Lawrenceoceras ebenus, Kröger & Pohle, 2021

Kröger, Björn & Pohle, Alexander, 2021, Early-Middle Ordovician cephalopods from Ny Friesland, Spitsbergen - a pelagic fauna with Laurentian affinities, European Journal of Taxonomy 783 (1), pp. 1-102 : 10-12

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.

Figures

Fig. 5. Cyrtoconic cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A–C. Lawrenceoceras larus sp. nov., FMNH-P30351, holotype, from bed PO 131. A. Lateral view with siphuncle on left side. B. Ventral view, prosiphuncular side. C. Adoral view of septum and septal perforation.D–E. Lawrenceoceras ebenus sp. nov., FMNH-P30335, holotype, from bed PO 123.3. D. Lateral view with siphuncle on left side. E. Ventral view, prosiphuncular side. F–G. Olenidslettoceras farmi gen. et sp. nov., FMNH-P30334, holotype, from bed PO 123.3. F. Lateral view with siphuncle on left side. G. Ventral view, prosiphuncular side. H–N. Vallhalloceras floweri King & Evans, 1990. H–I. Specimen FMNH-P30337, from bed PO 131. H. Lateral view, siphuncle on right side I. Ventral view, prosiphuncular side. J–L. Specimen FMNH-P30343 from bed PO 123.3, J. Lateral view with siphuncle on left side. K. Ventral view, prosiphuncular side. L. Dorsal view, antisiphuncular side.M–N. Specimen FMNH-P30338 from bed PO 131. M. Lateral view with siphuncle on left side. N. Ventral view, prosiphuncular side. O–Q. Cyclostomiceras profilstrandense sp. nov., specimen FMNH-P30336, from bed PO 123.3. O. Lateral view with siphuncle on left side. P. Ventral view, prosiphuncular side. Q. Dorsal view, antisiphuncular side. Scale bar = 10 mm for all figures.

Fig. 6. Median sections of cyrtoconic cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A. Lawrenceoceras ebenus sp. nov., FMNH-P30335, holotype, from bed PO 123.3. B. Lawrenceoceras larus sp. nov., FMNH-P30355, paratype, from bed PO 131. C. Vallhalloceras floweri Evans & King, 1990, FMNH-P30340, from bed PO 131. D. Olenidslettoceras farmi gen. et sp. nov., FMNH-P30334, holotype, from bed PO 123.3. Scale bar = 5 mm for all figures.

Fig. 7. Details of siphuncle and septal necks, median sections of cyrtoconic ellesmeroceratids from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. Note the loxochoanitic septal necks and the concave siphuncular segments. A. Lawrenceoceras larus sp. nov., FMNH-P30355, paratype, from bed PO 131. B. Lawrenceoceras ebenus sp. nov., FMNH-P30335, holotype, from bed PO 123.3. Scale bar = 1 mm for all figures.

Fig. 8. Reconstruction and interpretation of details of connecting ring and septal necks in cyrtoconic cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A. Lawrenceoceras ebenus sp. nov., FMNH-P30335, holotype, see also Fig. 7B. B. Vallhalloceras floweri Evans & King, 1990, FMNH-P30340, see also Fig. 50B. C. Olenidslettoceras farmi gen. et sp. nov.,FMNH-P30334, holotype, see also Fig. 50A.D. Nyfrieslandoceras bassleroceroides gen. et sp. nov., FMNH-P30353, holotype, see also Fig. 49C. Black: septal neck and septum. Dark grey: connecting ring. Light grey: cameral deposits. Without scale.