The early gephuroceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea)

The ammonoids of the suborder Gephuroceratina from the Roteisenstein (Red Ironstone) Formation of the area around Dillenburg (eastern Rhenish Mountains) are revised, mainly based on historical collections stored in the Museum für Naturkunde, Berlin. The new species Ponticeras materni sp. nov. is described and the species Pseudoprobeloceras pernai (Wedekind, 1918), Pseudoprobeloceras applanatum (Wedekind, 1918), Ponticeras aequabile (Beyrich, 1837), Darkaoceras galeatum (Matern, 1931), Taouzites acutus (Matern, 1931), Koenenites lamellosus (Sandberger & Sandberger, 1851), Acanthoclymenia forcipifera (Sandberger & Sandberger, 1851) and Acanthoclymenia planorbis (Sandberger & Sandberger, 1851) are revised. The stratigraphic distribution of the genera is discussed; they are assigned to three assemblages: (1) Pseudoprobeloceras pernai Zone (latest Givetian; genera Pseudoprobeloceras, Ponticeras, Darkaoceras and Taouzites), (2) Koenenites lamellosus Zone (early Frasnian, containing Koenenites lamellosus and Acanthoclymenia forcipifera) and (3) Mesobeloceras kayseri Zone (middle Frasnian, containing Acanthoclymenia planorbis).


Introduction
Ammonoids from the Roteisenstein (Red Ironstone) Formation near Dillenburg on the eastern edge of the Rhenish Mountains (Fig. 1) are among the objects widely found in fossil collections. They already became quite well known in the 19 th century and were already published by the pioneers in palaeontology (von Buch 1832;Beyrich 1837;d'Archiac & de Verneuil 1842;Sandberger & Sandberger 1850-1856. Even after that, there was quite a lot of interest in these fossils; they were especially investigated in the studies of Frech (1888), Wedekind (1918) and Matern (1931).
(2) Koenenites lamellosus Zone (early Frasnian), containing Koenenites lamellosus (Sandberger & Sandberger, 1851) and Acanthoclymenia forcipifera (Sandberger & Sandberger, 1851). All of the specimens of Koenenites lamellosus in the MfN collection, except for one, are from a very dense haematite ore, four of which from the Koch collection (probably from the second half of the 19 th century) of the Anna Mine near Oberscheld. From the same lithology at the same locality, Koch also collected numerous specimens of Acanthoclymenia forcipifera as well as specimens of Pharciceras, Lunupharciceras and Synpharciceras, but the latter are from a haematitic limestone.

