Biostratigraphic remarks

It is difficult to reconcile the First Appearance Data (FADs) and Last Appearance Data (LADs) of trilobite taxa within the Bonnia–Pagetides elegans Biozone of North Greenland presented by Sundberg et al. (Reference Sundberg, Webster and Geyer2022, fig. 4) with the basic distribution information of trilobites from the primary sources (Geyer and Peel, Reference Geyer and Peel2011; Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016). According to Sundberg et al. (Reference Sundberg, Webster and Geyer2022, fig. 4), the ranges of Protoryctocephalus arcticus and Lancastria plana extend substantially beyond (are younger than) those of Ovatoryctocara granulata and O. yaxiensis, whereas range charts in Geyer and Peel (Reference Geyer and Peel2011, figs. 4–6) and Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 2) indicate that the LADs for the four taxa are at the same level.

Furthermore, due to an inadvertent error, Sundberg et al. (Reference Sundberg, Webster and Geyer2022, fig. 4) placed Oryctocarella duyunensis within the Bonnia–Pagetides elegans Biozone instead of the older Eoagnostus roddyi–Oryctocarella duyunensis Biozone. This stratigraphic position in the figure should be assigned to Pagetides elegans. Unfortunately, as a result of the error, both Oryctocarella duyunensis and Pagetides elegans are omitted from the biozones that carry their names in the Greenland column of Sundberg et al. (Reference Sundberg, Webster and Geyer2022, fig. 4).

Materials

Samples from southern Freuchen Land (Fig. 1.2, fossil locality 1) were collected on the southwestern corner of a nunatak (82°09´N, 42°25´W) illustrated by Ineson and Peel, (Reference Ineson and Peel1997, fig. 35) and Geyer and Peel (Reference Geyer and Peel2011, fig. 2B) from dark thin limestone lenses located 1–2 m above the base of the upper member of the Henson Gletscher Formation (Fig. 2.1). This is locality 1 of Blaker and Peel (Reference Blaker and Peel1997, figs. 8A, 10) and Geyer and Peel (Reference Geyer and Peel2011, figs. 1D, 2B; see also Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 1E; Oh et al., Reference Oh, Peel, Zhen, Smith, Lee and Park2024, fig. 1C). The succession forms the reference section (thickness 112 m) of the Henson Gletscher Formation described by Ineson and Peel (Reference Ineson and Peel1997, figs. 21, 32, 33). GGU samples 315109, 315112 and 315113, the last two being splits of the same sample, were collected by J.S. Peel on 21 July 1984. GGU sample 298550 was collected by J.S. Peel on 6 July 1985. GGU samples 301346 and 301347 (two splits of the same sample) were collected by J.S. Peel and M.R. Blaker on 17 August 1985.

Samples from Løndal (Fig. 1.2, fossil locality 3) were collected from a small stream on the western side of the valley (82°17.5’N, 37°03’W) and were located on a geological section by Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 2). GGU samples 218680 and 218681 were collected by J.R. Ineson (14 July 1979). GGU samples 225709–225714 were collected by J.S. Peel on 15 July 1979.

GGU sample 482331 (Figs. 1.2, 2.1, fossil locality 2) was collected by J.S. Peel on 4 August 2006 from the upper member of the Henson Gletscher Formation on the south side of Fimbuldal (82°17.7´N, 39°42´W), about 5 m above the top of the middle sandstone member and 20 m below the boundary with the overlying Sydpasset Formation (Geyer and Peel, Reference Geyer and Peel2011, figs. 2D, E, 5). The calcareous specimens occur on bedding surfaces within thinly bedded limestone.

Samples from southern Freuchen Land (except Fig. 10.5, 10.6) and Løndal (except Fig. 9.1) were treated with 10% acetic acid. Selected specimens from sieved residues were gold-coated before imaging in a Zeiss Supra 35VP scanning electron microscope. Crack-out specimens from GGU sample 482331 were coated with ammonium chloride sublimate and photographed with a Lumenera Infinity X32 digital camera attached to a Wild stereo microscope. All images were assembled using Adobe Photoshop CS4.

Repositories and institutional abbreviations

GGU prefix indicates a sample collected during field work by Grønlands Geologiske Undersøgelse (Geological Survey of Greenland), now part of the Geological Survey of Denmark and Greenland, Copenhagen, Denmark. Specimen repositories: MGUH, paleontological type collection of the Natural History Museum of Denmark, Copenhagen, Denmark; PMU, paleontological type collection of the Museum of Evolution, Uppsala University, Sweden.

Type species

Stenotheca elongata Walcott, Reference Walcott1884, Prospect Peak, Eureka District, Nevada, Cambrian, Miaolingian Series, late Wuliuan Stage, Bathyuriscus–Elrathina Biozone.

Remarks

A detailed description and analysis of Miaolingian Stenothecoides was given by Johnston and Streng (Reference Johnston and Streng2021) on the basis of silicified material from the Burgess Shale Formation (Wuliuan Stage) of British Columbia. As recounted by Peel (Reference Peel2021c) and Johnston and Streng (Reference Johnston and Streng2021), stenothecoids have been variously interpreted as univalved or bivalved mollusks, crustaceans, and relatives of brachiopods. However, the widely accepted opinion of Yochelson (Reference Yochelson1969) that stenothecoids were bivalved mollusks has been rejected, and Johnston and Streng (Reference Johnston and Streng2021) proposed that stenothecoids represent a stem group of pan-brachiopods.

Peel (Reference Peel2021c) described stenothecoids from the Henson Gletscher Formation (Wuliuan Stage) of North Greenland on the basis of phosphatized internal molds, rare silicified specimens, and crack-out material in limestone. Evidence of fibrous pedicle attachment at the apical (posterior) termination of internal molds in juveniles around 1 mm in length suggested a relationship with brachiopods rather than mollusks.

Stenothecoides sp.

Figure 3

Figure 3.

Stenothecoides sp., GGU sample 315113, upper Henson Gletscher Formation, southern Freuchen Land; Cambrian Series 2, Stage 4. (1, 5) PMU 17880 in plan and oblique apico-lateral views. (2, 3) PMU 17881 in plan and lateral views. (4) PMU 17882 in oblique apico-lateral view. Scale bars = 200 μm.

