Early Carboniferous nautiloids from the Central Sahara, southern Algeria

. Coiled nautiloids of the Tournaisian and early to middle Viséan (Early Carboniferous) have so far only become known from a few regions. Here we describe material from ﬁ ve localities in southern Algeria; these belong to four stratigraphic horizons (two horizons in the late Tournaisian, one horizon near the Tournaisian–Viséan boundary, one horizon in the early to middle Viséan). From these, the new genera Stroborineceras gen. nov. and Trilobitoceras gen. nov. and the following new species are described: Rineceras tenerum sp. nov., Stroborineceras insalahensis gen. et sp. nov.,

1 specimen Lispoceras sp. 2 1 specimen (4) Area of Oued Temertasset, 150 kilometres east-southeast of the town In Salah (central coordinates: 26.6178° N, 3.8392° E); Argiles de Teguentour. The fossil site was probably discovered by Follot (1951) and later mentioned by Conrad & Pareyn (1968) and Conrad (1984). Korn et al. (2010c) described diverse ammonoid assemblages from a number of localities in this area; the nautiloidbearing single assemblages can, according to their lithology, be grouped in two stratigraphic units. The material is present in three different types of preservation, depending on the lithology of the fossilbearing strata: (1) Calcitic -the specimens from Azzel Matti come from carbonate layers of the 'Dalle des Iridet'; they are preserved as internal moulds with partial shell preservation.
(2) Sideritic -the specimens from Hassi Habadra and the locality MOU-C1 of Oued Temertasset are sideritic nodules. They are mostly internal moulds with rare shell preservation. (3) Haematitic -all others, and in fact the vast majority of the specimens, are from dark shales and are preserved as internal moulds. Almost the complete material consists of phragmocone fragments; body chambers are rarely present. In most cases the fragments are quite small and belonged to specimens less than 50 mm in diameter.
The description of the specimens follows the terminology of conch, ornament and suture line proposed by Korn (2010) and Klug et al. (2015) for the description of ammonoids (Fig. 3). The terminology of conch geometry used here largely corresponds to that proposed by Teichert (1964). The only differences are in the following terms: umbilical angle or shoulder (= umbilical margin) and umbilical area (= umbilical width).

Diagnosis
Genus of the family Trigonoceratidae with evolute conch; whorls detached or slightly in contact; whorl profi le elliptical or rounded-triangular with broad venter. Ornament with coarse growth lines and fi ne or coarse spiral lines; coarse granulation at the crossing points of growth lines and spiral ridges. Suture line with shallow external and lateral lobes. Siphuncle small with subcentral position (after Kummel 1964; emended by Korn et al. 2022).

Remarks
Due to differing opinions on the signifi cance of the general shape of the conch, there is disagreement on the species spectrum of the genus Rineceras. Turner (1953) revised the species originally described by Martin (1793Martin ( , 1809 as "Conchyliolithus N. Ammonites (Luidii)", and subsequently, he introduced the genus Pararineceras on the basis of this species (Turner 1954). This species differs from the type species of Rineceras only by the more densely coiled conch and the supposed "straightening out in late maturity". The fi rst of these two characters might be gradual and not useful for a separation of genera and the second cannot really be demonstrated in the holotype, which has a conch diameter of only 28 mm. Kummel (1964) accepted both genera without providing clear distinguishing characters, but Shimansky (1967) and Dzik (1984) regarded Pararineceras as a synonym of Rineceras. In the following, we treat Pararineceras as a junior synonym of Rineceras until a clear separation can be demonstrated.
Rineceras is restricted here to those species that have a whorl profi le with a rounded outline. This means that the species Nautilus (Trematodiscus) Meekianus Winchell, 1862 and Nautilus (Trematodiscus) strigatus Winchell, 1862, both with longitudinal grooves on the venter, placed in Rineceras by Miller & Garner (1953), are excluded from Rineceras and listed in the new genus Stroborineceras gen. nov.
Rineceras belongs to the ancestral Early Carboniferous genera in the evolution of the nautilid family Trigonoceratidae. This is supported not only by the early stratigraphic occurrence in strata of the early late Tournaisian, but also by the morphology with a rather simple overall whorl profi le without the longitudinal grooves and ridges often present in many derived forms, which there lead to a more complex geometry.

Etymology
From the Latin 'tenerum', meaning 'tender' and referring to the comparatively delicate spiral lines.

