmoceratidae that lived in what is now Europe and North America during the Middle Silurian.
Octamerella has a breviconic shell and a mature aperture that is contracted so as to have four pairs of dorsolateral sinusus, four on each side, and a narrow mid dorsal salient. The two ventral-most sinus pairs are typically the larges while the dorsal-most pair is short and wide, forming a circular opening. (Sweet, 1964)