Fig. 4

Dolorthoceras sp. (PIN-1894/100); River Malaya Usa, Polar Urals, NW Russia; Frasnian, Late Devonian. Median conch section. The clutch along with thin connecting ring continues on the adapical septal surface. Note the ultrastructural difference between the regular mineralization of the septum and septal neck, on the one hand, and on the other hand, the irregular mineralization of the clutch continutaion along septum indicative the post-mortem diagenetic fossilization of the primarily organic matter. Scale bar is 0. 1 mm. ch chamber, cr connecting ring, cls clutch continuation along septum, s septum, ls lens-shaped structure (sectioned clutch), siph siphuncle, sn septal neck