Materials

Figured, silicified specimens PMU 17880, PMU 17881, and PMU 17882 and an unfigured crack-out specimen, all from GGU sample 315113. Upper Henson Gletscher Formation, Cambrian Stage 4, southern Freuchen Land (Figs. 1.2, 2.1, locality 1).

Remarks

The small size (length 2–3 mm) and elongate form (width about one-third of length) indicate that the silicified replicas are disarticulated valves of juveniles; they are narrower than larger specimens of stenothecoids described from the Miaolingian Series of North Greenland by Peel (Reference Peel1988, 2021c).

A presumed ventral valve is almost bilaterally symmetrical in plan view (Fig. 3.1). The sub-apical margin, posterior in the terminology of Johnston and Streng (Reference Johnston and Streng2021), is truncated with a shallow sub-apical sinus (Fig. 3.1, 3.5). A presumed dorsal valve has a slightly sinuate form in plan view (Fig. 3.2), with the apex overhanging the sub-apical margin (Fig. 3.3). Preserved ornamentation on the coarsely preserved replicas consists of comarginal growth lines that tend to be rugose on the median line.

Phylum Mollusca Cuvier, Reference Cuvier1797

Class Helcionelloida Peel, Reference Peel1991a

Order Helcionellida Geyer, Reference Geyer1994

Family Helcionellidae Wenz, Reference Wenz and Schindewolf1938

Genus Capitoconus Skovsted, Reference Skovsted2004

Type species

Capitoconus inclinatus Skovsted, Reference Skovsted2004 from the Bastion Formation of North-East Greenland, Cambrian Series 2, Stage 4.

Remarks

Capitoconus Skovsted, Reference Skovsted2004 was considered to be a junior subjective synonym of Parailsanella Zhegallo in Voronova et al., Reference Voronova, Drozdova, Esakova, Zhegallo, Zhuravlev, Rozanov, Sayutina and Ushatinskaya1987 by Kouchinsky et al. (Reference Kouchinsky, Bengtson, Clausen and Vendrasco2015), but it is distinguished by its distinctive swollen protoconch visible on internal molds (Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016).

Capitoconus borealis Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016

Figure 4

Figure 4.

Capitoconus borealis Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, upper Henson Gletscher Formation, Løndal, Peary Land, Cambrian Series 2, Stage 4. (1, 2, 4, 7) PMU 28864 from GGU sample 218681, holotype, in lateral, dorsal, and oblique sub-apical views, with detail of shell microstructure (4, located by arrow in 1). (3, 5, 6) PMU (17883) from GGU sample 218681. (1, 2, 5–7) Scale bars = 100 μm; (3) scale bar = 20 μm; (4) scale bar = 40 μm.

Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016 Capitoconus borealis Peel et al., p. 262, fig. 13A–H.

Holotype

PMU 28864 from GGU sample 218681, Henson Gletscher Formation, North Greenland (Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 13A–F non Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 13G–H).

Materials

In addition to the holotype (PMU 28864) and figured specimen (PMU 17883), Capitoconus borealis was recorded by Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 2B) from GGU samples 225709, 225712, 225714, and 218681 near the top of the middle sandstone member in Løndal (Fig. 2.1, locality 3).

Occurrence

Henson Gletscher Formation, North Greenland, Cambrian Series 2, Stage 4.

Remarks

Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016) inadvertently illustrated images of a second specimen from GGU sample 218681 together with the holotype, PMU 28864. This number is here restricted to the specimen illustrated as Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 13A–F; Fig. 4.1, 4.2, 4.4, 4.7); the second specimen (Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 13G–H; Fig. 4.3, 4.5, 4.6) is here assigned the number PMU 17883 (Fig. 4.3, 4.5, 4.6).

Illustrated specimens of Capitoconus borealis clearly display the diagnostic feature of Capitoconus Skovsted, Reference Skovsted2004 in having the distinctive swollen protoconch delimited by the pronounced constriction visible on the internal mold (Fig. 4.1, 4.7). Skovsted (Reference Skovsted2004) commented that no specific micro-ornamentation was observed on the internal molds of the type species, Capitoconus inclinatus Skovsted, Reference Skovsted2004, although fine pits were present on the molds of comarginal rugae of Capitoconus artus Skovsted, Reference Skovsted2004. The internal molds of C. borealis from the upper Henson Gletscher Formation in Løndal display a pattern of widely spaced fine tubercles representing infilled pores in the shell (Fig. 4.3, 4.6). The fine tubercles are restricted to the protoconch, and the internal molds of the teleoconch have a smooth surface (Fig. 4.3, 4.7). The tubercles are sometimes associated with a phosphatic coating of the shell exterior, suggesting that the shell pore system may penetrate the entire shell. The shell pore system has been documented in other helcionelloids, including Mellopegma Runnegar and Jell, Reference Runnegar and Jell1976, in which Vendrasco et al. (Reference Vendrasco, Kouchinsky, Porter and Fernandez2011) noted that the shell pores may have extended from the inner surface of the shell beyond the base of the outer layer. Some tubercles observed in Capitoconus borealis have a polygonal base (Fig. 4.3). The holotype specimen PMU 28864 shows polygonal impressions on the internal mold surface, particularly on the rugae crests (Fig. 4.1, 4.4). This type of shell microstructure is closely comparable to Davidonia, where it was interpreted as “prismatic shell microstructure” by Vendrasco and Checa (Reference Vendrasco and Checa2015) in Mackinnonia davidi (Runnegar in Bengtson et al., Reference Bengtson, Conway Morris, Cooper, Jell and Runnegar1990) [= Davidonia rostrata (Zhou and Xiao, Reference Zhou and Xiao1984)], although the polygonal structure has also been interpreted as epithelial cell imprints (e.g., Ushatinskaya and Parkhaev, Reference Ushatinskaya and Parkhaev2005).

Genus Dorispira Parkhaev in Parkhaev and Demidenko, Reference Parkhaev and Demidenko2010

Type species

Helcionella terraustralis Runnegar and Jell, Reference Runnegar and Jell1976 from the Coonigan Formation of New South Wales, Australia; Cambrian, Miaolingian Series.

Dorispira tippik Peel and Kouchinsky, Reference Peel and Kouchinsky2022

Figure 5.1–5.3, 5.6, 5.8

Figure 5.

