Abstract In comparison to other cephalopods such as ammonites and belemnites, nautilid shells are relatively rare fossils in Jurassic marine deposits and knowledge of their taxonomy is therefore still patchy. We describe herein a new species of Cenoceras, C. rumelangense, from the early Bajocian Humphriesianum Zone of Luxembourg and Southwest Germany. In Luxembourg, the type material occurs in the ‘Marnes sableuses d’Audun-le-Tiche’ unit, which yields other large-sized cephalopods, such as the largest known belemnite genus, Megateuthis. The new species reaches a remarkable size, with diameters up to 610 mm. Thus, it is amongst the largest known post-Triassic nautilids worldwide, together with Paracenoceras giganteum and Paracenoceras ingens from the Upper Jurassic. Additionally, we discuss some aspects of the taphonomy of these large shells deposited in a shallow marine setting.