Kinnekulloceras kinnekullense ( Foord, 1887 )

Kröger, Björn, 2004, Revision of Middle Ordovician orthoceratacean nautiloids from Baltoscandia, Acta Palaeontologica Polonica 49 (1), pp. 57-74 : 72

Kinnekulloceras kinnekullense ( Foord, 1887)

Fig. 12D .

* Orthoceras kinnekullense sp. nov.; Foord 1887: 400, fig. 2a–c. Orthoceras kinnekullense Foord ; Foord 1888: 2, fig. 1a–c. Orthoceras kinnekullense Foord ; Crick 1898: 85.

Orthoceras kinnekullense Foord ; Phillips 1982: 38.

Orthoceras kinnekullense Foord ; Hughes 1985: 178, fig. 3A, E. Orthoceras kinnekullense Foord ; Phillips 1987: 81.

“ Geisonoceras ” kinnekullense (Foord) ; King 1999: 147, fig. 5C, D.

Material.— Seventeen specimens from the collection of the NRM were considered; most specimens are testiferous, some with preserved body chamber .

Description.—Conch form: Cross section nearly circular. Apical angle of the conch of the specimen figured in Foord (1888): 6.3°. Mean apical angle of the entire material (n = 12): 4.6°, with a maximum apical angle of 6.3° and a minimum angle of 1.7°.

Ornamentation: Shell transversally striated. In between the striae smooth, flat raised lirae ( Fig. 6C ) (called “ribblets” by Foord 1888). The distance of the lirae varies in the course of the ontogeny of the specimens and between the specimens (mean ca. 0. 5 mm).

Phragmocone: Chamber height with x: 0.73 (n = 9) varies strongly between the observed specimens as well as in the ontogeny between max: 0.9 and min: 0.2of the respective diameter. Foord (1888) gives a chamber height of 0.33 of the respective diameter. Sutures straight. Shape of the septa mammoidal. Orthochoanitic septal necks. Connecting ring bulging slightly outwards. Irregular endosiphuncular annuli are sometimes very well developed and may fuse to form an endosiphuncular lining ( Fig. 12D ). Irregular, bullet−like, hypo− and episeptal deposits vary in their grade of exposition. The cameral deposits of the antisiphonal part of the phragmocone are generally strongly developed as in Nilssonoceras nilssoni , thus cutt specimens could show endosiphuncular lining, endosiphuncular annuli, and cameral deposits in any variety. The position of the siphuncle is subcentral (sp = 0.42). The thickness of the siphuncle is ca. 0.1 of the respective shell diameter.

Living chamber: Not known. The maximum known diameter of Kinnekulloceras kinnekullense is 82mm, but most fragments of the shell show diameters lower than 10 mm.

Comparison.— Kinnekulloceras kinnekullense differs from Nilssonoceras nilssoni in its different ornamentation.

Distribution.— Kinnekulloceras kinnekullense occurs in the Folkeslunda Limestone (Lasnamägian) of Öland, Västergötland, Östergotland, and Dalarna.

Figures

Fig. 12. Polished sections of the siphuncle. A. Archigeisonoceras folkeslundense sp. nov., NRM−Mo 3223, Källa (Öland), showing the structure of the connectig ring and the layered structure of the endosiphuncular annuli, × 35. B. Archigeisonoceras picus sp. nov., NRM−Mo 14455, Resmo (Öland), apical part of the phragmocone, × 8. C. Nilssonoceras nilssoni (Boll), NRM−Mo 3328, Hulterstad Kanalen (Öland), middle part of the phragmocone, × 12. D. Kinnekulloceras kinnekullense (Foord), NRM−Mo 155245, Utby (Dalarna), × 12. E. Archigeisonoceras picus sp. nov., NRM−Mo 14455, Resmo (Öland), middle part of the phragmocone, × 8. F. Nilssonoceras nilssoni (Boll), NRM−Mo 3328, Hulterstad Kanalen (Öland), apical part of the phragmocone with irregular endosiphuncular annuli and lining and strong cameral deposits, × 12. G. Arionoceras lotskirkense sp. nov., NRM−Mo 3296, Hällar (Öland), × 25.

Fig. 6. Schematic sketches of the cross section of the shell. Shell ornamentation of Orthoceras (A), Nilssonoceras (B), and Kinnekulloceras (C) (aperture to the right).