Dorispira from the upper Henson Gletscher Formation, southern Freuchen Land, Cambrian Series 2, Stage 4. (1–3, 6, 8) Dorispira tippik Peel and Kouchinsky, Reference Peel and Kouchinsky2022. (1, 2) PMU 17884 from GGU sample 298550. (3, 6, 8) PMU 17885 from GGU sample 301346, internal mold with spiral grooves on sub-apical surface. (4, 5, 7) Dorispira sp., PMU 17886 from GGU sample 298550. (1, 2, 4, 5, 7) Scale bars = 400 μm; (3) scale bar = 200 μm; (6, 8) scale bars = 300 μm.

Reference Peel, Simonetta and Conway Morris1991b Latouchella spp.; Peel, p. 34, fig. 24A–G.

Reference Yang, Zhao, Peng and Yang2012  Oelandiella cf. O. accordionata; Yang et al., p. 312, fig. 3, pl. 1.1–12, pl. 2.1–4.

Reference Hu, Holmer, Liang, Duan and Zhang2021  Oelandiella accordionata; Hu et al., p. 19, fig. 4A1, A2, B, C, D1, D2.

Reference Peel and Kouchinsky2022  Dorispira tippik Peel and Kouchinsky, p. 85, figs. 4A–C, E, G, 7B–D, G–M, O–R.

Holotype

PMU 39189 from GGU sample 271718 (Peel and Kouchinsky, Reference Peel and Kouchinsky2022, fig. 7M, O, R) Henson Gletscher Formation, Løndal, western Peary Land, North Greenland. Cambrian, Miaolingian Series, Wuliuan Stage.

Materials

PMU 17884 and one additional specimen from GGU sample 298550; PMU 17885 from GGU sample 301346, internal mold; upper Henson Gletscher Formation, southern Freuchen Land; Cambrian Series 2, Stage 4.

Occurrence

Cambrian Series 2, Stage 4 of South China (Yang et al., Reference Yang, Zhao, Peng and Yang2012) and North Greenland. Miaolingian Series of North Greenland (Peel and Kouchinsky, Reference Peel and Kouchinsky2022) and North China (Hu et al., Reference Hu, Holmer, Liang, Duan and Zhang2021).

Description

Tall, laterally compressed shell openly coiled through about half of a whorl. Coarsely spaced comarginal rugae prominent on dorsal and lateral surfaces but absent on the sub-apical surface in later growth stages (Fig. 5.2). Apertural outline ovoid to sub-rectangular with concave lateral areas at adult stage (Fig. 5.2, 5.8). Sub-apical surface with one pair of continuous grooves on the sub-apical surface of the internal mold (Fig. 5.3, 5.8), and the median area between the pair of grooves with comarginal grooves that are abapically V-shaped (Fig. 5.8).

Remarks

Three Dorispira specimens, consisting of two silicified shells and one internal mold, are referred to Dorispira tippik Peel and Kouchinsky, Reference Peel and Kouchinsky2022 on the basis of their prominent, slightly nodose comarginal rugae and laterally flattened shell. Dorispira tippik was originally described from the Henson Gletscher Formation in Løndal (Peel and Kouchinsky, Reference Peel and Kouchinsky2022; Fig. 1.2, from a locality adjacent to fossil locality 3). Both occurrences are from the same formation, but the original material is biostratigraphically slightly younger (Miaolingian Series, Wuliuan Stage; Peel and Kouchinsky, Reference Peel and Kouchinsky2022) than the material described here from Freuchen Land (Ovatoryctocara granulata assemblage; Cambrian Series 2, Stage 4). Dorispira is not known from the Ovatoryctocara granulata assemblage in the Løndal region.

One internal mold specimen (Fig. 5.3, 5.6, 5.8) shows a pair of sub-apical grooves corresponding to ridges on the shell interior, which are also observed in type specimens of Dorispira tippik from North Greenland (Peel and Kouchinsky, Reference Peel and Kouchinsky2022) and North China (Hsuzhuang Formation; Miaolingian Series; Hu et al., Reference Hu, Holmer, Liang, Duan and Zhang2021). Corresponding ridges are found in silicified specimens of Dorispira accordionata (Runnegar and Jell, Reference Runnegar and Jell1976) from Australia (Coonigan Formation, Cambrian Series 2, Stage 4; Smith et al., Reference Smith, Brock and Paterson2015).

Dorispira sp.

Figure 5.4, 5.5, 5.7

Materials

PMU 17886 from GGU sample 298550, upper Henson Gletscher Formation, southern Freuchen Land; Cambrian Series 2, Stage 4.

Occurrence

Cambrian Series 2, Stage 4 of North Greenland.

Remarks

This single silicified shell differs from Dorispira tippik in its less tightly coiled, more pointed apex. Both forms have prominent comarginal rugae. In Dorispira sp. they are continuous across the sub-apical surface (Fig. 5.7), as is also the case in early growth stages of Dorispira tippik. However, rugae are absent from the sub-apical surface near the apertural margin in later growth stages of Dorispira tippik (Fig. 5.2).

Dorispira sp. is similar in lateral profile to Dorispira? lemdadensis Mgazhli et al., 2023 from the Brèche à Micmacca Member of the High Atlas of Morocco described by Mgazhli et al. (2023) but differs in the rounded form of the comarginal rugae. In Dorispira? lemdadensis, the rugae are sharp with concave interspaces.

Genus Ressericonella Oh and Peel, Reference Oh and Peel2024

Type species

Helcionella aequa Resser, Reference Resser1939 from the Langston Formation, Naomi Peak Limestone Member, Wasatch Mountains near Malad, Idaho, Cambrian, Miaolingian Series, Wuliuan Stage, Albertella Biozone.

Diagnosis

Laterally compressed helcionelloid curved through about three-quarters of a whorl such that the tightly coiled apex overhangs the sub-apical margin. Lateral surfaces shallowly concave to shallowly convex, passing abruptly onto the shallowly convex supra-apical surface. Aperture sub-rectangular. Sub-apical surface arched into an apertural sinus. Ornamentation of numerous spiral cords crossed by comarginal growth lines, sometimes with weak rugae (after Oh and Peel, Reference Oh and Peel2024).

