Terminology

Morphologic terminology generally follows that of Whittington and Kelly (Reference Whittington, Kelly and Kaesler1997). Use of “glabella” here excludes the occipital ring. “Long” and “short” are used with reference to longitudinal (sagittal, sag., and exsagittal, exs.) dimensions, and “broad” (or “wide”) and “narrow” are used with reference to transverse (tr.) dimensions (see Whittington, Reference Whittington and Kaesler1997, p. O2).

Type genus

Liostracina Monke, Reference Monke1903.

Diagnosis

Ptychopariid trilobite having parallel-sided or forward-tapering glabella; small, posteriorly placed palpebral lobes; strongly convex fixigena; variably expressed median furrow in preglabellar area; bacculae variably sized or absent; and opisthoparian facial suture; ventral cephalon has submarginal rostral suture, rostral plate with closely or widely spaced connective sutures; natant hypostomal condition.

Remarks

The diagnosis of Howell (in Harrington et al., Reference Harrington, Henningsmoen, Howell, Jaanusson, Lochman-Balk and Moore1959) is emended here to include newer information, especially information reported herein. Howell (Reference Howell, Harrington, Henningsmoen, Howell, Jaanusson, Lochman-Balk and Moore1959) included the family Liostracinidae Raymond, Reference Raymond1937, together with the family Emmrichellidae Kobayashi, Reference Kobayashi1935, in the superfamily Emmrichellacea Kobayashi, Reference Kobayashi1935 (order Ptychopariida Swinnerton, Reference Swinnerton1915). The concept of the family Liostracinidae was discussed in detail by Öpik (Reference Öpik1967). Öpik (Reference Öpik1967) included the trilobite family Liostracinidae in the suborder Ptychopariina. He also proposed the superfamily Liostracinoidea, embracing only the family Liostracinidae. On the basis of the dorsal morphology and newly ascertained ventral features of Liostracina, and on the presence of a connective suture and rostral plate in Doremataspis (which is also assigned to the family Liostracinidae), Öpik's (Reference Öpik1967) assignment is followed here.

Fortey and Chatterton (Reference Fortey and Chatterton1988) referred the Liostracinidae to the superfamily Trinucleoidea, which was then classified in the suborder Asaphina. The Asaphina was elevated to order level, as the order Asaphida, by Fortey (Reference Fortey and Kaesler1997), and this assignment was followed by Adrain (Reference Adrain and Zhang2011). As discussed below, assignment of the Liostracinidae to the Asaphida implies the presence of a ventral median suture in Liostracina, the type genus, however new evidence presented here shows that Liostracina lacks that character. Instead, the presence of a rostral plate and natant hypostomal attachment in Liostracina prompts assignment to the order Ptychopariida, which is essentially the same as Öpik's (Reference Öpik1967) suggestion.

Differences of opinion exist on whether to recognize the Ptychopariida as a formal taxonomic entity. Adrain (Reference Adrain and Zhang2011), for example, argued for abandoning use of the terms order Ptychopariida, suborder Ptychopariina, and superfamily Ptychoparioidea, because he considered these taxa to be polyphyletic. In so doing, he assigned 58 families to an order Uncertain (Incertae Ordinis). Most of the families assigned to an uncertain order were previously included in the order Ptychopariida. Lieberman and Karim (Reference Lieberman and Karim2010) and Paterson (Reference Paterson2020) likewise questioned the practicality of recognizing the order Ptychopariida. Alternatively, Yuan et al. (Reference Yuan, Li, Mu, Lin and Zhu2012, Reference Yuan, Zhang and Zhu2016), Laibl et al. (Reference Laibl, Fatka, Crônier and Budil2014), Esteve (Reference Esteve2015), Krylov (Reference Krylov2018), and Bignon et al. (Reference Bignon, Waisfeld, Vaccari and Chatterton2020), among others, recently have argued for continued recognition of the order Ptychopariida. Bignon et al. (2020, p. 1062) noted the “Ptychopariida still exists as an order even if it only includes the genus Ptychoparia, unless it can be demonstrated conclusively that it is a junior synonym of another order.”

