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Keywords:

  • Strophomenide brachiopods;
  • palaeobiogeography;
  • Late Ordovician;
  • South China

Abstract

  1. Top of page
  2. Abstract
  3. Brief notes on regional geology
  4. Faunal development of ordovician strophomenides in south china
  5. Palaeobiogeographic affinities
  6. Systematic Palaeontology
  7. Acknowledgments
  8. References
  9. Appendix

Abstract:  Late Ordovician strophomenide brachiopods (superfamilies Strophomenoidea and Plectambonitoidea) from the upper Changwu Formation (mid Ashgill, late Katian) of Jianglütang, Chun’an County, western Zhejiang Province, consist of ten genera and 12 species. Five new species of three new genera are recognized: Chunanomena triporcata, Chunanomena sembellina, Cheramomena subsolana, Lateriseptomena modesta, and Lateriseptomena rugosa. The strophomenide brachiopods from the upper Katian strata described in this study and those from the border region of Zhejiang and Jiangxi provinces reported in previous work contain 16 strophomenoid and 12 plectambonitoid genera, and most of the strophomenoids are endemic to South China. Numerical analysis of well-documented late Katian strophomenide brachiopod faunas indicates a strong provincialism, characterized by the highly distinct North American province (Laurentia), the South China-Kazakhstan province, and the Avalonia-Baltica province (Wales, Belgium and Sweden). Surprisingly, the Girvan district of Scotland, which was a peri-Laurentian terrane during the Ordovician, contains a late Katian brachiopod fauna that is more closely related to the contemporaneous brachiopods of Avalonia-Baltica than to those of North America.

As a main component of the Palaeozoic Evolutionary Fauna (Sepkoski 1981, 1984; Sheehan 1982), brachiopods were major contributors to the Ordovician biodiversification event (Webby 2000; Webby et al. 2004). Orthides, strophomenides, and pentamerides (syntrophidines) were important brachiopod groups that went through three pulses of radiation during the Ordovician (Harper et al. 2004), with the origin and proliferation of strophomenide post-dating those of pentamerides and orthides. Within the Order Strophomenida, the oldest reported plectambonitoid, AkelinaSevergina, 1967, came from the late Tremadoc Algan Formation of Gorny Altai, Russia, although the taxonomic position of this genus remains questionable (e.g. Cocks and Rong 1989, 2000). The undisputed first appearance of plectambonitoids is PlectellaLamansky, 1905 from lower Arenig strata in the Tallinn area of Estonia (Öpik 1933; Cocks and Rong 2000).

Pioneer taxa of the strophomenoids have been reported from Mid Ordovician strata in several palaeocontinents, such as Laurentia (Salmon 1942; Cooper 1956), Baltica (Neuman and Bruton 1974), Avalonia (Lockley and Williams 1981), and South China (Rong et al. 1999). The oldest known so far is from South China (Zhan and Rong 2003, 2006; Zhan et al. 2004) where plectambonitoids and strophomenoids first appeared in the Acrograptus filiformis Biozone (earliest Arenig, early Floian) and the Expansograptus hirundo Biozone (early late Arenig, early Mid Ordovician) respectively, and reached their first diversity acme during the Llanvirn (Darriwilian). Thus, the first diversification of strophomenides in South China predated that in most other regions of the world by 2–3 graptolitic biozones (see Harper et al. 2004).

Globally, the last radiation of strophomenide brachiopods in the Ordovician occurred during the mid Ashgill. Among the best examples of this event are the Richmondian brachiopod fauna of Laurentia (e.g. Howe 1965, 1988; Dewing 1999) and the unusually rich and diverse strophomenides of the Boda Limestone of Sweden (Cocks 2005). In South China, rich and diverse brachiopod faunas of mid Ashgill age are known only in western Zhejiang and north-eastern Jiangxi provinces, with a number of localities yielding abundant strophomenides, as well as orthides (Zhan and Rong 1994, 1995a; Zhan and Cocks 1998).