Remarks

In addition to the type species Ressericonella aequa (Resser, Reference Resser1939), from the Wuliuan Stage (Albertella Biozone) of Idaho, Oh and Peel (2024) described Ressericonella pipalukae Oh and Peel, Reference Oh and Peel2024 from the Henson Gletscher Formation (Cambrian Series 2, Stage 4, Ovatoryctocara granulata assemblage) of southern Freuchen Land (Fig. 1, fossil locality 1), North Greenland.

The rate of lateral expansion of the shell in Ressericonella slows after the early growth stage to produce an unusually narrow shell in dorsal view with sub-parallel sides (Fig. 6.5, 6.6, 6.11). The coiled shell with flattened lateral surfaces and sub-rectangular aperture of Ressericonella is reminiscent of Coreospira Saito, Reference Saito1936, but the lateral margins of the supra-apical (dorsal) surface of the latter form a broad rounded ridge that overhangs lateral areas with prominent comarginal rugae. In Coreospira rugosa Saito, Reference Saito1936 and Coreospira walcotti Knight, Reference Knight1947, the shell is tightly coiled through more than one whorl (Saito, Reference Saito1936; Knight, Reference Knight1947; Oh et al., Reference Oh, Lee, Lee and Lee2021), but Coreospira carinata (Rasetti, Reference Rasetti1957) has a cyrtoconic shell form as in Ressericonella.

Figure 6.

Ressericonella pipalukae Oh and Peel, Reference Oh and Peel2024, silica replicas from the upper Henson Gletscher Formation, southern Freuchen Land, Cambrian Series 2, Stage 4. GGU sample 301346 unless stated. (1, 7, 8) PMU 18378 from GGU sample 298550, sub-apical (1) and lateral (7) views with detail of margin (8). (2–4) PMU 18379, sub-apical view (3) with detail of apertural emargination (4) and oblique lateral view (2). (5, 6, 9, 11) PMU 18380, holotype, supra-apical (5, 11) and oblique lateral (6, 9) views. (10, 12) PMU 17887, lateral (10) and dorsolateral (12) views. (1–3, 6, 9) Scale bars = 300 μm; (4, 8) scale bars = 200 μm; (5, 7, 10–12) scale bars = 400 μm.

Ressericonella pipalukae Oh and Peel, Reference Oh and Peel2024

Figure 6

Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016 Coreospira sp.; Peel et al., p. 264, fig. 14N, O.

Reference Oh and Peel2024 Ressericonella pipalukae Oh and Peel, p. 203, figs. 4, 5A, 5B

Holotype

PMU 18380 from GGU sample 301346, upper member of the Henson Gletscher Formation, southern Freuchen Land. Cambrian Series 2, Stage 4, Bonnia–Pagetides elegans Biozone.

Materials

PMU 18380, holotype, PMU 18379, and PMU 17887 from GGU sample 301346; PMU 18378 from GGU sample 298550; PMU 18381 of Oh and Peel (2024, fig. 4) from southern Freuchen Land. PMU 28970 of Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 14N, O) from Løndal. Upper member of the Henson Gletscher Formation, southern Freuchen Land. Cambrian Series 2, Stage 4.

Occurrence

Cambrian Series 2, Stage 4 of North Greenland.

Description

Moderately expanding, laterally compressed shell coiled through half to two-thirds of a whorl; shell length about twice to three times shell width (Fig. 6.6, 6.10). Degree of lateral expansion becomes slower in the later growth stage, such that shell width becomes almost constant in the adults (Fig. 6.5, 6.12). Aperture sub-rectangular, with the apertural sinus in the sub-apical margin most prominent in juvenile shells (Fig. 6.3, 6.4). Apex pointed and recurved, overhanging the sub-apical surface. Shallow constrictions possibly denote the protoconch (Fig. 6.3). Supra‑apical surface initially shallowly convex in transverse profile, becoming flattened in later growth stages. Initial rounded transition from supra‑apical surface to the flattened lateral surfaces becomes more abrupt, slightly angular, in later growth stage (Fig. 6.6, 6.9). Sub-apical surface strongly concave in lateral profile but with variable degree of curvature (Fig. 6.10). Shell surface ornamented by fine spiral threads crossed by comarginal growth lines that may become more prominent near the aperture (Fig. 6.7, 6.8), usually without comarginal rugae. Shell composed of two shell layers, an outer spirally ornamented layer overlying an inner layer with transverse fibrous structure.

Remarks

Ressericonella pipalukae differs from the type species Ressericonella aequa by its more rounded, less angular transition from the supra-apical surface to the lateral surfaces, finer spiral and comarginal ornamentation, and general absence of rugae. In lateral view, Ressericonella pipalukae appears to expand much more rapidly than the holotype of Ressericonella aequa, but the latter is a larger specimen in which the rate of expansion is reduced with increase in size (Oh and Peel, Reference Oh and Peel2024, fig. 3). Ressericonella pipalukae is variable in form, particularly with regard to the degree of curvature of the early growth stages, although this may be influenced by lateral crushing of the silicified shells.

Ressericonella ? sp.

Figure 7.7, 7.8

Figure 7.

Helcionellids and pelagiellids, upper Henson Gletscher Formation, Cambrian Series 2, Stage 4. (1, 5) Helcionellid sp. 1, PMU 17888 from GGU sample 301346, lateral view with detail of apex (1), southern Freuchen Land. (2, 3, 6) Helcionellid sp. 2, PMU 17889 from GGU sample 298550, southern Freuchen Land. (4) Helcionellid sp. 3, PMU 17890 from GGU sample 301346, southern Freuchen Land. (7, 8) Ressericonella? sp., PMU 18383 from GGU sample 301346, lateral and oblique sub-apical views, southern Freuchen Land. (1) Scale bar = 100 μm; (2–8) scale bars = 200 μm.

Materials

PMU 18383 from GGU sample 301346, upper member of the Henson Gletscher Formation, southern Freuchen Land. Cambrian Series 2, Stage 4.

Remarks

This single, slightly crushed, silica replica with a damaged apex is tentatively assigned to Ressericonella due to its lateral compression and spiral ornamentation as associated specimens of Ressericonella pipalukae, from which it differs in the greater tightness of coiling (Fig. 7.7).

