Type species

Ulugtella turgida Petrunina in Repina et al., Reference Repina, Yaskovich, Askarina, Petrunina, Poniklenko and Rubanov1975, from the “Keananella–Tretaspis beds,” upper Katian, Turkestan.

Diagnosis

See Hammann (Reference Hammann1992, p. 75).

Remarks

Given the uncertainty in the generic assignment of the species Ulugtella? biformis n. sp., a list of other species of Ulugtella will not be given here. For detailed information on the genus, reference is made to the work of Hammann (Reference Hammann1992, p. 75–78) and Hammann and Leone (Reference Hammann and Leone1997, p. 92–97). However, it is important to add a few remarks concerning the current concept of the genus Ulugtella and another genus that may be closely related. There are several blind illaenid genera from the peri-Gondwanan realm whose validity needs revision. Among others, these include Ulugtella and Zbirovia Šnajdr, Reference Šnajdr1956. The genus Zbirovia is represented by a single species—the type species Zbirovia arata (Barrande, Reference Barrande1872)—spanning from the Dobrotivian (ca. uppermost Darriwilian) Dobrotivá Formation to the middle Berounian (ca. upper Sandbian–lower Katian) Vinice Formation. This form is characterized by a relatively narrow glabella and ten thoracic segments (at least, in specimens from the older Dobrotivá Formation, where complete specimens are available). It is difficult to understand the origin of Zbirovia. It recalls some blind Ectillaenus species, such as E. sarkaensis (Novák in Perner, Reference Perner1918) and E. benignensis (Novák in Perner, Reference Perner1918), whose pygidial structure is similar to Zbirovia arata.

On the other hand, the type species of Ulugtella was defined in the upper Katian of Turkestan, which is younger than Zbirovia, bearing only nine thoracic segments, a cephalic anterior border, a strongly convex cephalon, and a well-defined pygidial axis. Nevertheless, the current concept of the genus (sensu Hammann, Reference Hammann1992, and Hammann and Leone, Reference Hammann and Leone1997), is based on a group of species that were assigned to Ulugtella and not necessarily related to the type species, which is poorly known. In this sense, Hammann (Reference Hammann1992, p. 75–76) listed several records that he considered could belong to Ulugtella, including material from Spain, Czech Republic, Sardinia (Italy), United Kingdom, Poland, Germany, Turkey, and China. The wide geographical distribution given by Hammann, Reference Hammann1992, to Ulugtella makes its monophyly suspect, although in fact many trilobite genera became widespread during the late Katian (e.g., Fortey and Cocks, Reference Fortey and Cocks2005).

Holotype

One complete exoskeleton (internal mold; Fig. 2.1–2.3), MGM-7666X housed in the paleontological collections of the Museo Geominero (CN Instituto Geológico y Minero de España, CSIC, Madrid).

Figure 2. (1–8) Ulugtella? biformis n. sp., from the Bofloss locality, Morocco. (1‒3) Exoskeleton, internal mold, holotype, MGM-7666X: (1) dorsal view; (2) left lateral view; (3) anterior view. (4) Exoskeleton, internal mold, paratype, MGM-7667X: dorsal view. (5) Exoskeleton, internal mold, paratype, MGM-7668X: dorsal view. (6) Exoskeleton, internal mold, paratype, MGM-7669X: dorsal view. (7, 8) Exoskeleton, paratype, MGM-7670X: (7) external mold of the left librigena; (8) latex cast of the external mold, MGM-7670X-1: dorsal view. (9) Hypostome, internal mold, paratype, MGM-7671X-1: ventral view. Specimens (1–3) and (9) are preserved in full relief (sandstones); the remaining specimens are preserved in mudstones, flattened. Scale bars = 5 mm.

Paratypes

Four exoskeletons (MGM-7667X, MGM-7668X, MGM-7669X, MGM-7670X); one hypostome (MGM-7671X-1).

Diagnosis

Parabolic cephalic outline; well-defined hourglass-shaped glabella, occupying about one-third of maximum cranidial width; axial reaching up to 40% sagittal cephalic length; facial sutures curving abaxially opposite the anterior ends of axial furrows; facial suture smoothly curving opposite anterior ends of the axial furrows; posterior ends of the facial suture curving abaxially; subtriangular librigenae with broadly rounded genal angles. Pygidium subpentagonal, with parabolic posterior margin; length ~90% of the maximum pygidial width (tr.); axis poorly defined, with a faint subtriangular outline in flattened specimens, weakly convex, anterior width ~30% of maximum pygidial width; pygidial doublure broad, ~50% pygidial sagittal length, anterior margin of doublure slightly convergent with lateral pygidial margin abaxially, medially with posteriorly convex indentation.

Occurrence

“Declivolithus Fauna beds,” upper part of the Lower Ktaoua Formation–?lower half of the Upper Tiouririne Formation, from the middle to upper Berounian boundary beds (ca. lower Katian), Bofloss locality, Tizi n'Ounfite location, 9 km SW of Oukhit (or Oukrite: 31°25′24.7″N, 04°33′59.0″W), northeastern Anti-Atlas, Morocco.

Description

Cranidium maximum width (at posterior margin) ~110% of sagittal length in full-relief specimens, with steep librigenae. Cranidium strongly vaulted (sag. and tr.); frontal part overhanging anterior margin. Axial furrows moderately deep, reaching 35–40% of sagittal cephalic length, slightly curved inwards; hourglass-shaped glabella, moderately convex, slightly exceeding height of fixigena in lateral view, merging with fixigenae anteriorly. Posterior glabellar width corresponding to 35% of posterior cephalic width; cranidium width ~90% cephalic width. Facial suture very hard to observe in most of the specimens; one specimen with displaced librigenae shows divergent posterior end of the facial suture (Fig. 2.7); facial suture then running straight forwards up to opposite the anterior limit of the axial furrows, where it smoothly inflexes adaxially and then runs straight again anteriorly, converging at anterior margin, crossing the anterior border at a distance approximately twice the posterior width of the glabella. Fixigenae maximum width at posterior margin, ~85% glabellar posterior width. Librigenae subtriangular, with broadly rounded genal angle; maximum width at posterior margin ~60% glabellar posterior width. Anterior margin defined by a rim, which continues posteriorly into lateral librigenal border, fading backwards (Fig. 2.2, 2.3). Rostral plate subtrapezoidal, posterior width ~60% anterior width and 150% sagittal length; connective suture converging backwards at 50–55° to sagittal line; surface bearing about 10 well-marked terrace ridges, subparallel to anterior rostral plate margin, being more regular anteriorly and becoming more sinuous posteriorly. Hypostome with semicircular posterior margin. Large subtriangular (almost rectangular) wings, length (exsag.) ~40% hypostome sagittal length; middle body divided by a shallow middle furrow; anterior lobe convex, suboval, wider (tr.) than long (sag.); posterior lobe sickle-shaped, slightly convex, its sagittal length about half the length of anterior lobe. No maculae. Lateral and posterior border very narrow, limited by a furrow that meets the oblique middle furrow at about half the hypostome length (sag.), forming deep grooves. Three transverse terrace ridges are observed on the anterior lobe of the middle body.

Nine thoracic segments. Axis moderately arched (tr.), about one-third of thoracic width anteriorly, slightly narrowing backwards, more strongly in last five segments. Axial furrow deeper than on cephalon; subcircular axial processes visible on internal molds. Pleurae as wide anteriorly as posteriorly, fulcrum located ~50% of pleural width. Inner portion of pleurae flattened and smooth; outer portion deflected downwards and slightly backwards, bearing a broad (exsag., tr.) and smooth facet.

Pygidium subpentagonal in full-relief specimens (in flattened specimens pygidium acquires an almost subcircular outline, short, sag.), length/width ratio ~70% (in full-relief specimens); posterior margin parabolic. Pygidial axis poorly defined, broadly triangular in flattened specimens, weakly convex, anterior width ~30% of maximum pygidial width. Axial furrow not defined. Doublure very broad, corresponding to 50% of pygidial sagittal length medially; anterior margin of doublure slightly convergent with lateral pygidial margin abaxially, medially with posteriorly convex indentation; the pygidium, both in full-relief specimens and flattened ones, often exfoliates, exposing the medial indentation very prominently (Fig. 2.1, 2.2, 2.4, 2.5); sculpture of terrace ridges running subparallel to pygidial margin, becoming more sinuous medially.

Dorsal surface of exoskeleton densely covered with circular pits, more evident on cephalon and pygidium, obliterated in most specimens, better preserved in a single example (Fig. 2.6). This sculpture is not preserved in full-relief specimens.

Etymology

From the Latin adjective biformis, bis (twice) + -fōrmis (having form of), meaning having two forms, or two faces (like Janus), reflecting the different morphologies shown by the specimens of this species when preserved in full relief or flattened. Ulugtella gender feminine.

Remarks

We considered whether a Portuguese species (“Ulugtella? guedesi n. sp.” in the unpublished PhD thesis by Pereira, Reference Pereira2017, p. 268–272, pl. 19, figs. A–K; pl. 20, figs. A–J; pl. 21, figs. A–M) and these Moroccan specimens are conspecific but decided not to assume that to be the case. The very distinct subtrapezoidal morphology of the librigenae of the Portuguese specimens, with sharp right genal angle (90°), the strongly inflected facial suture (suggesting recent loss of the eyes), with posterior branch curving adaxially (and not abaxially as in the Moroccan specimens). and the more heart-shaped pygidium, with no evidence of any indentation on the inner edge of the doublure suggest that although extremely similar, the Portuguese species differs in characters that are significant within Illaenidae.

Ulugtella? biformis n. sp. is here only tentatively assigned to Ulugtella due to the current unsatisfactory knowledge on Upper Ordovician illaenid lineages from the peri-Gondwana realm. Nevertheless, we think it is closely related to Zbirovia arata. The number of thoracic segments has been treated in Illaenidae as being relevant at a genus level. Zbirovia bears 10 thoracic segments, and because the new species fits the current diagnosis of Ulugtella (Hammann, Reference Hammann1992), we chose to assign it to this genus and not to the former. The current Ulugtella diagnosis and concept of Ulugtella were established by Hammann (Reference Hammann1992) based on the assumption that a group of occurrences from Spain, Sardinia, Sweden, and Poland are congeneric with the type species U. turgida. If U. turgida is not related to these peri-Gondwanan occurrences and the species described herein, then either a new genus to include this group of nine-segmented blind illaenids related to Zbirovia would be appropriate or Zbirovia should encompass all of them, regardless of the number of thoracic segments. This awaits detailed revision of this group, and we follow Hammann's (Reference Hammann1992) proposal for now.

Ulugtella? biformis n. sp. shows more similarities to a group of occurrences assigned by Hammann (Reference Hammann1992) and Hammann and Leone (Reference Hammann and Leone1997) to U. angelini (Holm, Reference Holm1883, p. 120, pl. 4, fig. 29), defined in the “Red Tretaspis Mudstone” (Upper Jonstorp Formation) of the upper Katian of Sweden by Holm (Reference Holm1883). These came from the Cystoid Limestone Formation (Kralodvorian, ca. upper Katian) of Spain (Hammann, Reference Hammann1992, p. 75–77, pl. 14, figs. 1–10) and from the Domusnovas Formation (Kralodvorian, ca. upper Katian) of Sardinia (Hammann and Leone, Reference Hammann and Leone1997, p. 93–95, pl. 16, figs. 1–16). Despite their similar overall appearance, the Baltic U. angelini differs from U.? biformis n. sp. by having a marginal, posteriorly transverse, facial suture, a simple cephalic border, a definite narrower (tr.) thoracic and pygidial axis, and a simple, shorter (sag./exsag.) pygidial doublure, with no evidence of indentation of its anterior margin. These are significant characters within the group (Jaanusson, Reference Jaanusson1954). Both in the facial suture and in pygidial doublure outline, Sardinian and Spanish specimens seem to be more similar to U.? biformis n. sp., but it is very difficult to conduct further analyses due to the poor state of preservation. All the other species assigned to Ulugtella, and other material classified as congeneric (listed exhaustively by Hammann, Reference Hammann1992, p. 75, 76, and Hammann and Leone, Reference Hammann and Leone1997, p. 94–95) are very distinct from U.? biformis n. sp. in having much narrower glabella and/or long genal spines (e.g., group U. bornholmiensis [Kielan, Reference Kielan1960] sensu Hammann and Leone, Reference Hammann and Leone1997, p. 95).