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 profi le is rounded-triangular with a somewhat fl attened venter and continuously rounded dorsum. There is no overlap upon the previous whorl (Fig. 5A). On the fl anks 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 fl anks and dorsum the suture line is almost straight (Fig. 5B).  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.
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 profi le is similar to the large segment, but the venter is slightly more fl attened 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 fl ank, 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 unfi gured paratype MB.C.30442 has, at a whorl height of 21 mm, a whorl profi le almost identical to the holotype; it also possesses twelve coarse spiral lines on the fl anks 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 profi le (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 fl ank, the non-embracing whorls, and the whorl profi le with a rounded-triangular outline.

Diagnosis
Genus of the family Trigonoceratidae with evolute conch; whorls not embracing; whorl profi le depressed and rounded-triangular (escutcheon-shaped) with fl attened or weakly concave venter and pronounced ventrolateral shoulders. Ornament with some spiral ridges on the fl ank, sometimes also on the margin of the venter. Suture line with broad, shallow external lobe and narrowly rounded ventrolateral saddle. Siphuncle small with subcentral position slightly shifted towards the venter.

Etymology
A combination of the two genus names Stroboceras and Rineceras, because of the presence of characters of both genera in the new genus.

Remarks
Stroborineceras gen. nov. combines the morphological features of the apparently ancestral genus Rineceras (simple whorl profi le and spiral lines on the fl ank) and descendant genera such as Stroboceras or Vestinautilus (pronounced ventrolateral shoulder with sharp longitudinal ridges and submarginal ventral grooves).
Stroborineceras gen. nov. differs from Rineceras in the more pronounced ventrolateral shoulder, which is reinforced by some raised longitudinal ridges, whereas in Rineceras it is rounded. In addition, the submarginal ventral longitudinal groove, which in Rineceras is only present on the juvenile stage, is still distinct in Stroborineceras gen. nov. in the middle growth stage.
Stroborineceras gen. nov. differs from Stroboceras and Vestinautilus in the absence of the strong longitudinal ridges and broad longitudinal grooves that cause a polygonal whorl profi le in these two genera. Instead, Stroborineceras gen. nov. merely has spiral lines on the fl anks.  Table 2 Diagnosis Species of Stroborineceras gen. nov. wi th depressed, rounded-triangular whorl profi le (ww/wh ~ 1.50), venter strongly fl attened, ventrolateral shoulder subangular with sharp longitudinal ridges. Whorls not embracing. Ornament with fi ne spiral ridges in the submarginal ventral position; fi ve or six spiral ridges are located on the fl ank.

Etymology
Named after the town of In Salah in the central Sahara Desert.

Description
Holotype MB.C.30445.1 is a whorl fragment of about 90 degrees angular length, consisting of the last chambers of the phragmocone and part of the body chamber (Fig. 6B). The maximum whorl height is 11 mm. The whorl profi le is rounded-triangular and depressed (ww/wh = 1.51) with a fl attened venter and an almost semi-circular area encompassing the fl anks and dorsum (Fig. 7A); the ventrolateral shoulder is subangular. The specimen bears at least eight longitudinal lines, two of which are on the edge of the venter and six on the fl ank. The suture line shows a broad, almost semi-circular external lobe, a tightly rounded ventrolateral saddle and a shallow and very broad lateral lobe. On the dorsum the suture line shows an almost straight course (Fig. 7E).
The paratypes illustrate that the variation is quite low; all specimens show very similar whorl profi les, ornament and suture line. Compared to the holotype, the paratype MB.C.30445.2 ( Fig. 6A) has more strongly developed spiral lines on the fl anks and the paratypes MB.C.30445.3 (Fig. 6C) and MB.C.30446.1 (Fig. 6D) show slightly more distinct submarginal ridges on the venter.    Table 3 Diagnosis Species of Stroborineceras gen. nov. with weakly depressed, rounded-pentagonal whorl profi le (ww/wh ~ 1.20), venter concave, ventrolateral shoulder angular. Whorls not embracing. Ornament with fi ve faint spiral ridges located on the fl ank.

Etymology
From the Latin 'felis', meaning 'cat' and referring to the characteristic whorl profi le resembling a cat's head.

