Striatocycloceras, in Kroger & Isakar, 2006

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 29-30

Striatocycloceras ? sp.

Fig. 15

Material

One specimen: PMU 26699, Kallholn, Siljan District, Sweden; Boda Limestone.

Description

The 90 mm long shell fragment consists in part of a body chamber. The maximum width of the fragment is 57 mm, from which a conch of ca. 70 mm in diameter may be reconstructed, based on the cross section. The conch was slightly curved and annulated with prominent, directly transverse annuli. The distance between the annuli is 10–15 mm, with a tendency to decrease toward the aperture (ca. 0.14–0.2 of conch cross section; seven to five chambers in a distance equal to the corresponding cross section). The shell surface is ornamented by narrowly, irregularly spaced distinctive growth lines (ca. 4 per one millimeter; Fig. 15 ). Additionally, on the inner surface of the shell, fine inconspicuous longitudinal lirae are visible (ca. one per millimeter).

Remarks

This orthoconic shell fragment is only provisionally assigned within Striatocycloceras . Nothing is known about the internal characters of this specimen. This generic identification is solely based on the annulated orthoconic shell, which is additionally transversally striated, a feature that is known exclusively from Striatocycloceras in the Late Ordovician beds of Baltoscandia.

Figures

Fig. 15. Fragments of the outer shell and negative shell impression of Striatocycloceras? sp., PMU 26699, Kallholn, Boda Limestone. Scale bar = 10 mm.