Pharciceras kayseri Wedekind 1918

Pharciceras kayseri Wedekind, 1918 Figs 17–19; Tables 8–9 Pharciceras Kayseri Wedekind, 1918: 127, 169, pl. 20 fig. 2, text-fig. 37c1–c2. Pharciceras kayseri – Matern 1931: 92. non Pharciceras kayseri – Petter 1959: 134, pl. 7 figs 1, 14, text-fig. 33j. — Kullmann & Ziegler 1970: 78, pl. 1 fig. 4, text-figs 2b, 3b, 4. — Bockwinkel et al. 2009: 93, text-figs 10g, 16. Diagnosis Pharciceras with thinly discoidal, subinvolute conch at 30 mm dm (ww/ dm ~0.45; uw/ dm ~0.28); extremely discoidal, subinvolute at 60 mm dm (ww/ dm ~ 0.30; uw / dm ~0.25). Whorl profile compressed at 30 mm dm (ww / wh ~ 0.95) and rounded-triangular, compressed at 60 mm dm (ww / wh ~ 0.70); whorl expansion rate low to moderate. Preadult and adult stages with broadly convex, strongly converging flanks continuing to the very narrowly rounded venter. Growth lines fine, strongly biconvex; ventrolateral shoulder with two faint spiral grooves. Outer suture line with short pointed E 1, symmetric, narrowly V-shaped prongs of the external lobe, a small, V-shaped lateral lobe and a very small V-shaped U 2 lobe. Material examined Holotype GERMANY • Rhenish Mountains, Oberscheld (Grube Prinzkessel); late Givetian (Red Ironstone); Welsch 1913 Coll.; illustrated by Wedekind (1918: pl. 20 fig. 2), re-illustreted here in Fig. 17; SMF.Mbg.2317. Additional material GERMANY • 3 specimens; Rhenish Mountains, Oberscheld (Westfeld der Grube Königszug, Firste der 120–150 m Sohle); late Givetian (Red Ironstone); Ahlburg Coll.; MB.C.3621, MB.C.3622, MB.C.3630 • 1 specimen; Rhenish Mountains, Dillenburg; late Givetian (Red Ironstone); Krüger 1873 Coll.; MB.C.22172 • 2 specimens; Rhenish Mountains, probably a mine near Oberscheld; late Givetian (Red Ironstone); Krüger 1873 Coll.; MB.C.30235.1, MB.C.30235.2. Description Five specimens are selected for description and illustration: Holotype SMF.Mbg.2317: rather well-preserved specimen with 80 mm conch diameter in haematitic limestone (Fig. 17). MB.C.3630: incomplete specimen with 78 mm conch diameter in haematitic, micritic limestone (Fig. 18A). MB.C.30235.1: deformed specimen with 71 mm conch diameter in haematitic, micritic limestone, showing the suture line (Fig. 18B). MB.C.30235.2: deformed specimen with 64 mm conch diameter in haematitic, micritic limestone, showing parts of the suture line (Fig. 18C). MB.C.22172: strongly deformed specimen with 42 mm conch diameter in haematitic iron-ore (Fig. 18D). The material allows the description of conch geometry and ornament of the growth interval between 42 and 80 mm conch diameter. In this interval, the conch becomes slenderer (ww/ wh decreases from ~0.42 to ~0.28), while the umbilical opening rate is rather constant (uw / dm ~ 0.25). The coiling rate increases slowly form WER ~1.70 to ~ 1.85. The whorl profile is rounded triangular, it is widest near the rounded umbilical margin. The flanks are weakly convex and converge towards the narrowly rounded venter. Two faint ventrolateral grooves are present in all specimens. Shell remains are preserved only occasionally; it appears that the growth lines are very delicate, even in the inner whorls. The suture line of specimen MB.C.30235.1 has a large external lobe with a median saddle raised to three quarters of the lobe depth (Fig. 19A). On the flanks, there is a rather small, V-shaped lateral lobe and an even much smaller, V-shaped umbilical lobe. Remarks Pharciceras kruegeri sp. nov. is a similar species but differs in the stouter conch (ww /dm ~ 0.40; ww / wh ~ 1.05) from P. kayseri (ww/ dm ~ 0.30; ww / wh ~0.65) at 60 mm diameter. The ornament reveals more separating characters; it consists of very delicate growth lines in P. kayseri but coarse growth lines in P. kruegeri sp. nov. Pharciceras ferrum sp. nov. is rather similar in conch proportions, but differs in less strongly convergent flanks and wider venter. P. galeatum is similar in the juvenile and preadult stage, but is more widely umbilicate and develops a tectifom venter in the adult stage. The Moroccan specimens, placed in P. kayseri by Bockwinkel et al. (2009), differ in the suture line; they have short lobes of about the same height, while the Rhenish material has deep lobes of varying depth. Furthermore, the Moroccan specimens are stouter and the umbilicus is wider and the venter is not tabulate in P. kayseri.Published as part of Korn, Dieter & Bockwinkel, Jürgen, 2021, The pharciceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), pp. 1-79 in European Journal of Taxonomy 771 on pages 23-26, DOI: 10.5852/ejt.2021.771.1503, http://zenodo.org/record/553609