Description
Holotype MB.C.30454 is a phragmocone fragment of slightly less than 90 degrees in length (Fig. 8A). It reaches a whorl height of 13 mm and the profi le is weakly depressed (ww/wh = 1.22). The characteristic whorl profi le has the outline of a cat's head shape (Fig. 8B); its general shape is rounded-pentagonal. The venter is concavely incurved and is bordered by the very prominent, angular ventrolateral shoulder. The profi le is widest at the middle of the whorl height; from here the fl anks converge with a slight concave incurvation. The dorsum is broadly rounded. On the fl ank about fi ve spiral lines are visible; they become weaker towards the dorsum. The suture line shows a deep, almost semicircular external   (Korn et al. 2002 Coll.). A. Lateral and ventral views. B. Suture line, at ww = 9.4 mm, wh = 6.6 mm. Scale bar units = 1 mm.

Diagnosis
Genus of the family Trigonoceratidae with discoidal, evolute conch; whorls slightly embracing, outer whorl may have lose contact with preceding whorls. Adult conch with a polygonal whorl profi le; venter slightly convex, fl attened, less often slightly concave, fl anks almost fl at or irregularly concave, dorsum slightly concave. Prominent longitudinal keels usually well developed, separated by concave zones.
Suture line with small lobes and saddles refl ecting keels and longitudinal grooves on the surface of the conch. Siphuncle small with subcentral position between septum centre and venter (after Shimansky 1967; emended).

Included species
Nautilus

Remarks
A systematic treatment of the morphologically diverse Stroboceras form complex is diffi cult and it is not clear what the relationships between the numerous species are. Turner (1954) introduced the genus Epistroboceras to separate the laterally compressed forms. These forms are supposed to differ from Stroboceras by the narrower coiling: Stroboceras should be tarphophioceraconic (i.e., with the last whorl detached), while Epistroboceras should be tarphyceraconic (i.e., with the last whorl in close contact with the preceding one).
This distinguishing criterion was also mentioned by Kummel (1964), but Gordon (1965) pointed out that only the type species S. hartii has a straightened-out whorl at maturity. However, Miller & Garner (1953) had already pointed out that the holotype of this species is "slightly crushed". They also reported "… that the conch is coiled and is very slightly involute; though at full maturity the adoral portion of the body chamber straightens and loses contact with the preceding whorl but retains, however, the slight impressed zone." (Miller & Garner 1953: 134). This combination of characters is questionable; a concave whorl zone is practically always created by enclosing the preceding whorl. Therefore, it cannot be excluded that it is a preservation effect. Gordon (1965) accepted Epistroboceras only as a subgenus of Stroboceras, distinguished by the loss of longitudinal sculpture in late ontogeny. Shimansky (1967) discussed the relationship between the two genera in detail and concluded that the relationships and boundaries of the genera Stroboceras and Epistroboceras were not entirely clear. He considered it possible that, in addition to the whorl profi le, the size of the umbilical window could also serve to distinguish between the two genera.  Histon (1999) characterised the genus Epistroboceras, among other characteristics, by the strongly compressed conch, converging fl anks and narrow concave venter. More recently, Niko & Mapes (2004) discussed the relationship between Stroboceras and Epistroboceras; in distinguishing the two genera, they upheld the presumed detachment of the adult whorl in Stroboceras. As a further difference between the two genera, they mentioned that the "… lateral grooves developed in the juvenile stage become obsolescent with maturity" in Epistroboceras (Niko & Mapes 2004: 341).
The distinction between the two genera is an issue that cannot be solved with the material available from the Sahara Desert, it is beyond the scope of our investigations. For the time being, we follow the path suggested by Shimansky (1967) (Korn et al. 2002 Coll.). A. Ventral and lateral views. B. Cross section. C. Suture line, at ww = 9.9 mm, wh = 5.5 mm. Scale bar units = 1 mm.

Description
Holotype MB.C.30458.1 is a phragmocone fragment with about 22 mm conch diameter; it is partly embedded in a haematite nodule (Fig. 10A) and was sectioned for the study of the whorl profi le. The conch is discoidal and evolute (ww/dm = 0.51; uw/dm = 0.45). The whorl profi le is rounded-trapezoidal with almost fl at venter separated from the convex fl anks by an angular ventrolateral shoulder. Next to this shoulder is a shallow, wide longitudinal groove (Fig. 10B). The whorls apparently do not touch each other, but this may be caused by dissolution of the shell wall.
The suture line has a very broad external lobe, an angular ventrolateral saddle in the area of the ventrolateral shoulder and a fl at, somewhat undulating lateral lobe (Fig. 10C). The siphuncle has a subcentral position.

