Pharciceras ferrum Korn & Bockwinkel 2021, sp. nov.

Pharciceras ferrum sp. nov.

urn:lsid:zoobank.org:act: EE697AD8-5DEF-46FB-A9E0-FBA03C1EC485

Figs 23–24; Tables 12–13

Diagnosis

Pharciceras with thinly discoidal, subevolute conch at 30 mm dm (ww / dm ~ 0.42; uw/ dm ~0.32); extremely discoidal, subevolute at 60 mm dm (ww /dm ~ 0.32; uw / dm ~0.32). Whorl profile nearly circular at 30 mm dm (ww / wh ~ 1.05); weakly compressed at 60 mm dm (ww / wh ~ 0.75); whorl expansion rate low to moderate. Venter continuously rounded throughout ontogeny. Adult stage with broadly convex, converging flanks continuing to the narrowly rounded venter. Growth lines coarse, strongly biconvex; ventrolateral shoulder with two spiral grooves. Outer suture line with symmetric, U-shaped, blunt prongs of the external lobe, a V-shaped lateral lobe and a shallow and wide U 2 lobe.

Etymology

Named after the Latin ‘ ferrum ’, meaning ‘iron’, after the occurrence of the specimen in iron ore.

Material examined

Holotype GERMANY • Rhenish Mountains, Oberscheld (Eiserne Hand, Grube Friedrich); late Givetian (Red Ironstone); MB.C.30238. (Fig. 23A)

Paratypes GERMANY • 2 specimens; Rhenish Mountains, Oberscheld (Westfeld der Grube Königszug, Firste der 120–150 m Sohle); late Givetian (Red Ironstone); Ahlburg Coll.; MB.C.3619, MB.C.3623 • 1 specimen; Rhenish Mountains, Oberscheld (Grube Stillingseisenzug, 30 m Sohle); late Givetian (Red Ironstone); Euel 1902 Coll.; MB.C.3646 • 2 specimens; Rhenish Mountains, Oberscheld; late Givetian (Red Ironstone); Lotz Coll.; MB.C.22165, MB.C.22166 • 1 specimen; Rhenish Mountains, Oberscheld (Grube Königszug, 120 m Sohle); late Givetian (Red Ironstone); MB.C.22192 • 1 specimen; Rhenish Mountains, Oberscheld (Grube Königszug); late Givetian (Red Ironstone); Etzold 1910 Coll.; MB.C.30237 • 1 specimen; Rhenish Mountains, Oberscheld (Grube Königszug, 90 m Sohle, Westflügel); late Givetian (Red Ironstone); Lotz 1902 Coll.; MB.C.30239 • 1 specimen; Rhenish Mountains, Oberscheld (Grube Prinzkessel, 100 m Sohle, Westflügel); late Givetian (Red Ironstone); Lotz 1901 Coll.; MB.C.30240.

Description

Six specimens are selected for description and illustration:

Holotype MB.C.30238: laterally deformed steinkern specimen with 78 mm conch diameter at the contact between a basaltic volcanic rock and a haematite ore (Fig. 23A).

Paratype MB.C.3619: incomplete specimen with 59 mm conch diameter in iron-rich micritic limestone (Fig. 23B).

Paratype MB.C.22165: incomplete, laterally deformed specimen with 50 mm conch diameter in haematite ore. Parts of the suture line are visible (Fig. 23C).

Paratype MB.C.30239: incomplete, partly crushed specimen with 47 mm conch diameter in iron-rich limestone (Fig. 23D).

Paratype MB.C.3646: incomplete specimen with 29 mm conch diameter in ironstone (Fig. 23E).

Paratype MB.C.30237: sectioned specimen with 76 mm conch diameter in iron-rich limestone.

The material allows the description of conch geometry from 29 to 78 mm diameter. During this interval, the ww / dm ratio decreases continuously from 0.45 to 0.30, while the umbilical width ratio is stable at 0.30–0.35. The coiling rate is also rather stable between 1.62 and 1.78. Holotype MB.C.30238 has, at 75 mm diameter, a compressed whorl profile with very shallow umbilical wall, convergent flanks and a narrowly rounded venter (Fig. 23A). A pair of faint spiral grooves is present in the ventrolateral area. Shell ornament is preserved in some specimens; it possesses coarse biconvex growth lines, which have an appearance of faint riblets in the inner whorls visible in the umbilicus of some specimens.

Paratype MB.C.3646 shows the suture line of the preadult stage (Fig. 24A); at a phragmocone diameter of 24 mm, it shows a parallel-sided external lobe with lanceolate, blunt prongs. The lateral lobe is V-shaped with weakly convex flanks and the U 2 lobe is small and rounded.

Remarks

Pharciceras ferrum sp. nov. has some similarity to P. oberscheldense, but differs in the shape of the lateral lobe (V-shaped in P. ferrum sp. nov. but rounded in P. oberscheldense) and in the narrower whorl profile with a weakly flattened venter.