Description
Seven specimens are selected for description and illustration: Lectotype SMF.Mbg.2322: rather well-preserved specimen with 38 mm diameter, shell surface and suture line preserved (Fig. 4A).
MB.C.22164: fragmentary, somewhat corroded specimen with 53 mm conch diameter in haematitic, micritic limestone; one third of the last volution belongs to the body chamber (Fig. 5B).
MB.C.30417.1: exfoliated specimen with 37 mm conch diameter in haematitic limestone; only a small part belongs to the body chamber (Fig. 5E).
MB.C.30418: deformed but otherwise rather well-preserved specimen with 59 mm conch diameter in haematitic sparitic limestone; conch widely covered with shell. Part of the external suture line visible (Fig. 5A).
Lectotype SMF.Mbg.2322 is a specimen with 38 mm diameter (Fig. 4A). It is thinly discoidal; the venter is weakly fl attened. It is separated, on the last quarter whorl, from the converging fl anks by a pronounced ventrolateral shoulder. The specimen has rather coarse growth lines, particularly in inner whorls; they become lamellar on last volution with a high ventrolateral projection.
Specimen SMF.Mbg.2326, the holotype of Pseudoprobeloceras barroisi, is a specimen 51 mm in diameter (Fig. 4C). Its umbilical wall is oblique, the fl anks converge and the ventrolateral shoulder is prominent. On the last half volution, the specimen shows the transformation from the preadult stage into the adult stage by a rather rapid opening of the umbilicus. The shell ornamentation is poorly preserved.  (Wedekind, 1918 The additional material allows the study of the proportions, ornamentation and suture lines of the shell in a growth interval between 27 and 59 mm diameter (Fig. 5). In the interval between 30 and 50 mm diameter, the conch becomes slenderer (ww/dm decreasing from ~ 0.35 to ~ 0.25) and more widely umbilicate (uw/dm increasing from ~ 0.30 to ~ 0.28). The coiling rate is moderately high (WER ~ 1.95) at 50 mm dm. The compressed whorl profi le (ww/wh decreasing from ~ 0.80 to ~ 0.65) has an oblique umbilical wall, rounded umbilical margin, weakly converging fl anks and rounded venter. Shell remains are poorly preserved in the material; the ornament is obviously very weak.
Specimen MB.C.30418 shows the transformation from the pre-adult to adult morphology (Fig. 5A). Up to a conch diameter of 45 mm the proportions are similar to the other specimens, but thereafter there is a rapid change in the rate of overlap of the earlier whorls and a reduction in the rate of coiling. Although the specimen is somewhat distorted by tectonics, it shows the differences from the pre-adult stage. At 59 mm conch diameter, the whorl profi le is compressed with a rounded umbilical margin, weakly convergent fl anks, subangular ventrolateral shoulders and a weakly fl attened venter.
Parts of the suture line are visible in several specimens. In specimen MB.C.30417.1 it shows the outline characteristic of the genus with a V-shaped external lobe with strongly diverging fl anks, a very low lateral saddle, a deep E 1 lobe and narrowly rounded E 2 lobe. The ventrolateral saddle is almost symmetrical and broadly rounded, the lateral lobe is broadly rounded (Fig. 6A). (Wedekind, 1918). A. Suture line of specimen MB.C.30417.1 (Etzold 1910 Coll.) from Oberscheld ("Tiefe Grube"), at dm = 27.0 mm, ww = 9.0 mm, wh = 11.0 mm. B. Suture line of specimen MB.C.30418, probably from Oberscheld, at dm = 48.3 mm, ww = 11.9 mm, wh = 15.6 mm. C-F. Ontogenetic trajectories of the cardinal conch parameters. Scale bar units = 1 mm.  (Wedekind, 1918

Remarks
Pseudoprobeloceras barroisi is here synonymised with P. pernai, although its holotype is not well preserved and thus does not allow an accurate description. Up to about 40 mm conch diameter, it closely resembles the typical morphology of P. pernai; on the last half volution it shows the transformation to the adult morphology with its opened umbilicus.
Pseudoprobeloceras pernai differs from P. applanatum (Wedekind, 1918) in the shape of the venter; this is rounded in P. pernai, whereas in P. applanatum it is slightly fl attened and bordered by a narrow, rounded ventrolateral shoulder on the fl anks.
The specimens from Hassi Nebech attributed to P. pernai by Petter (1959), House et al. (1985) and Bockwinkel et al. (2013a) differ by their much higher coiling rate (WER = 2.30-2.45 between 27 and 32 mm dm) from the material from the type region (WER ~ 1.90 at 45 mm dm). They have to be attributed to the species Pseudoprobeloceras nebechense Bensaïd, 1974, as originally stated by Bensaïd (1974).

Diagnosis
Species of Pseudoprobeloceras reaching about 50 mm conch diameter with thinly discoidal, subinvolute conch at 30 mm dm (ww/dm ~ 0.35; uw/dm ~ 0.28); coiling rate moderate (WER ~ 1.95). Whorl profi le weakly compressed (ww/wh ~ 0.85); umbilical wall oblique, umbilical margin broadly rounded, venter weakly fl attened, ventrolateral shoulder narrowly rounded. Growth lines very fi ne, strongly biconvex with linguiform ventrolateral projection. Suture line with V-shaped external lobe with diverging fl anks; median saddle low, E 2 lobe small, rounded, ventrolateral saddle almost symmetrically rounded, lateral lobe asymmetrically rounded. Holotype SMF.Mbg.2323 with 24 mm diameter is discoidal and subinvolute (Fig. 4B). Its umbilical wall is rounded; the fl anks slightly fl attened and converge to the rather broad venter. A pronounced, weakly angular ventrolateral shoulder is present on the entire last volution. The growth lines are lamellar; there are faint riblets around the umbilicus. The suture line has a large, subdivided external lobe with very small E 1 prongs, a low median saddle and a very deep E m lobe.

