Stroboceras ancilis, Korn & Bockwinkel, 2022

Korn, Dieter & Bockwinkel, Jürgen, 2022, Early Carboniferous nautiloids from the Central Sahara, southern Algeria, European Journal of Taxonomy 831, pp. 67-108 : 82-84

Stroboceras ancilis sp. nov.

urn:lsid:zoobank.org:act:BA91AA8E-DD89-4E1E-8781-0BF2ADB763E1

Figs 11–12 , Table 6

Diagnosis

Species of Stroboceras with weakly depressed, rounded-trapezoidal whorl profile (ww/wh ~ 1.40), venter flat, ventrolateral shoulder angular with sharp longitudinal ridges. Whorls weakly embracing. Whorl profile with a wide longitudinal groove on the outer flank near the ventrolateral margin and a midflank longitudinal ridge.

Etymology

From the Latin noun ‘ ancilis ’, meaning ‘shield’ and referring to the whorl profile.

Type material

Holotype ALGERIA • Sebkha de Timimoun 14.5 km west-southwest of Timimoun (locality TIM-C8); Argiles de Timimoun supérieur (Upper Bollandoceras Assemblage ; early to middle Viséan); Korn et al. 2002 Coll.; illustrated in Fig. 11C ; MB.C.30459.1 .

Paratypes ALGERIA • 4 specimens; Sebkha de Timimoun 14.5 km west-southwest of Timimoun (locality TIM-C8); Argiles de Timimoun supérieur (Upper Bollandoceras Assemblage ; early to middle Viséan); Korn et al. 2002 Coll.; MB.C.30459.2 – MB.C.30459.5 .

Description

Holotype MB.C.30459.1 is a phragmocone fragment of a quarter whorl without shell preservation ( Fig. 11C ). It has a depressed pentagonal whorl profile and is widest at about the middle of the flank. The outer half of the flank is occupied by a shallow longitudinal groove, delimited on the ventral side by an angular ventrolateral shoulder and on the umbilical side by a rounded ridge. On the venter, near the ventrolateral shoulder, there is a finer ridge accompanied on both sides by a shallow longitudinal groove. The venter is slightly concave. The umbilical wall is oblique and almost flat; it ends at the umbilical seam. There is a small, very shallow dorsal whorl zone ( Fig. 12A ).

The suture line shows four rounded lobes each on the venter, flank, umbilical wall and dorsal whorl zone ( Fig. 12B ). Of these, the rounded V-shaped external lobe is the deepest; the lateral lobe is somewhat asymmetrical and broadly rounded and the lobe on the umbilical wall is shallow. The internal lobe is small and broadly V-shaped.

The paratypes show little variation in conch shape and suture line. The ww/wh ratio is between 1.30 and 1.40 in all specimens and the whorl profile has a very similar shape. Paratype MB.C.30459.2 ( Fig. 11B ), however, shows slightly more sharply defined longitudinal ridges; its suture line ( Fig. 12D ) has slightly shallower lobes than the holotype.

Paratype MB.C.30459.3 is a heavily corroded specimen 37 mm in diameter ( Fig. 11A ). Although incomplete, it shows the general advolute conch form with whorls touching the preceding.

Remarks

Stroboceras ancilis sp. nov. differs from all other species of the genus by its almost rectangular whorl profile with a right-angled ventrolateral shoulder.

Figures

Fig. 11. Stroboceras ancilis sp. nov. from Timimoun (all Korn et al. 2002 Coll.). A. Paratype MB.C.30459.3. B. Paratype MB.C.30459.2. C. Holotype MB.C.30459.1. Scale bar units= 1 mm.

Fig. 12. Stroboceras ancilis sp. nov. from Timimoun (both Korn et al. 2002 Coll.). A. Whorl profile of holotype MB.C.30459.1. B. Suture line of holotype MB.C.30459.1, at ww =11.6 mm, wh =8.8 mm. C. Whorl profile of paratype MB.C.30459.2. D. Suture line of paratype MB.C.30459.2, at ww = 10.4 mm, wh =7.1 mm. Scale bar units =1 mm.

Tables

Table 6. Conch dimensions (in mm) and ratios of Stroboceras ancilis sp. nov.

Specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZW
MB.C.30459.3	36.6	16.8	12.1	15.1	12.1	0.46	1.39	0.41	2.23	0.00
MB.C.30459.1	–	12.5	9.2	–	–	–	1.36	–	–	–
MB.C.30459.2	–	10.7	7.8	–	–	–	1.37	–	–	–
MB.C.30459.4	–	10.8	8.0	–	–	–	1.36	–	–	–
MB.C.30459.5	–	7.5	5.7	–	–	–	1.31	–	–	–