At the Jianglütang section in Chun’an County, western Zhejiang Province, strophomenide brachiopods are unusually rich and diverse at some levels in the upper Changwu Formation. During the 2003 field season, a rich suite of brachiopods was collected from a fossiliferous horizon in the upper part of the formation, which also yielded trilobites, bivalves, ostracods, and bryzoans. In taxonomic composition, the brachiopod fauna of the Changwu Formation is similar to that from the coeval mid Ashgill rocks in the border region of Zhejiang and Jiangxi provinces (Zhan and Cocks 1998), but the abundance of strophomenide brachiopods is a distinct character of the Changwu fauna in the Chun’an area. In this respect, the strophomenides from the Changwu Formation of western Zhejiang hold important information on mid Ashgill brachiopod radiation in South China. The main objectives of this paper are to provide a systematic description of this group of brachiopods and to analyse their faunal affinities with coeval faunas in other palaeogeographical regions.

Brief notes on regional geology

  1. Top of page
  2. Abstract
  3. Brief notes on regional geology
  4. Faunal development of ordovician strophomenides in south china
  5. Palaeobiogeographic affinities
  6. Systematic Palaeontology
  7. Acknowledgments
  8. References
  9. Appendix

During the Early–Mid Ordovician, the palaeogeographical framework of South China was dominated by three tectonic elements from the north-west to the south-east: the Yangtze Platform, the Jiangnan Transitional Belt and the Zhujiang Basin (for a recent summary illustration, see Zhan et al. 2006). From late Mid Ordovician time, however, this broad pattern was transformed by the Chongyu Orogeny (Wu 2000, 2003), when the docking of an exotic terrane from the south-east led to an orogenic uplift of the south-eastern margin of the South China palaeoplate to form the Cathaysian Land (Rong and Chen 1987; Rong et al. 2003). In the palaeogeographical zone between the Yangtze Platform to the north-west and the Cathaysian Land to the south-east, a complex suite of carbonate and siliciclastic deposits accumulated during the Ashgill (Lu et al. 1976; Liang 1977; Rong and Chen 1987; Lai et al. 1993; Zhan and Fu 1994). The Changwu Formation, the subject of this study, is a flyshoid facies within this complex, consisting of shales, mudstones, silty mudstones, siltstones and sandstones (Lu et al. 1955; Rong and Chen 1987).

At its type locality (Shangwu, 3 km north of the Jiangshan County town, western Zhejiang Province), the Changwu Formation is about 280 m thick. It is underlain conformably by the lower Ashgill Huangnehkang Formation and overlain unconformably by the lower Carboniferous Yejiatang Formation. Palaeogeographically, the formation was widespread on the Zhexi Slope (Rong and Chen 1987), corresponding to the present western Zhejiang and north-eastern Jiangxi provinces (Jiangxi Geological Bureau 1988; Zhejiang Geological Bureau 1989). A complete deep-water facies of the Changwu Formation may attain a great thickness, up to 2118 m. In the Longtan area (Chun’an County) of western Zhejiang Province, it is conformably underlain by the Huangnehkang Formation and overlain by the Hirnantian Wenchang Formation (Liang 1977; Zhejiang Geological Bureau 1989; Chen et al. 1995). Both graptolites and shelly fossils tend to be rare in the deposits of the Changwu Formation, which accumulated rapidly. In some intervals, particularly in the upper part of the formation, however, shelly fossils become relatively common.

The Changwu Formation at Jianglütang, south-west of the Chun’an County town (Text-fig. 1), is about 1300 m thick, with a wide range of lithofacies characterized by mudstone, silty mudstone, siltstone, and sandstone. The section was first measured by the Regional Geological Survey Team of the Anhui Geological Bureau in 1971, but they treated the upper part of the Changwu Formation as the lower Wenchang Formation (Hirnantian). In our 2003 field work, the section was shown to have a relatively consistent lithofacies and, more importantly, the shelly fauna in the upper part of the sequence is mid Ashgill rather than Hirnantian in age. In this study, therefore, the entire section measured at Jianglütang is treated as the Changwu Formation.

