Stockumites intermedius (Schindewolf, 1923)

Figs 8–9; Table 4

Imitoceras intermedium Schindewolf, 1923: 333, pl. 16 fig. 2, text-fig. 4f.

Imitoceras intermedium – Librovitch 1940: pl. 2 fig. 5a–b. — Vöhringer 1960: 131, pl. 3 figs 2, 7–8, text-fig. 11. — Furnish & Manger 1973: 20, text-fig. 2b, d. — Weyer 1977: 177, text-fig. 2.1. — House 1985: pl. 6.7.29, text-fig. 6.7.14b.

Acutimitoceras intermedium – Korn 1984: 75, pl. 3 figs 20–23, text-figs 4e, 5h–I; 1992b: 15, pl. 1 figs 22–27, 30, pl. 2 figs 2–3, 7–9, 15–16, 21–22, 26–27; 1992c: 178, pl. 1 figs 7–11; 1994: 47, text-figs 37a–c, 40c, 41a–e, 44a–c, 45a–c, 47b, 48a–b, 56d–f, 57b–c; 1999: 166, pl. 2 fig. 8. — Schönlaub et al. 1992: pl. 4 figs 22–27, 30, pl. 5 figs 2–3, 7–9, 15–16, 21–22, 26–27. — Korn et al. 1994: text-fig. 20b. — Belka et al. 1999: pl. 5 figs 7–8. — Kullmann 2000: text-fig. 4g. — Korn & Klug 2002: 197, text-fig. 173b. — Korn & Weyer 2003: pl. 2 figs 12–13. — Bockwinkel & Ebbighausen 2006: 97, text-figs 13–14. — Ebbighausen & Bockwinkel 2007: 131, text-figs 8f–g, 10, 12a–b. — Korn & Feist 2007: 106, text-fig. 6b–c, h.

Stockumites intermedius – Becker et al. 2002: pl. 2 figs 13–14. — Korn & Weyer 2023: 51, figs 7d, 31–34.

Aganides infracarbonicus – Schmidt 1924: 149, pl. 8 figs 1–2; 1929: 61, pl. 15 fig. 8.

non Imitoceras intermedium – Librovitch 1940: 138, pl. 35 figs 2–3. — Schindewolf 1952: 291, textfigs 4–6. — Balashova 1953: 198, pl. 12 figs 11–20. — Furnish & Manger 1973: 20, pl. 1 figs 11–15.

non Imitoceras (Imitoceras) intermedium – Ruan 1981: 64, pl. 12 figs 1–6, 9–13, 17–28.

Diagnosis

Species of Stockumites with a conch reaching 120 mm diameter. Conch at 5 mm dm thinly pachyconic, subinvolute to subevolute (ww/dm ~ 0.70; uw/dm=0.20–0.40); at 15 mm dm thinly pachyconic, involute (ww/dm ~ 0.65; uw/dm ~ 0.00); at 30 mm dm thinly pachyconic, involute (ww/dm ~ 0.65; uw/dm ~ 0.00). Whorl profile at 30 mm dm weakly depressed (ww/wh = 1.10–1.20); coiling rate moderately high (WER =1.85–1.95). Venter broadly rounded, umbilical margin very broadly rounded. Growth lines lamellar, wide-standing, with convex course. Without constrictions on the shell surface; without internal shell thickenings. Suture line with narrowly lanceolate external lobe and narrowly V-shaped adventive lobe (from Korn & Weyer 2023).

Material examined

Lectotype GERMANY • Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1916 Coll.; illustrated by Schindewolf (1923: pl. 16 fig. 2), Librovitch (1940: pl. 2 fig. 5) and Korn (1994: text-fig. 56f); re-illustrated here in Fig. 8A; SMF Mbg.3111.

Paralectotypes GERMANY • 9specimens; Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1916 Coll.; SMF Mbg.7563–SMF Mbg.7571.

Additional material GERMANY • 31 specimens; Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1934 Coll.; BGRB X13384, BGRB unnumbered • 1 specimen; Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Paul Coll.; BGRB unnumbered • 5 specimens; Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21a (“ Gattendorfia Limestone ”); Korn 1989 Coll.; MB.C.31263.1–MB.C.31263.5 • 2 specimens; Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21c–d (“ Gattendorfia Limestone ”); Korn 1989Coll.; MB.C.31264.1–MB.C.31264.2 • 1 specimen; Upper Franconia, 400 m north-west of Kirchgattendorf; bed 21f (“ Gattendorfia Limestone ”); Korn 1989 Coll.; MB.C.31265.

Description

Lectotype SMF Mbg.3111 is a rather poorly preserved specimen with 46 mm conch diameter; the last half whorl is deformed and partly eroded (Fig. 8A). The penultimate half whorl appears to be only slightly deformed and allows the study of conch morphology and ornament. At 36 mm in diameter, the conch is thickly discoidal (ww/dm ~ 0.60) with an almost closed umbilicus that is characterised by its very broadly rounded margin. The shell bears lamellar growth lines running in a convex arc across the flank and forming a broad, deep sinus on the venter (Fig. 9E).

Paralectotype SMF Mbg.7563 is a rather well-preserved specimen with 19 mm diameter (Fig. 8B). It is thickly pachyconic (ww/dm ~ 0.78) with an almost closed umbilicus, a broadly rounded umbilical margin and a broadly rounded venter. The well-preserved shell ornament shows lamellar growth lines that are rursiradiate with a very weakly biconvex course across the flanks and a broad ventral sinus (Fig. 9C). The suture line has a lanceolate and deep external lobe, a broadly rounded ventrolateral saddle and a weakly asymmetrical adventive lobe (Fig. 9D).

Specimens BGRB X13384 (60 mm dm; Fig. 8C) and MB.C.31263.1 (39 mm dm; Fig. 8D) have similar conch shapes to the lectotype. The only small difference is that specimen MB.C.31263.1 is stouter (ww/ dm =0.67) than the lectotype.

The two cross sections SMF Mbg.7564 (Fig. 9A) and SMF Mbg.7565 (Fig. 9B) show deformed specimens. Although the morphometric data cannot be precisely extracted, they allow an insight into ontogenetic changes in the interval between 4 and 30 mm conch diameter. Due to the partly strong deformation of the body chambers, the values of the coiling rate are particularly problematic. However, the trajectories of the conch parameters ww/dm, uw/dm and ww/wh (Fig. 9F–G) agree quite well with the comparison sample from bed 6 of the Oberrödinghausen section.

Remarks

“ Imitoceras intermedium ” was established by Schindewolf (1923) for forms that occupy a morphological position between the slender form “ Imitoceras Gürichi ” (= S. hofensis sp. nov.) and the stout form “ Imitoceras Denckmanni ” (= Stockumites kleinerae) in their conch morphology, i.e., “rather thickly discoidal” shapes.

Stockumites intermedius differs from the simultaneously occurring species S. kleinerae by the more strongly compressed conch (ww/dm= 0.60–0.65 in S. intermedius, but 0.75–0.80 in S. kleinerae at 30 mm dm). In addition, S. intermedius has lamellar growth lines, which are very coarse in S. kleinerae and are also visible on the inner surface of the shell.