Examples of nautiloid muscle scars. Muscle attachment scars preserved on the internal moulds of body chambers. a–c Ventral, lateral (dorsum on left), and dorsal views of the dorsomyarian muscle attachment scars of Orthoceras regulare (Schlotheim, 1820), × 0.57; d internal mould of the body chamber of the oncocerid Diestoceras sp. showing multiple pairs of muscle attachment scars circumscribing the base of the body chamber, with a pair of enlarged scars over the venter; eUranoceras (?) longitudinale (Angelin, 1880), bilobed ventromyarian scar at base of body chamber, × 0.8; f Body chamber of Estoniceras perforatum Schröder, 1888 with large ventral muscle attachment area × 1.0; g Line diagrams showing the four main types of muscle attachment scars seen on nautiloid cephalopods. Arrows indicate direction of aperture, V venter, D dorsum.