Hibernicoceras mediocre Moore & Hodson 1958
Creators: name: Korn, Dieter
name: Ebbighausen, Volker
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Goniatitida
Goniatitidae
Hibernicoceras
Hibernicoceras mediocre

description: Hibernicoceras mediocre Moore & Hodson, 1958
Figs 18–19; Tables 11, A 6
Hibernicoceras mediocris Moore & Hodson, 1958: 93, pl. 6 figs 1–2, text-fig. 5.
Hibernicoceras mediocris – Kumpera & Lang 1975: pl. 1 fig. 5.
non Hibernicoceras mediocris – Liang & Wang 1991: 99, pl. 22 figs 9–10, pl. 23 figs 1–8, pl. 24 figs 13–14, text-fig. 71.
Diagnosis
Species of Hibernicoceras with a thickly pachyconic conch at 5 mm diameter (ww/dm ~ 0.80), a thickly pachyconic conch at 10 mm diameter (ww/dm ~ 0.80) and a thinly pachyconic conch at 30 mm diameter (ww/dm ~ 0.65). Umbilicus very wide in early juvenile stage (uw/dm ~ 0.45 at 2 mm dm) and becoming continuously narrower throughout ontogeny (uw/dm ~ 0.15–0.20 at 10 mm dm, uw/dm ~ 0.15 at 30 mm dm); umbilical wall sigmoidal with shallow spiral groove. Ornamentation at 20 mm conch diameter with moderately wide-standing, rectiradiate growth-lines with low lateral projections. Spiral lines in a narrow zone on the inner flank; growth lines weakly crenulated on the flank but almost smooth on the venter. Suture line with a weakly Y-shaped, moderately wide external lobe in the adult stage (0.70–0.75 of the external lobe depth; 1.45 of the adventive lobe width), and a moderate median saddle (almost 0.45 of the external lobe depth). Ventrolateral saddle very narrowly rounded, adventive lobe with slightly sinuous flanks.
Type material
Holotype
IRELAND – County Leitrim • Townland of Carraun, north-east slope of Dough Mountain, two miles south-west of Kiltyclogher; beds a few feet above the highest beds with G. sphaericostriatus (Late Viséan); Moore and Hodson Coll.; GSM ZI3014; illustrated by Moore & Hodson (1958: pl. 6 figs 1–2), re-illustrated here in Fig. 18A.
Material examined
MOROCCO – Central Meseta • 18 specs; Sidi Amar, southern side of the Tabaïnout mountain ridge; Late Viséan; 2011; Korn and Ebbighausen leg.; MB.C. 32218.1 to MB.C. 32218.18.
Description
Specimen MB.C.32218.1 (Fig. 18B) is an incomplete, fully chambered conch with a diameter of 32 mm. The conch is almost entirely covered by a recrystallised shell, which may also be encrusted. It is thinly pachyconic and involute (ww/dm = 0.65; uw/dm = 0.14), with a moderately high whorl expansion rate (WER = 1.90).
The two sectioned specimens MB.C.32218.2 and MB.C.32218.3 (Fig. 19A–B) are largely identical in terms of their conch geometry but differ in the development of the umbilical width. In specimen MB.C.32218.2, the umbilicus opens slowly after reaching a conch diameter of 8 mm, with the uw/ dm ratio remaining almost constant at 0.19. In contrast, specimen MB.C.32218.3 exhibits a tubular umbilicus with a stagnant umbilical width, leading to a decreasing uw/dm ratio, which eventually reaches 0.11. Both specimens show a sinuous umbilical wall from a conch diameter of about 8 mm. In particular, specimen MB.C.32218.2 displays a distinct incurve in the middle of the umbilical wall.
Remarks
Moore & Hodson (1958) described the species as Hibernicoceras mediocris, i.e., with a masculine ending, although Hibernicoceras actually requires a neuter ending. As “ mediocris / mediocre ” is an adjective, the ending needs to be corrected to “ mediocre ” according to Article 34.2 of the ICZN Code (ICZN 1999).
Hibernicoceras mediocre differs from most other species in the genus by its rectiradiate growth lines, which have a rather pronounced ventrolateral projection. Additionally, the growth lines in H. mediocre are finer than those found in most other species.
The specimens identified by Liang & Wang (1991) as Hibernicoceras mediocris, with a ww/dm ratio of about 0.70 at 40 mm conch diameter, appear to be too stout to be attributed to this species.
description: Published as part of Korn, Dieter & Ebbighausen, Volker, 2025, Late Viséan (Mississippian) ammonoids (Cephalopoda) from the Central Moroccan Meseta, pp. 50-93 in European Journal of Taxonomy 989 on pages 74-76, DOI: 10.5852/ejt.2025.989.2885, http://zenodo.org/record/15298185