Helcionellid sp. 1

Figure 7.1, 7.5

Materials

PMU 17888 from GGU sample 301346, upper member of the Henson Gletscher Formation, southern Freuchen Land. Cambrian Series 2, Stage 4.

Remarks

This single, laterally compressed silica replica has a more upright form than associated specimens of Ressericonella pipalukae but retains similar reticulate ornamentation. Widely spaced radial ribs on the early growth stage may delimit the protoconch.

Helcionellid sp. 2

Figure 7.2, 7.3, 7.6

Materials

PMU 17889 from GGU sample 298550, upper member of the Henson Gletscher Formation, southern Freuchen Land. Cambrian Series 2, Stage 4.

Remarks

A single silica replica of a low, elongate shell with a relatively rapid rate of expansion along the median plane, an overhanging apex, and reticulate ornamentation. Hensoniconus siku (Peel and Kouchinsky, Reference Peel and Kouchinsky2022) from the Henson Gletscher Formation (Miaolingian Series, Wuliuan Stage) of Løndal is more upright in lateral perspective, with a less curved sub-apical wall (Peel, Reference Peel2023, fig. 3A).

Helcionellid sp. 3

Figure 7.4

Materials

PMU 17890 from GGU sample 301346, upper member of the Henson Gletscher Formation, southern Freuchen Land. Cambrian Series 2, Stage 4.

Remarks

The blunt apex in this silica replica is located at about one-third of the distance between the sub-apical and supra-apical margins and does not overhang the sub-apical surface. In this respect it resembles helcionellid sp. indet. of Peel and Kouchinsky (Reference Peel and Kouchinsky2022, fig. 10A) from the Henson Gletscher Formation (Miaolingian Series, Wuliuan Stage) of Løndal. Ornamentation consists of fine radial ridges visible near the broken margins, crossed by obscure growth lines.

Family Stenothecidae Runnegar and Jell, Reference Runnegar and Jell1976

Genus Mellopegma Runnegar and Jell, Reference Runnegar and Jell1976

Type species

Mellopegma georginensis Runnegar and Jell, Reference Runnegar and Jell1976. Cambrian, Miaolingian Series, Australia.

Mellopegma georginense Runnegar and Jell, Reference Runnegar and Jell1976

Figure 8.1–8.3, 8.5–8.7, 8.10, 8.11

Figure 8.

Mellopegma Runnegar and Jell, Reference Runnegar and Jell1976, upper Henson Gletscher Formation, Cambrian Series 2, Stage 4. (1–3, 5–7, 10, 11) Mellopegma georginense Runnegar and Jell, Reference Runnegar and Jell1976, GGU sample 482331, Fimbuldal, western Peary Land unless stated; lateral views: (1) MGUH 34949; (2) MGUH 34950; (3) MGUH 34951; (5) MGUH 3495.2; (6) MGUH 34953; (7) MGUH 34954; (10, 11) PMU 17897 from GGU sample 225714, Løndal, lateral view of internal mold, with detail of infilled pores on crest of comarginal ruga on dorsal surface (10). (4, 8, 9) Mellopegma simesi (MacKinnon, Reference MacKinnon1985) from GGU sample 218681, Løndal: (4, 8) PMU 28873, dorsal and lateral views of internal mold; (9) PMU 28968. (1–3, 5–7, 9) Scale bars = 500 μm; (4, 8) scale bars = 100 μm; (10) scale bar = 10 μm; (11) scale bar = 200 μm.

Reference Runnegar and Jell1976 Mellopegma georginensis Runnegar and Jell, p. 130, fig. 8b1, 7, 9–11.

?Reference Robison, Simonetta and Conway Morris1991 Mellopegma georginensis; Robison, p. 83, fig. 5.10.

Reference Landing, Geyer and Bartowski2002  Mellopegma georginensis; Landing, Geyer, and Bartowski, p. 298, fig. 8.1, 8.2.

Reference Vendrasco, Kouchinsky, Porter and Fernandez2011  Mellopegma georginense; Vendrasco et al., p. 9, figs. 5, 6, 7.3, 7.4.

Reference Pojeta, Simes and Cooper2014  Mellopegma georginense; Pojeta, Simes, and Cooper, p. 6, fig. 4A–F.

?Reference Caron, Gaines, Aria, Mángano and Streng2014  Mellopegma sp. aff. M. georginense; Caron et al., supplementary fig. 6r.

Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016  Mellopegma sp.; Peel et al., p. 266, fig. 13N.

Holotype

ANU 29091, Department of Geology, Australian National University, Canberra, Australia, Gowers Formation, Currant Bush Limestone, Cambrian, Miaolingian Series.

Materials

MGUH 34949, MGUH 34950, MGUH 34951, MGUH 34952, MGUH 34953, MGUH 34954, and numerous unfigured specimens from GGU sample 482331, Fimbuldal. PMU 17897 from GGU sample 225714, Løndal. Also PMU 28869 from GGU sample 225710, Løndal, illustrated by Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 13N). Henson Gletscher Formation, Peary Land.

Occurrence

Mellopegma georginense occurs in late Cambrian Stage 4 to Miaolingian strata from two major paleocontinents. In Laurentia, it is reported from North Greenland (this study), Utah, (Robison, Reference Robison, Simonetta and Conway Morris1991), Quebec (Landing et al., Reference Landing, Geyer and Bartowski2002), and British Columbia (Caron et al., Reference Caron, Gaines, Aria, Mángano and Streng2014). In Gondwana, it has been described from Australia (Runnegar and Jell, Reference Runnegar and Jell1976; Vendrasco et al., Reference Vendrasco, Kouchinsky, Porter and Fernandez2011) and New Zealand (Pojeta et al., Reference Pojeta, Simes and Cooper2014).

Description

Shell elongate, laterally compressed, bilaterally symmetrical, and open coiled through less than half of a whorl. Supra-apical surface gently convex in lateral view with the concave sub-apical surface extended distally, becoming almost parallel to the dorsum (Fig. 8.3). Lateral profile is low to moderate, with length greater than height, and with the blunt apex recurved toward the sub-apical margin. Apertural margin convex in lateral view, slightly upturned at both the sub-apical and supra-apical ends (Fig. 8.2, 8.3). Comarginal rugae distinct, more closely spaced at the sub-apical surface than at the supra-apical surface. A thin, partly exfoliated outer shell layer is ornamented by closely spaced, fine comarginal cords that often display a fine, irregular zig-zag pattern. The internal mold (Fig. 8.10, 8.11) carries narrow tubercles representing pores into the shell.