Bignon et al. (Reference Bignon, Waisfeld, Vaccari and Chatterton2020) elevated Trinucleoidea to ordinal status. They included the family Liostracinidae in the order Trinucleida, as they construed it, and the results of their cladistic analysis showed that the liostracinids are the sister group to all other trinucleoids. That cladistic work supports a common ancestry for trinucleoids and some ptychopariids that lie outside the Asaphida. The topology of their strict consensus tree shows the Liostracinidae in a position between more-basal Ptychopariida and more-derived Trinucleida, indicating that the trinucleids also share a close relationship with ptychopariids.

As information presented here now shows, inclusion of the Liostracinidae in the concept of Trinucleida as construed by Bignon et al. (Reference Bignon, Waisfeld, Vaccari and Chatterton2020) is unacceptable because some important characters, ones characteristic of ptychopariids (e.g., the presence of a median preglabellar furrow, a ventral assembly comprising a rostral suture, a rostral plate, and a natant hypostome), were not coded into the data set. In addition, some characters considered synapomorphies of ptychopariids are now recognized as present in Liostracina. These characters, which include the absence of a ventral median suture, a non-asaphoid-type protaspis, a glabellar node situated on the occipital ring, and a parallel-sided anterior section of the facial suture, were interpreted as features of early trinucleids by Bignon et al. (Reference Bignon, Waisfeld, Vaccari and Chatterton2020). Unambiguous trinucleids, such as dionids, raphiophorids, and trinucleids, lack these characters. The median preglabellar furrow is known in some ptychopariids (e.g., Xilingxia Lu in Zhang et al., Reference Zhang, Lu, Zhu, Qian, Lin, Zhou, Zhang and Yuan1980; Paleonelsonia sulcata Yuan et al., Reference Yuan, Zhang and Zhu2016), and a parallel-sided anterior section of the facial suture is known in a number of ptychopariid species. Finally, inclusion of Liostracinidae in the Trinucleoidea by Bignon et al. (Reference Bignon, Waisfeld, Vaccari and Chatterton2020) seems related to a mistaken understanding of the ventral median suture in Liostracina. By regarding L. simesi Jago and Cooper, Reference Jago and Cooper2005, as a rostellum-bearing species, and L. volens Öpik, Reference Öpik1967, as a median-suture-bearing species, L. simesi can be inferred to show a rostral plate condition intermediate between ptychopariids and L. volens (Bignon et al., Reference Bignon, Waisfeld, Vaccari and Chatterton2020, p. 1070). As discussed below, however, the medial suture is actually absent in both species, meaning that L. simesi does not exhibit a transitional character state.

Historically, more than one-third of trilobite families have been assigned to the order Ptychopariida, which raises considerable issues related to our understanding of phylogenetic relationships. The Ptychopariida has undergone several revisions since its original conception, and is now commonly considered to be a paraphyletic or polyphyletic group (Babcock, Reference Babcock1994; Cotton, Reference Cotton2001; Lieberman and Karim, Reference Lieberman and Karim2010; Adrain, Reference Adrain and Zhang2011; Bignon et al., Reference Bignon, Waisfeld, Vaccari and Chatterton2020; Paterson, Reference Paterson2020). A thorough restudy of the ‘ptychopariids’ is long overdue, and it will undoubtedly lead to significant revision of the concept of the group. Pending further information bearing on the phylogenetic relations among ‘ptychopariids,’ here we provisionally assign Liostracinidae to the Ptychopariida because the characteristics of this family revealed by this study are most similar to those occurring in taxa among classic ptychopariids. The natant hypostomal condition and rostral plate, in particular, suggest an affinity with some taxa assigned to the order. Those characters, combined with others (e.g., median preglabellar furrow, lack of a ventral median suture, a non-asaphoid-type protaspis, which is inferred from a congeneric species, and a parallel-sided anterior section of the facial suture), strengthen that indication of affinity.