Holotype
Specimen MB.C.22157, 35 mm in diameter, has a thinly discoidal and subinvolute conch with a compressed whorl profi le (Fig. 7A). It is widest near the mid-fl ank and has an oblique umbilical wall and broadly rounded umbilical margin; the fl anks are convex and weakly convergent, the outer fl anks are weakly concave and separated from the weakly fl attened venter by a narrowly rounded ventrolateral shoulder. The shell remains show rhythmically strengthened growth lines with broadly rounded dorsolateral projection, a wide lateral sinus and a narrow and high, lingulate ventrolateral projection. The suture line is barely visible in the ventral portion because of poor preservation; it possesses a V-shaped external lobe, a narrowly rounded ventrolateral saddle and a broadly rounded lateral lobe (Fig. 7B).

Remarks
Pseudoprobeloceras applanatum differs in the slightly stouter conch shape (ww/dm ~ 0.35) from P. pernai (ww/dm = 0.20-0.30) and the narrower umbilicus (uw/dm ~ 0.28 in contrast to ~ 0.33). The main distinguishing character to separate P. applanatum from P. pernai is the shape of the venter; while this is rounded in P. pernai, in P. applanatum it is slightly fl attened and bordered by a narrowly rounded ventrolateral shoulder from the fl anks.  (Wedekind, 1918 Table 2. Conch dimensions and ratios of selected specimens of Pseudoprobeloceras applanatum (Wedekind, 1918).

Diagnosis
Genus of the subfamily Ponticeratinae with extremely discoidal, subevolute to evolute conch. Often with ventrolateral grooves. Suture line with very wide external lobe, moderately high median saddle, small E 2 lobe, shallow and rounded lateral lobe. Suture line formula (E 2 E 1 E 2 ) L : I or (E 2 E 1 E 2 ) L : U I.

Included species
Ammonites

Remarks
Ponticeras is, next to Pseudoprobeloceras, the stratigraphically oldest genus of the Gephuroceratoidea. The two genera mainly differ in the shape of the external lobe; in Pseudoprobeloceras it is quite narrow with a low median saddle and in Ponticeras it is very broad with a quite high median saddle. The genera of the closely related family Gephuroceratidae differ from Ponticeras in the acute lateral lobe, which is rounded in Ponticeras.

Description
Nine specimens are selected for description and illustration: Holotype MB.C.4289.1: rather poorly preserved, worn specimen with 43 mm conch diameter in haematitic ironstone. Shell ornament barely visible (Fig. 8D).
The material allows the study of conch geometry between 36 and 105 mm conch diameter. Only slight changes in proportions can be recognised in this growth interval (Fig. 9A). The conch is always extremely discoidal and subevolute to evolute (ww/dm = 0.20-0.25; uw/dm = 0.39-0.47) with a weak tendency towards a wider umbilicus at a larger diameter. The whorl profi le of the sectioned specimen MB.C.30419 KORN D. & BOCKWINKEL J., Ammonoids from the Roteisenstein Formation is always compressed (ww/wh = 0.64-0.70) with a broadly rounded or slightly fl attened and oblique umbilical wall, a rounded umbilical margin, strongly converging fl anks and a narrowly rounded venter. Rarely, as in specimen MB.C.4290, there is a weak depression visible in the ventrolateral area (Fig. 8B).
The ornament is preserved in several specimens. In specimen MB.C.4290 the shell is decorated with irregular coarse growth lines with a strongly biconvex course; the dorsolateral projection is low, the ventrolateral projection is very high and narrow and the ventral sinus is narrow and very deep. Specimen MB.C.4291 shows three faint spiral lines in the middle fl ank area (Fig. 8A).
Several of the specimens, such as MB.C.4291, possess a spiral ridge, of approximately 0.5 mm width, on the midfl ank parallel to the umbilical seem of the next volution. In specimen MB.C.4290, such a ridge is only developed on the right side.