Ulugtella? biformis n. sp. shares some important features with Zbirovia arata, namely the pygidial morphology, including the typical doublure (see Šnajdr, Reference Šnajdr1957, pl. 3, fig. 12), the rostral-plate configuration (see Šnajdr, Reference Šnajdr1957, pl. 3, fig. 9), the cranidium overhanging the anterior margin, which is defined by a rim (see Klouček, Reference Klouček1913, fig. 3a), and a densely pitted sculpture. Nevertheless, Zbirovia arata has a simple facial suture, with no inflexion, its thorax being composed of 10 thoracic segments and the pygidial doublure being longer (sag.). The difference in the length of the doublure would, however, be expected, given the reduction in the number of thoracic segments (paedomorphism?), but we do not know whether the suture could, by the same process, present these changes connected to an ancestor of both that had eyes. Furthermore, a specimen recently figured by Lebrun (Reference Lebrun2018, p. 117, fig. A) from the Lower Ktaoua Formation of Morocco suggests Zbirovia arata is also present in Morocco, in beds older than U.? biformis n. sp.

The discovery of this new species and its possible relationship with Zbirovia arata, entails another species, Zbirovia vaneki Šnajdr, Reference Šnajdr1958, from the Bohdalec Formation of the Czech Republic, later assigned to Vysocania (see Pereira et al., Reference Pereira, Marques da Silva, Sá, Pires, Marques Guedes, Budil, Laibl and Rábano2017, and references therein) based on additional cephala bearing eyes and the same typical pygidial morphology. But according to the doubts already expressed by Šnajdr (Reference Šnajdr1958) whether this species was blind or not, it is possible that two very similar illaenids occur in the Bohdalec Formation, one with eyes (Vysocania) and another without eyes. This was also mentioned by Bruthansová (Reference Bruthansová2003), but she considered these specimens with eyes to be Vysocania panderi (Barrande, Reference Barrande1852), which differs from the Bohdalec specimens in bearing librigenae with rounded genal angles. The holotype of “Zbirovia vaneki” (Šnajdr, Reference Šnajdr1958, pl. 2, fig. 10) corresponds to the eyed-illaenid form (Vysocania), but other specimens described under the same name may in fact represent a blind form, justifying Šnajdr's (Reference Šnajdr1958) concerns and original generic assignment. Whether or not this blind illaenid of the Bohdalec Formation that led Šnajdr to the erection of “Zbirovia vaneki” is conspecific with the new Moroccan species is hard to say, but the cephalic axial furrows of the Czech types repeatedly appear to be more curved and closer together. Similar thoughts were expressed by Pereira (Reference Pereira2017, p. 272) to differentiate Vysocania iberica (Hammann, Reference Hammann1976) from “Ulugtella? guedesi n. sp.” (Ulugtella? guedesi Pereira, Reference Pereira2017) when occurring in the same fossil locality.

Finally, the hypostome morphology of U.? biformis n. sp. is very similar to “illaenid hypostome B” documented by Hammann (Reference Hammann1992, pl. 18, figs. 5, 6) from the Cystoid Limestone Formation of Spain. It is an Ectillaenus-type specimen (e.g., Bruthansová, Reference Bruthansová2003, fig. 2e), but differs in having a more developed posterior lobe of the middle body. Although the hypostome is unknown in many illaenids, this morphology also points to Ulugtella? biformis n. sp. being connected to a group of endemic illaenids from peri-Gondwana.

Type species

Odontopleura buchii Barrande, Reference Barrande1846, Letná Formation, lower Berounian (ca. Sandbian, Sa2), Czech Republic.

Other species

See Bruton (Reference Bruton2008, p. 4).

Diagnosis

See Bruton (Reference Bruton2008, p. 4).

Occurrence

Lower (Floian) to Upper Ordovician (topmost Katian) of Europe (Czech Republic, Great Britain, France, Portugal, Spain, Italy, Turkey), North Africa (Morocco), and the Middle East (Iraq).

Remarks

Selenopeltis was revised by Bruton (Reference Bruton2008) and partially also by Gutiérrez-Marco et al. (Reference Gutiérrez-Marco, Pereira, García-Bellido and Rábano2022b), to whom we refer for further information.

Selenopeltis cf. S. vultuosa Přibyl and Vaněk, Reference Přibyl and Vaněk1966
Figure 3.1, 3.2

cf. Reference Přibyl and Vaněk1966

Selenopeltis buchi vultuosa Přibyl and Vaněk, p. 292, pl. 4, fig. 2, pl. 8 figs. 1–3.

?p Reference Bruton2008

Selenopeltis vultuosa Přibyl and Vaněk; Bruton, p. 10, fig. 3 A–J, M, N.

Figure 3. (1, 2) Selenopeltis cf. S. vultuosa Přibyl and Vaněk, Reference Přibyl and Vaněk1966, from the Bofloss locality, Morocco. (1) Cranidium, internal mold, MGM-7673X: dorsal view; (2) left librigena, latex cast of the external mold, MGM-7674X-1. (3–15) Phacopidina quadrata (Hawle and Corda, Reference Hawle and Corda1847) from the Bofloss locality, Morocco. (3) Cephalon, internal mold, MGM-7675X: dorsal view; (4, 9, 10) cephalon, internal mold, MGM-7676X: (4) frontal view showing frontal lobe auxiliary impressions; (9) dorsal view; (10) right lateral view; (5, 6) cephalon, internal mold, MGM-7677X: (5) dorsal view; (6) left lateral view; (7, 8) cephalon, internal mold, MGM-7678X: (7) dorsal view; (8) left lateral view; (11, 12, 15) cephalon, internal mold, MGM-7679X: (11) dorsal view; (12) left lateral view; (15) anterior view; (13, 14) cephalon, latex cast of the external mold, MGM-7680X: (13) dorsal view; (14) right lateral view. All specimens are preserved in full relief (sandstones). Scale bars = 5 mm.

Remarks

Selenopeltis is a genus that has captured the attention of several researchers, with special emphasis on the works of Bruton (Reference Bruton1968, Reference Bruton2008), Přibyl and Vaněk (Reference Přibyl and Vaněk1973), Bruton and Henry (Reference Bruton and Henry1978), Romano (Reference Romano1982), Šnajdr (Reference Šnajdr1984), Hammann and Rábano (Reference Hammann and Rábano1987), and Ramsköld (Reference Ramsköld1991). The revision of Selenopeltis by Bruton (Reference Bruton2008) included material from Morocco, supplemented by the review of a purported endemic Moroccan species (Gutiérrez-Marco et al., Reference Gutiérrez-Marco, Pereira, García-Bellido and Rábano2022b). Given the existence of these works, we have chosen to follow here the considerations of Bruton (Reference Bruton2008) to identify Bofloss Selenopeltis. Only two fragmentary specimens (one cranidium and one librigenal; Fig. 3.1, 3.2) were collected, but complete exoskeletons coming from Declivolithus beds are relatively common in Moroccan trade. Thus, we include some characters observed in those in this discussion.

Following Bruton's (Reference Bruton2008) revision, the Bofloss specimens are more similar to Selenopeltis vultuosa from the Lower Ktaoua and Upper Tiouririne formations of Morocco, based solely on the presence of pygidial true major border spines overpassing the pygidial border. This character is stable in all the large holaspides observed and has been shown to be the only consistently assessable character unaffected by deformation, preservation, or ontogeny, if in mature holaspides (Šnajdr, Reference Šnajdr1984; Pereira, Reference Pereira2017). All the Berounian species of Selenopeltis defined for high-latitude peri-Gondwana realm (Selenopeltis buchi group) have supramarginal true major spines. Other characters that have been used to differentiate several Selenopeltis species, namely the external sculpture, are shown to be highly variable within the same locality and dependent on the size of the specimens, even in the holaspid stage (see Pereira, Reference Pereira2017, p. 334–336, pls. 39–41). Nevertheless, if the Moroccan specimens are compared with the type material of S. vultuosa from the Králův Dvůr Formation in the Czech Republic, a specific difference is probable. The Moroccan specimens do not show a sharp bend in the thoracic pleural ridge like the Czech types (see Shaw, Reference Shaw2000, pl. 2, figs. 15, 20), which is the most distinctive and persistent character of Selenopeltis vultuosa according to Šnajdr (Reference Šnajdr1984) and Shaw (Reference Shaw2000, p. 380). Here, we maintain the identification based on Bruton's (Reference Bruton2008) work, but the current state of knowledge of Selenopeltis species is not satisfactory.

Remarks

The systematic position of the basal Acastacea (= Acastoidea) remains unsolved. We follow the proposal of Edgecombe (Reference Edgecombe1993), which is possibly also the ongoing one for the revision of the Treatise on Invertebrate Paleontology (see Adrain, Reference Adrain2011, p. 105). According to Edgecombe (Reference Edgecombe1993), Acastacea s.l. includes genera that present the apomorphies of the superfamily Acastacea but lack the derived characters defining Siluro–Devonian Acastacea s.s. Edgecombe (Reference Edgecombe1993) considered these basal acastaceans to have evolved from Dalmanitoidea through a shift in feeding mechanisms. Although we have chosen to follow the most recent proposal, we express doubts in excluding this Ordovician group or, at least, some of its members from Dalmanitidae.

Type species

Phacopidina harnagensis Bancroft, Reference Bancroft1949, from the Smeathen Wood Formation, Aurelucian (ca. lower Sandbian) of Shropshire, England.

Other species

Portlockia? apiculata M'Coy in Sedgwick and M'Coy, Reference Sedgwick and M'Coy1851, Burrellian/Cheneyan, Shropshire, England; Dreyfussina armoricana Pillet, Reference Pillet1990, upper part of the Sangsurière Formation (“Schistes d'Angers”), middle Berounian, La Meinanne, Maine et Loire, France; Phacopidina micheli couyerensis Henry, Reference Henry1980, Andouillé Formation, Dobrotivian, France; Phacopidina makina Šnajdr, Reference Šnajdr1987, Zahořany Formation, middle Berounian, Czech Republic; Dalmanites micheli Tromelin, Reference Tromelin1877, Dobrotivian, France; Zeliszkella (Zeliszkella) neltneri Destombes, Reference Destombes1972, Ouine-Inirne Formation, Dobrotivian, Morocco; Phacops quadratus Hawle and Corda, Reference Hawle and Corda1847, Bohdalec Formation, upper Berounian, Czech Republic (= P. rebeka Šnajdr, Reference Šnajdr1982b, junior synonym).

Diagnosis

See Henry (Reference Henry1980, p. 126).

Occurrence

Middle to Upper Ordovician (Darriwilian to Katian) of Portugal, Spain, France, Czech Republic, Morocco, and United Kingdom.

Remarks

Regardless of the arguments used by Henry (Reference Henry1980, p. 123–127) to differentiate Kloucekia Delo, Reference Delo1935, from Phacopidina, he questioned their independence. The cephalic differences listed are questionable because of the existence of species showing intermediate features. Henry (Reference Henry1980) assigned a few species to Phacopidina in which the facial suture is not separated from the preglabellar furrow (P. harnagensis and P. apiculata). In addition, Kloucekia robertsi (Reed, Reference Reed1904), from the Redhill Mudstones and Sholeshook Limestone (upper Katian, Wales, United Kingdom) shows at the same time the cephalic diagnostic features of Phacopidina (broad preglabellar area) but pygidia lacking medial spine (one of the diagnostic characters of Kloucekia used by Henry, Reference Henry1980). On the other hand, the genus Dreyfussina Hupé in Choubert et al. (Reference Choubert, Hupé, Leckwijk and Suter1956) may fall within the compass of Kloucekia. The diagnostic characters usually mentioned for Kloucekia—presence of genal spines, strong pygidial segmentation, and existence of a concave pygidial border (Destombes, Reference Destombes1972; Hammann, Reference Hammann1974, Reference Hammann1976; Henry, Reference Henry1980)—are absent in its type species, Dalmania exophtalma Dreyfuss, Reference Dreyfuss1948 (see Henry, Reference Henry1980, pl. 44, figs. 5, 6, 8, 10). The current systematic classification of these genera is not satisfactory, but for the moment we follow previous authors who recognized three genera (e.g., Henry, Reference Henry1980; Hammann and Leone, Reference Hammann and Leone2007), and retain Phacopidina as a separate genus.

On the other hand, Phacopidina is a good example of the concerns in excluding these Ordovician “acastaceans” from Dalmanitidae. These concerns were expressed by Henry (Reference Henry1980, p. 127), who detailed several significant characters shared by Phacopidina and some Zeliszkellinae and Dalmanitininae. Accepting the detailed discussion provided by Destombes and Henry (Reference Destombes and Henry1987) about Calmoniidae versus Dalmanitidae, it is difficult to conceive that several species currently assigned to Phacopidina are not closely related to the dalmanitid Crozonaspis Henry, Reference Henry1968 (see Remarks on the different species that follow).

Phacopidina quadrata (Hawle and Corda, Reference Hawle and Corda1847)
Figures 3.3–3.15, 4.1–4.6

Reference Hawle and Corda1847

Phacops quadratus Hawle and Corda, p. 99.

