Olenidslettoceras farmi Kröger & Pohle 2021, gen. et sp. nov.

Olenidslettoceras farmi gen. et sp. nov.

urn:lsid:zoobank.org:act: 8AE46041-CAE1-4ABB-8082-A21AD56CB9E5

Figs 5F–G, 6D, 8C, 50A

Diagnosis

As for genus, by monotypy.

Etymology

Referring to M/S Farm, the transport vessel of Henningsen Transport & Guiding A/S that brought the specimen back from Profilstranda to Longyearbyen; Spitsbergen.

Type material

Holotype Specimen FMNH-P30380.

Paratype One additional specimen, FMNH-P30345, from type horizon and locality.

Type locality and horizon

From Profilstranda section, adjacent to Hinlopenstretet, Spitsbergen, bed PO 123.3, 120.3 m above base of Olenidsletta Member, V 2a trilobite zone, Blackhillsian, Floian

Description

The holotype is a 47 mm long fragment of a phragmocone with part of the body chamber preserved (Fig. 5F–G). The conch is exogastrically curved, more so in the apical parts of the specimen. The preserved part of the body chamber is ca 15 mm long. The conch cross section is elliptically depressed, it grows in width from 9.5 mm to 14 mm and in height from 7.6 mm to 10.8 mm at a length of 36 mm

(expansion of width 7°, of height 5°, rW ≈1.3). The surface of the holotype is relatively poorly preserved but is presumed originally smooth, with weak growth lines.

The second specimen has a well-preserved conch surface and shows weak growth lines which run directly transverse and form a shallow and wide sinus at the antisiphuncular side of the conch. The second specimen is a fragment of a phragmocone, which grows in width from 8.7 to 11 mm and in height from 7.2 mm to 9.2 mm (expansion of width 11°, and height 9°) at a length of 13 mm. The corresponding rW is 1.21 and 1.19, respectively.

The chamber spacing is narrow, seven to ten chambers occur at a distance similar to the conch height. The siphuncle is close to the conch margin, has thick connecting rings which are tubular at the dorsal side (the side directed toward the conch center) and concave at the ventral side (Fig. 6D). The septal necks are short, thickened and orthochoanitic to suborthochoanitic (Figs 8C, 50A).

Remarks

The curvature of the conch of this species is relatively weak compared with the other cyrtocones from the Olenidsletta Member (e.g., Lawrenceoceras larus sp. nov., Valhalloceras floweri). The species can be distinguished from the superficially similar Valhalloceras floweri by its weaker curvature and relatively low angle of expansion. The septal necks are very similar to the necks of Middle Ordovician species of Richardsonoceroides and Richardsonoceras (see Kröger et al. 2009b: fig. 9.10–11). The new genus differs from Richardsonoceroides in having a depressed conch cross section and siphuncular segments with a concave ventral and tubular dorsal shape. Olenidslettoceras farmi gen. et sp. nov. is provisionally placed within the Phtanoncoceratidae because of its combination of characteristic septal necks, the presence of a partly tubular siphuncle and exogastric conch curvature.