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Figure TEXT-FIG. 1..  Location of the study area. A, map of China with the South China palaeoplate outlined by a thick line. B, enlargement of inset box in A showing the western part of Zhejiang Province. C, enlargement of inset box in B; map showing Jianglütang Village in Chun’an County and simplified geology of the area. The fossil site (solid triangle) is accessible by boat. Abbreviations: Z, Precambrian; Є, Cambrian; O, Ordovician; S, Silurian; D, Devonian; C, Carboniferous; J, Jurassic; K, Cretaceous; γ, Mesozoic igneous rocks (adapted from Zhejiang Regional Geological Survey 1965).

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Faunal development of ordovician strophomenides in south china

  1. Top of page
  2. Abstract
  3. Brief notes on regional geology
  4. Faunal development of ordovician strophomenides in south china
  5. Palaeobiogeographic affinities
  6. Systematic Palaeontology
  7. Acknowledgments
  8. References
  9. Appendix

As discussed recently by Zhan et al. (2004), in South China plectambonitoid brachiopods first appear in lower Arenig strata (Acrograptus filiformis Biozone) of the basal Meitan and Dawan formations on the Upper Yangtze Platform. Among the pioneer taxa of plectambonitoids, Leptella grandisXu, Rong and Liu, 1974 was the most common species and formed a distinct Leptella grandis Association in a lower BA2 palaeoenvironment (Zhan et al. 2006). After their relatively early first appearance, the first plectambonitoid radiation did not occur until Darriwilian (roughly Llanvirn) time, when ten genera became common on the Yangtze Platform (Text-fig. 2).

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Figure TEXT-FIG. 2..  Stratigraphical distribution of strophomenide brachiopods (Plectambonitoidea and Strophomenoidea) in South China. Graptolitic biozones are from Zhang and Chen (2003, 2006). BD, ‘British subdivision’.

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Strophomenoids first appear in South China (the Upper Yangtze Platform) in the Expansograptus hirundo Biozone, approximately four graptolitic biozones above the first appearance of plectambonitoids. This coincides with the first brachiopod β-diversity maximum recognized in South China (Zhan et al. 2006). These pioneer strophomenoids also include the oldest known forms of the superfamily, from the middle Daguanshan Formation of southern Sichuan Province and the upper Meitan Formation of northern Guizhou Province (Zhan et al. 2004). Despite their late start, the strophomenoids radiated rapidly in South China, concomitant with the diversification of plectambonitoids during the Llanvirn.

Among the ten plectambonitoid and 13 strophomenoid genera that thrived during the Darriwilian strophomenide radiation, most of the newly arrived genera have a strikingly cosmopolitan aspect. For example, Leptellina, Leangella, Eoplectodonta, Christiania, Platymena, Leptaena and Strophomena have been found in more than four palaeoplates or terranes, whereas Aporthophyla, Leptestiina, Longvillia and Bellimurina occur in two to three such regions. Only a small number of taxa are endemic to South China (e.g. Halirhachis and Heteromena; see Zhan and Jin 2005b).

During the early Caradoc, the strophomenides in South China were dominated by a new group of plectambonitoids (Anisopleurella, Anoptambonites, Bilobia, Diambonioidea, Duranella, Kassinella and Multiridgia; see Chang 1983; Zeng et al. 1987; Rong et al. 1999), together with a few hold-over taxa from the Darriwilian (Text-fig. 2). In comparison, strophomenoids became impoverished during this early period of the Late Ordovician. One of the significant strophomenoids of this interval is Foliomena, which first appeared in the central part of the Yangtze Platform during the early Caradoc, forming a distinct Foliomena Fauna in a relatively deep-water, muddy-substrate environment (BA 5). The Foliomena Fauna from the Miaopo Formation (lower Caradoc) of South China is the oldest known. Subsequently, the fauna became cosmopolitan in late Caradoc and Ashgill times (for a recent summary, see Zhan and Jin 2005a). The Foliomena Fauna is thought to be the first well-documented example of successful colonization of a brachiopod fauna in deep-water environments (Rong et al. 1999). Thus strophomenide faunal evolution in South China during the early Caradoc reflects mainly their adaptation to deep-water conditions associated with a eustatic marine transgression.