Reference Destombes1972

Kloucekia (Phacopidina) aff. solitaria; Destombes, p. 60–63, pl. 14, figs. 1–16.

Reference Šnajdr1987

Phacopidina makina Šnajdr, p. 276, pl. 2, fig. 8.

Reference Vaněk and Vokáč1997

Phacopidina quadrata; Vaněk and Vokáč, p. 39–40, pl. 7, figs. 7–9, pl. 8, figs. 4–10, pl. 10, figs. 5, 6 (and synonymy therein).

pReference Vaněk and Vokáč1997

Sokhretia solitaria; Vaněk and Vokáč, pl. 7, figs. 10–15, pl. 8, figs. 15, 16.

Reference Destombes2006b

Kloucekia (Phacopidina) aff. solitaria; Destombes, pl. 36, figs. 1, 2.

Figure 4. (1–6) Phacopidina quadrata (Hawle and Corda, Reference Hawle and Corda1847) from the Bofloss locality, Morocco. (1–3) Cephalon, internal mold, MGM-7681X: (1) dorsal view; (2) ventral view; (3) anterior view; (4) cephalon and cephalic doublure, internal molds, dorsal and ventral views, MGM-7689X-1 and 7689X-2, respectively; (5) pygidium, internal mold, MGM-7690X: dorsal view; (6) pygidium, latex cast of the external mold, MGM-7674X-3: dorsal view. (7) Prionocheilus cf. P. verneuili Rouault, Reference Rouault1847, incomplete cephalon with thorax, latex cast of the external mold, MGM-7703X: dorsal view. (8, 9) Nobiliasaphus cf. N. kumatox Šnajdr, Reference Šnajdr1982a, pygidium, internal mold (field photograph): (8) dorsal view; (9) detail of the axis. All specimens are preserved in full relief (sandstones), except specimen (8, 9), preserved in mudstone. Scale bars = 5 mm.

Holotype

A holotype was not indicated by Hawle and Corda (Reference Hawle and Corda1847). The lectotype selected by Šnajdr (Reference Šnajdr1983, pl. 12, figs. 7, 8) is an internal and corresponding external mold of a cephalon (NM L5395–L5396) housed in the Národní Muzeum (Prague, Czech Republic).

Description

See Destombes (Reference Destombes1972, p. 60–63).

Remarks

The taxonomic problems surrounding Phacopidina quadrata and Dalmanites solitaria Barrande, Reference Barrande1852, later established as the type species of Sokhretia Hupé, 1956, have been discussed by previous authors (e.g., Šnajdr, Reference Šnajdr1984; Vaněk and Vokáč, Reference Vaněk and Vokáč1997) and will not be discussed further here. We should clarify that the identification of “Kloucekia (Phacopidina) aff. solitaria” by Destombes (Reference Destombes1972, Reference Destombes2006b) in Morocco, which we consider conspecific with the new Bofloss specimens, is due to this error and in fact the Moroccan cephala are conspecific with the “cephalon” used to define Sokhretia (a genus erected based on sclerites belonging to more than one species, including Phacopidina quadrata). Hence, the previous assignment by Destombes to Barrande's species “Kloucekia solitaria”. We consider that the Moroccan specimens are entirely comparable to Phacopidina quadrata from the Bohdalec Formation of the Czech Republic, a name that has nomenclatural priority. Similarly, we consider that several specimens figured as “Sokhretia solitaria” by Vaněk and Vokáč (Reference Vaněk and Vokáč1997), either cephala or pygidia, may belong to Phacopidina quadrata (see synonymy).

Our material adds little to the very good documentation of Phacopidina quadrata in Morocco by Destombes (Reference Destombes1972), except perhaps the morphology of the cephalic doublure (Fig. 4.2, 4.4). Destombes and Henry (Reference Destombes and Henry1987) considered “Kloucekia (Phacopidina) aff. solitaria” (= P. quadrata) to be closely related to Baniaspis globosa Destombes, Reference Destombes1972. Nevertheless, several characters used by these authors as evidence of a Calmoniidae relationship for Baniaspis (e.g., the small anteriorly located eye, the absence of palpebral lobe, the frontal glabellar lobe not limited anterolaterally and merging with genae) are not present in P. quadrata. In all these characters, P. quadrata differs from B. globosa and is entirely comparable to Crozonaspis. However, the organized pattern of frontal lobe auxiliary impressions is similar in B. globosa and P. quadrata, and this morphological detail can be seen both in the Moroccan specimens (Destombes and Henry, Reference Destombes and Henry1987, fig. 7) and in the Czech specimens from the Bohdalec Formation (Šnajdr, Reference Šnajdr1982b, pl. 2, figs. 6–9). Nevertheless, it is doubtful that they are very different from the pattern observed in some specimens of Crozonaspis (e.g., Pereira, Reference Pereira2017, pl. 56, fig. K) or Zeliszkella (Henry, Reference Henry1980, fig. 25, fig. 7b). The pygidium of P. quadrata is extremely similar to the typical structure of younger Crozonaspis species (e.g., Henry, Reference Henry1980, pl. 42, figs. 2, 3). The pygidium of P. quadrata differs from B. globosa because the pygidial spine arises from the border instead of the rachis. Regarding the ventral structures, the hypostome of P. quadrata (Destombes, Reference Destombes1972, pl. 14, fig. 11) is indistinguishable from that of Crozonaspis struvei Henry, Reference Henry1980, bearing uniform narrow posterior and lateral borders, and middle body not overhanging the lateral border as in Baniaspis globosa (Destombes and Henry, Reference Destombes and Henry1987, fig. 5). The cephalic doublure is simple, with no auxiliary impressions, and has a convex anterior border, not flattened as in B. globosa (see Destombes and Henry, Reference Destombes and Henry1987, fig. 3C and 3D). However, these details strongly depend on preservation, and observation in one single specimen of each species is not representative.

Phacopidina quadrata shows many characters typical of Dalmanitidae and is reminiscent of Crozonaspis, whose younger species (Late Ordovician) also have obsolete S2 and S3. It is possible that P. quadrata could be more closely related to this group of dalmanitids than to Calmoniidae, independently of the relationship and systematic position of Baniaspis globosa.

Type species

Dalmanites angelini Barrande, Reference Barrande1852, from the Bohdalec Formation, upper Berounian (ca. lower Katian, Ka2), Czech Republic (? =E. galafrea Šnajdr, Reference Šnajdr1987, Bohdalec Formation, upper Berounian, Czech Republic).

Other species

Eudolatites bondoni Destombes, Reference Destombes1972, Lower Ktaoua Formation, middle Berounian, Morocco; Phacops dubius Barrande, Reference Barrande1846, Zahořany Formation, middle Berounian, Czech Republic (? = E. sumptuosus Přibyl and Vanĕk, Reference Přibyl and Vaněk1972, Vinice Formation, lower Berounian, Czech Republic); E. flavus Rábano in Gutiérrez-Marco and Rábano, Reference Gutiérrez-Marco and Rábano1987, “Lumaquelas Terminales” Member, Bancos Mixtos Formation, upper Berounian, Spain; E. hastatus Přibyl and Vanĕk, Reference Přibyl and Vaněk1972, Letná Formation, lower Berounian, Czech Republic (? = E. promura Šnajdr, Reference Šnajdr1987, Letná Formation, lower Berounian, Czech Republic); E. inflatus Destombes, Reference Destombes1972, Upper Tiouririne Formation, middle Berounian, Morocco (= ?E. karmina Šnajdr, Reference Šnajdr1987, Zahořany Formation, middle Berounian, Czech Republic).

Diagnosis

Modified from Rábano in Gutiérrez-Marco and Rábano (Reference Gutiérrez-Marco and Rábano1987, p. 71). Exoskeleton fairly convex. Anterior cephalic border absent, with well-marked lateral and posterior furrows; genal spines present or absent. Glabella claviform, with prominent frontal lobe; S1 and S2 parallel or slightly convergent adaxially. Eyes small to large (A/G = 25−35%; A/Gn = 25−40%). Hypostome with long (sag.), complete, and rounded posterior border. Thorax composed of 11 segments; pleural furrows rectilinear and distal tips pointed. Pygidium of parabolic to subcircular outline, length (sag.) similar to that of cephalon, with rounded to pointed posterior margin. Pygidial border simple or defined by a rim, with variable convexity/length. Axis well defined, narrow (tr.; ~25% of pygidial width at anterior border), with 10–15 axial rings. Pleurae with 8–12 pleural furrows (defining up to 13 ribs); pleural and interpleural furrows well marked.

Occurrence

Upper Ordovician (Sandbian to Katian) of Portugal, Spain, France, Czech Republic, Italy (Sardinia) and Morocco.

Remarks

The current state of the systematics of Eudolatites was detailed by Hammann and Leone (Reference Hammann and Leone2007). We follow these authors considering the subgenera Banilatites Destombes, Reference Destombes1972, and Destombesites Šnajdr, Reference Šnajdr1987, as junior synonyms. The characters previously considered for distinction of these subgenera, including definition of the pygidial border and pygidial axial length/width ratios, have not proved unequivocal.

Eudolatites cf. E. bondoni Destombes, Reference Destombes1972
Figure 5

Reference Destombes1972

cf. Eudolatites bondoni Destombes, p. 42–43, pl. 4, fig. 1, text-fig. 12.

?Reference Lawrence and Stammers2014

Eudolatites sp. Lawrence and Stammers, p. 264.

Reference Fortey and Edgecombe2017

Eudolatites cf. E. galafrea Šnajdr; Fortey and Edgecombe, p. 320, fig. 4A, 4B.

Reference Lebrun2018

Eudolatites (Eudolatites) sp. Lebrun, p. 143.

Figure 5. (1–17) Eudolatites cf. E. bondoni Destombes, Reference Destombes1972, from the Bofloss locality, Morocco. (1–3) Cephalon, internal mold, MGM-7692X: (1) dorsal view; (2) right lateral view; (3) anterior view; (4, 5) incomplete cephalon, latex cast of the external mold, MGM-7696X-1: (4) left lateral view; (5) dorsal view; (6, 7) cephalon, internal mold, MGM-7693X: (6) dorsal view; (7) right lateral view; (8) cephalon, internal mold, MGM-7694X: detail of the frontal lobe showing auxiliary impressions; (9) hypostome, internal mold, MGM-7702X: ventral view; (10–12) pygidium, internal mold, MGM-7697X: (10) dorsal view; (11) posterior view; (12) right lateral view; (13) pygidium, internal mold, MGM-7699X: dorsal view; (14) pygidium, internal mold, MGM-7700X: dorsal view; (15) pygidium, latex cast of the external mold, MGM-7701X: dorsal view; (16, 17) pygidium, internal mold, MGM-7696X-2: (16) dorsal view; (17) left lateral view. All specimens are preserved in full relief (sandstones), except specimens (13–15), which are preserved in mudstones (flattened). Scale bars = 5 mm.

Description

Cephalon sub-ogival in outline, sagittal length ~60% maximum cephalic width (at posterior margin). Glabella flattened in its posterior half, anterior lobe sloping downwards anteriorly; posterior glabellar width corresponding to 30–35% maximum cephalic width (at posterior margin) and 50–60% glabellar width (at frontal lobe). Axial furrows deep, narrow, diverging more strongly anterior to S1, slightly convex and deeper against L3, strongly convex anterior to S3 to surround the enlarged frontal lobe; frontal lobe width ~50–55% maximum cephalic width, bearing a median pit. Adaxial edges of glabellar furrows almost located at the same exsagittal line, simple, non-bifurcated; S3 shallower, oblique. Eyes with anterior edge opposite S3, touching the axial furrow; posterior edge varying from opposite S2 to slightly posterior to S2 (anterior third of L2), located at a distance from the axial furrow about the width (tr.) of L1; visual surface subvertical, with a regular arrangement of the lenses in about 50 dorsoventral rows, with a maximum of 14 lenses per row. Genal angle enlarged (tr., exsag.) but devoid of spine. Genae sculpture of uniformly distributed pits, absent in the palpebral lobe.

Hypostome typical of Dalmanitidae, particularly elongated (sag.), with broad (sag.), flattened and rounded (not polygonal) posterior margin and middle body with faint ornamentation.

Pygidium sub-triangular in outline; axis moderately convex, protruding pleurae; abaxial half of the pleurae flat, with the adaxial part subvertical due to a sharp bend of the pleurae. Pygidial anterior width ~80−85% of pygidial length in full-relief specimens (~70−75% in flattened ones); pygidial axis ~35% pygidial width at the anterior margin (~25% in flattened specimens); pygidial axis narrowing backwards to ~20% of anterior width (~10% in flattened specimens), ending before it reaches the pygidial margin; its posterior limit is defined by a change in its convexity, which follows the general bend of the pygidial abaxial region. Thirteen axial rings, poorly defined posteriorly (from seventh on); terminal piece rounded, almost indistinct. Nine pairs of pleural and interpleural furrows, defining nine ribs (eighteen bands with a similar length, exsag.); pleural and interpleural furrows equally deep, sub-parallel; pleural furrows end immediately abaxial to the sharp bend in the pygidial pleurae; interpleural furrows longer than pleural furrows, almost reaching the pygidial margin (a very short, tr., abaxial surface of the pygidium that is unfurrowed, but it is not defined as a rim). Outline of posterior pygidial margin gently pointed medially (it is not a true pygidial spine, just a pointed curvature).