Remarks
House in House & Ziegler (1977: 77: pl. 1 fi g. 25) stated that the original specimen could not be traced and proposed a neotype from the Göttingen Collection (GZG 389-82), which was fi gured by Wedekind (1918: pl. 21 fi g. 6). However, specimen MB.C.4289.1 (Beyrich 1835 Coll.) is stored in the MfN collection; it was fi gured by Beyrich (1837: pl. 2 fi g. 1) and is re-illustrated here in Fig. 8D. As there were other specimens in the Beyrich collection, it is designated the lectotype here.  Table 3. Conch dimensions and ratios of selected specimens of Ponticeras aequabile (Beyrich, 1837). European Journal of Taxonomy 823: 10-47 (2022) Wedekind (1913) regarded specimens with a weakly applanate venter as belonging to P. aequabile var. nov. In a later paper, Wedekind (1918) introduced the new species "Gephyroceras Kayseri" (Fig. 4D) that is characterised by a narrow, blunt venter but clearly shows the morphology of the lectotype of P. aequabile.
Ponticeras aequabile differs from P. materni sp. nov., which also occurs in the Oberscheld assemblages, in the narrowly rounded venter, which is fl attened in the latter species.

Etymology
Named after Hans Matern to honour his work on Devonian ammonoids.

Description
Five specimens are selected for description and illustration: MB.C.22159: incomplete but rather well-preserved specimen with 49 mm conch diameter in haematitic ironstone (Fig. 11A).
MB.C.22175: moderately preserved specimen with 38 mm conch diameter in haematitic ironstone; the last quarter of the last volution belongs to the body chamber (Fig. 11B). MB.C.22178: well-preserved specimen with 25 mm conch diameter in haematitic limestone (Fig. 11C).
Holotype MB.C.22159 is, at 49 mm conch diameter, extremely discoidal and subevolute (Fig. 11A); the whorl profi le shows a fl attened, oblique umbilical wall, a rounded umbilical margin, weakly convergent fl anks with a faint longitudinal ventrolateral depression and a rounded venter that is separated from the fl anks by a weakly angular shoulder. The shell ornament is not well-preserved, but it appears that growth lines are fi ne and only strengthened rhythmically on the umbilical wall. The penultimate whorl shows very weak, short plications on the umbilical margin. Only a small portion of the ventral suture line is visible in the specimen; it shows the shape of the external lobe typical for Ponticeras.
Paratype MB.C.22175 has an extremely discoidal and subevolute conch with moderate coiling rate at 38 mm diameter; the whorl profi le is compressed with oblique, broadly rounded umbilical wall that continues into the broadly rounded umbilical margin (Fig. 11B). The fl anks are subparallel and separated from the narrowly rounded venter by a weakly angular ventrolateral shoulder. The venter becomes subacute during the last volution. Few shell remains show biconvex growth lines that form a very high, narrow ventrolateral projection and a deep ventral sinus. The suture line has a V-shaped external lobe with a median saddle reaching almost half of the height of the lobe depth. The ventrolateral saddle is rounded; the lateral lobe reaches only 60% of the E lobe depth and is broadly rounded (Fig. 12B).
The smaller paratype MB.C.22178 with 25 mm conch diameter does not show the suture line, species assignment is thus not completely clear. However, it shows the shell ornament well-preserved with strongly concavo-convex growth lines, which form a high linguiform ventrolateral salient. As in the holotype, the growth lines are strengthened rhythmically on the umbilical wall and the umbilical margin has weak plications (Fig. 11C). The specimens allow the study of a growth interval between 25 and nearly 60 mm diameter. The material is somewhat variable with respect to the shape of the whorl profi le, which in specimens MB.C.22159 and MB.C.22158 (the sectioned one) has a slightly fl attened, oblique umbilical wall and a more pronounced umbilical margin when compared with specimen MB.C.4297. The shape of the venter also shows some variation; it is more strongly fl attened in specimen MB.C.22158 (Fig. 12A) than in specimen MB.C.22159 (Fig. 11A).
All of the specimens show the shell ornament, which consists of very fi ne but rhythmically strengthened growth lines. These have a biconvex course with a low dorsolateral projection, a wide and shallow lateral sinus, a high and narrow ventrolateral projection and a deep ventral sinus. In the immature stage between about 15 and 30 mm diameter, there are weak and short radial plications visible on the umbilical margin. In specimen MB.C.22158, a faint spiral ridge accompanies the umbilical seam.
Specimen MB.C.22158 was sectioned and allows the study of conch geometry from the initial stage up to 68 mm conch diameter (Fig. 12A). The ontogenetic trajectories of the cardinal conch parameters are strikingly different: (1) The ww/dm and the ww/wh ratios are nearly monophasic with nearly continuously decreasing values; between 1 and 68 mm conch diameter, the ww/dm ratio decreases from 0.80 to 0.24 and the ww/wh ratio from nearly 2.00 to 0.75. (2) The uw/dm trajectory is triphasic with early ontogenetic increase from 0.32 to 0.43 between 1 and 4.5 mm dm, followed by a decrease to 0.33 at 16 mm dm and an adult re-increase to 0.40 at 40 mm. The umbilical ratio then remains at this value.
(3) The WER trajectory is also triphasic with an early juvenile decrease from 2.00 at 1 mm dm to 1.73 at 2 mm dm, followed by an accelerated increase to a maximum value of 2.06 at 16 mm dm and a terminal decrease to around 1.70 in the largest stage. The whorl profi le is crescent-shaped in the early juvenile stage up to 2 mm diameter and then becomes increasingly compressed. At about 10 mm conch diameter, the ww/wh ratio becomes lower than 1.00. Already at 8 mm diameter, the umbilical wall becomes very fl at and connects with the preceding whorl in a very small angle. At 22 mm diameter, the umbilical wall is weakly incurved, a character that is maintained until the terminal stage. The venter is narrowly rounded at 30 mm diameter, but in the last one and a half whorls, it becomes fl attened and gets bordered from the fl anks by a pronounced, subangular ventrolateral shoulder.

