Hasselbachia gracilis (Vöhringer, 1960)

Figs 8E, 98E, 100; Table 97

Imitoceras gracile Vöhringer, 1960: 143, pl. 4 fig. 6, text-fig. 20.

Acutimitoceras gracile – Korn 1994: 47, text-figs 49f, 55a.

Acutimitoceras (Stockumites) gracile – Becker 1996: 36.

Hasselbachia gracilis – Korn & Weyer 2003: 96, pl. 1 figs 9–10, 15–16.

Diagnosis

Species of Hasselbachia with a thickly discoidal and subinvolute conch at 15 mm dm (ww/dm ~0.55; uw/dm ~0.25); whorl cross section depressed (ww/wh ~1.50); coiling rate very low (WER ~1.50). Flanks strongly convergent. Fine lamellar growth lines with convex course. Shell and internal mould with short constrictions.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; illustrated by Vöhringer (1960: pl. 4 fig. 6), and Korn (1994: text-fig. 58b), re-illustrated here in Fig. 100A; GPIT-PV-63917.

Paratype

GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; GPIT-PV-63919 .

Additional material

GERMANY • 4 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d1b; Weyer 1993–1994 Coll.; MB.C.31196.1–4 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Weyer 1993–1994 Coll.; MB.C.31197.1–2 • 2 specimens; Rhenish Mountains, Hasselbachtal; Hangenberg Limestone, bed 53; Weyer 1993–1994 Coll.; MB.C.5238.1, MB.C.5238.2 • 1 specimen; Rhenish Mountains, Hasselbachtal; Hangenberg Limestone, bed 57; Weyer 1993–1994 Coll.; MB.C.5240.5.

Description

Holotype GPIT-PV-63917 is an incomplete specimen with 17 mm conch diameter (Fig. 100A). It is thickly discoidal and subinvolute (ww/dm = 0.54; uw/dm = 0.27) with a low coiling rate (WER = 1.49). The shell bears five shallow radial notches on the flank of the last half whorl. The growth lines are lamellar and very weakly convex across the flanks; they form a very shallow ventral sinus (Fig. 100B).

The moderately well-preserved specimen MB.C.31196.1 (Fig. 98E) with 17 mm dm has a thickly discoidal subinvolute conch (ww/dm = 0.54; uw/dm = 0.27) and a semilunate whorl section with very low aperture (WER = 1.49). The specimen is covered with shell remains, which show fine lamellar growth lines that extend backwardly directed across flanks and venter. The shell has some very shallow constrictions on the midflank.

Remarks

Hasselbachia gracilis differs from H. multisulcata by the more slender conch in combination with a wider umbilicus. The uw/dm ratio, at 17 mm conch diameter, is about 0.13 in H. multisulcata, but only about 0.27 in H. gracilis .