Lawrenceoceras ebenus Kröger & Pohle 2021, sp. nov

Lawrenceoceras ebenus sp. nov

urn:lsid:zoobank.org:act: C148361C-5535-4AE5-8835-282F9C8C3EC3

Figs 5D–E, 6A, 7B, 8A

Diagnosis

Exogastrically curved conch with angle of expansion of conch width of ca 8° and slightly depressed conch cross section (rW = 1.12); ornamented with fine directly transverse striae and rugae. Siphuncle small, 0.1 of conch height and near conch margin.

Etymology

In honour to the Svalbard Husky “Ebony”, from the Latin ‘ hebenus ’, ‘ebony’.

Type material

Holotype Specimen FMNH-P30335; by monotypy.

Type locality and horizon

Profilstranda section, adjacent to Hinlopenstretet, Spitsbergen, bed Po123.3, 120.3 m above base of Olenidsletta Member, V 2a trilobite zone, Blackhillsian, Floian.

Description

Specimen FMNH-P30335 is a fragment of a curved phragmocone and part of a body chamber with a length of 31 mm and a conch width of 9–13.3 mm (angle of expansion ca 8°). The preserved part of the body chamber is 8 mm long.

The conch surface is ornamented with fine directly transverse striae, 10–12 striae occur per mm at a conch height of ca 11 mm. The adoral ca 10 mm of the fragment surface is additionally ornamented with irregularly spaced rugae. Striae form a very shallow hyponomic sinus on the convex side of the conch curvature.

The conch cross section is slightly depressed, with a height of 11.1 mm where the width is 12.5 mm (rW = 1.12). The septa are narrowly spaced, ca 10–12 chambers occur per distance similar to corresponding conch.

At the adapical end of the specimen the septal perforation is positioned ca 0.7 mm from the conch margin positioned on the convex side of the conch curvature and has a diameter of 0.7 mm. The connecting ring is thick and with concave segments. The septal necks are short and loxochoanitic.

Comparison

Lawrenceoceras ebenus sp. nov. is similar in conch cross section to L. larus sp. nov., but differs from the latter species and other species of this genus in having a distinctively ornamented conch surface.