Remarks
Ponticeras materni sp. nov. is similar to P. aequabile but differs in the fl attened venter, which is narrowly rounded in the latter species. Ponticeras materni sp. nov. differs from the other species with a fl attened venter (P. auritum) in the much wider umbilicus (uw/dm = 0.35-0.40 in P. materni sp. nov. but only ~ 0.20 in P. auritum).  Family Taouzitidae Korn, 2001 Diagnosis Gephuroceratoidea with sutural formula (E 2 E 1 E 2 ) L U 2 : U 3 U 1 I to (E 2 E 1 E 2 ) L U 2 U 4 U 6 U 8 : U 7 U 5 U 3 U 1 I; lateral saddle narrow, rounded; lateral lobe simple, rounded or acute.

Remarks
The lineage of the family Taouzitidae partly resembles the morphological evolution of two Frasnian lineages of gephuroceratids, the koenenitids and the beloceratoids (e.g., Korn 2001). However, the major difference between the taouzitids and the beloceratids is that in the taouzitids the external lobe retained its original shape, whereas in the beloceratids there was a proliferation of both the umbilical lobes and the external lobes. In the koenenitids, the external lobe remained tripartite and there was the development of only three umbilical lobes in the terminal genus Timanites.

Diagnosis
Genus of the family Taouzitidae with extremely discoidal, subinvolute to involute conch; venter subacute or acute in the adult stage. With single ventrolateral grooves. Suture line with wide external lobe, high median saddle, V-shaped E 2 lobe, V-shaped lateral lobe and shallow, rounded umbilical lobes. Suture line formula (E 2 E 1 E 2 ) L U 2 U 4 : U 3 U 1 I.

Darkaoceras (with subacute venter and four umbilical lobes) is morphologically intermediate between
Mzerrebites (with narrowly rounded venter and three umbilical lobes) and Taouzites (with sharp venter and up to eight umbilical lobes).

Diagnosis
Spec ies of Darkaoceras reaching about 60 mm conch diameter with extremely discoidal, subinvolute conch between 30 and 50 mm dm (ww/dm = 0.25-0.30; uw/dm = 0.15-0.25). Whorl cross section strongly compressed (ww/wh = 0.45-0.60); venter acute with pronounced keel. Growth lines fi ne, bundled around the umbilicus, strongly biconvex with moderately high dorsolateral projection and very high and narrow ventrolateral projection; ventrolateral shoulder with weak spiral groove. Suture line with high median saddle, V-shaped prongs of the E lobe, V-shaped L lobe, and shallow and rounded U 2 lobe.