Remarks

The figured laterally compressed specimens from Fimbuldal preserve the outer shell surface, in contrast to the Australian type specimens, which are internal molds described by Runnegar and Jell (Reference Runnegar and Jell1976, fig. 8B). Radial periostracal ridges at the apex of the type reported by Vendrasco et al. (Reference Vendrasco, Kouchinsky, Porter and Fernandez2011) have not been observed. Internal molds of Mellopegma georginense generally exhibit less prominent comarginal rugae than the outer surface of the shells. A revised diagnosis of the species that accounts for the morphology of both the shell and internal mold was introduced by Vendrasco et al. (Reference Vendrasco, Kouchinsky, Porter and Fernandez2011). Specimens described in this study fit well to the diagnosis of Mellopegma georginense in having a low to moderate shell profile with a blunt apex, upturned apertural margins at both the supra- and sub-apical ends, and the presence of the comarginal rugae (Fig. 8).

The presence of tubercles on internal molds of Mellopegma, representing infilled pores penetrating into the shell, was discussed at length by Vendrasco et al. (Reference Vendrasco, Kouchinsky, Porter and Fernandez2011). Such pores are visible on the dorsal surface and at the apex of the illustrated specimen from Løndal (Fig. 8.10, 8.11) but are not preserved on external surfaces in specimens from Fimbuldal (Fig. 8.1–8.3, 8.5–8.7).

Mellopegma simesi (MacKinnon, Reference MacKinnon1985)

Figure 8.4, 8.8, 8.9

Reference MacKinnon1985 Anabarella simesi MacKinnon, p. 71, fig. 3A–J.

Reference Vendrasco, Kouchinsky, Porter and Fernandez2011 Mellopegma simesi; Vendrasco et al., p. 15, figs. 10, 11.

Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016 Mellopegma simesi; Peel et al., p. 266, fig 14D–G, L.

Holotype

UCM1299, Tasman Formation, Nelson Province, South Island, New Zealand, late middle Cambrian (Ptychagnostus cassis Zone).

Materials

PMU 28873 and 28968 from GGU sample 218681, Henson Gletscher Formation, Løndal, Peary Land, Cambrian Series 2, Stage 4.

Occurrence

Cambrian Series 2, Stage 4 of North Greenland; Cambrian, Miaolingian Series of New Zealand and Australia.

Remarks

In terms of the prominently overhanging apex, Mellopegma simesi (MacKinnon, Reference MacKinnon1985) resembles Erugoconus acuminatus Peel and Kouchinsky, Reference Peel and Kouchinsky2022 from the Miaolingian Series, Wuliuan Stage, in the upper member of the Henson Gletscher Formation in Løndal (Peel and Kouchinsky, Reference Peel and Kouchinsky2022, fig. 16F, H), but it is distinguished by its much greater rate of expansion of the shell in the median plane, in lateral aspect. Characteristically, internal molds of Erugoconus acuminatus display two deep spiral grooves on the sub-apical surface that are not seen in Mellopegma simesi.

Family Yochelcionellidae Runnegar and Jell, Reference Runnegar and Jell1976

Genus Yochelcionella Runnegar and Pojeta, Reference Runnegar and Pojeta1974

Type species

Yochelcionella cyrano Runnegar and Pojeta, Reference Runnegar and Pojeta1974.

Yochelcionella gracilis Atkins and Peel, Reference Atkins and Peel2004

Figure 9

Figure 9.

Yochelcionella gracilis Atkins and Peel, Reference Atkins and Peel2004, Henson Gletscher Formation, silica replicas from GGU sample 301346, southern Freuchen Land unless stated, Cambrian Series 2, Stage 4. (1) MGUH 27020 from GGU sample 225711, holotype, Løndal, lateral view of internal mold. (2, 3) PMU 28872 from GGU sample 225714, Løndal, lateral view with detail of ornamentation (2). (4) PMU 17891, lateral view. (5) PMU 17892, oblique lateral view. (6–8) PMU 17893, oblique dorsolateral, apical, and lateral views. (9) PMU 17894, lateral view. (10–12, 14) PMU 21540 from GGU sample 301347), lateral view with snorkel broken away, showing details of apex (11, 14) and comarginal ornamentation (12). (13, 15) PMU 21538 from GGU sample 301347, lateral view with broken apex and detail of ornamentation (13). (1, 4, 10) Scale bars = 300 μm; (2, 11, 14) scale bars = 100 μm; (3) scale bar = 500 μm; (5–9, 15) scale bars = 200 μm; (12, 13) scale bars = 50 μm.

Reference Atkins and Peel2004 Yochelcionella gracilis Atkins and Peel, p. 6, fig. 3.

Reference Atkins and Peel2008 Yochelcionella gracilis; Atkins and Peel, p. 34, figs. 6G, H, 8E–G, 8I–K.

Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016 Yochelcionella gracilis; Peel et al., p. 264, fig. 14A–C, 14H–K.

Reference Oh and Peel2024 Yochelcionella gracilis; Oh et al., figs. 1A–D, 3A–J, 5F, 8A–C.

Holotype

MGUH 27020 from GGU sample 225711 (Fig. 9.1); internal mold. Henson Gletscher Formation, North Greenland. Cambrian Series 2, Stage 4.

Materials

PMU 28872 from GGU sample 225713, Løndal. PMU 17891, PMU 17892, PMU 17893, and PMU 17894 from GGU sample 301346; PMU 21540 and PMU 21538 from GGU sample 301347, southern Freuchen Land. Henson Gletscher Formation, Cambrian Series 2, Stage 4.

Remarks

Yochelcionella gracilis Atkins and Peel, Reference Atkins and Peel2004 was based on the holotype internal mold from the Løndal area in North Greenland (Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016), and this study extends its occurrence to southern Freuchen Land in North Greenland.