Remarks

Currently, there is a great diversity of species described for Eudolatites, despite the relatively short stratigraphic (Berounian) and geographic (high-latitude peri-Gondwana) distribution. The genus appears to have undergone rapid speciation, with several of the defined species being reliable.

Among the Bofloss material, we have flattened specimens and specimens in full relief. Due to the sharing of very particular and significant characters by both sets of specimens (the small size and the anterior position of the eyes, the number of pygidial rings and pleural/interpleural furrows, the length and direction of pleural/interpleural furrows pairs, and the pointed pygidial margin), we assume they represent the same species. However, this is one of those cases in which flattening gives the specimens a very distinctive overall morphology, especially with regard to the pygidial axis, which appears much more imposing (sag. and tr.) in specimens in full relief than in flattened ones (compare Fig. 5.10–5.12, 5.16, 5.17 with Fig. 5.13–15.15). This is due to the “widening of the pleural areas” when their abaxial margins collapse since they were originally vertical. Hence, what most characterizes Bofloss Eudolatites species is (1) the relatively small (for this genus) and anteriorly located eyes; (2) the existence of 13 pygidial axial rings and nine pairs of pleural and interpleural furrows (defining 9 ribs/18 pleural bands), (3) the subparallel relationship between the pleural and interpleural furrows (even abaxially) and the greater length of the interpleural ones, (4) the absence of a pygidial inflated rim/border, and (5) the tipped medial termination of the pygidium. These are the only characters we judge to be useful within this genus. A sixth character, the apparently rounded genal angle (as opposed to species with a pointed genal angle), is poorly understood, but could provide an additional feature.

Among defined Eudolatites species, we can exclude a conspecific relationship with Eudolatites aff. E. dubius (documented by Destombes, Reference Destombes1972, pl. 3, fig. 1, pl. 4, figs. 2–7) because the pleural/interpleural furrows have the same length. We can exclude a conspecific relationship with Eudolatites maiderensis Destombes, Reference Destombes1972, and E. inflatus Destombes, Reference Destombes1972. because of the same character (equal pleural/interpleural length) plus the presence of a highly inflated and broad pygidial rim (Destombes, Reference Destombes1972, pl. 2, fig. 6, pl. 3, fig. 6). In addition, Eudolatites (Eudolatites) sp. described by Destombes (Reference Destombes1972, p. 43, 44, pl. 5, figs. 1–7) from the Lower Ktaoua Formation in Morocco and considered potentially conspecific with Bofloss specimens by Fortey and Edgecombe (Reference Fortey and Edgecombe2017), differs in having bigger (exsag.) eyes, fewer pygidial rings and pleural/interpleural furrows, rounded posterior pygidial margin, and, hypothetically, pointed genal angles.

The only previous occurrence of Eudolatites from Morocco that can be conspecific with Bofloss specimens is Eudolatites bondoni Destombes, Reference Destombes1972, which shares the same short and anteriorly located eyes (Destombes, Reference Destombes1972, pl. 4, fig. 1), but no pygidium is known. Given current knowledge of the genus Eudolatites, it is known that the pygidium is more diagnostic and has greater morphological variability than the cephalon. Until pygidia are documented in the type locality of E. bondoni, it is a risk to assign any other material to this species.

Therefore, to justify our assignment to Eudolatites cf. E. bondoni, it is important to clarify the relationships with species that have been defined in the Czech Republic. Šnajdr (Reference Šnajdr1987) briefly defined three new species of Eudolatites. He erected E. (Destombesites) promura from the Letná Formation, but did not differentiate it from the coeval E. hastatus because he did not include that species in his new subgenus Destombesites (to embrace species whose pygidia do not bear a posterior border). As explained in the remarks of the genus, and discussed by Hammann and Leone (Reference Hammann and Leone2007), the pygidial border is strongly affected by compaction and preservation, and there is no difference between the holotype of E. promura, figured by Šnajdr (Reference Šnajdr1987, pl. 1, fig. 1), and that of E. hastatus, figured by Přibyl and Vanĕk (Reference Přibyl and Vaněk1972, pl. 5, fig. 5). The cephala are not known or, at least, have never been figured. Therefore, E. promura is possibly a junior synonym of E. hastatus, sharing not only the same morphology, number, and configuration of pleural and interpleural furrows, but also the slightly pointed posterior pygidial margin, observed in the holotype of E. promura and described for E. hastatus by Přibyl and Vanĕk (Reference Přibyl and Vaněk1972, p. 19).

What characterizes most of the Letná Formation specimens (whether one or two species) is the configuration of pleural/interpleural furrows, being almost the same length (with interpleural furrows slightly longer anteriorly and curving backwards in their abaxial ends; see Destombes, Reference Destombes1972, pl. 3, fig. 2). The Bofloss specimens clearly differ in this character and since both are preserved in full relief, it is possible to verify that the pygidial profile is very different (E. hastatus does not have vertically truncated margins, but instead has a convex, inflated border). In the same work, Šnajdr (Reference Šnajdr1987) also erected E. galafrea, but did not differentiate it from the coeval E. angelini. Later, Vaněk and Vokáč (Reference Vaněk and Vokáč1997) tried to differentiate both, finding most of the putative differences on the cephalon, although no well-preserved cephala of E. galafrea is figured. The differences listed by Vaněk and Vokáč (Reference Vaněk and Vokáč1997, p. 38) to differentiate E. galafrea from E. angelini are seen among different specimens occurring in the same locality, thus, they are possibly not reliable, because (1) frontal lobe “highness” is preservational; (2) the presence/deepness of the frontal lobe median pit is highly dependent on preservation; (3) there is no difference between the distance of the posterior extremities of the eyes to the axial furrows in cranidia attributed to E. galafrea or to E. angelini (compare Vaněk and Vokáč, Reference Vaněk and Vokáč1997, pl. 7, figs. 3, 4, with Struve, Reference Struve1958, pl. 2, fig. 12) and the anterior eye contact with the axial furrows is exactly the same, with differences probably due to deformation (compare the anterior position of the ocular lobe on the right and on the left of the E. angelini cephalon figured by Vaněk and Vokáč, Reference Vaněk and Vokáč1997, pl. 6, fig. 8); (4) no free cheek of E. galafrea is shown by Vaněk and Vokáč, Reference Vaněk and Vokáč1997 (pl. 7, fig. 3, 4) and this feature will depend on the size of the eye (variable within the same population) and on deformation (just as the position of the anterior part of the eye in relation to the axial furrow); (5) the genal angle is often deformed/incomplete and it is comparable in figured cephala of E. angelini and E. galafrea (compare Vaněk and Vokáč, Reference Vaněk and Vokáč1997, pl. 6, fig. 8 and pl. 7, fig. 3); (6) the pygidial “inflated” rim depends on preservation, and the pygidial margin is entirely comparable in both specimens (compare Vaněk and Vokáč, Reference Vaněk and Vokáč1997, pl. 10, fig. 7 with Přibyl and Vanĕk, Reference Přibyl and Vaněk1972, p. 19, pl. 5, fig. 4); (7) the pygidial rachis bear the same number of rings (about 15); (8) the path and relationship between the pleural and interpleural furrows are the same in both “species”; and (9) since the relation between the articulating or inter-ring furrow and the pleural and interpleural furrows of at least half of the pygidial axis is clear, it is very doubtful that E. galafrea has five ribs fewer than E. angelini, although according to Vaněk and Vokáč (Reference Vaněk and Vokáč1997) the former has more axial rings than the latter. All figured E. galafrea pygidia are incomplete (Šnajdr, Reference Šnajdr1987; Vaněk and Vokáč, Reference Vaněk and Vokáč1997), so we cannot calculate the total number of pygidial furrows, and among specimens documented as belonging to E. angelini (e.g., Vaněk and Vokáč, Reference Vaněk and Vokáč1997, pl. 7, fig. 2) there are pygidia with the same number of ribs as described by these authors for E. galafrea.

Although it is not implausible that there may be more than one species of Eudolatites per lithostratigraphic unit in the Czech Republic, so far, the arguments and documentation presented are neither convincing nor reliable. As far as it is possible to ascertain, E. galafrea seems to be a junior synonym of E. angelini. In any case, specimens from the Bohdalec Formation have a higher number of pygidial axial rings and pleural/interpleural furrows than the specimens from Bofloss. Previously, Fortey and Edgecombe (Reference Fortey and Edgecombe2017) assigned Bofloss specimens, in open nomenclature, to E. galafrea, but admitted major doubts given the need for revision of several species. Nevertheless, the E. galafrea holotype, a pygidium with a well-preserved posterior border (Šnajdr, Reference Šnajdr1987, pl. 1, fig. 2), has no evidence of the medial pygidial point characteristic of the Moroccan specimens. Only a few specimens assigned to E. angelini show a very subtle angulate margin (e.g., Barrande, Reference Barrande1952, pl. 23, fig. 21; Přibyl and Vanĕk, Reference Přibyl and Vaněk1972, pl. 5, fig. 3), but clearly bearing a higher number of pleural/interpleural furrows (12 pairs instead of only 8–9).

Šnajdr (Reference Šnajdr1987) also erected the species Eudolatites karmina in the Zahořany Formation of the Czech Republic, considering it to be closely related to E. inflatus from Morocco. Although he listed several differences, they are not relevant within the genus because they are all related to preservation (e.g., S3 outline, vaulting of the cephalic border, pitting of the genal field, granulose sculpture), and he did not figure any cephalon. As far as can be observed in the existing figures of E. karmina, it is probably a junior synonym of E. inflatus.

Finally, there are E. sumptuosus and E. dubius from the Vinice and Zahořany formations, respectively. When defining E. sumptuosus, Přibyl and Vanĕk (Reference Přibyl and Vaněk1972) did not differentiate it from E. dubius. Later, Šnajdr (Reference Šnajdr1990, p. 240–241) figured the E. sumptuosus holotype as belonging to E. dubius, thus, as stated by Hammann and Leone (Reference Hammann and Leone2007), we assume he considered both to be synonyms. They probably are, but there are not enough published records of specimens from the Zahořany Formation and the Vinice Formation to allow a decision. As far as we can tell, E. dubius is quite similar to the Bofloss specimens, and at first analysis we attributed them, in open nomenclature, to the Czech species (Pereira et al., Reference Pereira, Rábano and Gutiérrez-Marco2020) because they share an equivalent number of pygidial axial rings and pleural/interpleural furrows, with a similar configuration, and, according to Přibyl and Vanĕk's (Reference Přibyl and Vaněk1972, p. 18–19) description for E. sumptuosus, the pygidial rachis extends to the pygidial margin, as in Bofloss specimens. However, an important and very characteristic feature of the Moroccan material, which should have significance within the genus since there are species with rounded edges and others with angulate-shaped ones, is the permanent presence of a medial pointed termination of the pygidium. Although remnants of a tendency to develop this tip are present (e.g., in E. hastatus of the Letná Formation), and an angular border is present in E. maiderensis from the Upper Ktaoua Formation, no known species presents a comparable spine-like margin like the Bofloss specimens. This differentiates the Moroccan material from E. dubius, a species that not only has the most subcircular edge, but even flattens out in the medial zone (see Barrande, Reference Barrande1852, pl. 26, fig. 40, and Přibyl and Vanĕk, Reference Přibyl and Vaněk1972, pl. 4, fig. 1). On the other hand, and although this character is variable and very few specimens of E. dubius are known, some have extremely big eyes, their posterior ends reaching S1, a condition never observed in Bofloss specimens.

Finally, the Bofloss specimens are different from the Iberian species E. flavus, from the Bancos Mixtos Formation in Spain, the latter having genal spines, a rounded pygidial margin, and pleural/interpleural furrows of same length, converging posteriorly. In addition, a new Eudolatites species described in an unpublished PhD thesis by Pereira (Reference Pereira2017) in the Cabeço do Peão Formation of Portugal also has a rounded pygidial margin and pleural/interpleural furrows of same length.

