Holmiceras havelense sp. nov.

urn:lsid:zoobank.org:act: C92771A7-17B5-4838-8B38-62884C9AAA5C

Fig. 29, Table 8

Lituites aff. praecurrens – Neben & Krueger 1971: pl. 21 figs 2–3.

Diagnosis

Species of the genus Holmiceras with coiled part 21 mm in diameter; uncoiled part nearly straight; expansion angle 7°. Shell surface with growth lines and fine, irregularly spaced lirae.

Etymology

From the river Havel, which flows through the type region.

Type material

Holotype GERMANY • Brandenburg, Werder (Potsdam); Ordovician, Upper Red Orthoceratite Limestone; Neben and Krueger Coll.; previously illustrated by Neben & Krueger (1971: pl. 21 figs 2–3), reillustrated here in Fig. 29A; MB.C.30526.

Description

Holotype MB.C.30526 (Fig. 29A) consists of the coiled part (dm = 21 mm; coiling probably loose, the end of the last volution nearly in contact with the preceding whorl; WER ah = 2.60; WER dm = 2.90) and a short part of the almost straight uncoiled part (length = 29 mm; wh = 14 mm; EA ~ 7°). The delicate shell ornament consists of growth lines and thin lirae, some of which are more raised than others; any prominent annulation is absent. The lirae are laterally oblique, sloping towards the dorsal side; the ventral sinus is deep and rounded and the dorsal projection is flat (Fig. 29B). The CLR is between 0.20 and 0.25.

Remarks

Specimen MB.C.30526 fits in the diagnosis of Holmiceras but differs from all species of this genus in the more delicate ornament and a much smaller expansion angle of the uncoiled conch part (7° in the new species but 20° in the others).

Geographic and stratigraphic occurrence

The holotype is from Werder (Brandenburg, Germany) and comes from erratics (Aseri Regional Stage, middle Darriwilian, Middle Ordovician) in Pleistocene gravel.