Strophomenide brachiopods are poorly known from the mid and upper Caradoc of South China. Their low diversity during the time interval represented may be the result of a combination of facies control and collection bias, because the Pagoda and Linhsiang formations consist mainly of massive to nodular limestones of deep water origin and brachiopods appear to be rare and difficult to collect.

The last radiation of strophomenides in the Ordovician of South China occurred during the mid Ashgill (Text-fig. 2; see also Rong and Harper 1999). This strophomenide fauna was dominated by newly evolved genera, many of which were endemic to South China. For example, the mid Ashgill strophomenide fauna contains 28 genera, of which 12 are new and endemic forms, mostly strophomenoids (8 out of 12). Apart from a few regional taxa that are found in two or three palaeoplates or terranes (e.g. Kassinella, Mabella, and Metambonites), the strophomenide radiation in the mid Ashgill of South China can be regarded largely as an endemic event, but coincident with the global trend.

Interestingly, the cosmopolitan pre-Ashgill and highly provincial Ashgill strophomenide faunas discussed above are comparable to Mid–Late Ordovician rhynchonellide palaeobiogeographic distributions (Jin 1996). Rhynchonellide genera that first appeared in Llanvirn (late Darriwilian) to mid Caradoc time usually attained a cosmopolitan distribution, whereas those originating from latest Caradoc to mid Ashgill times were largely endemic. This trend was particularly evident in the Hiscobeccus-Lepidocyclus-rich North American epicontinental fauna (Jin 2001).

The abrupt decrease in strophomenide diversity during the Hirnantian, particularly the extinction of endemic forms, implies that this group of brachiopods was highly sensitive to sea-level fall and perhaps oceanic cooling during the glacially induced Hirnantian mass-extinction event.

Palaeobiogeographic affinities

  1. Top of page
  2. Abstract
  3. Brief notes on regional geology
  4. Faunal development of ordovician strophomenides in south china
  5. Palaeobiogeographic affinities
  6. Systematic Palaeontology
  7. Acknowledgments
  8. References
  9. Appendix

The mid Ashgill marks the last pulse of global brachiopod diversification in the Ordovician, characterized by the proliferation and geographic segregation of low- to medium-latitude, shallow-marine faunas (Harper et al. 2004). Orthides, strophomenides and rhynchonellides are perhaps the most prominent components of the mid Ashgill brachiopod faunas world-wide. With the addition of a significantly large strophomenide fauna from South China, as reported herein, it is now possible to investigate the palaeobiogeographic relationships of this fauna to contemporaneous strophomenate faunas across the major plates and terranes of Late Ordovician time. For this analysis, the selected strophomenate-rich, mid Ashgill brachiopod faunas are confined to those that have been studied taxonomically in detail (see Appendix for faunal lists): (1) GIR, Girvan, Scotland (Harper 1989, 2006); (2) WAL, North Wales (Hiller 1980); (3) DAL, Dalarna, Sweden (Cocks 2005); (4) IKB, Pomeroy, Ireland (Mitchell 1977); (5) BFS, regions of the Sambre and Meuse rivers, Belgium (Sheehan 1987); (6) AMC, American mid-continent (Wang 1949; Davis 1985); (7) ANT, Anticosti Island, eastern Canada (Dewing 1999); (8) MAN, southern Manitoba, central Canada (Jin and Zhan 2001); (9) SCH, western Zhejiang and eastern Jiangxi, south-east China (this study).