In view of the impossibility of a confident assignment of our specimens to defined Eudolatites species but wanting as far as possible to avoid erection of new species that might prove to be synonyms later and increase the taxonomic chaos, we decided to identify our material in open nomenclature as Eudolatites cf. E. bondoni. As previously discussed, only cephala are known, but the cephala agree with our material in all the characters, including the quite small and anterior position of the eyes. This species also occurs in the same geological area of Morocco and, putatively, in coeval levels (“Caradocien moyen−supérieur” sensu Destombes, Reference Destombes1972). It will be necessary to describe pygidia from the type locality of E. bondoni to verify if they agree with the morphology of the Bofloss specimens: if so, one can refine the nomenclature and much better characterize the species of Destombes (Reference Destombes1972). If not, the Bofloss specimens should be formalized as a new species.

Type species

Prionocheilus verneuili Rouault, Reference Rouault1847, from the Riadan Formation, middle Berounian (ca. upper Sandbian/lower Katian), Armorican Massif, France.

Other species

See Pereira (Reference Pereira2017, p. 453).

Diagnosis

See Whittard (Reference Whittard1960, p. 132).

Occurrence

Ordovician (Floian–Hirnantian) of Portugal, Spain, France, Italy (Sardinia), Czech Republic, Morocco, Turkey, Sweden, Norway, Estonia, United Kingdom, Uzbekistan, Kazakhstan, China, USA, Canada, and Argentina.

Remarks

Hammann (Reference Hammann1992, p. 94–95) and Hammann and Leone (Reference Hammann and Leone2007 p. 128−133) made extended remarks on Prionocheilus occurrences, to which we refer.

Remarks

One single incomplete cephalon with thorax (Fig. 4.7) is too poorly preserved to allow a specific identification. Although the glabellar lobation and the external surface sculpture are comparable to those of the species-group from the Upper Ordovician of the high-latitude peri-Gondwanan domain—P. borni Vaněk, Reference Vaněk1995, from the Bohdalec Formation (upper Berounian) of the Czech Republic, P. pulcher (Barrande, Reference Barrande1846) from the Zahořany Formation (middle Berounian) of the Czech Republic, and the type species P. verneuili from the Riadan Formation (middle Berounian) of France—it is too poorly preserved for further discussion. For this reason, we also base the discussion and identification of Prionocheilus cf. P. verneuili on two additional specimens from the same locality that were observed during this work. The presence of six pygidial pleural ribs (instead of seven) excludes P. borni and relates the Moroccan occurrences to P. verneuili and P. pulcher. These species are differentiated by an apparently longer (sag.) preglabellar area in the former, although this character is highly dependent on preservation. The figured specimen does not preserve the preglabellar area, but the remaining observed ones are comparable with those documented by Destombes (Reference Destombes1966, p. 39–40, pl. 4, figs. 1–6) from the Upper Tiouririne Formation (upper Berounian, ca. lower Katian, Ka2) of Morocco. Although he assigned these occurrences to P. pulcher, he noted that the preglabellar field of the Moroccan specimens is larger (in relation to the anterior border) than in the Czech specimens. For this reason, the Moroccan specimens are here considered to be more closely related to P. verneuili, but additional specimens are necessary to strengthen this identification.

Type species

Asaphus nobilis Barrande, Reference Barrande1846, from the Zahořany Formation, middle Berounian (ca. upper Sandbian–lower Katian, Sa2–Ka1), Czech Republic.

Other species

See Gutiérrez-Marco et al. (Reference Gutiérrez-Marco, Pereira, García-Bellido and Rábano2022b, p. 122).

Diagnosis

See Hughes (Reference Hughes1979, p. 117).

Occurrence

Occurrence. Middle to Upper Ordovician (Darriwilian to upper Katian) of Portugal, Spain, France, Czech Republic, Morocco, Italy (Sardinia), Turkey, Wales, ?Belgium, Germany, Tajikistan, Afghanistan, and ?Syria.

Remarks

We follow Fortey et al. (Reference Fortey, Wernette and Hughes2022, p. 317), who considered that Nobiliasaphinae Balashova, Reference Balashova1971, falls within the Birmanitinae, which is the oldest available name for this asaphid group. Fortey et al. (Reference Fortey, Wernette and Hughes2022, p. 318) also considered that Ogygites Tromelin and Lebesconte, Reference Tromelin and Lebesconte1876, is the senior synonym of Nobiliasaphus, but this is one of those cases that we consider should not follow the rule of nomenclatural priority for reasons of taxonomic stability because Nobiliasaphus is has been a very firm and well-documented name in the trilobite nomenclature and bibliography for decades. As was discussed by Rábano (Reference Rábano1989), the type species of Ogygites, O. desmaresti (Brongniart, Reference Brongniart, Brongniart and Desmarest1822), is based on an unrecognizable fragment and the species should be restricted to its holotype by monotypy (Rábano, Reference Rábano1989, fig. 9). Ogygites originally was proposed as a replacement name for Ogygia Brongniart in Desmarest, Reference Desmarest1817, a name that was pre-occupied by a lepidopteran. Its original first-named species, “Ogygia” guettardi Brongniart in Desmarest, Reference Desmarest1817 (Brongniart, Reference Brongniart, Brongniart and Desmarest1822), clearly shows the characters of Nobiliasaphus. Nevertheless, the subsequent designation of O. desmaresti as the type species of Ogygites (Œhlert, Reference Œhlert1903; ICZN, 1983) highlighted the problematic concept of this genus as well, and strongly supports that Nobiliasaphus should be considered a nomen protectum.

Type species

Egle rediviva Barrande, Reference Barrande1846, from the Vinice Formation, middle Berounian, in Trubín, Beroun, Czech Republic.

Remarks

Hammann and Leone (Reference Hammann and Leone1997, p. 73–76) widely discussed the current state of knowledge of the genus Cyclopyge at that time. As noted by these authors and discussed previously by Zhou et al. (Reference Zhou, McNamara, Wenwei and Tairong1994), many Middle and Upper Ordovician species defined for Cyclopyge may be synonyms. We totally avoid differentiation based on pygidial and cranidial outline, expressed as length/width ratio. As Hammann and Leone (Reference Hammann and Leone1997, p. 72) stated, it is “… conspicuous fact that in many places several species comprising both glabellar types are described as coexisting in the same bed.” Other characters, especially those related to sculpture details or faint furrows/elevations, are very sensitive to deformation or type of preservation and should be avoided for differentiation of species as well. Cyclopygids are very conservative (Fortey and Owens, Reference Fortey and Owens1987; Adrain et al., Reference Adrain, Edgecombe, Zhou, Fortey, Hammer, Webby, Droser and Paris2004), so it would not be expected for these types of general characters to change reliably at a species level. Differentiating species based solely on different locations/lithostratigraphic units may create a sense of organizational comfort, but it serves no systematic purposes. Ontogeny, on the other hand, may play a relevant role in these characters and even among holaspides, because size can justify slight differences, as demonstrated by Tripp et al. (Reference Tripp, Zhou and Pan1989) for Cyclopyge occurrences from the Tangtou Formation (China), which led them to conclude that only one extremely variable species was present.

We reject Hammann and Leone's (Reference Hammann and Leone1997) revival of Phylacops Cooper and Kindle, Reference Cooper and Kindle1936, as a subgenus of Cyclopyge to embrace species with frontally fused eyes. As Karim (Reference Karim2009) noted, there is no phylogenetic understanding of the nature of anteriorly fused eyes (synophtalmy sensu Marek, Reference Marek1961) among cyclopygids and this character is unknown for many of the species. Thus, the supposition that eyes changed from separated to fused through time (e.g., Marek, Reference Marek1961; Hammann and Leone, Reference Hammann and Leone1997), and that this trend has phylogenetic significance, is not possible to verify. Furthermore, it is likely that ontogeny, already in holaspid stages, implies variation in the completeness of optical organs for the same species (see for instance the variation in Cyclopyge recurva Lu, Reference Lu and Wang1962, figured by Zhou et al., Reference Zhou, Zhou and Xiang2016, pl. 40, figs. 4, 6, pl. 41, fig. 4, and see remarks on Cyclopyge cf. C. rediviva below). The best way to overcome these difficulties is to have a very large number of co-occurring specimens (not always possible) and start from the assumption that only one single species of the same genus is represented in the same levels/localities (see discussion about Cyclopyge species from Kazakhstan in Hammann and Leone, Reference Hammann and Leone1997, p. 72). Frequently, even when having several specimens, only a few show the anterior configuration of the eyes. It is therefore difficult to know whether this character is fixed for all adult individuals, or if it has a larger range of morphological variability, as shown by Zhou et al. (Reference Zhou, Zhou and Xiang2016) for Cyclopyge recurva from the Pagoda Formation (China).

Cyclopyge cf. C. rediviva (Barrande, Reference Barrande1846)
Figures 6, 7

cf. Reference Barrande1846

Egle rediviva Barrande, p. 34.

cf. Reference Marek1961

Cyclopyge rediviva (Barrande); Marek, p. 19–21, pl. 1, figs. 1–6, text-fig. 4.

Reference Fortey and Edgecombe2017

Cyclopyge sibilla Šnajdr; Fortey and Edgecombe, p. 316, 318, fig. 3A–H.

Reference Lebrun2018

Degamella sandinoae Corbacho [sic]; Lebrun, p. 137, fig. C.

Reference Schoenemann and Clarkson2023

Cyclopyge sibilla Šnajdr; Schoenemann and Clarkson, figs. i–p.

Figure 6. (1–6) Cyclopyge cf. C. rediviva (Barrande, Reference Barrande1846) from the Bofloss locality, Morocco. (1) Two exoskeletons, latex cast of internal (MGM-7704X-1a, left) and external (MGM-7704X-2a, right) molds: dorsal view, showing traces of the visual surfaces; (2) exoskeleton (center), meraspis thorax with pygidium (upper left) and cephalon (lower right), internal and external molds, MGM-7705X-1, MGM-7705X-3, and MGM-7705X-2, respectively: dorsal and anterior views; (3–5) exoskeleton, internal mold, MGM-7706X: (3) dorsal view; (4) anterior view; (5) right lateral view; (6) visual surface and cephalic doublure, latex cast of the external mold, MGM-7707Xa: anteroventral view. Specimens (3–5) are preserved in full relief (sandstones); the remaining specimens are preserved in mudstones, flattened. Scale bars = 5 mm.

Figure 7. (1–11) Cyclopyge cf. C. rediviva (Barrande, Reference Barrande1846) from the Bofloss locality, Morocco. (1) Exoskeleton, internal mold, MGM-7708X: dorsal view; (2) exoskeleton, internal mold, MGM-7709X: dorsal view; (3) exoskeleton, latex cast of the external mold, MGM-7710Xa: dorsal view; (4–6) cephalon, internal mold, MGM-7711X: (4) dorsal view; (5) right lateral view; (6) anterior view; (7) cephalon, internal mold, MGM-7712X-1: anterior view; (8) visual surface and cephalic doublure, internal mold, MGM-7712X-2: anteroventral view; (9, 10) visual surface and cephalic doublure, internal mold, MGM-7713X: (9) anteroventral view; (10) anterior view; (11) thorax with pygidium, internal mold, MGM-7714X: dorsal view. Specimens (1–2) and (11) are preserved in mudstones, flattened; the remaining are preserved in full relief (sandstones). Scale bars = 2 mm.

Addenda to description

Fortey and Edgecombe (Reference Fortey and Edgecombe2017, p. 316) described in good detail specimens from the same beds, so we will only add additional morphological details, given the varied, complete, and well-preserved material available to us. Among holaspides, there is a tendency for the cranidium to become progressively more pointed anteriorly. This also led to an increase in the cranidial length/width ratio, which varies from ~105–110% in smaller holaspides and up to 120% in larger ones. In anterior view, the cranidium is rhomboid-shaped, extremely convex (sag.), and surrounded by the eyes, also very convex (laterally) and vertically positioned. The extreme anterior elongation of the cranidium separates the eyes, so in larger specimens the eyes seem prevented from meeting medially. In anterior–ventral view, the eyes meet medially to form an optical surface with an infinity symbol outline. The completeness of the fusion of the eyes is variable and hard to evaluate: in full-relief specimens, the coarser-grain preservation makes it difficult to see the medial edge of the eyes (e.g., Fig. 7.6. 7.7, 7.10); in the flattened specimens preserved in mudstones, it is not clear if the eyes are conjoined medially or not, if there are missing lenses due to exfoliation, of if they just meet but are not conjoined (e.g., Fig. 6.2). Thus, it seems that in some specimens they barely touch each other, which makes it possible to differentiate the right and the left eye and a very narrow depressed band (groove) between them. Other specimens do seem to have fused eyes, with very few lenses shared (2–3 lenses at the median suture). There are ~55 gently arched vertical rows of lenses, bearing a maximum of 27 lenses in the middle (widest) part of the eye. The lenses become larger towards the upper part of the eye (Fig. 6.6). Doublure subtriangular, developing a small medial depression at the contact with the eye, its posterior margin (ventrally) is subtransverse, embayed medially (median depression). The pygidium bears a very weak and narrow sagittal ridge, rarely visible, which starts at the posterior end of the pygidial axis, disrupting the axial furrow, and ends at the posterior margin (Figs. 6.2, 7.2, 7.11).