According to Jell and Adrain (Reference Jell and Adrain2003), the family Liostracinidae embraces four genera: Liostracina Monke, Reference Monke1903; Aplexura Rozova, Reference Rozova1963; Doremataspis Öpik, Reference Öpik1967; and Lynaspis Öpik, Reference Öpik1967. Another genus, Gibbura Varlamov et al., Reference Varlamov, Pak and Rozova2005, was added to the family since the time of Jell and Adrain's (Reference Jell and Adrain2003) work. Among these taxa, Aplexura and Gibbura, both from Yakutia (Siberia), Russia, are here excluded from the family. Aplexura is based on a single species, A. pallida Rozova, Reference Rozova1963, which is known only from the holotype cranidium (Rozova, Reference Rozova1963, p. 13–14, pl. 1, fig. 18). Gibbura is based a single species, G. lepida (Lazarenko, Reference Lazarenko1968), which originally was assigned to Aplexura by Lazarenko (Reference Lazarenko1968, p. 177). Both genera differ from all other liostracinid genera in having a prominent preglabellar boss, a subquadrate glabella that is truncated rather than rounded or acutely rounded anteriorly, and an ocular ridge having its abaxial end immediately posterior to the preglabellar furrow rather than well behind it. Based on current information, Liostracina, Doremataspis, and Lynaspis should be retained in the family Liostracinidae.

Type species

Liostracina krausei Monke, Reference Monke1903 (p. 114, pl. 3, figs. 10–17) from the Neodrepanura Zone, Kushan Formation, near Yanzhuang, Shandong, North China.

Other species

Liostracina volens Öpik, Reference Öpik1967, (p. 353–355, pl. 35, figs. 1–5) from the O'Hara Shale and Georgina Limestone, Georgina Basin, western Queensland, Australia; Liostracina nolens Öpik, Reference Öpik1967 (p. 355, pl. 35, figs. 6, 7) from the Georgina Limestone, Georgina Basin, western Queensland, Australia; Liostracina bella Lin and Zhou in Lin et al., Reference Lin, Lin and Zhou1983 (p. 407, pl. 3, figs. 7–10) from the Tuanshan Formation, southern Jiangsu, China; Liostracina bilimbata Zhang in Qiu et al., Reference Qiu, Lu, Zhu, Bi, Lin, Zhou, Zhang, Qian, Ju, Han and Wei1983 (p. 200, pl. 67, figs. 4, 5) from the Kushan Formation, northern Anhui, China; Liostracina qingyangensis Qian and Qiu in Qiu et al., Reference Qiu, Lu, Zhu, Bi, Lin, Zhou, Zhang, Qian, Ju, Han and Wei1983 (p. 201, pl. 67, fig. 1) from the Tuanshan Formation, southern Anhui; Liostracina suixiensis Bi in Qiu et al., Reference Qiu, Lu, Zhu, Bi, Lin, Zhou, Zhang, Qian, Ju, Han and Wei1983 (p. 201, pl. 67, fig. 2) from the Kushan Formation, northern Anhui, China; Liostracina simesi Jago and Cooper, Reference Jago and Cooper2005 (p. 671, fig. 4A–E) from the Spurs Formation, Northern Victoria Land, Antarctica; Liostracina kaulbacki Shergold et al., Reference Shergold, Laurie and Shergold2007 (p. 32, fig. 13), from the Skewthope Formation, Bonaparte Basin, Australia; Liostracina tangwangzhaiensis Park et al., Reference Park, Kihm, Kang and Choi2014 (p. 398, figs. 1, 2) from the Kushan Formation, Tangwangzhai, Changqing, Shandong, North China; Liostracina joyceae Smith et al., Reference Smith, Paterson and Brock2018 (p. 41, fig. 20) from the Shannon Formation, Amadeus Basin, Northern Territory, Australia; Liostracina cf. L. nolens Öpik sensu Cooper et al., Reference Cooper, Jago and Begg1996 (p. 381, fig. 6V, W) from the Molar Formation, Northern Victoria Land, Antarctica; Liostracina sp. sensu Park and Choi, Reference Park and Choi2011 (p. S6, sup. fig. S7) from the Sesong Formation, Jikdong, South Korea; Liostracina cf. L. kaulbacki Shergold et al., Reference Shergold, Laurie and Shergold2007, sensu Smith et al., Reference Smith, Paterson and Brock2018 (p. 44, fig. 21) from the Shannon Formation, Amadeus Basin, Northern Territory, Australia; Liostracina sp. sensu Smith et al., Reference Smith, Paterson and Brock2018 (p. 46, fig. 22) from the Shannon Formation, Amadeus Basin, Northern Territory, Australia; and Liostracina fuluensis n. sp.