Two Caradoc faunas, one from New South Wales, Australia (NSW; Percival 1979a, b) and another from the Chu-Ili Range of southern Kazakhstan (KAZ; Popov et al. 2000; Popov and Cocks 2006), are also included as outgroups because these faunas contain a number of taxa that extend from the Caradoc to the Ashgill. A binary dataset is constructed based on the presence/absence of strophomenide genera in the 11 regions. Principal component analysis (PCA) and cluster analysis (CA) were performed using PAST (Hammer and Harper 2006). From the numerical analyses, several faunal characteristics can be observed (Text-fig. 3).

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Figure TEXT-FIG. 3..  A–B, principal component analysis (PCA) and cluster analysis (CA) respectively of selected Late Ordovician (mainly mid Ashgill) strophomenide brachiopod faunas. For faunal details and abbreviations, see Appendix. Software, PAST (Hammer and Harper, 2006); PCA data matrix, variance-covariance; PCA biplot lines, for number-coded taxa, see Appendix; CA algorithm, paired group; CA similarity index, Simpson.

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  • 1
     The two Caradoc faunas appear to be dominated by plectambonitoids, whereas the mid Ashgill faunas are generally dominated by strophomenoids. The predominance of plectambonitoids in the Caradoc strophomenide faunas, however, may be regional phenomena because the Caradoc (Trentonian) brachiopod faunas of North America usually contain more strophomenoids than plectambonitoids.
  • 2
     The mid Ashgill faunas are strongly endemic, with 86 per cent of the taxa in each fauna present in one or two, rarely three, palaeoplates or terranes. Among the faunas analysed (92 strophomenate genera in total), only one genus (Strophomena) is widespread, occurring in 10 regions; three genera (Christiania, Leptaena, Sowerbyella) occur in seven regions, one subgenus, Sowerbyella (Rugosowerbyella), in six regions, three genera (Anoptambonites, Holtedahlina, Leangella) in five regions, and five (Anisopleurella, Bimuria, Gunnarella, Katastrophomena, Luhaia) in four regions. The high level of faunal endemism or provincialism is reflected by low similarity coefficients (ranging from 0.3–0.4) between major palaeotectonic regions (Text-fig. 3B).
  • 3
     Laurentia seems to have the most coherent suite of strophomenides, with the faunas from the intracratonic Williston Basin (southern Manitoba), American mid-continent (AMC), and continental-margin Anticosti Basin (ANT) forming a tight cluster. The two faunas from the Laurentian epicontinental seas (MAN and AMC), in particular, attain a similarity coefficient of 0.87, the highest value among all paired faunas included in the analysis. The Laurentian strophomenide fauna is typified by several endemic genera, such as Thaerodonta (87), Megamyonia (55), Nasutimena (58), Oepikina (60) and Tetraphalerella (86) (Text-fig. 3A; number codes of genera are given in the Appendix; for discussion on the validity of Thaerodonta, see Cocks and Rong 1989, 2000; Potter and Boucot 1992; Jin et al. 1997; Jin and Zhan 2001).
  • 4
     The strophomenide fauna of Girvan (GIR) is shown to have a closer affinity with those of the Baltica palaeocontinent and Avalonia palaeoterrane than to those of Laurentia during mid Ashgill time. This is in sharp contrast to the Scoto-Appalachian brachiopod fauna of Llanvirn (Darriwilian)–Caradoc times, when Scotland was part of Laurentia and the shelly organisms of these two tectonic units formed a single faunal province (Williams 1969; Jaanusson 1973; Spjeldnaes 1981; Harper and Parks 1989; Jin 2001). The mid Ashgill brachiopod fauna of Girvan shares several genera with those of Dalarna, Sweden (DAL), Glyn Ceiriog, Wales (WAL), Pomeroy, Ireland (IKB), and the Sambre and Meuse rivers region of Belgium (BFS), including Anisopleurella, Eoplectodonta, Gunnarella, Kiaeromena, Luhaia, Pomeromena and Sampo. This suggests that, during their northward drift, Baltica and Avalonia were sufficiently close to the eastern margin of Laurentia by the mid Ashgill to disrupt the faunal link between Scotland and the more southerly margin of Laurentia. Meanwhile, the tectonic convergence between Scotland and England probably facilitated a close faunal link between the Girvan District, Wales (Avalonia) and Sweden (Baltica).
  • 5
     Several earlier studies have shown that the Ordovician brachiopod fauna of South China had a close relationship with that of southern Kazakhstan (e.g. Zhan and Cocks 1998; Popov et al. 2000; Popov and Cocks 2006). The newly reported strophomenides in this study further corroborate these observations and suggest a close faunal affinity between the two regions from Caradoc to mid Ashgill times. Several mid Ashgill strophomenide genera from South China have also been found in older (upper Caradoc) strata in southern Kazakhstan, such as Eopholidostrophia (22), Holtedahlina (35), Kassinella (39), Leptellina (50) and Metambonites (56), among which some (e.g. Metambonites) have so far been found only in the two regions. The Caradoc strophomenides of New South Wales (Percival 1979a, b) have a very low similarity coefficient with any other faunas, although it has some genera in common with the southern Kazakhstan fauna, such as Dulankarella (18) and Gunningblandella (33).