Remarks

The Moroccan material agrees with the description of Barrande (Reference Barrande1852) and Marek (Reference Marek1961) for Cyclopyge rediviva from the Vinice Formation of the Czech Republic. Fortey and Edgecombe (Reference Fortey and Edgecombe2017) assigned these Moroccan occurrences to Cyclopyge sibilla Šnajdr, Reference Šnajdr1982a, a species defined in the Bohdalec Formation of the Czech Republic. As previously noted by Hammann and Leone (Reference Hammann and Leone1997) and Fortey and Edgecombe (Reference Fortey and Edgecombe2017), this species was erected by Šnajdr (Reference Šnajdr1982a) solely based on a non-diagnostic transitory pygidium, following the dangerous assumption that specimens from a distinct lithostratigraphic unit will potentially be different species. Later, Vaněk and Vokáč (Reference Vaněk and Vokáč1997) described holaspid specimens from the Bohdalec Formation and proposed a differentiation between C. sibilla and C. rediviva based on the absence of very fine terrace lines and a post-axial ridge in the pygidium of the former, the Bohdalec Formation form. For all the remaining characters, they largely copied Marek's (Reference Marek1961, p. 19–21) description of C. rediviva (Vaněk and Vokáč, Reference Vaněk and Vokáč1997, p. 27). As demonstrated for the material studied here, and as is clear from various studies on Cyclopyge (e.g., Zhou et al., Reference Zhou, McNamara, Wenwei and Tairong1994; Hammann and Leone, Reference Hammann and Leone1997), these features strongly depend on preservation and, indeed, the diagnostic characters of C. sibilla also are observed in many specimens of C. rediviva from the Vinice Formation, including the holotype, which preserves neither the terrace lines nor the pygidial ridge (Horný and Bastl, Reference Horný and Bastl1970, pl. 7, fig. 3). Furthermore, two “C. sibilla” specimens, a holaspid and a meraspid pygidium figured by Vaněk and Vokáč (Reference Vaněk and Vokáč1997, pl. 2, figs. 1, 7), bear the pygidial postaxial ridge. Other specimens (Vaněk and Vokáč, Reference Vaněk and Vokáč1997, pl. 2, figs. 6, 8) also show the second pair of pygidial ribs, a very characteristic feature of C. rediviva described by Marek (Reference Marek1961). Therefore, we consider C. sibilla a junior synonym of C. rediviva.

One of the major difficulties related to C. rediviva is that, despite the existence of abundant specimens from the Vinice Formation, the species is not properly documented. The description presented by Marek (Reference Marek1961) is insufficient for some details, particularly regarding the eye configuration. Marek (Reference Marek1961) indicated that the eyes are not conjoined medially, their anterior ends at a distance of one-third of the total cephalic width from each other. This large distance is highly unlikely. Knowing that even in very well-preserved material it is difficult to observe the contact between the eyes, which occurs ventrally, it is very difficult to know the true morphology of the optical organ of Cyclopyge rediviva from its type unit, the Vinice Formation. There is no figured specimen showing the anterior–ventral cephalic view. For this reason, the Bofloss specimens, even if so well preserved and known in detail, have to be left in open nomenclature until the optical organ of C. rediviva from the Vinice Formation is properly documented and it is demonstrated to have the same morphology and variability as shown here for the Moroccan specimens.

We agree with Fortey and Edgecombe (Reference Fortey and Edgecombe2017) that Moroccan specimens may be conspecific with Cyclopyge cf. C. recurva described by Zhou et al. (Reference Zhou, McNamara, Wenwei and Tairong1994) from Tarim, China. Both share the same diagnostic characters and differ from C. recurva from the Pagoda Formation of China (see Zhou et al., Reference Zhou, Zhou and Xiang2016) in having a significantly shorter pygidial axis. This short pygidial axis is very diagnostic within Cyclopyge, being a confident character to differentiate C. rediviva from several other species, such as the slightly younger C. marginata Hawle and Corda, Reference Hawle and Corda1847, from the Czech Republic (also described by Hammann and Leone, Reference Hammann and Leone1997, in Sardinia). As noted by Fortey and Edgecombe (Reference Fortey and Edgecombe2017), among the several Cyclopyge species defined by Koroleva (Reference Koroleva1967) in Kazakhstan (see Hammann and Leone, Reference Hammann and Leone1997, p. 72–75), there may be synonyms of “C. sibilla”/C. rediviva, but the latter will always take priority.

Recently, these Moroccan occurrences have come to prominence because Schoenemann and Clarkson (Reference Schoenemann and Clarkson2023) have documented possible median eyes in meraspides, which previously were unknown in trilobites but present in all other arthropods.

Type species

Aeglina armata Barrande, Reference Barrande1852, from the Králův Dvůr Formation, Kralodvorian (ca. upper Katian, Ka3–4), Czech Republic.

Diagnosis

See Marek (Reference Marek1961, p. 54).

Remarks

Except for the older species, Symphysops mitratus (Novák, Reference Novák1883) and Symphysops sulcatus (Barrande, Reference Barrande1872), which are known from the Middle Ordovician of the Czech Republic, there is much doubt as to the validity of the various forms described in the upper Katian (see Hammann and Leone, Reference Hammann and Leone1997, p. 80, 84–85; Owen and Bruton, Reference Owen and Bruton2012, p. 979). This is another of the genera of trilobites that became widespread during the late Katian, which previously seems to have originated and lived in an area that was limited to the peri-Gondwanan realm (see Colmenar et al., Reference Colmenar, Pereira, Pires, da Silva, Sá and Young2017, p. 452). Symphysops records prior to the late Katian from other than the Czech Republic (and now, Morocco) are doubtful, although some possibly are assignable to the closely related genus Pricyclopyge Richter and Richter, Reference Richter and Richter1954 (e.g., Zhou et al., Reference Zhou, Zhou and Xiang2016, p. 197, pl. 50, fig. 19). Unfortunately, in the Czech Republic there is a major gap between the oldest records, from the middle−upper Darriwilian Šárka Formation, and those from the upper Katian Králův Dvůr Formation. The genus was reported by Vanĕk (Reference Vaněk1995, pl. 2, fig. 1) in the Dobrotivá Formation (Dobrotivian, upper Darriwilian) as the species S. psyche Vanĕk, Reference Vaněk1995, for which, as far as it is possible to observe, not only is the figured pygidium unobservable and undiagnostic, but it also is doubtful if it could correspond to Pricyclopyge longicephala (Klouček, Reference Klouček1916), which is known from the same unit. In the Berounian (Sandbian–lower Katian) the genus was not known before, so the Moroccan record is important for understanding the early history of Symphysops.

Symphysops stevaninae López-Soriano and Corbacho, Reference López-Soriano and Corbacho2012
Figures 8, 9.1–9.4

Reference López-Soriano and Corbacho2012

Symphysops stevaninae López-Soriano and Corbacho, p. 2–4, pl. 1, figs. 1–3, pl. 2, figs. 1–6.

Reference Bonino and Kier2010

Symphysops sp. Bonino and Kier, p. 102, figs. b, c.

Reference Lebrun2018

Symphysops stevaninae López-Soriano and Corbacho; Lebrun, p. 137, figs. A–C.

Figure 8. (1–10) Symphysops stevaninae Lopéz-Soriano and Corbacho, Reference López-Soriano and Corbacho2012, from the Bofloss locality, Morocco. (1) Exoskeleton, internal mold, MGM-7731X: dorsal view; (2) exoskeleton, latex cast of the external mold, MGM-7732X: dorsal view; (3) incomplete cephalon with thorax, internal mold, MGM-7739X: dorsal view; (4) thorax with pygidium, latex cast of the external mold, MGM-7691X: dorsal view; (5, 6) cranidium, latex cast of the external mold, MGM-7733X: (5) dorsal view; (6) anterior view; (7) cranidium, internal mold, MGM-7734X: dorsal view, (8) pygidium, internal mold, MGM-7740X: dorsal view; (9, 10) cranidium, internal mold, MGM-7735X: (9) dorsal view; (10) left lateral view. Specimens (1–4) are preserved in mudstones, flattened; the remaining specimens are preserved in full relief (sandstones). Scale bars = 5 mm.

Figure 9. (1–4) Symphysops stevaninae Lopéz-Soriano and Corbacho, Reference López-Soriano and Corbacho2012, from the Bofloss locality, Morocco. (1, 2) Visual surface and cephalic doublure, internal mold, MGM-7737X: (1) ventral view; (2) anterior view; (3, 4) visual surface and cephalic doublure, latex cast of the external mold, MGM-7738X: (3) oblique ventral view; (4) oblique left anteroventral view. (5) Dionide sp. from the Bofloss locality, Morocco. Incomplete cephalon with thorax, internal mold, MGM-7671X-2: dorsal view. All specimens preserved in full relief (sandstones). Scale bars = 5 mm.

Holotype

López-Soriano and Corbacho (Reference López-Soriano and Corbacho2012) selected two holotypes, which is contrary to the ICZN recommendation. Here we designate as the lectotype the cephalon, an internal mold (López-Soriano and Corbacho, Reference López-Soriano and Corbacho2012, pl. 2, fig. 5) housed in the Back to the Past Museum (Cancún, México) with the registration number BPM1029.

Diagnosis

Smooth glabella, with almost indistinct glabellar impressions; eyes conjoined, with about 17 lenses medially. Pygidial axis with one ring and a subtriangular terminal piece.

Remarks

These Moroccan Symphysops occurrences were previously considered to represent a new species, S. stevaninae, by López-Soriano and Corbacho (Reference López-Soriano and Corbacho2012). Most of the differences pointed out by the authors are not valid, but after a detailed analysis of available specimens as well as the extensive remarks made by previous authors concerning the widespread occurrences of the genus in the upper Katian (e.g. Kielan, Reference Kielan1960; Marek, Reference Marek1961; Knüpfer, Reference Knüpfer1967; Owen and Ingham, Reference Owen and Ingham1996; Hammann and Leone, Reference Hammann and Leone1997; Shaw, Reference Shaw2000; Owen and Bruton, Reference Owen and Bruton2012), we consider that, potentially, the upper Sandbian–lower Katian (Sa2–Ka2) Moroccan specimens represent a distinct species, for which the name S. stevaninae must be used. However, if there were not an already established name for these occurrences, it would be equally sensible to assign our material to the type species S. armatus, which, as discussed by López-Soriano and Corbacho (Reference López-Soriano and Corbacho2012), may even prove to be the only valid species in the upper Katian, as a senior synonym of several others, such as S. subarmatus (Reed, Reference Reed1914), S. subarmatus elongatus Kielan, 1959, or S. spiniferus Cooper and Kindle, Reference Cooper and Kindle1936. Other occurrences (e.g., Kolova, Reference Kolova1936; Apollonov et al., Reference Apollonov, Bandaletov and Nikitin1980; Vanĕk, Reference Vaněk1995; Ghobadi Pour et al., Reference Ghobadi Pour, McCobb, Owens and Popov2011) are too poorly known to discuss about such a conservative cyclopygid, and we do not think any of those are conspecific with S. stevaninae.

Our collection includes specimens in full relief and flattened, that largely support the views of Hammann and Leone (Reference Hammann and Leone1997) and Owen and Bruton (Reference Owen and Bruton2012), who considered the features related to the cranidium outline and vaulting to be highly susceptible to distortion and other preservational effects. In body proportions (cephalon/thorax/pygidium/axis), in cephalic and pygidial outline, in the thorax morphology, including the elongated tip of the first thoracic segment as well as in the location of glabellar furrows and the position of the median tubercle, Moroccan specimens are indistinguishable from the type species S. armatus from the Králův Dvůr Formation and from S. subarmatus/S. subarmatus elongatus/S. spiniferus from the upper Katian of Girvan, Scotland (Owen and Ingham, Reference Owen and Ingham1996), Poland (Kielan, Reference Kielan1960), or Quebec, Canada (Cooper and Kindle, Reference Cooper and Kindle1936). The Bofloss specimens have two features that differentiate them: (1) the glabellar furrows/impressions are almost imperceptible, rarely observable even in very well-preserved specimens; and (2) the pygidium has only one single ring defined plus a subtriangular terminal piece. We are aware that these characters depend on taphonomy, to a certain extent, but they do seem stable and consistent, especially the obsolete glabellar furrows. It is very rare to observe the glabellar impressions on Moroccan specimens, especially on full relief material. As Marek (Reference Marek1961) noted, S. armatus glabellar furrows are quite distinct, and even in highly deformed material, such as that described by Hammann and Leone (Reference Hammann and Leone1997, pl. 10, figs. 1, 5, 8) from Sardinia, these are very well incised. The older representatives of Symphysops (S. mitratus and S. sulcatus) also have these furrows, albeit much less incised (Marek, Reference Marek1961, p. 58), and the closely related genus Pricyclopyge also has a smooth glabella, with almost imperceptible impressions, suggest this character to be relevant within the lineage. As noted by Fortey and Owens (Reference Fortey and Owens1987, p. 180), Symphysops has well-developed glabellar muscle impressions compared to Pricyclopyge. In this sense, S. stevaninae, which is older than the widespread S. armatus, may indeed represent a different Symphysops species.

