The post-cephalic morphology of the middle Ordovician trilobite Prionocheilus narinosus from the central Oslo Region, Norway

The thorax and pygidium of the rare middle Ordovician (clingani graptolite zone) trilobite Prionocheilus narinosus (Siveter, 1977) are described from a nearly complete specimen found at Ringåsen, Norderhov, Ringerike District, Oslo Region. This is the first known association of cranidium, thorax and pygidium of this species and this new record also extends its geographic distribution. It may be a junior synonym of P. foveolatum (Törnquist, 1884).