Remarks
Stroboceras mane sp. nov. is an ancestral species of the genus and differs from almost all other species by the non-embracing whorls. Another distinguishing criterion is the very weak formation of longitudinal ridges and grooves.

Etymology
From the Latin noun 'ancilis', meaning 'shield' and referring to the whorl profi le.

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 profi le and is widest at about the middle of the fl ank. The outer half of the fl ank 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 fi ner ridge accompanied on both sides by a shallow longitudinal groove. The venter is slightly concave. The umbilical wall is oblique and almost fl at; 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, fl ank, 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 profi le has a very similar shape. Paratype MB.C.30459.2 (Fig. 11B), however, shows slightly more sharply defi ned 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 profi le with a right-angled ventrolateral shoulder.

Description
The only specimen present is a phragmocone fragment consisting of three chambers (Fig. 13A). It has, at 10.5 mm whorl height, a depressed pentagonal whorl profi le (ww/wh = 1.44). It shows a prominent, rounded ventrolateral shoulder accompanied by shallow longitudinal grooves. The centre of the venter is shallowly convex and the umbilical margin separates the weakly convex fl ank from the almost fl at umbilical wall by a low ridge (Fig. 13B). A narrow, very shallow concave whorl zone is present. The suture line shows a course dependent on the outline of the whorl profi le; saddles lie in the infl ated areas of the profi le and lobes in the indented ones (Fig. 13C). Therefore, the external lobe appears trilobate and the ventrolateral saddle is raised. An internal lobe is induced by the concave whorl zone. Genus Vestinautilus Ryckholt, 1852

Diagnosis
Genus of the family Trigonoceratidae with evolute conch; whorls slightly impressed; whorl profi le rounded-triangular or trapezoidal with fl attened or weakly concave venter and pronounced ventrolateral shoulder. Ornament with fi ne lines and very coarse spiral ridges around the ventrolateral shoulder, sometimes also on the venter. Suture line slightly sinuous. Siphuncle small with subcentral position (after Kummel 1964; emended by Korn et al. 2022).

Included species
Nautilus (

Remarks
In the description of the nautiloids from the Dalle à Merocanites, Korn et al. (2022) discussed the relationships between the genera Vestinautilus and Subvestinautilus; they considered the latter as a junior synonym.  Vestinautilus differs from the other genera of the family Trigonoceratidae by the rather weakly ornamented shell in combination with a rounded-triangular or trapezoidal whorl profi le. However, it should be noted that some of these genera, such as Rineceras, Vestinautilus and Stroboceras, show quite similar conch and ornamentat morphology at the beginning of their occurrence in the Tournaisian.

Etymology
From the Latin 'angulatum', referring to the two angular ventrolateral ridges.

Description
Holotype MB.C.30461.1 is a phragmocone segment of about a quarter whorl with almost 9 mm whorl height (Fig. 14B). It shows a triangular whorl profi le with a shallow, almost fl at venter that is bordered on both sides by two elevated, sharp longitudinal ridges. Flanks, umbilical wall and dorsum form a broadly curved, semi-circular unit. On the fl anks there are two longitudinal ridges, which are considerably weaker than the ridges on the ventrolateral shoulder (Fig. 15C). The suture line shows a deep, broadly rounded outer lobe and a ventrolateral saddle which has two crests because of the two longitudinal ridges. The lateral lobe is very broad and continues into a very low internal saddle (Fig. 15D).

Remarks
Vestinautilus angulatus sp. nov. belongs to the few species of the genus with a moderately depressed whorl profi le (ww/wh ~ 1.50) and a very weak longitudinal sculpture; in these respects, the new species differs from all other species of the genus in which the whorls are not embracing.   Table 9 Diagnosis Species of Vestinautilus with moderately depressed, rounded-trapezoidal whorl profi le (ww/wh ~ 1.60-1.80), venter weakly fl attened, with three longitudinal grooves on each side, ventrolateral shoulder subangular. Whorls weakly embracing. Ornament with two or three weak but sharp ridges on the fl ank.

Etymology
From the Latin 'papilio', meaning 'butterfl y' and referring to the shape of the whorl profi le.

