Rineceras rectangulatum, Korn & Miao & Bockwinkel, 2022

Korn, Dieter, Miao, Luyi & Bockwinkel, Jürgen, 2022, The nautiloids from the Early Carboniferous Dalle à Merocanites of Timimoun, western Algeria, European Journal of Taxonomy 789, pp. 104-129 : 119-120

Rineceras rectangulatum sp. nov.

urn:lsid:zoobank.org:act:B6626858-751D-4EA3-B80C-76D5D11CAAC7

Fig. 9 ; Table 5

Etymology

Referring to the rectangular ventrolateral shoulder.

Type material

Holotype ALGERIA • Gourara , Sebkha de Timimoun 14.5 km west-southwest of Timimoun; “ Dalle à Merocanites ” (Tournaisian-Viséan boundary interval); illustrated in Fig. 9 , MB.C.30382 .

Diagnosis

Species of Rineceras with weakly depressed, rounded-trapezoidal whorl profile (ww/wh ~ 1.45), venter flattened, umbilical shoulder broadly rounded without clean boundary between the flank and the umbilical wall. Whorls slightly embracing. Ornament in the juvenile stage with weak spiral lines on the flank.

Description

Holotype MB.C.30382 is an incomplete specimen with 50 mm diameter ( Fig. 9 ). A little more than a quarter whorl belongs to the body chamber. The conch is thickly discoidal and subevolute (ww/dm = 0.57; uw/dm = 0.42) with a flat venter and an angular ventrolateral shoulder. The flanks are very slightly concave and diverge slowly towards the venter; the umbilical margin and the umbilical wall are broadly rounded. The penultimate volution differs in its oval whorl profile and the wider umbilicus (uw/dm = 0.50 at 24 mm dm). The umbilical window has a width of approximately 6 mm.

Most of the specimen is exfoliated and corroded, but the penultimate whorl shows about five spiral ridges on the flanks. Traces of these ridges are still visible on the last preserved volution. The suture line has a broadly V-shaped external lobe with rounded base on the venter, a shallow lobe on the flank and an incipient lobe on the umbilical wall.

Remarks

Rineceras rectangulatum sp. nov. differs from most species of the genus by the trapezoidal whorl profile with angular ventrolateral shoulder. Rineceras carinatiforme has a similar shape, but in this species the venter is broadly rounded here and not perfectly flat as in R. rectangulatum sp. nov. Rineceras strigatum ( Winchell, 1862) is also similar, but shows a sharp ventrolateral shoulder ( Shimansky 1967).

Figures

Fig. 9. Rineceras rectangulatum sp. nov., dorsal view reconstruction, lateral view and suture line (at 36 mm dm, 21 mm ww, 14 mm wh) of holotype MB.C.30382. Scale bar units = 1 mm.

Tables

Table 5. Conch dimensions (in mm) and ratios of Rineceras rectangulatum sp. nov.

Specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZW
MB.C.30382	50.7	29.0	20.1	21.2	18.9	0.57	1.44	0.42	2.54	0.06