Sandbergeroceras archiaci, 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 : 73-74

Sandbergeroceras archiaci sp. nov.

urn:lsid:zoobank.org:act:CA8E6D62-FBEF-45A7-B4F9-2C914A45B54D

Fig 50A ; Table 32

Diagnosis

Species of Sandbergeroceras with thinly discoidal, evolute conch at 30 mm dm (ww/ dm ~ 0.35; uw/ dm ~ 0.50). Whorl profile moderately depressed (ww/ wh ~1.55); venter flatly rounded. Two deep spiral grooves on the venter. Shell ornament with 30 sigmoidal, sharp ribs on the flanks and coarse growth lines.

Etymology

Named after Étienne Jules Adolphe Desmier de Saint-Simon, Vicomte d’Archiac (1802–1868), one of the pioneers of studying fossils from the Red Ironstone.

Material examined

Holotype GERMANY • Rhenish Mountains , Oberscheld (Grube Anna); early Frasnian (Red Ironstone); Koch Coll.; MB.C.3671 .

Description

Holotype MB.C.3671 is an incomplete, but rather well-prerserved specimen of 33 mm conch diameter in fossil-rich and iron-rich limestone ( Fig. 50A ). It allows the study of slightly more than two whorls up to a conch diameter of 33 mm. The conch is discoidal and evolute (ww / dm =0.35; uw / dm = 0.51)

with low coiling rate (WER =1.51); the whorl profile depressed (ww / wh =1.56) with continuously rounded umbilical wall, flanks and venter. The venter bears two rather deep spiral grooves. Both whorls bear rounded, forward-directed ribs; there are 30 such ribs on the last whorl and 40 on the penultimate. In addition, sharp growth lines are formed at almost equal intervals of about 0.2 mm. They extend almost straight across the flank and curve forward to a moderately high projection in the ventrolateral area.

Remarks

Sandbergeroceras archiaci sp. nov. differs from S. tuberculosocostatum and S. costatum in the form of the whorl profile and the umbilical width. The whorl profile is rounded-triangular with a tightly rounded venter in the latter two species, whereas the venter is weakly flattened in S. costatum . The ventrolateral grooves are less pronounced in S. tuberculosocostatum and S. costatum . The umbilicus is, at 30 mm conch diameter, wider in S. costatum (ww/ dm ~ 0.50 in S. costatum but only ~ 0.40 in S. tuberculosocostatum and S. costatum ).

Figures

Fig. 50. A. Sandbergeroceras archiaci sp. nov., holotype MB.C.3671 (Koch Coll.) from Oberscheld (Anna Mine). B. Sandbergeroceras costatum (d’Archiac & de Verneuil, 1842), neotype MB.C.7695 (Erbreich Coll.) from Dillenburg.C. Sandbergeroceras tuberculosocostatum (Sandberger & Sandberger, 1850), specimen SMF.Mbg.6360 from Oberscheld. Scale bar units = 1 mm.

Tables

Table 32. Conch dimensions and ratios of selected specimen of Sandbergeroceras archiaci sp. nov.

Specimen	dm	ww	wh	uw	ah	ww / dm	ww / wh	uw / dm	WER	IZR
MB.C.3671	31.1	11	7.05	15.9	5.8	0.35	1.56	0.51	1.51	0.18