Description
Holotype MB.C.30470.1 is a phragocone segment of about a quarter whorl with almost 10 mm whorl height; it consists of four chambers (Fig. 16A). The whorl profi le is depressed (ww/wh = 1.62) and kidney-shaped with a rounded venter, subangular ventrolateral shoulder and a convex curved area encompassing the fl anks and umbilical wall (Fig. 17A). The whorl weakly encloses the preceding whorl. On the venter there are three longitudinal marginal grooves on each side; the ventrolateral shoulder is defi ned by two slightly raised edges. The fl anks bear two coarse spiral lines near the ventrolateral shoulder. The suture line has a low amplitude course; it shows a very low external saddle and very shallow lateral lobe. Only the internal lobe is deeper and has a blunt V-shaped form (Fig. 17B).
Paratype MB.C.30470.2 shows, at a whorl height of 6 mm (Fig. 16B), a largely similar morphology to the holotype. However, there is the big difference that it does not have a concave whorl zone (Fig. 17C), probably due to its small size. Furthermore, the whorl profi le is broader (ww/wh = 1.82). The suture line is almost straight; there is no internal lobe (Fig. 17D).

Remarks
Vestinautilus papilio sp. nov. belongs to the species of the genus with a moderately depressed whorl profi le (ww/wh ~ 1.70), a character that distinguishes the new species from most of the other species of the genus with weakly embracing whorls. Another criterion that distinguishes the new species is the rather weak longitudinal sculpture.

Etymology
From the Latin 'infl exus', referring to the incurved septum.

Description
Holotype MB.C.30472.1 is a phragmocone fragment from a quarter whorl with 15 mm whorl height (Fig. 18B). It has a moderately depressed whorl profi le (ww/wh = 1.94) with a fl attened venter and broadly rounded lateral and dorsal zones. The ventrolateral shoulder is subangular and reinforced by two sharp longitudinal ridges; there are two more, weaker ridges on the outer fl ank (Fig. 19B). The suture line shows a broad external lobe, fl attened at the base. This particular shape is caused by an infl exion of the septum on the middle of the venter. There is a narrowly rounded saddle on the ventrolateral shoulder and a shallow, broadly rounded lobe on the fl ank (Fig. 19C).
Paratype MB.C.30472.2 is a desert-polished specimen with half a whorl preserved; it has a diameter of 24.5 mm (Fig. 18A). It was sectioned and shows one and a half whorls, which possess a similar profi le. The last preserved whorl does, at 24 mm conch diameter, not touch the preceding, but this may be caused by the lack of the original shell wall (Fig. 19A). The longitudinal ridges are only barely visible and rather weak when compared with the holotype. The suture line shows a deeper external lobe, which is less fl attened at the base.
The smaller paratype MB.C.30472.3 (Fig. 18C) with 6 mm whorl height has a less depressed whorl profi le, but shows very clearly the ventral infl exion of the septum and the resulting very deep external lobe (Fig. 19E).   Table 11 Diagnosis Species of Vestinautilus with strongly depressed, rounded-trapezoidal whorl profi le (ww/wh ~ 2.10), venter up to 30 mm conch diameter broadly arched with two shallow submarginal grooves, which disappear in the adult stage. Ventrolateral shoulder defi ned by a subangular margin; one sharp ridge is located on the umbilical wall near the ventrolateral shoulder. Whorls weakly embracing, coiling very high (WER ~ 2.55). Ornament with delicate growth lines.

Etymology
From the Latin 'crista', meaning 'crest' and referring to the two lateral longitudinal ridges.

Description
Holotype MB.C.30473 is a desert-polished specimen with a diameter of 38 mm, showing the conch shape and small areas of ornament (Fig. 20). The conch is broadly cylindrical and subevolute (ww/dm = 0.84; uw/dm = 0.37) with a very high coiling rate (WER = 2.57). The whorl profi le is strongly depressed (ww/wh = 2.13) and shows a fl attened venter, which possesses two submarginal external grooves at size stages between 17 and 35 mm diameter. These weaken considerably thereafter and are only visible as shallow longitudinal depressions at the maximum diameter of the specimen. The ventrolateral shoulder is distinguished by three edges, of which the two inner ones are strengthened by longitudinal ridges. Only small areas of shell ornament are visible; these show very fi ne growth lines on the venter with a deep external sinus.
Three paratypes in fragmentary preservation are available. They are larger specimens with whorl widths between 49 and 80 mm, thus belonged to conchs with 60 to 90 mm diameter. Two of them (MB.C.30474.2 and MB.C.30474.3; Fig. 21B-C) show the imprint of the preceding whorl with sublateral longitudinal grooves in the dorsal region; in paratype MB.C.30474.3 the edges of the ventrolateral shoulder are also still visible. Both have a broadly rounded venter. The largest paratype MB.C.30474.1 shows a shallow, broad depression in the middle of the venter at its largest diameter (Fig. 21A).
Paratype MB.C.30474.3 shows the suture line with a broad and shallow external lobe and a narrow and shallow lateral lobe, which has a position on the umbilical wall (Fig. 21C). The siphuncle has a slightly subcentral position towards the venter.

