Early Carboniferous nautiloids from the Central Sahara, southern Algeria Author Korn, Dieter 286CA4F3-7EBC-4AEF-A66A-B2508D001367 Museum für Naturkunde, Leibniz Institut for Research on Evolution and Biodiversity, Invalidenstrasse 43, 10115 Berlin, Germany. dieter.korn@mfn.berlin Author Bockwinkel, Jürgen F7FE7EEA-B678-4FEE-879C-8C429F66BF3A Dechant-Fein-Strasse 22, 51375 Leverkusen, Germany. jbockwinkel@t-online.de text European Journal of Taxonomy 2022 2022-07-20 831 67 108 http://dx.doi.org/10.5852/ejt.2022.831.1871 journal article 105313 10.5852/ejt.2022.831.1871 e697ba5c-5a96-4a28-985c-748890333d6c 2118-9773 6885198 EAA2EAE2-DA8B-4516-B332-CB8423B8EEAA Rineceras tenerum sp. nov. urn:lsid:zoobank.org:act: 94410544-F569-471D-A008-97466EB83BBF Figs 4–5 , Table 1 Diagnosis Species of Rineceras with weakly depressed, rounded-trapezoidal whorl profile (ww/wh ~1.45), venter slightly flattened, ventrolateral shoulder broadly rounded. Whorls not embracing. Ornament with a few spiral lines on the flank and the venter. Etymology From the Latin ‘ tenerum ’, meaning ‘tender’ and referring to the comparatively delicate spiral lines. Type material Holotype ALGERIA • Mouydir , south of Oued Temertasset (locality MOU-Z) ; Argiles de Teguentour ( Upper Pericyclus-Progoniatites Assemblage; early late Tournaisian ); Korn et al . 2002 Coll.; illustrated in Fig. 4A–B ; MB.C.30440.1 . Paratypes ALGERIA • 1 specimen ; Mouydir , south of Oued Temertasset (locality MOU-E07) ; Argiles de Teguentour ( Upper Pericyclus-Progoniatites Assemblage; early late Tournaisian ); Korn et al . 2002Coll.; illustrated in Fig. 4C ; MB.C.30441 • 8 specimens ; Mouydir , south of Oued Temertasset (localities MOU-Z, MOU-C5, MOU-B1, MOU-D1) ; Argiles de Teguentour ( Upper Pericyclus-Progoniatites Assemblage; early late Tournaisian ); Korn et al . 2002 Coll.; MB.C.30440.2 , MB.C.30442 , MB.C.30443.1–MB.C.30443.2 , MB.C.30444.1–MB.C.30444.4 . Description Holotype MB.C.30440.1 is a haematitic internal mould consisting of two fully chambered segments; however, some chambers between the two segments are missing ( Fig. 4A–B ). The total diameter is about 49 mm . At this diameter, the whorl profile is rounded-triangular with a somewhat flattened venter and continuously rounded dorsum. There is no overlap upon the previous whorl ( Fig. 5A ). On the flanks and the outer part of the venter, there are twelve spiral lines on each side. The suture line shows a low amplitude; there is a wide, shallow external lobe and a low, tightly rounded ventrolateral saddle. On the flanks and dorsum the suture line is almost straight ( Fig. 5B ). Fig. 4. Rineceras tenerum sp. nov. from Oued Temertasset (all Korn et al . 2002 Coll.). A . Holotype MB.C.30440.1 (larger segment). B . Holotype MB.C.30440.1 (smaller segment). C . Paratype MB.C.30441. Scale bar units = 1 mm . Table 1. Conch dimensions (in mm) and ratios of Rineceras tenerum sp. nov.

Specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZW
MB.C.30440.1	48.8	21.4	14.7	23.5	14.7	0.44	1.45	0.48	2.05	0.00
MB.C.30440.1	27.7	12.7	9.4	13.3	9.4	0.46	1.35	0.48	2.29	0.00
MB.C.30442	–	32.5	21.9	–	–	–	1.48	–	–	–
MB.C.30441	–	15.6	10.9	–	–	–	1.49	–	–	–

The segment of the younger stage ( Fig. 4B ) shows the conch dimensions and proportions better. The conch is evolute at 28 mm diameter (uw/dm =0.48). The whorl profile is similar to the large segment, but the venter is slightly more flattened and the ventrolateral shoulder is more pronounced with a very shallow submarginal ventral groove ( Fig. 5C ). From the margin of the venter and on the flank, there are about 12 spiral lines. However, it can be seen that the number of spiral lines decreases during ontogeny; over a distance of 180 degrees, the initially coarse spiral lines in the submarginal area of the venter become weaker gradually. The siphuncle has a position slightly off centre on the ventral side. The suture line shows a broad and shallow external lobe and a very shallow lateral lobe ( Fig. 5D ). Paratype MB.C.30441 closely resembles the holotype but has a slightly more pronounced ventrolateral shoulder ( Fig. 4C ). The large unfigured paratype MB.C.30442 has, at a whorl height of 21 mm , a whorl profile almost identical to the holotype ; it also possesses twelve coarse spiral lines on the flanks and the outer part of the venter. Remarks The species of the genus Rineceras can be divided into different groups according to various aspects: general conch shape (whorls detached or embracing), whorl profile (depressed oval, rounded-triangular or trapezoidal), formation of the ventrolateral shoulder (rounded or angular), spiral ornament (spirals equally strong or differently strong) etc. Rineceras tenerum sp. nov. differs from all other species of the genus by the combination of rather weak spiral lines that are restricted to the flank, the non-embracing whorls, and the whorl profile with a rounded-triangular outline.