Systematic Palaeontology

  1. Top of page
  2. Abstract
  3. Brief notes on regional geology
  4. Faunal development of ordovician strophomenides in south china
  5. Palaeobiogeographic affinities
  6. Systematic Palaeontology
  7. Acknowledgments
  8. References
  9. Appendix

Unless noted to the contrary, all of the material described in this paper is from the upper Changwu Formation (middle Ashgill), Jianglütang section, Chun’an County, western Zhejiang Province. Types and other figured specimens are deposited in the Nanjing Institute of Geology and Palaeontology (NIGP), Chinese Academy of Sciences, unless otherwise indicated.

Qualitative terms used to describe shell size are based on the average length or width measured for a sample: small, <10 mm; medium, 10–<20 mm; large, 20–30 mm; very large, >30 mm.

Abbreviations.  AVG, average; L, shell length; L1, length of cardinalia; L2, length of muscle field; L3, length (height) of ventral interarea; L4, length (height) of dorsal interarea; MAX, maximum; MIN, minimum; W, shell width; W1, width of cardinalia; W2, width of muscle field; W3, hinge width.

Order STROPHOMENIDA Öpik, 1934 Superfamily STROPHOMENOIDEA King, 1846 Family STROPHOMENIDAE King, 1846

Genus CHUNANOMENA gen. nov.

Derivation of name.  After Chun’an, the type area, where the new species constitutes the most abundant strophomenide within the study area.

Type species. Chunanomena triporcata sp. nov.

Species included. Chunanomena triporcata gen. et sp. nov., C. sembellina gen. et sp. nov.

Diagnosis.  Shell medium-sized to large, biconvex to weakly dorsibiconvex. Dental plates extending as posterolateral bounding ridges of flabellate or subrhomboidal muscle field; adductor scars elongate-oval, located in posterior part of muscle field and enclosed by diductor scars. Cardinalia type A (sensuRong and Cocks 1994 and Cocks and Rong 2000); two lobes of cardinal process sitting on weak notothyrial platform; sockets open anterolaterally; socket ridges undercut anterolaterally; central median ridge and a pair of side septa thin, confined to posterior half of valve.

