Hibernicoceras mediocre Moore & Hodson, 1958

Korn, Dieter & Ebbighausen, Volker, 2025, Late Viséan (Mississippian) ammonoids (Cephalopoda) from the Central Moroccan Meseta, European Journal of Taxonomy 989, pp. 50-93 : 74-76

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.

Figures

Fig. 18. Hibernicoceras mediocre Moore & Hodson, 1958.A. Holotype GSM ZI3014 (Moore and Hodson Coll.) from the Townland of Carraun (Ireland). B. Specimen MB.C.32218.1 (Korn and Ebbighausen 2011 Coll.) from the upper horizon of Sidi Amar (Central Moroccan Meseta). Scale bar units = 1 mm.

Fig. 19. Hibernicoceras mediocre Moore & Hodson, 1958 from Sidi Amar (Central Moroccan Meseta), all Korn and Ebbighausen 2011 Coll. A. Cross section of specimen MB.C.32218.2. B. Cross section of specimen MB.C.32218.3. C–E. Ontogenetic trajectories of the cardinal conch parameters. Scale bar units = 1 mm.