Three species are questionably assigned to the genus: Liostracina? pauper Resser and Endo, Reference Resser, Endo, Endo and Resser1937 (p. 239, pl. 45, fig. 10); L.? paupiforme Endo, Reference Endo1944 (p. 78, fig. 17) from the Changhia (=Taitzu) Formation, Liaoning, China; and Liostracina bifurcata Zhang in Qiu et al., Reference Qiu, Lu, Zhu, Bi, Lin, Zhou, Zhang, Qian, Ju, Han and Wei1983 (p. 200, pl. 67, fig. 3) from the Kushan Formation, northern Jiangsu, China. Liostracina? pauper and L.? paupiforme have short preglabellar fields. They were questionably assigned to Liostracina originally, and we concur with the assignments. Liostracina bifurcata has an anteriorly truncated and an unusually bifurcated eye ridge. In these respects, it differs from other species assigned to Liostracina. As noted by Park et al. (2014, p. 398), each of these species is represented by a single and poorly preserved cranidium. Two tiny cranidia from the DuNoir Limestone, Wyoming, USA, assigned as cf. Liostracina sp. by Lochman and Hu (Reference Lochman and Hu1961, p. 142, pl. 30, figs. 49, 50), appear to be erroneously assigned to this genus because the material has a highly convex cranidium, an anteriorly located palpebral lobe, a short preglabellar field, and a proportionately long glabella.

Diagnosis

Cephalon, excluding genal spines, lunate or semicircular; cranidium with moderately long (sag.) frontal area; median preglabellar furrow weak, variably incised or effaced; glabella slightly tapering forward to parallel-sided, acutely to obtusely rounded anteriorly, with three pairs of short, distinct to effaced lateral furrows; bacculae obliterated to distinct; palpebral lobe small, located posteriorly; eye ridge weak to distinct, gently oblique rearward; facial suture opisthoparian; rostral suture submarginal, connective sutures closely spaced, defining narrow rostral plate; librigenal spine broad proximally, with border ridge and slender, ribbon-like edge. Thorax of eight segments, fulcrate anteriorly and nonfulcrate posteriorly. Pygidium transversely subtriangular, with transverse pleural and interpleural furrows and upturned lateral and posterior borders. Surface smooth, granulate, or wrinkled on preocular field.

Remarks

The diagnosis is emended based on all known species referred to Liostracina. Previously, Monke (Reference Monke1903) provided a detailed description on Liostracina krausei, the type species, which formed the basis for understanding the generic concept; Lu et al. (Reference Lu, Qian and Zhu1963, p. 121) published a brief diagnosis; and Öpik (Reference Öpik1967) discussed the genus, as then known, in detail. New information provided here relates to the thoracic morphology and the ventral cephalic structure.