Remarks
Vestinautilus bicristatus sp. nov. belongs to the species of the genus that possess a very broad whorl profi le (ww/wh > 2.00) and an ornament with only a few spiral ridges. In this respect, V. cariniferus,  V. paucicarinatus, V. pinguis and V. semiplicatus are similar, but these four species have a concave venter at least at times in ontogeny (Sowerby 1825;de Koninck 1844;Foord 1891Foord , 1900. The most similar V. bicristatus sp. nov. is the species V. padus, which shows the same conch dimensions, but differs in the lack of the submarginal ventral grooves  Vestinautilus sp. Fig. 22, Table 12 Material examined ALGERIA • 1 specimen; Mouydir, south of Oued Temertasset (locality MOU-C1); Argiles de Teguentour (Helicocyclus-Ouaoufi lalites Assemblage; early late Tournaisian); Korn et al. 2002 Coll.; illustrated in Fig. 22; MB.C.30475.

Description
Specimen MB.C.30475 is a chambered fragment with a diameter of 72 mm, heavily affected by desert polishing (Fig. 22). Despite the erosion, the conch shape can still be recognised quite well; the conch is thickly discoidal and subevolute (ww/dm = 0.54; uw/dm = 0.25) with a depressed trapezoidal whorl profi le (ww/wh = 1.57). The whorls overlap each other slightly. The venter is concave in the middle and separated from the almost fl at area of the fl ank and umbilical wall by two sharp ridges on the ventrolateral shoulder.

Diagnosis
Genus of the family Trigonoceratidae with distinctly tripartite venter caused by two deep longitudinal grooves.

Etymology
After the superfi cial similarity in ventral view with the trilobites.

Included species
Nautilus ( Table 13 Diagnosis Species of Trilobitoceras gen. nov. with moderately depressed whorl profi le (ww/wh ~ 1.65). Suture line with a broadly rounded median saddle.

Etymology
From the Latin 'peculiaris', meaning 'peculiar' and referring to the unusual conch shape.

Description
Holotype MB.C.30477 is a phragmocone fragment with almost half a whorl length (Fig. 23A). It has a depressed whorl profi le (ww/wh = 1.63) with a broadly rounded venter characterised by two deep and wide ventral grooves. The fl anks are almost parallel in their middle and the umbilical wall is almost fl at (Fig. 24A). The suture line, whose course is determined by the shape of the whorl profi le, has a very wide external lobe in which a low, broadly rounded median saddle rises (Fig. 24B).
Paratype MB.C.30478 is a fragment consisting of only two chambers of the phragmocone (Fig. 23B). The conch geometry is very similar to the holotype, although the ww/wh ratio is slightly higher with a value of 1.72. (Fig. 24C) The suture line is also similar to the holotype; however, the specimen also shows the rather narrow, rounded V-shaped internal lobe (Fig. 24D).   Korn et al. 2002 Coll.). A. Whorl profi le of holotype MB.C.30477 (dorsal portion reconstructed). B. Suture line of holotype MB.C.30477, at ww = 13.6 mm, wh = 7.7 mm. C. Whorl profi le of paratype MB.C.30478. D. Suture line of paratype MB.C.30478, at ww = 13.6 mm, wh = 7.9 mm. Scale bar units = 1 mm.  Miller & Garner (1953).

Diagnosis
Genus of the family Trigonoceratidae with subevolute to evolute conch; whorls slightly impressed; whorl profi le compressed, venter concave and bordered by an angular ventrolateral shoulder, fl anks convex, convergent; umbilical margin rounded or subangular. Suture line with shallow external and lateral lobes. Siphuncle small with subcentral position (after Kummel 1964;emended).

Etymology
Named after the type locality Gara Azzel Matti.

