Stockumites undulatus (Vöhringer, 1960) comb. nov.

Figs 37–38; Tables 32–33

Imitoceras undulatum Vöhringer, 1960: 133, pl. 3 fig. 6, text-fig. 13.

Acutimitoceras undulatum – Korn 1994: 52, text-figs 49h–i, 50l, 52c, 55e–f. — Korn et al. 1994: text-fig. 20a.

Diagnosis

Species of Stockumites with a conch reaching 40 mm diameter. Conch at 5 mm dm thinly pachyconic, subinvolute (ww/dm ~0.70; uw/dm ~0.25); at 12 mm dm thinly pachyconic, subinvolute (ww/dm ~0.65; uw/dm ~0.05); at 20 mm dm thickly discoidal, involute (ww/dm ~0.55; uw/dm ~0.02). Whorl profile at 20 mm dm weakly compressed (ww/wh ~0.95); coiling rate moderately high (WER ~1.90). Venter broadly rounded, umbilical margin broadly rounded. Growth lines lamellar, wide-standing, with biconvex course. Without constrictions on the shell surface; without internal shell thickenings. Suture line with V-shaped external lobe and V-shaped adventive lobe.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 5; Vöhringer Coll .; illustrated by Vöhringer (1960: pl. 3 fig. 6) and Korn (1994: text-fig. 49i); re-illustrated here in Fig. 37A; GPIT-PV-63877.

Paratypes

GERMANY • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone,bed5;Vöhringer Coll.;GPIT-PV-64022• 2specimens;Rhenish Mountains,Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 6; Vöhringer Coll.; GPIT-PV-63879, GPIT-PV-63881.

Additional material

GERMANY • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 6; Vöhringer Coll.; MB.C.31089 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 5c; Weyer 1993–1994 Coll.; MB.C.31090 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 6a; Weyer 1993– 1994 Coll.; MB.C.31091 • 1 specimen; Rhenish Mountains, Oese, old quarry; bed interval III; Paproth Coll.; MB.C.5271.

Description

Holotype GPIT-PV-63877 is a specimen that is largely covered with shell and has 23 mm diameter (Fig. 37A). It is thickly discoidal (ww/dm = 0.52) with a closed umbilicus. The conch is widest at the rounded umbilical margin; from there the flanks converge to the continuously rounded venter. The ornament consists of lamellar growth lines with a biconvex course; the dorsolateral projection and ventrolateral projection have about the same height (Fig. 38E).

Paratype GPIT-PV-63879 with 20.5 mm diameter is very similar to the holotype in conch parameters and ornament (Fig. 37B). The suture line has a lanceolate external lobe, accompanied by an asymmetrical ventrolateral saddle. The almost symmetrical adventive lobe is broadly lanceolate with outwardly curved flanks (Fig. 38C).

Specimen MB.C.31091 shows the ornament in particularly good preservation (Fig. 38A). The lamellar growth lines with biconvex course form a dorsolateral projection on the inner third of the flank, a shallow lateral sinus on the outer third of the flank and a ventrolateral projection on the ventrolateral shoulder.

Remarks

Stockumites undulatus is an easily recognisable species because it is clearly distinguished from all other species of the genus by the characteristic, lamellar growth lines with a distinctive biconvex course.