López-Soriano and Corbacho (Reference López-Soriano and Corbacho2012) described the pygidial axis segmentation in S. stevaninae as bearing one single ring and a triangular terminal piece. Nevertheless, one of the specimens figured by these authors (López-Soriano and Corbacho, Reference López-Soriano and Corbacho2012, pl. 1, fig. 2) clearly shows two axial rings plus a terminal piece. Whether this character is real or resulted from fossil preparation, we do not know. Among our material, no pygidium preserves any traces of a second axial ring, not even well-preserved external molds. Other specimens of Symphysops from Morocco, but whose exact geographical and lithostratigraphic provenance is not known, also show two rings (e.g., Bonino and Kier, Reference Bonino and Kier2010, pl. 15, fig. c; Lebrun, Reference Lebrun2018, p. 137, figs. A, B). But apart from these specimens, which show mechanical preparation, there are several specimens, including our “raw” materials, with no traces at all of a second ring, not even when delicate features, such as fine terrace ridges, are preserved.

On the other hand, Marek (Reference Marek1961) described three pygidial axial rings plus a terminal piece for S. armatus, and although only the first ring is distinctively separated, this pygidial segmentation is quite distinct and observed in all the other upper Katian records of the genus (e.g., Kielan, Reference Kielan1960; Owen and Ingham, Reference Owen and Ingham1996). Finally, when comparing the detail of the number of lenses in the medial line in Bofloss specimens and, for example, in S. armatus from Sardinia (Hammann and Leone, Reference Hammann and Leone1997), they both have 17 lenses medially (Fig. 9.2). In S. armatus type material, as far as it is possible to count the lenses in the lectotype figured by Marek (Reference Marek1961, pl. 6, fig. 2) and Horný and Bastl (Reference Horný and Bastl1970, pl. 7, fig. 4), there is also approximately the same number of lenses medially. One specimen from the Upper Ordovician of Morocco, identified as S. armatus by Lawrence and Stammers (Reference Lawrence and Stammers2014, p. 270), for which the provenance is impossible to identify based on the transliteration of the name (“Kharkhize”), the eyes are not conjoined medially. Whether this represents another, putatively older, Symphysops species, or results from poor fossil preparation, is impossible to know. It would not be unlikely, since Pricyclopyge, a closely related genus, is characterized by having separate eyes.

To summarize, S. stevaninae diagnostic characters are not definite, but considering the knowledge about this particular group of cyclopygids (Pricyclopyginae of Fortey and Owens, Reference Fortey and Owens1987, p. 179), we do think they may be relevant. If these differences are real, they could justify the fact that Symphysops has not yet been documented in the Berounian (Sandbian–lower Katian) of the Czech Republic, since isolated cephala, without preservation of the stout frontal spine, are unlikely to be identified as belonging to the genus because they are smooth, with no traces of the characteristic glabellar furrows.

Remarks

Two other cyclopygid genera possibly occur in the studied Declivolithus assemblage of Morocco, but no additional specimens were collected during this work. These are Heterocyclopyge Marek, Reference Marek1961 (type species Cyclopyge pachycephala Hawle and Corda, Reference Hawle and Corda1847, from the Vinice Formation, middle Berounian of the Czech Republic) and Degamella Marek, Reference Marek1961 (type species Aeglina princeps Barrande, Reference Barrande1872, from the Dobrotivá Formation, Dobrotivian of the Czech Republic). These records are based on previous authors. Fortey and Edgecombe (Reference Fortey and Edgecombe2017, p. 318–319, fig. 3I, J) identified, described, and discussed Heterocyclopyge sp. Although only a thorax with pygidium was available, we agree it mainly recalls Heterocyclopyge pachycephala (see Horný and Bastl, Reference Horný and Bastl1970, pl. 7, fig. 7). Were it not for the adult size (> 1 cm) of the specimen, it would be indistinguishable from meraspides of Cyclopyge rediviva (see Fig. 6.2).

Another specimen that hypothetically occurs with Symphysops stevaninae from an unknown locality in Morocco, identified as ?Cyclopyge sp. by Bonino and Kier (Reference Bonino and Kier2010, p. 102, fig. e) could also correspond to Heterocyclopyge. It seems to bear only five segments, and the pygidial axis looks too long (sag.) and segmented to correspond to Cyclopyge. As for the possible presence of Degamella, it is based on two specimens figured by Bonino and Kier (Reference Bonino and Kier2010, p. 102, fig. a), hypothetically coming from the same unknown Moroccan locality as the previous Heterocyclopyge, and by Lebrun (Reference Lebrun2018, p. 137, fig. D), identified as Cyclopyge sp. but clearly differing by the short (exsag.) eye, the narrow and elongate glabella, the large thoracic axis, and the smooth pygidium. That specimen came from Jbel Tijarfaïouine where it occurs with Declivolithus alfredi and Symphysops stevaninae, among other species (see Lebrun, Reference Lebrun2018, p. 138). López-Soriano and Corbacho (Reference López-Soriano and Corbacho2012, p. 1) also listed the occurrence of Degamella in an assemblage from the same area.

Type species

Dione formosa Barrande, Reference Barrande1846, from the Vinice Formation, middle Berounian (ca. upper Sandbian–lower Katian), Czech Republic.

Remarks

Only a single poorly preserved specimen is available, corresponding to a cephalon articulated to two thoracic segments (Fig. 9.5). No details of fringe pitting are preserved, and the upper lamella of the fringe is missing. On the right side, it is possible to see the marginal facial suture. Despite the poor state of preservation, the subquadrate glabella, with rounded anterior margin and narrowing backwards with two basal lateral lobes, the broad fringe, and the “inflated” first segment clearly indicate this genus.

Destombes (Reference Destombes1967) documented the genus in the Upper Ktaoua Formation (upper Katian) of Morocco, but the very incomplete state of the single specimen does not allow further comparison with coeval known species from related geographical regions. Subsequently, Corbacho et al. (Reference Corbacho, Morrison and Ait Addi2014) erected the new species Dionide carlottae Corbacho, Morrison, and Ait Addi, Reference Corbacho, Morrison and Ait Addi2014, from beds that should correlate with Bofloss strata, with a trilobite assemblage that shares most of the taxa. This species presents the same significantly reduced number of pygidial rings and pleural furrows as Dionide vokaci Vanĕk and Vonka, Reference Vaněk and Vonka2004, from the Bohdalec Formation of the Czech Republic, being possibly a junior synonym of the Czech species.

Type species

Trinucleus alfredi Želízko, Reference Želízko1906, from the Voltuš Formation, middle–upper? Berounian, Rožmitál pod Třemšínem, in the Rožmitál Block of the Czech Republic.

Remarks

Declivolithus is a very distinctive trinucleid whose strange appearance has been highlighted by previous authors (e.g., Hughes et al., Reference Hughes, Ingham and Addison1975; Shaw, Reference Shaw1995; Fortey and Edgecombe, Reference Fortey and Edgecombe2017). It is particularly large for the group, and its extremely wide fringe and long genal prolongations give it an almost harpid-like appearance. Declivolithus was placed in Trinucleinae by Hughes et al. (Reference Hughes, Ingham and Addison1975) due to its resemblance to Trinucleus Murchison, Reference Murchison1839, and Telaeomarrolithus Williams, Reference Williams1948. Later, Tripp et al. (Reference Tripp, Zhou and Pan1989) and Zhou and Hughes (Reference Zhou and Hughes1989) suggested that a group of genera closely related to Nankinolithus Lu, Reference Lu1957, including Declivolithus, may better be allied with Reedolithinae Hughes, Ingham, and Addison, Reference Hughes, Ingham and Addison1975. At that point, they preferred to maintain these forms in Trinucleinae, but assumed a probable polyphyletic condition for such a subfamily. More recently, Zhou et al. (Reference Zhou, Zhou and Xiang2016) also discussed this problem and considered that the subfamily systematics for these groups needs revision.

According to Hughes et al. (Reference Hughes, Ingham and Addison1975), who revised all Trinucleidae known at the time, Declivolithus differs from Nankinolithus in having one single external arc (E1) instead of two (E1–2). Nevertheless, as Tripp et al. (Reference Tripp, Zhou and Pan1989) stated, “early Ashgill” Nankinolithus from China, including the type species of the genus N. nankinensis Lu, Reference Lu1957, only have one external arc, E1, the same condition of Declivolithus, making it hard to tie down trustworthy morphological differences between Nankinolithus and Declivolithus. This ambiguity led to likely misidentifications of several trinucleines that were assigned to Nankinolithus, but whose possibly close relationship to Declivolithus should be considered.

A group of species currently attributed to Nankinolithus, the so-called granulatus-group (sensu Zhou and Hughes, Reference Zhou and Hughes1989), which mainly occur in Europe, resemble Declivolithus in having a much wider fringe with more arcs and rows of pits and longer genal prolongation. Nevertheless, they bear a second external arc (E2), although it is often very incomplete, only frontally developed, and may be a character derived from a condition with only one external arc (Zhou and Hughes, Reference Zhou and Hughes1989). Among these are, for example, “Nankinolithus granulatus” (Wahlenberg, Reference Wahlenberg1818) from the Upper Ordovician of Sardinia (Hammann and Leone, Reference Hammann and Leone1997, pl. 24) and Nankinolithus? sp. from the Şort Tepe Formation in the Upper Ordovician of Turkey (Dean and Monod, Reference Dean and Monod1990, fig. 8f, i). The E2 is also present in morphologically similar species assigned to Bergamia Whittard, Reference Whittard1955, including Bergamia praecedens (Klouček, Reference Klouček1916) from the Middle Ordovician of the Czech Republic. Zhou and Hughes (Reference Zhou and Hughes1989) rejected the view of Hughes et al. (Reference Hughes, Ingham and Addison1975), who considered that Bergamia praecedens should be assigned to Nankinolithus, and Shaw (Reference Shaw1995) strengthened the assignment to Bergamia but suggested that this Czech species may be the predecessor of Declivolithus. Another closely related genus is Kimakaspis Ghobadi Pour et al., Reference Ghobadi Pour, McCobb, Owens and Popov2011, also bearing an E2 arc but abaxially instead of frontally. Ghobadi Pour et al. (Reference Ghobadi Pour, McCobb, Owens and Popov2011, p. 175–176) discussed possible homology between E2 arcs in Kimakaspis and the Nankinolithus granulatus species-group. In any case, the close relationship between these taxa seems plausible.

The cephalic similarity between Declivolithus and Jianxilithus Zhang and Zhou in Lu et al., Reference Lu, Chu, Chien, Zhou, Chen, Liu, Yu, Chen and Xu1976, from the Upper Ordovician of China, has been emphasized by Zhou and Hughes (Reference Zhou and Hughes1989) and Zhou et al. (Reference Zhou, Zhou and Xiang2016). However, these authors considered that the isolation of the pseudofrontal glabellar lobe by a transglabellar furrow located in the posterior glabellar third, together with a higher number of pygidial furrows in Declivolithus, justified retaining both genera as valid. Notwithstanding the very particular characteristics of Declivolithus, its phylogenetic relationships certainly should be closely linked to these other taxa. If the development of the cephalic fringe and pygidial segmentation suggests a greater relationship to other undisputed trinucleines such as Trinucleus and Telaeomarrolithus, it is also possible that these characters could be more related to the large dimensions of Declivolithus rather than to a close phylogenetic relationship, its origin being related to this paleogeographically more restricted Nankinolithus group.

The first mention of Declivolithus in Morocco was made by Destombes (Reference Destombes1971) and, curiously, it was not in the Anti-Atlas, but in a small inlier located in the southern border of the High Atlas, in the Skoura region. This information was later reproduced in Destombes et al. (Reference Destombes, Hollard, Willefert and Holland1985) and Destombes (Reference Destombes2006a).

Declivolithus alfredi (Želízko, Reference Želízko1906)
Figures 10–12

Reference Želízko1906

Trinucleus alfredi Želízko, p. 16, pl. 1, figs. 1–6.

Reference Chlupáč1952

Tretaspis novaki Chlupáč, p. 183, pl. 1, figs. 1–8, pl. 2, figs. 1–6, pl. 3, figs. 1–2.

