Fig. 11 in Revision of Middle Ordovician orthoceratacean nautiloids from Baltoscandia

Fig. 11. Polished sections of the siphuncle. A. Ctenoceras schmidti (Noetling), NRM−Mo 160668b, Kandel (Estonia). Note the calcified connecting ring and the thin lining of a sphaerolitic−prismatic layer at the outer surface of the connecting ring, × 25. B. Archigeisonoceras folkeslundense sp. nov., NRM−Mo 3223, Källa (Öland). Note the porous structure of the calcified connecting ring and the sphaerolitic−prismatic layer, × 10. C. Orthoceras scabridum Angelin, NRM−Mo 154771, Södre Bäck (Öland), × 30. D. Plagiostomoceras fragile sp. nov., NRM−Mo 160559, Gardslösa (Öland), × 6.3. E. Archigeisonoceras repplingense sp. nov., NRM−Mo 3285 not numbered, Hälludden (Öland), note the asymmetrical development of the endosiphuncular annuli, × 18. F. Archigeisonoceras repplingense, NRM−Mo 3284, Hälludden (Öland), apical part, × 18. G. Archigeisonoceras repplingense sp. nov., NRM−Mo 3293, Torp (Öland), note the thin sphaerolithic−prismatic layer of the connecting ring, × 22.