Description
Holotype MB.C.30479.1 is an incomplete, partially broken and desert-eroded specimen with a conch diameter of almost 120 mm (Fig. 25). The conch is very thinly discoidal (ww/dm = 0.19) with a rather wide umbilicus (uw/dm = 0.44) and moderate coiling rate (WER = 1.95). The conspicuous, lyriform whorl profi le is widest at the distinct, subangular umbilical edge. It shows an oblique, concave umbilical wall, convergent fl anks and a double-keeled venter with a deep longitudinal median groove.
Paratype MB.C.30479.2 is an incomplete specimen with 60 mm diameter, which largely complements the morphology of the holotype.

Diagnosis
Genus of the family Trigonoceratidae with evolute conch; whorls slightly impressed; whorl profi le hexagonal or pentagonal with fl attened or slightly concave venter and narrowly rounded umbilical margin. Ornament in the adult stage with coarse growth lines, in the preadult stage with fi ne spiral lines. Suture line with shallow external and lateral lobes. Siphuncle small with subcentral position (after Kummel 1964; emended by Korn et al. 2022).

Etymology
Named after the occurrence in the Sahara Desert.

Description
Holotype MB.C.30480.1 is the fragment of a phragmocone of a quarter whorl length (Fig. 26A); it has a whorl height of 16 mm. The whorl profi le is subquadratic with fl attened, very weakly convergent fl anks, a broadly rounded venter and a broadly rounded dorsum (Fig. 27A). The internal mould shows no ornament, but very faint remnants of spiral striation are visible. The suture line extends with a slight   depression on the venter, a slightly deeper, very broadly rounded lobe on the fl ank and a very shallow internal lobe (Fig. 27B).
Paratype MB.C.30481 shows the chambered remains of two whorls that touch but do not overlap (Fig. 26B). On the outer whorl with 12 mm whorl height, the profi le is subquadrate (ww/wh = 1.04) with a wider, fl attened venter, weakly divergent, also fl attened fl anks and a more tightly rounded dorsum (Fig. 27C). The penultimate whorl, 3.8 mm high, is rounded-triangular in profi le and somewhat depressed (ww/wh = 1.28). The suture line is similar to that of the holotype, but shows a higher ventral area with a slightly deeper external lobe (Fig. 27D).

Remarks
Maccoyoceras saharensis sp. nov. differs from the other species of the genus by the whorl profi le form with a strongly rounded ventrolateral shoulder. Another difference could be the strength of the ornament; in M. saharensis sp. nov. no spiral lines were impressed into the internal mould. However, since no shell specimens of the new species are known, it is impossible to say whether spiral lines were actually present. It is therefore also possible that the new species belongs to another genus, for example Lispoceras.
Maccoyoceras habadraense sp. nov. urn:lsid:zoobank.org:act:CDDB23E7-2380-4600-BCF0-71E3F2159BF2 Fig. 28, Table 16 Diagnosis Species of Maccoyoceras reaching about 100 mm conch diameter. Conch with weakly depressed whorl profi le (ww/wh ~ 1.10); venter fl attened, ventrolateral shoulder narrowly subangular. Whorls just touching the preceding. Ornament in the juvenile stage with few coarse, granulated spiral lines on the fl ank, in the adult stage without spiral lines. Fine, sharp growth lines on the fl ank, with weakly biconvex course with a shallow lateral sinus and a moderately high ventrolateral projection. Venter with delicate growth lines with deep sinus.

Etymology
Named after the type locality Hassi Habadra.

Description
Holotype MB.C.30485 is an incomplete specimen with 66 mm conch diameter (Fig. 28). It allows the study from both sides. The conch is extremely discoidal (ww/dm = 0.34) and evolute (uw/dm = 0.46) with a high coiling rate (WER = 2.17). The whorl profi le is weakly depressed hexagonal (ww/wh = 0.93) and widest at the rounded umbilical margin. The fl anks converge barely towards the subangular ventrolateral shoulder that separates the fl anks from the fl attened venter. The umbilical wall is convexly rounded.
There are two ontogenetic stages in the ornament development; the fi rst ranges up to about 35 mm conch diameter and possesses about ten spiral lines on the fl ank. The second stage does not show spirals but only fi ne, narrow-standing growth lines with weakly biconvex course. These are restricted to the fl anks, while the venter shows very delicate growth lines forming a very deep sinus.

