Pleurorthoceras, from Ancient Greek πλευρά (pleurá), meaning "rib or side", ὀρθός (orthós), meaning "straight", and κέρας (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.
References Sweet, Walter C. 1964. Nautiloidea-Orthocerida. Treatise on Invertebrate Paleontology, Part K. Geological Soc of America and Univ Kansas Press.