Pharciceras beyrichi, Korn & Bockwinkel, 2021

Korn, Dieter & Bockwinkel, Jürgen, 2021, The pharciceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 771, pp. 1-79 : 13-15

Pharciceras beyrichi sp. nov.

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Figs 8–9 ; Table 3

Diagnosis

Species of Pharciceras with thickly discoidal, subevolute conch at 35 mm dm (ww / dm ~ 0.55; uw/ dm ~ 0.38). Whorl profile depressed, crescent-shaped at 35 mm dm (ww / wh ~1.75); whorl expansion rate low (WER ~1.55). Whorl profile with broadly convex flanks continuing to the very broadly rounded venter. Growth lines coarse, strongly biconvex; ventrolateral shoulder with two spiral grooves. Outer suture line with symmetric, V-shaped prongs of the external lobe, a lancolate, blunt lateral lobe and very small rounded U 2 and U 4 lobes.

Etymology

Named after Heinrich Ernst Beyrich (1815–1896), one of the pioneers of studying fossils from the Red Ironstone.

Material examined

Holotype GERMANY • Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); Koch Coll.; MB.C.22174 . ( Fig. 8 )

Paratype GERMANY • 1 specimen; Rhenish Mountains , probably from Oberscheld; late Givetian (Red Ironstone); MB.C. 30231 .

Description

Holotype MB.C.22174 is laterally slightly deformed, completely chambered specimen with 34 mm conch diameter in haematitic limestone; small parts of the specimen are covered with shell, the phragmocone is filled with sparry calcite ( Fig. 8 ). The specimen has a thickly discoidal and subevolute conch shape with a low coiling rate at 34 mm diameter; the whorl profile is depressed with steep umbilical wall and broadly rounded flanks and venter. Two faint ventrolateral spiral grooves on each side separate the flanks from the venter, which is broadly rounded at the largest diameter of the specimen but flattened up to the last volution ( Fig. 9B ). The ornament shows lamellar growth lines. The suture line has a very wide external lobe with nearly parallel flanks and lanceolate prongs. Two lobes are located on the flank: the asymmetric lateral lobe that is larger than the prongs of the external lobe and the small, rounded U 2 lobe ( Fig. 9A ). A very small U 4 lobe is located on the umbilical wall.

Remarks

The two specimens, of which only the holotype is rather well-preserved, are described here as a new species because a conch morphology cannot be attributed to any other species of Pharciceras . Its conch is stouter (ww / dm ~ 0.55 at 35 mm conch diameter) than in most of the other species of Pharciceras . Juveniles of P. kruegeri sp. nov. are also stout, but they possess a narrower umbilicus (uw / dm ~0.33) than P. beyrichi sp. nov. (uw / dm ~ 0.38) and much weaker ventrolateral grooves.

Pharciceras tridens is a similar form, but is slenderer with a ww / dm ratio of ~ 0.45 at 35 mm conch diameter. In smaller stages at 25 mm diameter, the venter is broadly rounded in P. tridens , in contrast to the slightly flattened venter in P. beyrichi sp. nov.

Figures

Fig. 8. Pharciceras beyrichi sp. nov., holotype MB.C.22174 (Koch Coll.) from Oberscheld. Scale bar units = 1 mm.

Fig. 9. Pharciceras beyrichi sp. nov. A. Suture line of holotype MB.C.22174 (Koch Coll.) from Oberscheld, at dm = 26.0 mm, ww =16.5 mm, wh= 9.0 mm. B. Surface of the last septum of the holotype. Abbreviations: see Material and methods. Scale bar units = 1 mm.

Tables

Table 3. Conch dimensions and ratios of selected specimen of Pharciceras beyrichi sp. nov.

Specimen	dm	ww	wh	uw	ah	ww / dm	ww / wh	uw / dm	WER	IZR
MB.C.22174	34.7	18.7	10.8	13.2	6.8	0.54	1.73	0.38	1.55	0.37