The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden Author Kröger, Björn text European Journal of Taxonomy 2013 2013-03-27 41 1 110 journal article 22319 10.5852/ejt.2013.41 386010a0-6da4-4fa3-9d1a-4b3b5427cac5 2118-9773 3814221 A2F1B9ED-870A-466E-B35E-BD5DA782476E Nathorstoceras adnatum sp. nov. urn:lsid:zoobank.org:act: 58064C88-D4A3-4CA4-B6EA-DE719EE0F724 Figs 10C , 13F , 19A , 20A , 21B Diagnosis Nathorstoceras with nearly straight and very weakly annulated conch with angle of expansion of 8°; annulations more pronounced in late growth stages; shell ornamented with regularly spaced transverse lirae and distance between annulations ca. 0.2 of corresponding conch height; annuli and lirae form shallow sinus on prosiphuncular side; conch cross section compressed with width/height ratio of ca. 0.8; septal distance ca. 0.24 of corresponding conch height; siphuncle subcentral with SPR 0.41; septal perforation with diameter of ca. 0.05 of corresponding conch height; siphuncular segments abruptly expanded at septal foramen with maximum diameter of ca. 0.14 of corresponding conch cross section; endosiphuncular deposits unknown. Etymology Refers to the strongly expanded, adnate siphuncular segments of this species. Holotype PMU 26733 . Type locality and horizon Kallholn, Siljan District, Sweden , Boda Limestone, Boda Core Member, late Katian, Ordovician. Description The specimen is a portion of phragmocone ca. 50 mm long, with a height of 37–44 mm and a width at the adoral end of 30 mm (width/height ratio 0.81, angle of expansion 8°) ( Fig. 10C , 19A ). The conch is faintly annulated with a distance between two successive annuli of ca. 0.2 of the corresponding conch cross section, and ornamented with pronounced, regularly spaced lirae, with a distance between two subsequent lirae of ca. 1. 5 mm . The conch is is nearly straight, with a subcentrally positioned siphuncle; at the apical end of the specimen its distance from the conch margin is 15 mm (SPR 0.41). The connecting ring is much wider than the septal perforation ( Figs 20A , 21B ). At the adapical end of the specimen the septal perforation is ca. 2 mm and the maximum diameter of the siphuncle is 5 mm (0.05 and 0.14 of the corresponding conch cross section, respectively). The sutures are directly transverse and form shallow lateral lobes. At the adapical end of the specimen the distance between two septa is 9 mm (0.24 of corresponding conch cross section). The septal necks are achoanitic and the siphuncular segments are adnate, abruptly expanded at septal foramen. No cameral and endosiphuncular deposits occur. Comparison See comparison with Nathorstoceras kallholnense sp. nov. (above). Family Geisonoceratidae Zhuravleva, 1959