Peng et al.—Revision of oryctocephalid genra
2011 2013 2015 2016
2016 2016
Haliplanktos jishouensis; Geyer and Peel, p. 499, fig. 15A–F.
Arthricocephalus xinzhaiheensis; Lei, p. 72, figs. 24, 25.
Arthricocephalus chauveaui; Peng et al., p. 89, pl. 1, figs. 1–4.
Arthricocephalites xinzhaiheensis; Shen et al. (part), p. 16, fig. 1.8–1.11; non fig. 1.1–1.7.
Arthricocephalites intermedius Zhou; Shen et al., p. 15, fig. 2.1–2.3, 2.6–2.13, ?2.4, ?2.5.
Lectotype.—Disarticulated exoskeleton (E.M. 90001a; Figs. 1.1, 2.2, 2.3, 2.10); also illustrated by Lane et al. (1988,
pl. 1, fig. 1), Blaker and Peel (1997, fig. 62.1), and Geyer (2005, fig. 3.7), from the Balang Formation, north of Tongren, eastern Guizhou, China; original of Bergeron (1899, fig. 9).
Diagnosis.—Arthricocephalus with glabellar furrows con- tinuous transversely across glabella, reaching to axial furrow; glabella expanded forward of S2 or S3; preocular area nearly half as long (exsag.) as frontal lobe (sag.); palpebral lobe slightly oblique to almost exsagittal in holaspid stage with posterior end at a level corresponding to S1; posterior branch of facial suture strongly divergent, curving poster- olaterally to meet cephalic margin at genal corner or faintly anterior to it. Dorsal surface smooth or covered with fine granules.
Occurrence.—Arthricocephalus chauveaui has been reported from the Jiangnan Slope Belt of eastern Guizhou and western Hunan, South China, and (as Haliplanktos jishouensis) from North Greenland. In Guizhou and Hunan, it occurs in dark-gray, calcareous mudstone and shale (weathering yellow-green) in the middle part of the Balang Formation (Cambrian Stage 4 or Duyunian according to South China regional stratigraphy). In Greenland, it occurs in the Olenellus Zone of the Henson Gletscher Formation (Cambrian Stage 4).
Description.—Exoskeleton ovate, length ~1.5 times width. Cephalon semicircular; glabella forwardly expanding or pestle- shaped, expanded anterior to S2 or S3, with transverse occipital furrow. Four pairs of glabellar furrows present; S1–S3 trans- verse across glabella, extending to axial furrows and deepened laterally into paired pits near axial furrows, S4 narrow incision, reaching to axial furrow abaxially. Occipital ring wider and
Arthricocephalus chauveaui; Lei (part), p. 496, figs. 3.1–3.4, 3.6, ?3.8, 3.9–3.12, 3.14, ?3.15, 4.1–4.3, 4.5, 4.6, 4.8, ?4.9–4.16; non figs. 3.5, 3.7, 3.13, 4.2, 4.7.
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slightly shorter than L1, S0 and S1–S4 subequally spaced, frontal lobe slightly longer than L4. Palpebral lobe medium- sized, of ~0.33–0.36 (N = 6) of cephalic length in adult specimens, gently curved, moderately to gently oblique and directedmoderately forward,with posterior tip in adult specimens opposite S1; palpebral area about three-quarters width of glabella at L2. Anterior branch of facial suture short and straight, diag- onally convergent forward; posterior branch strongly divergent for about two-thirds its length, then curving smoothly to meet cephalic margin at genal corner or faintly anterior to it. Librigena narrow, lateral border narrow and upturned, with well-defined border furrow. Anterior cranidial border ridge-like and narrow, upturned, with well-defined border furrow; posterior border slightly shorter than occipital ring, becoming much longer abaxi- ally, with well-developed and moderately long (exsag.) posterior furrow.
Rostral-hypostomal plate (Fig. 2.10) shield-shaped; middle
body of hypostoma large, elliptical, gently convex, divided by a faint medial furrow, posterior portion short crescentic; anterior wing triangular, about half as long as hypostome, lateral and posterior borders narrow (tr., sag.), with deep border furrows. Rostral plate narrow, ridge-like, separated from ridge-like cephalic doublure by short connective suture. Thorax fulcrate, with eight segments. Axis gently narrow-
ing posteriorly, slightly expanded medially, pleural region ~1.5 as broad as axis, fulcrum present about halfway across width (tr.) of pleura; anterior and posterior bands of pleura subequally long (exsag.), separated by deep and long pleural furrow; anterior margin of pleura curves backward to a sharply pointed or acute posterolateral tip. Pygidium semicircular, as long as cephalon or slightly
shorter, length/width ratio ~0.48–0.53 (N = 8). Axis consists of five rings and a tiny terminal piece, tapering rapidly rearward, of
about two-thirds of pygidial length. Pleural region moderately convex, with five or six pleurae consisting of subequal anterior and posterior bands; pleural furrow nearly straight, well impressed and broad (exsag.); interpleural furrows less well developed, sometimes faint. Lateral and posterior borders upturned; border furrows broad, shallow, of unequal depth due to faintly elevated parts in continuation of the pleural bands. Pygidial doublure narrow, belt-like. Dorsal surface smooth or covered with fine but densely
spaced granules.
Materials.—Eight exoskeletons including five in collection LYX-1 (NIGP 164838–164841, 164952), one in collection WWf2 (NIGP 164842), and two in collection XHZA329-13 and XHZA325-27, respectively (NIGP 163349, 163354).
Figure 4. Arthricocephalus chauveaui Bergeron, 1899 from the Balang Formation in northwestern Hunan (1–5, 7, 8, 10–12) and eastern Guizhou (6, 9), China. White arrowhead indicates posterior margin of thorax; arrowhead with black outline indicates posterior margin of partially released segment of transitory pygidium; all in dorsal view; b = border, d = doublure; f = facet: (1) NIGP 164838, exoskeleton, meraspis degree 4, LYX-1; (2) NIGP 164839, exoskeleton, meraspis degree 4, LYX-1; (3) NIGP 163346, exoskeleton, meraspis degree 5, XHZA407-3, original of Lei (2015, fig. 3.3); (4) NIGP 164952, distorted exoskeleton, meraspis degree 5, LYX-1; (5) NIGP 164840, exoskeleton, meraspis degree 6, LYX-1; (6) NIGP 38233, exoskeleton, meraspis degree 6, HN-GZ, holotype of Arthricocephalus (Arthricocephalites) pulchellus Zhang and Qian in Zhang et al. (1980, pl. 92, fig. 3); illustrated originally as Arthricocephalus chauveaui by Lu et al. (1965, pl. 17, fig.
1), reillustrated as Arthricocephalus taijiangensis by Yuan et al. (2001, pl. 2, fig. 5; 2006, fig. 2c) and as Arthricocephalus pulchellus by McNamara et al. (2003, pl. 2, fig. 12); (7) NIGP 164841, exoskeleton, meraspis degree 6, LYX-1; (8) enlargement of the right side of the thorax of NIGP 164841 in 7, showing pleural facets; (9) NIGP 164842, exoskeleton, meraspis degree 7, WWf2; (10) NIGP 163349, exoskeleton, holaspid, latex cast from external mold, XHZA329-13; (11), NIGP 163354, exoskeleton, holaspid, XHZA325-27; (12) NIGP 163357, latex cast of external mold of incomplete holaspid exoskeleton lacking librigenae and with displaced cranidium, XHZA416-9, original of Lei (2016, fig. 3.14). All scale bars represent 1.0mm.
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