Liostracina is a distinctive ptychopariid trilobite that has a median preglabellar furrow on the dorsal side and rostral and connective sutures on the ventral side. The ventral connective sutures are closely spaced, and define a narrow rostral plate. Liostracina differs from Doremataspis by the presence of median preglabellar furrow, the narrower anterior area of fixigena, the more anteriorly placed palpebral lobe, and much smaller rostral plate in ventral side. Lynaspis bears a median preglabellar furrow, but differs in having an undivided anterior area of fixigena and more divergent anterior branch of facial suture. In Liostracina, the median preglabellar furrow on the dorsal side is variable in length and degree of incision. The preglabellar median furrow is commonly well defined, complete to nearly complete in L. bella, L. bilimbata, and L. volens (Öpik, Reference Öpik1967, pl. 35, figs. 1–3; Lin et al., Reference Lin, Lin and Zhou1983, pl. 3, figs. 7, 8; Peng et al., Reference Peng, Babcock and Lin2004a, pl. 61, figs. 6, 11, pl. 62, figs. 2, 4), faint and incomplete in L. qingyangensis, L. simesi, L. suixiensis, L. tangwangzhaiensis, L. joyceae, and L. cf. L. kaulbacki (Qiu et al., Reference Qiu, Lu, Zhu, Bi, Lin, Zhou, Zhang, Qian, Ju, Han and Wei1983, pl. 67, figs. 1, 2; Jago and Copper, Reference Jago and Cooper2005, fig. 4A, B, D; Park et al., Reference Park, Kihm, Kang and Choi2014, figs. 1.1, 2; Smith et al., Reference Smith, Paterson and Brock2018, figs. 20, 21), and effaced in L. kaulbacki (Shergold et al., Reference Shergold, Laurie and Shergold2007, fig. 13A–G). The distinctness or relative effacement of the bacculae, lateral glabellar furrows, and eye ridges varies among and sometimes within species of Liostracina. The bacculae are well defined in most species, but obscure in L. tangwangzhaiensis (Park et al., Reference Park, Kihm, Kang and Choi2014, fig. 2.20) and absent in L. kaulbacki and L. sp. sensu Park and Choi (Shergold et al., Reference Shergold, Laurie and Shergold2007, fig. 13A–G; Park and Choi, Reference Park and Choi2011, sup. fig. S7.1, S7.5, S7.8). In L. fuluensis n. sp., the length of bacculae varies intraspecifically. The lateral glabellar furrows, especially the S1 and S2 furrows, are clearly defined in some species, but faint or effaced in others. The eye ridge is well defined in most species, but obscure or absent in L. tangwangzhaiensis and L. kaulbacki.

Liostracina fuluensis new species
Figures 2–7

Reference Peng, Yang, Liu, Zhu, Sun, Zamora, Mao and Zhang2020

Liostracina sp., Peng et al., p. 456, fig. 3O.

Figure 7.

Liostracina fuluensis n. sp. from the Longha Formation, Guzhangian, Fulu area, southeastern Yunnan; specimens showing ventral structure; white arrowhead indicates the posterior margin of thorax; for abbreviations see caption of Figure 4; (1, 3, 7–9, 11, 12) ventral views, (2, 4–6, 10) dorsal views; (1) NIGP 173769, degree 5 meraspid exoskeleton lacking cranidium; (2, 3) NIGP 173770, degree 6 meraspid exoskeleton with cephalic doublure, (3) is the reversed image of (2) in gray tone; (4, 7) NIGP 173771, degree 6 meraspid exoskeleton with cephalic doublure and missing cranidium, (7) is latex cast of (4); (5, 8) NIGP 173772, partly disarticulated, holaspid exoskeleton with cephalic doublure and latex cast; (6, 9) NIGP 173773, holaspid exoskeleton and latex cast, with cephalic doublure; (10–12) NIGP 173774, holaspid exoskeleton (10) and latex cast (11, 12), with cephalic doublure. All scale bars represent 2 mm.

Holotype

NIGP 171341, external mold of exoskeleton (Fig. 3.2, 3.3) from the upper part of the middle member of the Longha Formation, Fulu, Funing, Yunnan, China.

Paratypes

NIGP 173732–173774, including 26 variously complete, figured exoskeletons, seven cephala, five cranidia, four librigenae, and one pygidium, from the same location and stratigraphic interval as the holotype.

Diagnosis

A species of Liostracina with long preglabellar area, incomplete and weakly defined median preglabellar furrow, weakly to well-defined eye ridge, and baccula; facets present on anterior four thoracic pleurae.

Occurrence

Lower part of the middle member of the Longha Formation, equivalent to the upper Proagnostus bulbus and lower Linguagnostus reconditus zones.