Remarks
Maccoyoceras habadraense sp. nov. has similarities with M. pentagonum, but has a wider umbilicus (uw/dm = 0.45 in M. habadraense sp. nov. but only 0.40 in M. pentagonum). Furthermore, the spiral lines are markedly coarser in M. habadraense sp. nov.; this feature also distinguishes the new species from the other species of the genus.
Maccoyoceras concavum sp. nov. urn:lsid:zoobank.org:act:CC00C3E7-5DF4-4FA9-844C-AAA60F1F5016 Fig. 29, Table 17 Diagnosis Species of Maccoyoceras reaching about 100 mm conch diameter. Conch with weakly compressed whorl profi le (ww/wh ~ 0.90); venter weakly concave, ventrolateral shoulder narrowly subangular. Whorls weakly embracing the preceding. Ornament in the juvenile stage with few coarse, granulated spiral lines on the fl ank, in the adult stage without spiral lines. Fine, sharp growth lines on the fl ank, with weakly biconvex course with a shallow lateral sinus and a moderately high ventrolateral projection. Venter with delicate growth lines with deep sinus.

Description
Holotype MB.C.30486 is a rather well-preserved, almost completely chambered specimen with 76 mm conch diameter, from which the last, poorly preserved segment was removed before photography (Fig. 29). The specimen allows the study from both sides. The conch is extremely discoidal (ww/ dm = 0.32) and subevolute (uw/dm = 0.41) with a very high coiling rate (WER = 2.35). The whorl profi le is compressed hexagonal (ww/wh = 0.93) and widest at the rounded umbilical margin. The fl anks stand almost parallel and converge barely towards the angular ventrolateral shoulder that separates the fl anks from the weakly concave venter. The umbilical wall is convexly rounded.
Two ontogenetic stages of the ornament development can be separated: up to 17 mm conch diameter, six coarse, crenulated spiral lines on the fl ank are the dominant elements in the juvenile stage. Thereafter, fi ne but sharp narrow-standing growth lines with weakly biconvex course form the ornament on the fl anks, but the venter bears very delicate growth lines with a deep ventral sinus. The suture line shows a shallow ventral lobe and a shallow lateral lobe. The siphuncle is almost central.

Remarks
Maccoyoceras concavum sp. nov. has conch proportions very similar to those of M. pentagonum from the contemporaneous 'Dalle à Merocanites' of Timimoun. However, the new species differs from this and from the other species of the genus by the concave venter.  Genus Lispoceras Hyatt, 1893 Type species Lispoceras trivolve Hyatt, 1893; original designation.

Diagnosis
Genus of the family Trigonoceratidae with evolute conch; whorls just touching each other; whorl profi le weakly depressed elliptical or circular. Ornament in the adult stage with fi ne growth lines, in the preadult stage with fi ne spiral lines. Suture line with shallow external and lateral lobes. Siphuncle small with subcentral position (after Kummel 1964; emended by Korn et al. 2022).

Description
Specimen MB.C.30487 is a body chamber fragment that belonged to a conch approximately 10 mm diameter (Fig. 30). It has an almost circular whorl profi le with a slightly clearer umbilical margin. The last whorl only slightly encompassed the previous one, recognisable by the very small dorsal whorl zone. The shell surface, although marred by desert grinding, is clearly recognisable. The ornament consists of fi ne growth lines running in a slightly posterior direction across the umbilical wall and fl anks, then forming a deep ventral sinus.  Table 19 Material examined ALGERIA • Ahnet, west-southwest of Gara Azzel Matti; 'Dalle des Iridet' (Ammonellipsites-Merocanites Assemblage; Tournaisian-Viséan boundary interval); Wendt and Kaufmann 1995 Coll.; illustrated in Fig. 31; MB.C.30488.

Description
Specimen MB.C.30488 is a fragmented conch with a diameter of almost 70 mm, it consists of a part of the body chamber, the phragmocone of the last whorl and a small piece of the second last whorl (the best-preserved piece is illustrated in Fig. 31). The conch is discoidal and subevolute (ww/dm = 0.46; uw/ dm = 0.41) with a depressed rectangular whorl profi le. The fl anks are almost parallel and separated from the fl attened venter by a rounded but distinct ventrolateral shoulder. Any overlap of the whorls is not visible. The suture line shows a broadly rounded external lobe and a rounded lateral lobe.

Discussion
Coiled nautiloids of the Tournaisian and Viséan (Early Carboniferous) are only known from a few localities in North Africa. Here, we describe material from fi ve localities in southern Algeria. These belong to four stratigraphic horizons (named in terms of ammonoid stratigraphy): ( Of these assemblages, the fi rst is particularly important because it is one of the oldest Early Carboniferous occurrences of coiled nautiloids. All species belong to the family Trigonoceratidae Hyatt, 1884.