Remarks.  In the revised ‘Treatise’ (Cocks and Rong 2000), the family Strophomenidae is divided into two subfamilies: Strophomeninae, with obsolete or weak side septa, and Furcitellinae, with strong side septa. However, most species of Strophomena from North America, including S. planumbona and S. vetusta from the Cincinnati type area, have relatively strong side septa in the dorsal valve (Davis 1985; Dewing 1999). It is possible that the dorsal valve used by Rong and Cocks (1994) and Cocks and Rong (2000) is just a variant of S. planumbona with very weak transmuscle ridges or side septa. In this study, therefore, the division of two strophomenid subfamilies is not followed because the subfamilies are difficult to separate.

Chunanomena is distinguished from other genera of the Strophomenidae by a combination of characters, including a dorsibiconvex shell, scalloped ventral muscle field with posteriorly located adductor scars, small cardinalia, strongly curved socket ridges and anterolaterally open sockets, and short, subparallel central median septum and side septa. In the family Strophomenidae, the new genus resembles certain genera that also have a biconvex shell, e.g. BajanhongorellaRozman, 1977, FurcitellaCooper, 1956, HoltedahlinaFoerste, 1924, InfurcaPercival, 1979a, MurinellaCooper, 1956, QuondongiaPercival, 1991 and Trotlandella Neuman, inNeuman and Bruton 1974. Holtedahlina, from the Whitewater Formation (mid Katian) of Ohio, has multicostellate ornamentation, a dorsal fold and ventral sulcus commonly developed anteriorly, and much more elongated ventral adductor scars that are not enclosed anteriorly by the diductors (see also Cooper 1956). Infurca, from the Caradoc of New South Wales, differs from Chunanomena in its much coarser, multicostellate ornamentation, much smaller cardinalia with a pair of linear socket ridges subparallel to the hinge line, and a pentagonal ventral muscle field. Trotlandella, from Llanvirn rocks in Norway, has multicostellae, a suboval ventral muscle field with a pair of medially curved lateral bounding ridges, and delicate cardinal process lobes. Furcitella, from the Upper Ordovician of North America, can be distinguished from Chunanomena by its relatively even-sized costellae, subcircular ventral muscle field with anteriorly open adductor scars, and much weaker dorsal transmuscle ridges. Bajanhongorella, from the Upper Ordovician of Mongolia, has a much more convex dorsal valve and fascicostellate ornamentation, which makes it unique in the Strophomenidae, although its interior characters are poorly known (Cocks and Rong 2000). The North American Murinella has much larger and stronger cardinalia, a clearly elevated notothyrial platform, and a subcircular ventral muscle field with anteriorly open adductor scars. The Caradocian Australian genus Quondongia is similar to Chunanomena in its biconvexity and dorsal interior, but its shell may vary from planoconvex to biconvex, and its coarser ribbing may change from posteriorly multicostellate to anteriorly parvicostellate (Percival 1991); it also has a subquadrate, anteriorly elevated ventral muscle field.

The planoconvex Maakina Andreeva, inNikiforova and Andreeva 1961, which was reported from the Caradoc of the Siberian Platform, Russia, differs from Chunanomena not only in its shell profile and ornamentation (rounded multicostellate) but also in its strongly laterally extending socket ridges and lack of a dorsal median septum. Its ventral interior is poorly known. LuhaiaRõõmusoks, 1956 from the upper Katian of the Baltic region is similar to Chunanomena in its dorsal internal structures, but it can be distinguished from it by its convexoconcave profile, ventral muscle field with apparent bounding ridges but adductors not enclosed by diductors, and socket ridges that are not undercut and more widely divergent.

Chunanomena triporcata sp. nov. Plates 1–3; Plate 4, figures 1–12

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Figure EXPLANATION OF PLATE 1.  Figs 1–15. Chunanomena triporcata gen. et sp. nov. 1–2, 4, paratype, NIGP142016; ventral internal mould (1) and its latex cast (4) with local enlargement (2) showing details of dental plates and muscle field; some bryzoan remains encrusted on the interior surface of the shell. 3, 5–6, paratype, NIGP142017; ventral internal and external moulds with local enlargement (6) showing details of dental plates and muscle field. 7–9, paratype, NIGP142018; ventral internal mould (7) and its latex cast (9) with local enlargement (8) showing details of dental plates and muscle field. 10–11, paratype, NIGP142019; ventral internal mould and local enlargement showing details of dental plates and muscle field. 12, paratype, NIGP142020; ventral internal mould. 13–14, paratype, NIGP142021; ventral internal mould and local enlargement showing details of dental plates, muscle field and vascular genitalia. 15, paratype, NIGP142022; ventral internal mould. Scale bars represent 2 mm.