Description

Exoskeleton subrounded, about as long as wide; axis narrow, occupying 0.78–0.80 sagittal length of exoskeleton. Cephalon large, lunate in outline (or semicircular if the librigenal spines are excluded), occupying a little more than one-half exoskeletal length. Glabella moderately convex, tapering slightly forward or parallel-sided, acutely rounded to rounded anteriorly, occupying about one-half cephalic length; with three pairs of straight lateral furrows, equally spaced; S1 and S2 weak to deeply incised, gently oblique rearward; S3 faint; occipital ring long (sag.), slightly shortened abaxially, about one-fourth of sagittal length of glabella, with curved posterior margin and faint or effaced occipital node; occipital furrow transverse; baccula distinct to faint, long, oval, distinct from glabella. Median preglabellar furrow incomplete, weak. Anterior border convex, smoothly curved, defined by shallow and long (sag., exs.) anterior border furrow; preocular field of fixigena long and broad, occupying more than one-half fixigenal length (exs.); palpebral lobe reniform, located posteriorly; eye ridge usually distinct, rarely weak, at angle of ~75° to sagittal line; palpebral and postocular areas grade gently to axial furrow; posterior border furrow prominent, posterior cranidial border short (exs.), uniform in length; anterior branch of facial suture diverges, then curves inward and forward, continuing onto ventral side; posterior branch short, diverging at angle of ~40° to sagittal line. Librigena half as wide as cranidium, exsagittal length including spine greater than sagittal length of exoskeleton; genal spine broad proximally, curving inward as it extends posteriorly, with convex ridge on lateral and posterior borders.

Ventrally, cephalic doublure is short and wide anteriorly, bounded posteriorly by submarginal stenoptychopariid rostral suture; lateral cephalic (or librigenal) doublure widest at posterior margin of cephalon, narrowing gently both anteriorly to connective suture and posteriorly to tip of librigenal spine; paired connective sutures are closely spaced, straight or gently curved, parallel or at an acute angle to sagittal line, and define a narrow, subtrapezoidal or rectangular rostral plate.

Hypostome in natant condition, shield-shaped, with gently inflated middle body comprising oval anterior lobe, faint middle furrow, and apparently semicircular posterior; lateral border narrow and convex; posterior border not well known, probably with rounded posterior margin.

Holaspid thorax with eight segments; axis moderately convex, nearly as wide as pleural area anteriorly but progressively narrowing posteriorly; pleurae of low convexity; anterior four segments with pointed tips and facets; fifth segment may have incomplete facet; posterior three or four segments with straight tips. Ventral thoracic doublure c-shaped on anterior four segments (Figs 4, 5.16, 6.1, 6.20, 7.11), narrow and thin (tr.), bar-shaped on posterior four segments.

Figure 4.

Reconstruction of Liostracina fuluensis n. sp.; dorsal exoskeleton (left) and ventral exoskeleton (right). Sculpture on preocular fields and terrace ridges on cephalic doublure are omitted. Abbreviations for this figure and Figures 5–7: cd, cephalic doublure; cs, connective suture; e, eye; es, eye socle; f, facet; fs, facial suture; h, hypostome; pd, pygidium doublure; pl, palpebral lobe; rp, rostral plate; rs, rostral suture; td, thoracic doublure. Scale bar represents 2 mm.

Figure 5.

Liostracina fuluensis n. sp. from the Longha Formation, Guzhangian, Fulu area, southeastern Yunnan; specimens showing ventral structure; white arrowhead indicates the posterior margin of thorax; for abbreviations see caption of Figure 4; (1, 2, 4–10, 12) dorsal views; (3, 11, 13–16) ventral views; (1) NIGP 173746, degree 7 meraspid exoskeleton with cephalic doublure; (2, 3) NIGP 173747, external mold of degree 7 meraspid exoskeleton and latex cast with cephalic doublure; (4) NIGP 173748, enrolled holaspid exoskeleton; (5) NIGP 173749, exoskeleton with cephalic doublure; note the right librigena has moved inward slightly, resulting in a narrow look to the rostral plate; (6, 7) NIGP173750, cephalon bearing two thoracic segments, with doublure; note specimen seems to be compressed transversely, resulting a narrow look to the rostral plate; (8, 9, 14, 15) NIGP 173751, 173752, holaspid exoskeleton with cephalic doublure, (14) is the latex cast of (8), and (15) is latex cast of (9); (10, 11) NIGP 173753, cranidium and its latex cast, showing a long baccula; (12) NIGP 173754, cranidium; (13) NIGP 173755, latex cast of cranidium; (16) NIGP 173756, latex cast of incomplete exoskeleton lacking the right librigena and having a displaced left librigena. All scale bars represent 2 mm.