Among the 16 other valid species of Yochelcionella Runnegar and Pojeta, Reference Runnegar and Pojeta1974 (listed by Parkhaev et al., Reference Parkhaev, Zhegallo and Dorjnamjaa2024, p. 3), Yochelcionella gracilis is most comparable to Yochelcionella ostentata Runnegar and Jell, Reference Runnegar and Jell1976, with both displaying the sigmoidal shape of the tall shell, steep inclination of the snorkel, a slightly hooked apex, and acute comarginal rugae (Gubanov et al., Reference Gubanov, Kouchinsky, Peel and Bengtson2004; Kouchinsky et al., Reference Kouchinsky, Bengtson, Clausen, Gubanov, Malinky and Peel2011; Peel et al., Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016). Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016) differentiated Yochelcionella gracilis from Yochelcionella ostentata on the basis of the absence of radial threads, a feature subsequently reinterpreted as periostracum-derived by Oh et al. (Reference Oh, Peel, Zhen, Smith, Lee and Park2024). While some specimens of Y. gracilis from southern Freuchen Land even exhibit the radial threads, the spacing of the rugae can serve as a distinguishing feature between the two species. In Yochelcionella gracilis, the rugae show a transition from closely spaced in the early growth stage to widely spaced in the main conch, while they are more regularly spaced in Yochelcionella ostentata (Kouchinsky et al., Reference Kouchinsky, Bengtson, Clausen, Gubanov, Malinky and Peel2011).

Genus Eotebenna Runnegar and Jell, Reference Runnegar and Jell1976

Type species

Eotebenna pontifex Runnegar and Jell, Reference Runnegar and Jell1976 from the Currant Bush Limestone, Queensland, Australia, Cambrian, Miaolingian Series.

Eotebenna arctica Peel, Reference Peel1989

Figure 10

Figure 10.

Eotebenna arctica Peel, Reference Peel1989, Henson Gletscher Formation, southern Freuchen Land, Cambrian Series 2, Stage 4. (1–4) PMU 17895 from GGU sample 301346, lateral, oblique lateral, sub-apical, and supra-apical views. (5) MGUH 18702 from GGU sample 315109, holotype, lateral view. (6) MGUH 18701 from GGU sample 315109, lateral view. (1–4) Scale bars = 200 μm; (5, 6) scale bars = 1 mm.

Reference Peel1989 Eotebenna arctica Peel, p. 1501, fig. 3A–3D.

Reference Peel, Simonetta and Conway Morris1991b Eotebenna arctica; Peel, p. 38, fig. 29.

Reference Peel2004  Eotebenna arctica; Peel, text-fig. 1E.

Holotype

MGUH 18702 from GGU sample 315109, Henson Gletscher Formation, southern Freuchen Land, Cambrian Series 2, Stage 4.

Materials

In addition to the holotype, PMU 17895 from GGU sample 301346 (a silica replica) and MGUH 18701 from GGU sample 315109, Henson Gletscher Formation, southern Freuchen Land, Cambrian Series 2, Stage 4.

Diagnosis

Species of Eotebenna with gentle curvature. Onamentation of sharp, prominent comarginal rugae and concentric lines; rugae absent at the emargination (the sub-apical fold) surface.

Description

Shell moderately expanded with similar length and height but narrower width. In lateral view, the apex is situated at the middle. The sub-apical emargination forms a narrow slit developed on the dorsal surface of a flange-like median fold in the sub-apical surface (Fig. 10). In larger specimens, the shell is coiled through about a quarter whorl (Fig. 10.5, 10.6) with a uniformly convex supra-apical surface in lateral view. The sub-apical surface is concave but with a prominent flange-like median fold corresponding to the sinus (Fig. 10.5); the degree of curvature becomes more pronounced during ontogeny (compare Fig. 10.1 and 10.5). Aperture elliptical with a slight lateral compression. The deep, sub-apical emargination increases slightly in width during ontogeny, but it is tube-like along its adapical margin, at its adapical tip (Fig. 10.3). Ornamentation of sharp, prominent comarginal rugae with intervening areas carrying finer comarginal growth lines that are crossed by fine radial lines; the comarginal rugae are not present on the flange-like sub-apical fold.

Remarks

The median emargination on the flange-like fold on the sub-apical surface of Eotebenna, probably related to water circulation (Peel, Reference Peel, Simonetta and Conway Morris1991b, Reference Peel2004), was described as a subapical fold by Peel (Reference Peel1989, p. 1502), the anterior tube by Runnegar and Jell (Reference Runnegar and Jell1976, p. 130), and the snorkel by Gubanov et al. (Reference Gubanov, Kouchinsky, Peel and Bengtson2004).

We provide a revised description of Eotebenna arctica Peel, Reference Peel1989 following the discovery of a well-preserved silica replica. Peel (Reference Peel1989) erected Eotebenna arctica Peel, Reference Peel1989 to include three specimens from the lower Cambrian of Freuchen Land, North Greenland, in which the pronounced curvature in lateral view (Fig. 10.5, 10.6) provided a key character for differentiation from the other species in Eotebenna Runnegar and Jell, Reference Runnegar and Jell1976: Eotebenna pontifex Runnegar and Jell, Reference Runnegar and Jell1976 and Eotebenna papilio Runnegar and Jell, Reference Runnegar and Jell1976 from Australia. The new specimen is less coiled due to its smaller size. Eotebenna arctica is especially similar to Eotebenna papilio in terms of the overall shape and the expanded degree of the sub-apical fold, but Eotebenna arctica shows greater curvature and has more prominent comarginal rugae. Recently, Mghazli et al. (Reference Mghazli, Lazreq, Geyer, Landing, Boumehdi and Youbi2023) reported Eotebenna cf. E. papilio from Wuliuan strata (the Jbel Wawrmas Formation) of West Gondwana (Morocco). The incomplete three Eotebenna specimens in Mghazli et al. (Reference Mghazli, Lazreq, Geyer, Landing, Boumehdi and Youbi2023) are somewhat similar to Eotebenna arctica from the lateral views, but they have much narrower, laterally compressed shells with less prominent comarginal rugae.

