Hasselbachia gracilis ( Vöhringer, 1960 )

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), European Journal of Taxonomy 882, pp. 1-230 : 165-166

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 .

Figures

Fig. 8. Early Tournaisian representative ammonoids of the family Gattendorfiidae from the Hasselbachtal section, all Weyer 1993–1994 Coll. A. Gattendorfia rhenana sp. nov., paratype MB.C.5244.1 from bed 71. (Illustrated by Korn & Weyer 2003: pl. 2 figs 10–11, as Gattendorfia subinvoluta.) B. Weyerella molaris (Vöhringer, 1960), specimen MB.C.5240.8 from bed 57. C. Weyerella reticulum (Vöhringer, 1960), specimen MB.C.5242.1 from bed 62. D. Hasselbachia multisulcata (Vöhringer, 1960), specimen MB.C.5240.1 from bed 57. E. Hasselbachia gracilis (Vöhringer, 1960), specimen MB.C.5240.5 from bed 57. F. Pseudarietites westfalicus Schmidt, 1924, specimen MB.C.5236.1 from bed 49. Scale bar units =1 mm.

Fig. 98. Hasselbachia from the Oberrödinghausen railway cutting, all Weyer 1993–1994 Coll. A. Hasselbachia multisulcata (Vöhringer, 1960), specimen MB.C.31195.1 from bed 3e. B. Hasselbachia multisulcata (Vöhringer, 1960), specimen MB.C.31195.2 from bed 3e. C. Hasselbachia multisulcata (Vöhringer, 1960), specimen MB.C.31194.1 from bed 3d2. D. Hasselbachia multisulcata (Vöhringer, 1960), specimen MB.C.31195.3 from bed 3e. E. Hasselbachia gracilis (Vöhringer, 1960), specimen MB.C.31196.1 from bed 3d1b. Scale bar units =1 mm.

Fig. 100. Hasselbachia gracilis (Vöhringer, 1960) from the Oberrödinghausen railway cutting. Scale bar units= 1 mm. A. Holotype GPIT-PV-63917 (Vöhringer Coll.) from bed 3d. B. Growth line course of holotype GPIT-PV-63917, at dm=16.6 mm, ww ca. 9.0 mm, wh =8.3 mm. Scale bar units =1 mm.