Fig. 3 in Enrolment in a Middle Ordovician agnostoid trilobite

Fig. 3. Trinodus elspethi (Raymond, 1925), silicified specimens from Edinburg Formation, Virginia, USA, PMO 206.304/1. A. Detail of articulating groove on posterior margin of the first thoracic segment. B. Lateral view showing inflated distal end and flange. During enrolment the latter slots into the base of the posterolateral spine of the cephalon. C. Detail of articulating groove along anterior margin.