Description
Five specimens are selected for description and illustration: MB.C.3658: well-preserved, slightly deformed specimen with 48 mm conch diameter in iron-rich micritic limestone; largely covered with shell (Fig. 13A).
MB.C.3633: deformed specimen with about 50 mm conch diameter in iron-rich micritic limestone; cut for a cross section but inner whorls not preserved. Outer suture line visible (Fig. 14A).
The two specimens MB.C.3658 and MB.C.3635, both with about 48 mm conch diameter, have an extremely discoidal and subinvolute conch with very high coiling rate and strongly compressed whorl profi le (Fig. 13A-B). The umbilical wall is very shallow and the fl anks converge towards the subacute venter. The ornament consists of fi ne growth lines with biconvex course; the ventrolateral projection is high and narrow. Faint short riblets are present around the umbilicus.
The suture line of specimen MB.C.3633 has a wide external lobe; this is subdivided by a median saddle that has a height of two thirds of the external lobe depth (Fig. 14A). The prongs of the external lobe are slightly asymmetric and V-shaped. On the fl ank follows a V-shaped lateral lobe and, on the umbilial margin, a broadly rounded umbilical lobe.

Remarks
The specimens from Dillenburg are quite large; smaller specimens from 3 up to 38 mm conch diameter were described by Bockwinkel et al. (2013b) from Hagen-Herbeck, northern margin of the Rhenish Mountains.
A similar species to D. galeatum is D. meridionale, but this species differs in having slightly thicker inner whorls. D. velox Bockwinkel, Becker & Ebbighausen, 2013 also differs by the broader inner whorls.

Diagnosis
Genus of the family Taouzitidae with extremely discoidal, involute conch; venter acute in the adult stage. With single ventrolateral grooves in the juvenile and pre-adult stage. Suture line with wide external lobe, high median saddle, lanceolate E 2 lobe, V-shaped lateral lobe and acute or rounded umbilical lobes. Suture line formula formula (E 2 E 1 E 2 ) L U 2 U 4 U 6 U 8 : U 7 U 5 U 3 U 1 I.

Remarks
Taouzites presents the morphological end member of an evolutionary series in the Givetian, which, starting from simple gephuroceratids, is characterised by a fl attening of the conch with a sharpening venter and simultaneous proliferation of the umbilical lobes (Korn 2001). (Matern, 1931) Fig. 15 Pharciceras acutum Matern, 1931: 88, pl. 2 fi g. 8.

Description
Two specimens are selected for description and illustration: Holotype MB.C.3664: slightly deformed specimen with 29 mm conch diameter in tuffi tic ironstone (Fig. 15A).
Holotype MB.C.3664 has a thinly discoidal and involute conch with very high coiling rate (Fig. 15A). The whorl profi le strongly compressed; the umbilical wall is very shallow and the fl anks converge towards the acute venter that possesses a fi ne keel. Rather coarse growth lines with biconvex course are visible on the fl anks; they extend with a low dorsolateral projection and a high, narrow ventrolateral projection. The suture line possesses a wide, parallel-sided external lobe, a V-shaped lateral lobe, a small and V-shaped U 2 lobe and a shallow, rounded U 4 lobe (Fig. 15B). (Matern, 1931). Holotype MB.C.3664 (Etzold 1910 Coll.) from Oberscheld ("Tiefe Grube"). A. Lateral view and dorsal projection. B. Suture line, at dm ca 9 mm, ww = 3.0 mm, wh = 4.5 mm. Scale bar units = 1 mm.

Additional material
MB.C.22184: incomplete specimen with 73 mm conch diameter in haematitic iron ore, the last whorl is partly crushed (Fig. 17A).
MB.C.4306.1: well-preserved, complete steinkern specimen with 36 mm conch diameter in haematitic ironstone (Fig. 17C). (Sandberger & Sandberger, 1851). A. Lectotype 40a in the Wiesbaden collection from Nanzenbach. B. Lectotype 40a, reproduction of the fi gure of Sandberger & Sandberger (1850-1856 fi g. 1). C. Probably lost specimen, original of "Goniatites sublamellosus", reproduction of the fi gure of Sandberger & Sandberger (1850-1856. D. Paratype 40b in the Wiesbaden collection from Nanzenbach. E. Paratype 40b, reproduction of the fi gure of Sandberger & Sandberger (1850-1856. F. Suture line of paratype 40b, reproduction of the fi gure of Sandberger & Sandberger (1850-1856. Scale bar units = 1 mm. 823: 10-47 (2022) The three specimens MB.C.4306.1, MB.C.4306.2 and MB.C.4306.3 allow the study of conch proportions and ornament between 19 and 36 mm diameter (Fig. 17C-E). They are similar in shape with a weak ontogenetic trend towards a slenderer conch (ww/dm decreasing from 0.35 to 0.29). They show an oblique, broadly convex umbilical wall and fl anks that converge slowly towards the narrowly rounded venter. The ornament shows lamellar growth lines, which in the two smaller specimens MB.C.4306.2 and MB.C.4306.3 are particularly well-preserved; they extend with a low dorsolateral projection, a deep and wide lateral sinus and a very narrow, very high linguiform ventrolateral projection across the fl anks and then turn back to form a narrow, very deep ventral sinus.