Order Pelagiellida MacKinnon, Reference MacKinnon1985

Family Pelagiellidae Knight, Reference Knight1956

Genus Pelagiella Matthew, Reference Matthew1895

Type species

Cyrtolites atlantoides Matthew, Reference Matthew1894 from the Hanford Brook Formation, Cambrian Series 2–3, New Brunswick, Canada.

Remarks

Pelagiella Matthew, Reference Matthew1895 was recently interpreted by Thomas et al. (Reference Thomas, Runnegar and Matt2020) as belonging to the Total Group Gastropoda Cuvier, Reference Cuvier1797 on the basis of specimens of Pelagiella exigua Resser and Howell, Reference Resser and Howell1938 from the Kinzers Formation (Cambrian Series 2, Stage 4) of Pennsylvania, which are preserved with chaetae (or setae). However, Landing et al. (Reference Landing, Geyer, Jirkov and Schiaparelli2021) restricted Pelagiella to the type species, Pelagiella atlantoides (Matthew, Reference Matthew1895) from the Hanford Brook Formation (Cambrian Series 2, Stage 4) of New Brunswick, which they considered to be a mollusk, and controversially interpreted Pelagiella exigua and other members of that morphological group as annelids. In contrast to most specimens assigned to Pelagiella in the literature, in which the presumed lower surface expands to give a distinctly trochispiral form (Thomas et al., Reference Thomas, Runnegar and Matt2020, fig. 1; Fig. 7.10), Pelagiella atlantoides was considered to have an oval aperture and therefore an almost planispiral form.

Landing et al. (Reference Landing, Geyer, Jirkov and Schiaparelli2021) designated Pelagiella exigua Resser and Howell, Reference Resser and Howell1938 as type species of a new genus, Pseudopelagiella. The establishment of Pseudopelagiella for its type species Pelagiella exigua may be justified on account of the differences in shape from Pelagiella atlantoides. However, Peel and Kouchinsky (Reference Peel and Kouchinsky2022) did not accept that all other pelagiellids in the common usage of that name should be interpreted as annelids, largely on the basis of descriptions of shell structure by Kouchinsky (Reference Kouchinsky2000), Vendrasco et al. (Reference Vendrasco, Porter, Kouchinsky, Li and Fernandez2010), and Li et al. (Reference Li, Zhang, Yun and Li2017, Reference Li, Zhang, Skovsted, Yun, Pan and Li2021). This conclusion is followed here, and current material is referred to Pelagiella, although it is evident that the relationship of Pelagiella atlantoides to other pelagiellids needs clarification. Thomas et al. (Reference Thomas, Runnegar and Matt2020) reviewed various pelagiellid taxa and records in connection with the redefinition of Pelagiella exigua.

Pelagiella sp.

Figure 11

Figure 11.

Pelagiella sp., Henson Gletscher Formation, southern Freuchen Land and Løndal, Cambrian Series 2, Stage 4. (1–3) PMU 17896 from GGU sample 301346, southern Freuchen Land. (4) PMU 28865 from GGU sample 218680, Løndal. (1) Scale bar = 100 μm; (2–4) scale bars = 200 μm.

Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016 Pelagiella sp., Peel et al. p. 266, fig. 13I–M.

Materials

PMU 17896 from GGU sample 301346, southern Freuchen Land; PMU 28865, from GGU sample 218860, Løndal. Upper Henson Gletscher Formation, Cambrian Series 2, Stage 4. In addition, Pelagiella sp. of Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 13J–M; PMU 28866, PMU28867, PMU 28868) from GGU sample 218681, Henson Gletscher Formation, Løndal. Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, table 1) also recorded Pelagiella sp. from GGU samples 271749 and 225707, from the lower member of the Henson Gletscher Formation just below the middle sandstone member.

Remarks

Pelagiellids illustrated by Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016) from Løndal have the apex depressed within the shallowly concave upper surface and a strongly inflated base, as is the case with specimens illustrated here from southern Freuchen Land (Fig. 11.1–11.3), but also specimens from the Kinzers Formation illustrated by Skovsted and Peel (Reference Skovsted and Peel2010) and Thomas et al. (Reference Thomas, Runnegar and Matt2020). The base is less inflated in Wuliuan specimens from Løndal that Peel and Kouchinsky (Reference Peel and Kouchinsky2022) referred to Costipelagiella cf. C. nevadense Skovsted, Reference Skovsted2006 because of the prominent comarginal ribs, although the degree of expansion is clearly a function of ontogeny. Ornamentation in the present material consists of irregular-in-detail beaded comarginal cords crossed by widely spaced spiral lines, grooves, and ridges (Fig. 11.1–11.3).

Pelagiella sp. illustrated in this study includes two specimens: one from southern Freuchen Land (Fig. 11.1–11.3) and the other from Løndal (Fig. 11.4) in North Greenland. The latter was originally illustrated by Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016, fig. 13I). Peel et al. (Reference Peel, Streng, Geyer, Kouchinsky and Skovsted2016) noted that Pelagiella sp. from Løndal most closely resembles Pelagiella subangulata (Tate, Reference Tate1892), due mainly to the similar ornamentation visible in the external phosphatic coating. The umbilical region of the internal molds described in this study is also similar to that of Pelagiella subangulata (Tate, Reference Tate1892) illustrated by Parkhaev in Gravestock et al. (Reference Gravestock, Alexander, Demidenko, Esakova and Holmer2001, pl. 47), but our specimens lack the “V-shaped ridges” typical of P. subangulata (Parkhaev in Gravestock et al., Reference Gravestock, Alexander, Demidenko, Esakova and Holmer2001, p. 194; Skovsted, Reference Skovsted2004, fig. 8A–C). The ornamentation of the Freuchen Land specimen (Fig. 11.1–11.3) is well identified, including both the reticulate pattern and granules on the surface of the shell (Fig. 11.1). The ornamentation is more closely similar to Pelagiella madianensis (Zhou and Xiao, Reference Zhou and Xiao1984) than to P. subangulata, as illustrated by Li et al. (Reference Li, Zhang, Yun and Li2017, fig. 2). Interestingly, Parkhaev in Gravestock et al. (Reference Gravestock, Alexander, Demidenko, Esakova and Holmer2001) noted that P. subangulata and P. madianensis are “twin species” as they commonly occur together and the juvenile internal molds of two species are indistinguishable. For this reason, species-level identification remains pending in this study.