936


Journal of Paleontology 91(5):933–959


intended type specimen (a lectotype by ICZN convention). The cranidium selected by Lane et al. (1988) as the lectotype (Figs. 1.5, 2.5, 2.6), by contrast, belongs to Oryctocarella duyunensis. The designating of this specimen by Lane et al. (1988) created confusion about the generic concept because most authors seem to have relied on Bergeron’s line drawing for guidance on the species and generic concepts. Photographs of Bergeron’s (1899) specimens published by


Lane et al. (1988, pl. 1, figs.1–5) as A. chauveaui show great morphologic differences among the sclerites in the type series, suggesting different species are included. Bergeron’s slab was not re-examined in the preparation of the 1988 paper (P.D. Lane, personal communication, 2016). In 2002, SP examined the type material of Arthricocephalus chauveaui at the museum of the Geological Department, Claude Bernard University, Lyon, France, and rephotographed all exposed sclerites. The examination demonstrated that Bergeron’s line drawing of A. chauveaui (Fig. 2.1) is generally accurate, as concluded by Lane et al. (1988, p. 558). The examination also indicated that the line drawing was based principally on the largest exoskele- ton on the slab. That specimen (Fig. 2.2, 2.3, 2.10) is easily identifiable among the sclerites on the slab. The specimen that evidently served as the basis for the illustration and much of the original description (Bergeron, 1899) is an exuvium of the exoskeleton having the cranidium, librigenae, and hypostome disarticulated from the thoracopygon and overturned (Figs. 1.1, 2.2, 2.3, 2.10). Features showing that the exoskeleton is the basis for Bergeron’s illustration and description include: (1) outline of glabella, which is pestle-shaped, expanded for- ward anterior to the S3 furrow, and defined laterally by curved axial furrows; (2) nature of the posterior three glabella furrows (S1–S3), which are transversely continuous across the glabella and reach to the axial furrows; (3) shape of the posterior three glabellar lobes (L1–L3), which are narrow, subrectangular, about three times wider than long, and subequal in length; (4) length of the “anterior lobe” of the glabella (formed by fusion of L4 and the frontal lobe), which is twice as long as L3; (5) segmentation pattern of the thorax, with eight segments, the posteriormost of which is incompletely released; (6) semicircular outline of the pygidium (subequal to the cranidium in length); (7) segmentation of the pygidial axis (five rings and a terminal piece); (8) faint interpleural furrows of the pygidium; and (9) smooth, con- tinuous arc forming the posterior margin of the pygidium. Bergeron’s (1899) original description of A. chauveaui


provides further evidence that the species’ description was principally based on the largest exoskeleton on the slab. Characters noted by Bergeron include: (1) expansion in width of the anterior glabellar lobe and expansion of its length to twice that of the other lobes, implying the glabella is expanded for- ward anterior to S3; (2) eight thoracic rings (segments); (3) six rings in the pygidial axis; (4) cranidial length of 2.5mm; and (5) pygidial length of 2.5mm. None of the other exoskeletons present on the slab has this combination of characters. The sum of information published by Bergeron (1899) indicates that the largest exoskeleton on the original limestone slab was the basis for most of the species description and for the illustration, and it is inferred that this exoskeleton was the intended type specimen. Examination of Bergeron’s type exoskeleton reveals some misinterpretation of features in the original illustration


(Bergeron, 1899, fig. 9). The ridge-like structure along the pygidial border as illustrated is actually the ventral doublure (compare Fig. 2.1, 2.11). This misinterpretation may have been influenced in part by the appearance of the largest pygidium on the slab (Fig. 1.2), which is preserved as an external mold. The latex cast of the pygidial external mold reveals that the “ridge” is the ventral doublure (Fig. 2.11). This pygidium is the only sclerite on Bergeron’s (1899) slab that is conspecific with the largest exoskeleton. Fulcra and facets on the thoracic segments were not illustrated by Bergeron (1899), although they are pre- sent. The fulcra and facets are not well exposed on the type specimen, and are not presented on the other thoracic material on the slab except for the smallest exoskeleton (Fig. 2.12). Apart from the specimen illustrated here in Figure 2.2 and


2.3, there are four additional exoskeletons on Bergeron’s slab (E.M. 90001c [thoracopygon associated with cranidium, 90001b], 90001d, 90001e, 90001f), but none of them matches the original illustration and description.Anumber of differences between these exoskeletons and the largest exoskeleton on the slab (E.M. 90001a) indicate that they are not the specimens on which Bergeron’s illustration was based, and that they are neither conspecific nor congeneric with A. chauveaui. Three exoskeletons (E.M. 90001b and 90001c, 90001d, 90001e; Figs. 1.3–1.6, 2.4–2.8) are reassigned herein to Oryctocarella duyunensis (Qian, 1961). New, abundant and well-preserved material from the Balang Formation helps to clarify the differ- ences between A. chauveaui and O. duyunensis (Fig. 3), and each of the distinguishing characteristics of O. duyunensis is present on the three sub-largest exoskeletons of Bergeron’s slab. These exoskeletons differ from A. chauveaui in: (1) having a narrow cylindrical glabella that is parallel-sided and defined laterally by straight axial furrows; (2) having pit-like glabellar furrows that are isolated from the axial furrows and two or three pairs of furrows (S1, S2, S3) connected transversely by furrows, but not extending abaxially to the axial furrows; (3) having straight rather than curved axial furrows; (4) having pro- portionally long L1–L3 and a short “anterior lobe” (L4 plus frontal lobe, nearly as long as L3); (5) having an upturned rather than ridge-like cranidial border; (6) having palpebral lobes in a relatively anterior position; (7) having an ocular ridge relatively closer to the anterior border furrow; (8) having a thorax with more than eight segments (up to 10 or 11; Fig. 2.4); (9) having a smaller pygidium that is shorter than the cephalon; (10) having a pygidial axis with three rather than five axial rings; (11) having well-defined interpleural furrows; (12) having a medial notch at the posterior margin of the pygidium; and (13) lacking a pygi- dial border rather than having an upturned border (Figs. 2.4, 2.7–2.8, 3.2). The thoraxes in each of these three exoskeletons are apparently non-fulcrate, differing in this character from the fulcrate thorax with geniculate segments of the largest exoske- leton. This difference was suggested by Whittington (1995, p. 555) who found that the “weakly geniculated pleurae” described by Lane et al. (1988, p. 559) for A. chauveaui are not present on some specimens assigned to Arthricocephalus by Zhang et al. (1980). Cephala on each of the three sub-largest exoskeletons appear to have proparian facial sutures, whereas on E.M. 90001a the sutures are gonatoparian. The smallest exoskeleton on Bergeron’s (1899) slab (E.M. 90001f, Figs. 1.8, 2.12) also is not conspecific with A. chauveaui


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