Peng et al.—Revision of oryctocephalid genra
Description.—Exoskeleton elliptic in outline, about twice as long as wide. Cephalon subsemicircular in outline, with rounded genal corners; glabella subcylindrical, about four times as long as broad, widest part generally across L4; axial furrow more or less straight, parallel-sided or faintly divergent forward to near glabellar front; occipital furrow weak, deepened at lateral ends as incisions. Four pairs of glabellar furrows present; S1–S3 pit- like, each pair connected by a weak or faint transverse furrow that stops within pit, without extending outward to reach axial furrows; S4 narrow incision reaching to axial furrow abaxially; occipital ringwider, butmuch shorter than L1; L1–L3 subequal in length; L4 shorter than L3, and frontal lobe shorter than L4; L4 plus frontal lobe slightly longer than L3. Palpebral lobe medium- sized, ~0.26–0.31 (N = 11) of cephalic length in adult specimens, gently curved, about 40º oblique to sagittal line, lying anterior to glabellar mid-length, posterior tip opposite S2; palpebral area about as wide as glabella or slightly narrower. Anterior branch of facial suture short, with straight posterior portion, moderately convergent and curved in anterior portion; posterior branch diverging outward and somewhat rearward, meeting lateral cephalic margin opposite L1. Librigena narrow, with wire-like, poorly defined lateral border; somewhat upturned posteriorly and progressively elevated anteriorly to merge with upturned anterior border of cranidium. Anterior cranidial border furrow well defined; posterior cephalic border transverse, broadening abaxi- ally; posterior border furrow well defined. Hypostome (Fig. 9.17, 9.18) subovate with inflated middle
body and broad lateral and posterior borders, posterior margin gently curved, anterior margin (?hypostomal suture) horizontal. Thorax non-fulcrate, with 11 or possibly 12 segments. Axis
about half as broad as pleural region, gently narrowing rearward, slightly expanded medially, widest at segments 3–6; pleura with obtusely rounded tip, unequally divided into a shorter (exsag.) anterior band and a longer (exsag.) posterior band by well-incised pleural furrow, which runs slightly oblique to the longitudinal direction of the pleura and shows a weak rearward swing near abaxial termination. Pygidium in holaspis (Fig. 8.14) subelliptical, transverse,
about twice as broad as long. Axis small, containing a prominent articulating half-ring, three rings and a terminal piece, tapering rapidly rearward, occupying about half of pygidial length; ring furrows weakly to moderately defined. Pleural region gently convex, with 3–4 pleurae; pleural furrows and interpleural furrows well defined, gently curved; interpleural furrows slightly less well developed than pleural furrows. Posterior margin with a medial notch. Dorsal surface covered with densely spaced granules.
953
Materials.—Hundreds of sclerites from three sections (Mozichong, Bulin and Paiwu), Huayuan, northwestern Hunan, of which 22 exoskeletons (NIGP 164844–164851; NIGP 164858–164870; NWU-DYXJT 1823), three cranidia (NIGP 164852–164854) and three pygidia (NIGP164855–164857) are illustrated; reillustrated specimens include the holotype exos- keleton of the species (NIGP 11494) and an exoskeleton designated as holotype of Arthricocephalus horridus Qian and Lin in Zhang et al., 1980 (NIGP 38236).
Remarks.—Oryctocarella duyunensis was originally referred to Arthricocephalus (Qian, 1961). Lane et al. (1988) regarded the species as a junior synonym of A. chauveaui, and selected a ‘lectotype’ for A. chauveaui (suppressed here) that in fact belongs to O. duyunensis. For three decades, the concepts of Arthricocephalus and A. chauveaui were thus based on speci- mens that are here referred to O. duyunensis. As discussed above and summarized in Figure 3, this species differs significantly from A. chauveaui. This species is similar to Oryctocarella sibirica (Tomashpolskaya in Khalfin, 1960) (Fig. 6), the type species of
Oryctocarella.In O. duyunensis,the palpebral lobe is located somewhat more anteriorly, and its pos- terior tip is opposite S2, whereas in O. sibirica the posterior tip of the palpebral lobe is opposite L2, and as a result, it appears to have more strongly diverging posterior branches of the facial suture. The neotype of O. sibirica (Fig. 6.1) and some other cranidia (Fig. 6.2, 6.3) differ from O. duyunensis in its glabellar shape (being subrectangular rather than cylindrical) and proportion (glabellar length ranging up to three times its width). There is considerable variability in these characters among the topotype material (Korovnikov and Novozhilova, 2017, pl. 5, figs.1,3; Fig. 6.2, 6.3), but O. duyunensis differs further in having 11 or 12 thoracic segments in the holaspid stage and bearing a distinct posteromedial notch in the pygidial margin, whereas O. sibirica has only nine or possibly 10 thoracic segments, and evidently lacks a distinct posteromedial notch in the pygidial margin.
Genus Duyunaspis Zhang and Qian in Zhou et al., 1977
1977 Duyunaspis Zhang and Qian in Zhou et al., p. 131. 1988 Arthricocephalus Bergeron; Lane et al. (part), p. 555.
Type species.—Duyunaspis duyunensis Zhang and Qian in Zhou et al., 1977, p. 132, pl. 41, figs. 5, 6, from the Balang Formation, Palang, Duyun, southeastern Guizhou; by original designation.
Figure 8. Oryctocarella duyunensis (Qian, 1961) from the Balang Formation in northwestern Hunan (1–15) and eastern Guizhou (16–18), China; all in dorsal view. White arrowhead indicates the posterior margin of thorax; arrowhead with black outline indicates the posterior margin of partially released segment of transitory pygidium; black triangle indicates medial notch at pygidial margin. (1) NIGP 164844, exoskeleton, meraspis degree 2, MZC-1; (2) NIGP 164845, exoskeleton, meraspis degree 4, MZC-1; (3) NIGP 164846, exoskeleton, meraspis degree 8, MZC-1; (4) NIGP 164847, exoskeleton, meraspis degree 9, MZC-1; (5) NIGP 164848, exoskeleton, meraspis degree 9, MZC-1; (6) NIGP 164849, exoskeleton, meraspis degree 9, MZC-1; (7) NIGP 164850, exoskeleton, meraspis degree 9, MZC-1; (8) NIGP 164851, exoskeleton, holaspid, thorax with possibly twelve segments, MZC-1; (9) NIGP 164852, cranidium with one thoracic segment, meraspis, MZC-1; (10) NIGP 164853, cranidium with two thoracic segments, meraspis, MZC-1; (11) NIGP 164854, cranidium with one thoracic segment, meraspis, MZC-1; (12) NIGP 164855, transitory pygidium with the anterior segment almost completely released, MZC-1; (13) NIGP 164856, transitory pygidium with the anterior segment partly released, MZC-1; (14) NIGP 164857, pygidium, holaspid, MZC-1; (15) NIGP 164858, exoskeleton, meraspis degree 9, MZC-1; (16) NIGP 38246, exoskeleton, meraspis degree 10, holotype of Arthricocephalus granulus Qian and Lin in Zhou et al., 1977 (pl. 42, fig. 2), retrodeformation with inferred strain ellipse, KH020; (17) holotype NIGP 11494, exoskeleton, meraspis degree 9, originally assigned as Arthricocephalus duyunensis Qian, 1961 (pl. 2, fig. 8), GY207; (18) NIGP 38236, exoskeleton, meraspis degree 9, holotype of Arthricocephalus horridus Qian and Lin in Zhang et al., 1980 (pl. 92, fig. 7), GY203. All scale bars represent 1.0mm.
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