Pleurorthoceras, from Ancient Greek ÃÂûõàÃÂì (pleurá), meaning "rib or side", á½ÂÃÂøÃÂà(orthós), meaning "straight", and úÃÂÃÂñà(kéras), meaning "horn", is an orthocerid cephalopod from the Upper Ordovician of North America (Ohio, Manit). The shell externally is like that of Michelinoceras in being long and slender with a circular cross section. It differs in having a subcentral siphuncle with somewhat inflated segments.