Coelorinchus nordenskjoeldi Schwarzhans & Mors & Engelbrecht & Reguero & Kriwet 2017, sp. nov.

Coelorinchus nordenskjoeldi sp. nov.

(Figs 4N—R, 6J—L)

Material. Holotype: NRM-PZ P.15978 (Figs 4N—P, 6J—L). Paratypes: eight specimens, NRM-PZ P.15979—15980 (Fig. 4Q, R). Other material: 11 eroded or fragmentary specimens, NRM-PZ P.15981—15982.

Occurrence. Telm 5 unit; ‘ Natica horizon’, Cucullea I member, La Meseta Formation, late Ypresian, early Eocene. Site IAA 1/90, Seymour Island, Antarctica.

Etymology. Named in honour of Dr Otto Nordenskjold, leader of the Swedish South Polar Expedition 1901—1903.

Diagnosis. OL:OH = 1.9—2.0. Dorsal rim with broad predorsal angle. Ventral rim rather shallow, deepest anteriorly, sometimes flattened at deepest point. CCL: OCL = 1.3; CaL:OsL = 1.3—1.45. Collum narrow, ventrally indented, without pseudocolliculum.

Description. Moderately elongate and moderately thin otoliths of up to at least 6 mm in length (holotype 5.7 mm long). OH:OT = 2.6—3.0. Dorsal rim highest anteriorly above ostial collum with broad predorsal angle, rim somewhat undulating, posteriorly regularly declining with very broad, indistinct postdorsal angle near end of cauda. Ventral rim moderately shallow, deepest below ostium and deepest area flattened in large specimens. Anterior rim with obtuse angular tip at level of ostium; posterior rim tapering, somewhat projecting, rounded, with tip at level of cauda.

Inner face slightly convex with distinctly supramedian, moderately narrow and shallow sulcus. Ostium distinctly shorter than cauda. Ostial and caudal colliculi well marked, with narrow, ventrally indented collum; no pseudocolliculum. Dorsal depression narrow, indistinct; ventral furrow feeble, close to ventral rim of otolith; few radial furrows along rims, diminishing in large specimens. Outer face almost flat, with many radial furrows coalescing at centre of outer face without umbo.

Remarks. Coelorinchus nordenskjoeldi was the most common species at the collection site. Yet it shows little variability, being mainly restricted to the expression of the ornamentation of the otolith rims and the outer face.

Coelorinchus nordenskjoeldi is readily distinguished from the co-occurring C. balushkini through its more elongate shape (OL:OH = 1.9—2.0 vs. 1.7) and narrow, indented collum without pseudocolliculum (vs. moderately wide collum and with pseudocolliculum). There are no comparable species from other Eocene locations of the Southern Ocean.