Figure 6.

Liostracina fuluensis n. sp. from the Longha Formation, Guzhangian, Fulu area, southeastern Yunnan; specimens showing ventral structure; white arrowhead indicates the posterior margin of thorax; for abbreviations see caption of Figure 4; (1–10, 13, 14, 18–20) dorsal views; (11, 12, 15–17) ventral views; (1, 2) NIGP 173757, external mold of holaspid cephalon with cephalic doublure, six thoracic segments and broken left librigena; (3, 4) NIGP 173758, holaspid cephalon with cephalic doublure; (5, 6) NIGP 173759, holaspid cephalon with cephalic doublure, five inverted thoracic segments, and missing occipital ring; (7, 8, 11) NIGP 173760, holaspid exoskeleton (7, 8) and latex cast with cephalic doublure (11); (9, 10) NIGP 173761, cephalon missing the right librigena; (12) NIGP 173762, latex cast of holaspid exoskeleton; (13, 14) NIGP 173763, latex cast of cephalon with cephalic doublure and lacking occipital ring; (15–17) NIGP 173764, 173765, 173766, doublure of librigena, note the straight adaxial tip; (18) NIGP 173767, latex cast of librigena; (19, 20) NIGP 173768, exoskeleton lacking the librigenae, and enlargement of part of the same specimen. All scale bars represent 2 mm.

Pygidium of low convexity, subtriangular in outline, wide and short, with upturned lateral and posterior border. Axis conical, faintly divided into three rings and a terminal piece that reaches almost to posterior border furrow. Pleural field flat, with faint, transverse pleural and interpleural furrows. Pygidial doublure forms a narrow ridge rim.

Dorsal surface mostly smooth, except for preocular field, which is covered with radial wrinkles; doublure of librigena bears fine terrace ridges.

Etymology

After Fulu Village, Funing County, southeastern Yunnan Province; site of the section yielding the Fulu Biota, including this species.

Remarks

The new species is most similar to Liostracina volens Öpik, Reference Öpik1967, from Australia, but differs in having a broader (sag, exsag.) anterior cranidial border, shallower border furrow, and an incomplete, less-distinct median preglabellar furrow. The new species also appears to differ from L. volens in having a longer preglabellar area in large holaspides. In L. fuluensis n. sp., the proportional length of the preglabellar area varies from 0.74–0.95 of the glabellar length (excluding occipital ring), and in most specimens it is more than 0.80 of the glabellar length. For comparison, the holotype cranidium of L. volens (Öpik, Reference Öpik1967, pl. 35, fig. 1), has a proportionate length of 0.70–0.72. The new species differs further in having three pairs of lateral glabellar furrows with S1 and S2 strongly incised, a much shallower and wider (sag., exs.) anterior cranidial border, and an incomplete preglabellar median furrow. In L. volens, there are only two pairs of shallow glabellar furrows, the anterior border furrow is narrow (sag., exs.) and deeply incised and the preglabellar median furrow is longer, nearly reaching to the anterior cranidial furrow.

The long preglabellar area of L. fuluensis n. sp. also helps differentiate the new species from some other congeneric species that have shorter preglabellar areas. Liostracina kaulbacki, L. suixiensis, L. simesi, L. krausei, and L. joyceae and all have proportionate preglabellar lengths of <0.70 (~0.48 in L. kaulbacki, ~0.65 in L. simesi, ~0.68 in both L. bilimbata and L. suixiensis, ~0.69 in L. krausei, and ~0.58 to ~0.69 in L. joyceae).

Liostracina nolens, L. simesi, and L. joyceae differ from L. fuluensis n. sp. in having granulate sculpture dorsally, whereas L. tangwangzhaiensis, L. kaulbacki, and L. krausei show greater degrees of effacement. Liostracina bella and L. qingyangensis are easily distinguished from L. fuluensis n. sp. by having a curved ridge immediately behind the anterior cranidial border furrow.