784
Journal of Paleontology 89(5):768–790
Remarks.—Stouge (1984) described P. aculeatus zgierzensis in detail as a multielement subspecies from the Table Head Formation of western Newfoundland. He differentiated this sub- species fromthe younger type species P. aculeatus mainly by the Melement,whose ratio of length of oral edge to length of cusp is 3:4 for P. aculeatus zgierzensis but 1:1 for P. aculeatus.Other- wise,Melement of this subspecies bears fewer anterior denticles than that of P. aculeatus. Rasmussen (2001), Zhen and Percival (2004) and Chen et al. (2006) referred P. aculeatus zgierzensis to P. macrodentatus. Although Rasmussen (2001) distinguished an early-stage Periodon species as P. zgierzensis, Stouge (2012) considered it as P. hankensis. Stouge (2012) proposed as char- acteristic of P. zgierzensis, there are four denticles on the anterior process of Pa element. In addition, theMelement of P. zgierzensis has a more sinuous aboral edge and the S elements have a more developed zone of recessive basal margin than those of the ancestral species. Also, the strong sinuous aboral edge of theM element makes the connection of the cusp and the base show a near quadrate outline (Stouge, personal communication, 2014). On balance, most characteristics of our specimens correspond to descriptions by the above authors of P. zgierzensis. Genus Phragmodus Branson and Mehl, 1933
Type species.—Phragmodus primus Branson and Mehl, 1933.
Remarks.—Sweet (1981) proposed a seximembrate skeletal apparatus for the genus Phragmodus, including dichognathi- form or ozarkodiniform Pa, dichognathiform Pb, oistodontiform or cyrtoniodontiform M, phragmodontiform Sa and Sb, phrag- modontiform or cordylodontiform Sc elements. The repre- sentatives of this genus have been discovered on all the continents in the stratigraphic interval spanning from the uppermost Dapingian to the uppermost Hirnantian (Tolmacheva et al., 2013). Hitherto, at least ten species are known to be included in the genus Phragmodus, but only five of them are universally recognized: P. polonicus, P. flexuosus, P. inflexux, P. cognitus, and P. undatus.
Phragmodus polonicus Dzik, 1978 Figure 7.12–7.14, 7.18, 7.23, 7.24
1978 Phragmodus polonicus Dzik, p. 63, pl. 14, figs. 1–2,4–5.
1983 Plectodina onychodonta An and Xu; An et al., only pl. 23, figs. 1–5, pl. 25, fig. 7.
1987 Plectodina onychodonta; Pei and Cai, only pl. 7, figs. 5–7,9.
2013 Phragmodus polonicus; Tolmacheva et al., pp. 402–403, pl. 3, figs. 1–12. [see for synonymy]
2014 Plectodina onychodonta; Wang et al., 2014, only pl. 2, figs. 11–12.
Material.—Twenty sepcimens (Table 1).
Occurrence.—W-1-2, W-2-1, W-2-2, W-3-1, W-6-1, W-8-2, W-9-1.
Remarks.—Dzik (1978) and Tolmacheva et al. (2013) described this species in detail. A septimembrate species apparatus (Pa, Pb, M, Sa, Sb, Sc, and Sd elements) was indicated by Tolmacheva et al. (2013). Mature elements of P. polonicus from Poland (Dzik, 1976, 1978, 1994), Estonia (Viira et al., 2006) and Russia (Tolmacheva et al., 2013) are all relatively large, the S elements are laterally flattened, the M element has a massive denticle and nondenticulate posterior process, and the P elements bear denticulate posterior and lateral processes. Our specimens possess the essential characters of this species. Based on the P elements, Dzik (1994) distinguished two mor- photypes of P. polonicus, the early form has a smooth anterior costa on the cusp, and a late form that has a serrate anterior costa. In our collections, the Pb elements of P. polonicus (Figure 7.12–7.14) carry slightly undulating margin on the anterior process, and this indicates that they are comparatively advanced as the late form. In addition, we discovered several phragmodontiform (S) elements (Figure 7.15–7.17) from the Wolongang section, which have separated denticles on the posterior processes, and these denticles are mostly circular or ovoid in cross section. Because the characteristics of these ele- ments differ from those of P. polonicus, we tentatively assign them to P. sp.
Genus Plectodina Stauffer, 1935 Type species.—Prioniodus aculeatus Stauffer, 1930.
Remarks.—A seximembrate apparatus of this genus was reconstructed by Sweet et al. (1975), then Sweet (1981) revised the six morphologically distinct elements as dichognathiform or prioniodiniform Pa, ozarkodiniform Pb, prioniodiniform M, trichonodelliform Sa, zygognathiform Sb, and cordylodonti- form or eoligonodiniform Sc elements. The shallow and warm water living habit of Plectodina (Sweet, 1988) led to much more endemic species than the deep or cold water genera (Zhen and Percival, 2003). As one of the numerous endemic Plectodina species, P. onychodenta is morphologically prominent and
Figure 9. (1, 2, 10) Pygodus lunnensis Zhang, 1998; (1, 2) Pa, upper view, from W-6-1, CUGB-jxch662, CUGB-jxch665; (10) Sb, outer lateral view, from W-6-1, CUGB-jxch695. (3–9) Pygodus anitae Bergström, 1983; (3–5) Pa, upper view; (3) from W-9-3, CUGB-jxch762; (4) from W-10-3, CUGB-jxch775; (5) from W-9-3, CUGB-jxch763; (6, 7, 9) Pb, outer lateral view; from W-10-3, CUGB-jxch776, CUGB-jxch778, CUGB-jxch777; (8) Sd, lateral view, from HT-1-1, CUGB-jxch787. (11–29) Pygodus anserinus Lamont and Lindström, 1957; (11–16) Pa, upper view; (11) from HT-5-2, CUGB-jxch789; (12–15) from HT-6-1, CUGB-jxch832, CUGB-jxch814, CUGB-jxch811, CUGB-jxch810; (16) from HT-6-2, CUGB-jxch845; (17–22) Pb; (17–19, 21, 22) outer lateral view; (17, 19) from HT-6-1, CUGB-jxch821, CUGB-jxch828; (18, 21, 22) from HT-5-2, CUGB-jxch796, CUGB-jxch792, CUGB-jxch793; (20) inner lateral view, from HT-6-2, CUGB-jxch849; (23, 24) Sa, (23) posterior view, from HT-6-2, CUGB-jxch852; (24) lateral view, from HT-5-2, CUGB-jxch799; (25–27) Sb, lateral view; (25, 26) from HT-6-1, CUGB-jxch841, CUGB-jxch842; (27) from HT-5-2, CUGB-jxch800; (28, 29) Sd, lateral view; (28) from HT-5-2, CUGB- jxch798; (29) from HT-6-2, CUGB-jxch848. (30–34) Spinodus spinatus (Hadding, 1913); (30, 31) Sd, lateral view; (30) from W-6-1, CUGB-jxch714; (31) from W-9-2, CUGB-jxch757; (32) Sb, lateral view, from W-4-3, CUGB-jxch651; (33, 34) Sc, lateral view; (33) from W-9-3, CUGB-jxch767; (34) from W-7-1, CUGB-jxch734. (35, 36) Yangtzeplacognathus foliaceus (Fåhræus, 1966); (35) sinistral Pa, upper view, from W-10-3, CUGB-jxch774; (36) sinistral Pb, upper view, from W-10-3, CUGB-jxch784. Scale bars represent 50 μm.
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