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946


Journal of Paleontology 91(5):933–959


Holotype.—Exoskeleton (NIGP 38234, Fig. 5.1) from the Balang Formation, Xinzhaihe, Songtao, northeastern Guizhou, China; by monotypy. The holotype was figured by Lu et al.


(1974, pl. 36, fig. 7), and refigured by Yin and Li (1978, pl. 157, fig. 1), Zhang et al. (1980, pl. 92, fig. 5), and Yuan et al. (2002, pl. 30, fig. 6). It is not the exoskeleton illustrated by Yuan et al. (2006, fig. 2a) as the holotype of the species.


Diagnosis.—Arthricocephalus with glabellar furrows S1–S3 pit-like, connected by weak transverse furrows, separated from axial furrow; palpebral lobe variably oblique in meraspis and holaspis with posterior end at a level corresponding to the pos- terior half or mid-length of L2; dorsal surface smooth or covered by densely spaced granules.


Occurrence.—Arthricocephalus xinzhaihenesis co-occurs with A. chauveaui in the Balang Formation of the Jiangnan Slope Belt, eastern Guizhou and western Hunan, South China. It is present in dark-gray, calcareous mudstone and shale (weath- ering yellow-green) in the middle part of the Balang Formation (Cambrian Stage 4 or Duyunian according to South China regional stratigraphy).


Materials.—One exoskeleton (NIGP 164843) in collections LYX-1. Reillustrated specimens include the holotype exoske- leton of Arthricocephalus (Arthricocephalites) xinzhaiheensis Qian and Lin in Lu et al., 1974 (NIGP 38234), the holotype exoskeleton of A.(Arthricocephalites) intermedius Zhou in Lu et al., 1974 (NIGP 21481), an exoskeleton assigned to A. (Arthricocephalites) xinzhaiheensis by Zhanget al., 1980(NIGP 38235); three exoskeletons assigned to Arthricocephalus balangensis Lu andQian in Yin and Li, 1978 (notQian and Lin, as documented in Zhang et al., 1980) by McNamara et al., 2003 (NIGP 135415–135417); and four specimens assigned to Arthricocephalus chauveaui Bergeron by Lei (2016), including two exoskeletons (NIGP 163348, 163356), an incomplete cephalon (NIGP 163365), and an incomplete cranidium (NIGP 163362).


Remarks.—Lei (2016) suppressed Arthricocephalus xinzhaiheensis as a junior synonym of A. chauveaui. In most respects, such as shape of the glabella, morphology of the glabellar furrows, course of the facial suture, presence of thoracic fulcra, shape and subdivision of the pleurae, segmentation of the thorax and pygidium, faint interpleural furrows on the pygidium, and the upturned cephalic and pygidial borders, A. xinzhaiheensis closely resembles A. chauveaui. However, the species is distinct from A. chauveaui in having S1–S3 glabellar furrows that do not extend abaxially to the axial furrow, although they are joined by weak transverse furrows medi- ally on the glabella. The palpebral lobe ofA. xinzhaiheensis seems to be more oblique in adults, and the anterior tip of the palpebral lobe appears to be closer to the glabella than it is in A. chauveaui and the posterior tip places further back. In the holotype of A. xinzhaiheensis the axis of the thorax (Fig. 5.1) is proportionately broader than in A. chauveaui, but another specimen (Fig. 5.5) suggests variation in this character. In addition, the specimen in Figure 5.5 is indistiguishable from A. chauveaui in the proportion of the thoracic axis. In A. xinzhaiheensis the forward expansion of the glabella is variable.


McNamara et al. (2003, pl. 2, figs. 6, 8, 9, text-fig. 5; Fig. 5.6, 5.7) differ significantly from the holotype of A. balangensis and are here transferred to A. xinzhaiheensis based on the morphology of the glabella and glabellar furrows, and on the presence of fulcra in the thorax. The holotype of A. balangensis (Yin and Li, 1978, pl. 157, fig. 10; refigured by Zhang et al., 1980, pl. 93, fig. 2; Fig. 7.1, 7.2) is similar to A. xinzhaiheensis in having pit-like S1–S3 joined by transverse furrows across the middle of the glabella. However, the glabella of A. balangensis is subrectangular or subcylindrical in shape, and defined by nearly straight, parallel axial furrows. Importantly, the thorax of A. balangensis lacks fulcra. The thorax normally has 11 segments, but in some examples one more segment may be developed. These characters support a reassignment of A. balangensis to Oryctocarella (and recombination as Oryctocarella balangensis, see below). Specimens assigned to Arthricocephalus xinzhaihenesis


Specimens assigned to Arthricocephalus balangensis by


by McNamara et al. (2003, pl. 2, figs. 1–4, text-fig. 4A–D) are reassigned here as Oryctocarella balangensis (see below), and specimens assigned to A. xinzhaihenesis by Yuan et al., 2006 (fig. 2b) are reassigned here as Arthricocephalus chauveaui. The specimens illustrated by McNamara et al. (2003), from Palang, Duyun, southeastern Guizhou, are all meraspid exoskeletons; the largest one has only seven thoracic segments (McNamara et al., 2003, pl. 2, fig. 4; Fig. 5.8). In one exoskeleton assigned to A. xinzhaihenesis by Yuan et al. (2006), the glabellar furrows S1–S3 are transglabellar and reach to the axial furrows. This character is regarded as indicative of A. chauveaui. Shen et al. (2016) referred numerous specimens to


1980, pl. 93, fig. 8) is questionably assigned to Arthricocephalus. It has a glabella with pit-like glabellar furrows and a fulcrate thorax with facets. However, the interpleural furrows in the pygidium are clearly incised, making it difficult to confidently assign the specimen to a certain species. As discussed above, S1 through S3 are isolated from


the genus Arthricocephalites, either as Arthricocephalites xinzhaihenesis or as A. intermedius. Most of these specimens, in fact, represent Arthricocephalus chauveaui because their glabellar furrows S1 through S3 are transglabellar. Arthricocephalites (Arthricocephalites) sp. 2 (Zhang et al.,


the axial furrows in Arthricocephalus xinzhaihenesis, unlike the transglabellar development of S1 through S3 in Arthricocephalus chauveaui. In oryctocephalids, the nature of S1 through S3 appears to be a critical specific character. In addition, the palpebral lobes and ocular ridges of A. xinzhaihenesis aremore obliquely directed to the length of axis than those of A. chauveaui, suggesting that A. xinzhaihenesis is a species separate from A. chauveaui. However, the differences between both species in other features seem minimal, and both species share almost the same stratigraphic occurrences as well. For these reasons, the possibility that they represent sexual dimorphs of a single species can not be ruled out.


Genus Oryctocarella Tomashpolskaya and Karpinski, 1961


1961 Oryctocarella Tomashpolskaya and Karpinski, p. 156. 1988 Arthricocephalus Bergeron; Lane et al., p. 555 (part).


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