Redpathoceras depressum Kröger 2013, sp. nov.
Creators: name: Kröger, Björn
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Ascocerida
Probillingsitidae
Redpathoceras
Redpathoceras depressum

description: Redpathoceras depressum sp. nov.
urn:lsid:zoobank.org:act: C6767BCC-4FD2-4A7E-BE5C-F4738889A43E
Figs 10E, 18G, 42, 43 D-F
Diagnosis
Redpathoceras with curved mature body chamber; inflated in lateral view with maximum height of ca. 55 mm at mid-length of body chamber; mature body chamber margin at concave side of conch curvature concave throughout total length; conch cross section depressed; premature conch expands with angle of expansion less than 10°; diameter of terminal septum of truncation ca. 45 mm; ornamented with fine longitudinal striae and irregularly spaced transverse growth lines, which form a wide hyponomic sinus.
Etymology
Refers to the distinctively depressed conch cross section of this species.
Type material
Holotype
PMU 26927.
Paratypes
Seven paratypes (PMU 26928–26934), Kallholn, Dalarna, Sweden, Boda Limestone, late Katian.
Type locality and horizon
Kallholn, Dalarna, Sweden, Boda Limestone, Boda Core Member, late Katian, Ordovician.
Description
The holotype is a nearly complete mature conch, 120 mm long. The conch is depressed with a height of 41 mm and width of 48 mm at the septum of truncation (width/height ratio 1.2). At the aperture, these measurements are 50 mm and ca. 65 mm, respectively (width/height ratio 1.3; Figs 10E, 43D, F). The mature conch is moderately curved. The convex side of the conch curvature is more strongly curved than the concave side, resulting in a maximum conch height at approximately the mid-length of the mature body chamber of 55 mm. Immediately adoral to the septum of truncation the conch appears to be a slighty constricted. The length of the phragmocone and the numbers of chambers of the phragmocone are not known, as the conch wall obscures details of the septa. The outermost layer of the shell is poorly preserved, with no traces of the ornamentation remaining (Fig. 18G).
Four specimens (PMU 26930–26933) represent truncated portions of the phragmocone. All four specimens possess at their apical end a deeply curved septum of truncation. The conch height at the septum of truncation varies between 23 and 28 mm and the adoral-most diameters lie between 36 and 38 mm, giving angles of expansion ranging from 6 to 8° (Fig. 42). The conch cross section in these specimens is depressed (width/heigh ratio 1.03–1.16) and they are more curved than the mature fragment (holotype). In specimen NRM Mo 152301 the entire length comprises seven chambers. The suture is nearly directly transverse, but forms a shallow, wide lobe on the convex side of the conch curvature. All four specimens are distinctively ornamented with fine longitudinal striae and fine, irregularly spaced growth lines, forming a wide sinus on the convex side of the conch curvature.
Comparison
This species of Redpathoceras is similar to the type of the genus in having a depressed conch cross section, but differs in having a larger adult size. The adult size is similar to that seen in R. bullatum sp. nov., which in turn differs in having a circular-compressed conch cross section in premature growth stages.
Stratigraphic and geographic range
Boda Limestone, late Katian, Dalarna, Sweden.
description: Published as part of Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, pp. 1-110 in European Journal of Taxonomy 41 on pages 91-92, DOI: 10.5852/ejt.2013.41, http://zenodo.org/record/3814221