Reference Přibyl and Vaněk1967

Declivolithus alfredi; Přibyl and Vaněk, p. 454, pl. 1, fig. 2, pl. 2, fig. 1.

?Reference Destombes1971

Declivolithus aff. alfredi; Destombes, p. 253.

Reference Přibyl and Vaněk1972

Declivolithus alfredi; Přibyl and Vaněk, p. 19, pl. 1, figs. 1–6 (and synonymy therein).

Reference Hughes, Ingham and Addison1975

Declivolithus alfredi; Hughes et al., p. 557–558, pl. 3, figs. 38, 39.

Reference Hughes, Ingham and Addison1975

D. sp. Hughes et al., p. 557.

?Reference Destombes, Hollard, Willefert and Holland1985

Declivolithus aff. alfredi; Destombes et al., p. 227.

Reference Shaw1995

Declivolithus alfredi; Shaw, p. 7, figs. 10.5, 10.7–10.13, 11.1–11.3.

Reference Vaněk and Vokáč1997

Declivolithus alfredi; Vaněk and Vokáč, p. 29–30, pl. 3, figs 1–5.

?Reference Destombes2006a

Declivolithus cf. alfredi; Destombes, p. 11–13, fig. F 5.

Reference Fortey and Edgecombe2017

Declivolithus titan Fortey and Edgecombe, p. 313–314, 316, fig. 2A–F.

Reference Lebrun2018

Declivolithus titan; Lebrun, p. 138–139, figs. A–D.

Figure 10. (1–6) Declivolithus alfredi (Želízko, Reference Želízko1906) from the Bofloss locality, Morocco. (1) Exoskeleton (molting configuration), internal mold, MGM-7742X: dorsal and ventral (lower lamella) views; (2, 3) incomplete cephalon with thorax, latex cast of the external mold, MGM-7743X: (2) dorsal view; (3) detail of the external sculpture of the left genal lobe; (4–6) exoskeleton (upper lamella missing), dental plaster replica of the internal mold, MGM-7744X-R: (4) dorsal view; (5) dorsoposterior view; (6) oblique left anterolateral view. Specimens (1, 2) are preserved in mudstones, flattened; specimen (4–6) preserved in full relief (sandstone). Scale bars = 5 mm.

Figure 11. (1–10) Declivolithus alfredi (Želízko, Reference Želízko1906) from the Bofloss locality, Morocco. (1) Exoskeleton, latex cast of the external mold, MGM-7745X: dorsal view; (2) incomplete thorax with pygidium, latex cast of the external mold, MGM-7765X: dorsal view; (3–6) cephalon, internal mold (lower lamella missing), MGM-7749X: (3) dorsal view; (4) left lateral view; (5) anterior view; (6) right lateral view; (7–9) cephalon (fringe missing), internal mold, MGM-7750X: (7) dorsal view; (8) oblique right posterolateral view; (9) anterior view; (10) meraspis cephalon, latex cast of the external mold, MGM-7771X: dorsal view. All specimens are preserved in full relief (sandstones), except specimen (1), preserved in mudstone, flattened. Scale bars = 5 mm, except (10) = 2 mm.

Figure 12. (1–12) Declivolithus alfredi (Želízko, Reference Želízko1906) from the Bofloss locality, Morocco. (1–3) Cephalon, internal mold, MGM-7751X: (1) dorsal view; (2) anterodorsal view; (3) left lateral view; (4, 5) lower lamella of the fringe, internal mold, MGM-7761X: (4) ventral view; (5) oblique right ventrolateral view; (6) cephalon (upper lamella missing), internal mold, MGM-7752X: dorsal view; (7) incomplete cephalon (left genal lobe and posterior left part of the fringe), internal mold, MGM-7753X: dorsal view; (8) incomplete cephalon, latex cast of the external mold, MGM-7754X: anterodorsal view; (9) pygidium, latex cast of the external mold, MGM-7768X: dorsoposterior view. (10–12) Pygidium, internal mold, MGM-7767X-1: (10) dorsal view; (11) posterior view; (12) right lateral view. All specimens are preserved in full relief (sandstones), except specimen (9), preserved in mudstone, flattened. Scale bars = 5 mm.

Holotype

A holotype was not designated by Želízko (Reference Želízko1906). A lectotype was selected by Přibyl and Vaněk (Reference Přibyl and Vaněk1967), which is a cephalon (old number P 8454; new number NM L17150) figured in Želízko (Reference Želízko1906, pl. 1, fig. 1), and figured again in Přibyl and Vaněk (Reference Přibyl and Vaněk1972, pl. 1. fig. 2) and in Shaw (Reference Shaw1995, fig. 10.12).

Addendum to description

Several authors have described Declivolithus alfredi in detail (e.g., Přibyl and Vaněk, Reference Přibyl and Vaněk1969, p. 101–102; Shaw, Reference Shaw1995, p. 7; Fortey and Edgecombe, Reference Fortey and Edgecombe2017, p. 313, 314). We add here new information and a few remarks concerning some characters that were possible to observe in our material.

Half fringe counts (N = 17) of Moroccan specimens are: E₁, 35–43 (39); I₁, 34–38 (36), I₂, 35–37 (36). It is important to note that the number of E₁ pits (1–28) reported by Přibyl and Vaněk (Reference Přibyl and Vaněk1969) is a typo (it would probably be 38), as can be counted in their figured specimens (e.g., Přibyl and Vaněk, Reference Přibyl and Vaněk1969, pl. 4, fig. 2). The I₂ is the innermost of the outer arcs, which is possible to calculate, although it is irregular due to several cut-off points. Inner arcs, adjacent to the genal and glabellar flanks, are organized in radial rows, with I_n varying from 24–29 pits. The adaxially following 1–2 arcs are also radially aligned. Despite the random distribution of pits in the area abaxial to I₂, it is possible to estimate up to 7–8 pseudoarcs (pits in a row) in front of the glabella, and 10–14 pits in a row in the widest part of the fringe. In front of the glabella, the radial outer sulci of the fringe are shared more frequently by E₁ and I₁, but occasionally they also include I₂.

There is a tendency for the number of pits and arcs to increase ontogenetically, with smaller specimens having fewer pits. Surface of the upper lamella concave, more strongly bent anteriorly and flatter laterally. Surface of lower lamella strongly convex, almost subvertical in the inner margin of the fringe, especially at the posterior region, then sloping regularly in anterior and lateral directions. Outer margin of the fringe (E₁ arc) subhorizontal. Frontal margin of the fringe tends to be medially transverse and slightly elevated compared to the lateral margin. Flattening of the fringe produces a subcircular appearance. The pygidium, which is preserved in full relief, shows a very sharp, abrupt, and significantly high external margin, vertical in relation to the dorsal surface.

Remarks

When erecting Declivolithus titan, Fortey and Edgecombe (Reference Fortey and Edgecombe2017) stated that they only had flattened specimens. In fact, given the material they had available, it was not possible to assess the variability of the characters they took as diagnostic. Among our material, there are several specimens in full relief (Figs. 10.4–10.6, 11.3–11.10, 12.1–12.12), allowing comparison of the Moroccan specimens with similar Declivolithus alfredi from the Czech Republic. One of the main differences that justified the erection of D. titan was the greater organization of the innermost arcs in the Czech species, distributed in radial sulci along the flanks of the genal lobes. In the flattened Moroccan specimens studied by Fortey and Edgecombe (Reference Fortey and Edgecombe2017) it is not possible to see this arrangement, due to the collapse of the genal lobe over the flank, but in the full-relief specimens, it is possible to verify that the pits of the innermost arcs have the same configuration (radially aligned and organized in fringe sulci) as in Declivolithus alfredi from the Czech Republic (compare Shaw, Reference Shaw1995, fig. 10.5, 10.10 with Figs. 11.5, 11.6, and 12.7 herein, respectively). Generally, these sulci are more marked on the anterior half of the fringe, and occasionally they are also present in front of the glabella, with small ridges developed between the sulci (Fig. 11.5). Posteriorly, the sulci are less defined. As in the Czech material, this configuration is not always observed in Moroccan specimens and, sometimes, the same specimen only preserves these sulci and the obvious radial arrangement of the inner pit rows on one side. Although weakly marked, the holotype and another specimen of D. titan figured by Fortey and Edgecombe (Reference Fortey and Edgecombe2017, fig. 2A, B) also show these sulci, but they are visible only on the left side. This character is highly susceptible to taphonomy, but the new material shows it is entirely comparable in D. titan and D. alfredi. A very small cephalon (Fig. 11.10), probably corresponding to a meraspis, also seems to show these sulci adjacent to the glabella and to the genal lobes.

Another difference described by Fortey and Edgecombe (Reference Fortey and Edgecombe2017) is the fringe outer sulci, which in D. titan barely extend only one-third and includes two pits/arcs (E₁ and I₁) frontally and a third anterolaterally. In some D. alfredi specimens the fringe outer sulci are longer (about halfway across the fringe) and include three pits/arcs anteriorly, and sometimes even a fourth posterolaterally. However, not only is this character highly variable from specimen to specimen (even among specimens preserved in full relief) but it is also observed in the new Moroccan specimens (Figs. 10.1, 11.1, 12.1–12.3). Occasionally there are three pits/arcs between the anterior sulci (see also Lebrun, Reference Lebrun2018, p. 139, fig. D), and four pits posterolaterally, just as in the Czech specimens. When Declivolithus specimens from the famous El Qaid Errami area began to appear very frequently in the Moroccan trade, we observed many specimens for sale that show great variability of fringe characters. There are specimens whose furrowed margin occupies 70% of the width (sag.) of the fringe, others in which the furrows are almost indistinct, and still others whose preservation has exaggerated the sulci to such an extent that there are strong ridges between the sulci, similar to the general appearance of the specimen figured by Hughes et al. (Reference Hughes, Ingham and Addison1975, pl. 3, fig. 39). Even within the Czech material, many details of the description, such as this particular character described by Chlupáč (Reference Chlupáč1952), were based on a single specimen from a collection of fragmentary material. As Vaněk and Vokáč (Reference Vaněk and Vokáč1997, p. 29) noted, the presence of I₂ is common, but it does not always occur.

We consider that Declivolithus titan is a junior synonym of D. alfredi and that the Czech and Moroccan representatives of this genus are conspecific. We also clarify that two specimens figured by Přibyl and Vaněk (Reference Přibyl and Vaněk1969, pl. 5, figs. 4, 9) as Declivolithus alfredi, which Fortey and Edgecombe (Reference Fortey and Edgecombe2017, p. 316) considered not to correspond to this species because they “show the dorsal surface of the fringe carrying a prominent ridge parallel to the cephalic margin inside the E arc” were misinterpreted. As Přibyl and Vaněk (Reference Přibyl and Vaněk1969) indicated in their figure caption, the former is an enrolled specimen, thus showing the lower lamella in ventral view (the prominent ridge is the girder; see also the same specimen figured by Shaw, Reference Shaw1995, fig. 10.13). The second specimen is an exfoliated cephalon exposing the lower lamella as well, but in dorsal view (compare to a specimen with similar exfoliation figured by Shaw, Reference Shaw1995, fig. 10.9).

An interesting detail in some Moroccan material of Declivolithus is a characteristic molting configuration. As discussed by Fortey and Owens (Reference Fortey and Owens1987) and Drage (Reference Drage2019), trinucleids, as well as harpetids, may have molted by opening the marginal suture that separates the upper and lower lamella of the fringe, a mechanism similar to modern xiphosurans, in which a marginal gape opens between the dorsal and ventral parts. In some trinucleids, the molting took place with the lower lamella of the fringe displaced away from the remainder of the exuvia (see also Drage, Reference Drage2019, fig. 5.1; the displaced lamella is the lower and not the upper one). This is common for Declivolithus alfredi, with a frequent 8-shaped molting configuration (see Fig. 10.1 and Fortey and Edgecombe, Reference Fortey and Edgecombe2017, fig. 2B) in which the lower lamella appears rotated 180° and overlapped at the posterolateral ends with the upper lamella. However, there are also specimens where it is the upper lamella that is missing but not around (e.g., Fig. 10.4), making it difficult to ensure that this is a molting configuration, and not the result of post-mortem disarticulation. Other trinucleids (e.g., Deanaspis Hughes, Ingham, and Addison, Reference Hughes, Ingham and Addison1975) present different molting procedures, through the disarticulation of the cephalon and sometimes the first thoracic segment, which may or may not still be articulated to the cephalon, leaving a typical configuration in which these anterior-separated sclerites are slightly rotated with respect to the sagittal axis of the thorax with pygidium (e.g., Přibyl and Vaněk, Reference Přibyl and Vaněk1969, pl. 14, fig. 4; Pereira, Reference Pereira2018, fig. 3G, I–K).