Fig. 6 in Morphology and ontogeny of some Middle Ordovician gonambonitid brachiopods from Baltoscandia

Fig. 6. Gonambonitid brachiopod Antigonambonites planus (Pander, 1830) from the Volkhovian regional stage, Darriwilian, Middle Ordovician of the Leningrad Region, Russia; ontogenetic series of dorsal valves. A. PIN 4921/792, exterior of 2 mm wide valve (A1), ribs crossing the halo rings (A2). B. PIN 4921/905, interior of 2.7 mm wide valve. C. PIN 4921/793, umbone of 3.2 mm wide valve showing ribs crossing the halo rings. D. PIN 4921/902, exterior of 3.5 mm wide valve (D1), dorsal umbone (D2), valve interior (D3). E. PIN 4921/899, 4 mm wide valve in exterior view. F. PIN 4921/903, interior of broken 5.5 mm wide valve (F1), dorsal adductor scars (F2).