European Journal of Taxonomy
The larger specimens MB.C.22183 (53 mm dm) and MB.C.22184 (73 mm dm) are thinly discoidal and subinvolute with a compressed whorl profi le; the umbilical wall is steep and the fl anks converge towards the narrowly rounded venter (Fig. 17A-B). The ornament shows biconvex growth lines, The sectioned specimen MB.C.22201 (Fig. 18A) shows signifi cant ontogenetic changes in the conch parameters: (1) the ww/dm ratio has a nearly monophasic ontogeny with a rather continuous decrease from 0.75 at 1 mm dm to = 0.25 at 77 mm dm. (2) The ww/wh ratio has a similar course (from 2.05 to 0.50) but with more accelerated decrease between 3 and 10 mm dm. (3) The uw/dm ratio is conspicuously biphasic with a juvenile increase from 0.35 to 0.45 at 5 mm dm and an adult decrease to 0.23. (4) The coiling rate is also biphasic, but not parallel to the uw/dm ratio; the WER shows a juvenile decrease   (2022) to 1.68 at 3.5 mm dm, followed by a decelerated increase with asymptotic approximation of a value of 2.40 at 30 mm dm (Fig. 18C-F). The ontogeny of the whorl profi le is rather simple with a continuous transformation of a depressed shape into a compressed shape; the value falls below a value of 1.00. Above this diameter, the whorl profi le has a steep umbilical wall, a broadly rounded umbilical margin, moderately strong converging fl anks and a rounded venter.

Diagnosis
Genus of the family Acanthoclymeniidae with extremely discoidal, subinvolute to subevolute conch; venter fl attened or concave. Suture line with relatively narrow wide lobe, moderately high median saddle, V-shaped E 2 lobe, shallow and rounded lateral lobe. Suture line formula (E 2 E 1 E 2 ) L : U I.

Remarks
In the description of the type species as well as its assignment to a genus, it was erroneously assumed that it was a clymeniid; this error was corrected by House (1961) (Fig. 20). The conchs are extremely discoidal and subinvolute with very high coiling rate; the whorl profi le is compressed. The umbilical wall is very shallow; the fl anks converge towards the angular ventrolateral shoulder, the outer fl anks are weakly incurved and the venter is fl at. The ornament consists of fi ne growth lines with biconvex course; they extend with a very low dorsolateral projection on the umbilical margin and a high and narrow ventrolateral projection across the fl anks. Faint short riblets are present around the umbilicus.

Remarks
When Sandberger & Sandberger (1850-1856) described the new species Goniatites forcipifer, they did not make it clear whether the species name ("carrying a fi re tong") was a noun or an adjective. Since such species names are usually considered adjectives, we here decline it to the feminine form.
The specimens contribute only little to our knowledge of the species. All are embedded on rock slabs (Fig. 22), which prevents precise measurement of the whorl width, but it is clear that the conch is extremely discoidal. It is also clear that the whorl profi le is pear-shaped with a rounded umbilical wall, convex fl anks, a subangular ventrolateral shoulder and a fl attened venter. The umbilicus has nearly exactly half the value of the conch diameter.  (Sandberger & Sandberger, 1851). A. Lectotype 46a in the Wiesbaden collection from Oberscheld; photograph and reproduction of the fi gure of Sandberger & Sandberger (1850-1856 fi g. 3a). B. Paratype 46b in the Wiesbaden collection from Oberscheld; photograph and reproduction of the fi gure of Sandberger & Sandberger (1850-1856 pl. 9 fi g. 3). C. Probably lost specimen; photograph and reproduction of the fi gure of Sandberger & Sandberger (1850-1856 fi g. 3d, e). Scale bar units = 1 mm.