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Figure EXPLANATION OF PLATE 2.  Figs 1–15. Chunanomena triporcata gen. et sp. nov. 1–2, paratype, NIGP142023; ventral internal mould and local enlargement showing details of dental plates and muscle field. 3, paratype, NIGP142024; ventral internal mould. 4–7, holotype, NIGP142025; dorsal internal (4) and external (7) moulds, and latex cast of internal mould (5) with local enlargement (6) showing details of cardinalia and muscle field. 8–9, paratype, NIGP142026; dorsal internal mould and its latex cast. 10–12, paratype, NIGP142027; dorsal internal mould (10) and its latex cast (12) with local enlargement showing details of cardinalia and muscle field (11). 13–15, paratype, NIGP142028; dorsal internal mould (13) and its latex cast (15) with local enlargement showing details of cardinalia, muscle field and vascular genitalia (14). Scale bars represent 2 mm except where noted.

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Figure EXPLANATION OF PLATE 3.  Figs 1–15. Chunanomena triporcata gen. et sp. nov. 1, paratype, NIGP142029; dorsal internal mould. 2, paratype, NIGP142030; dorsal internal mould. 3, paratype, NIGP142031; dorsal internal mould. 4–5, paratype, NIGP142032; dorsal view of internal mould of conjoined shell and local enlargement showing details of cardinalia and muscle field. 6, 9, paratype, NIGP142033; dorsal internal mould and local enlargement showing details of cardinalia, muscle field and vascular genitalia. 7, paratype, NIGP142034; dorsal internal mould. 8, paratype, NIGP142035; dorsal internal mould. 10, paratype, NIGP142036; dorsal view of internal mould of conjoined shell. 11, paratype, NIGP142037; dorsal internal mould. 12, paratype, NIGP142038; dorsal internal mould. 13–14, paratype, NIGP142039; dorsal internal mould and local enlargement showing details of cardinalia. 15, paratype, NIGP142040; dorsal internal mould with clearly impressed palial markings. Scale bars represent 2 mm except where noted.

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Figure EXPLANATION OF PLATE 4.  Figs 1–12. Chunanomena triporcata gen. et sp. nov. 1, paratype, NIGP142041; dorsal internal mould. 2–3, paratype, NIGP142042; dorsal internal mould and local enlargement showing details of cardinalia and muscle field. 4–5, paratype, NIGP142043; dorsal internal mould and local enlargement showing details of cardinalia and muscle field. 6, paratype, NIGP142044; dorsal external mould. 7–8, paratype, NIGP142045; ventral external mould and local enlargement showing details of costellae and concentric fila. 9, paratype, NIGP142046; dorsal external mould. 10–12, paratype, NIGP142047; dorsal external mould (10) and its latex cast (12) with local enlargement of mould (11) showing details of costellae and concentric fila.Figs 13–15. Chunanomena sembellina gen. et sp. nov., holotype, NIGP142048; ventral internal mould (13) and its latex cast (15) with local enlargement of mould (14) showing details of dental plates and muscle field. Scale bars represent 2 mm except where noted.

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Derivation of name.  Latin, tri-, three, and porca, ridge; triporcata refers to the three well-developed longitudinal ridges (central median ridge and side septa) in the dorsal valve of the new species.

Types.  Thirty-two specimens: holotype, NIGP142025 (Pl. 2, figs 4–7); paratypes, NIGP142016–142024, 142026–142047; upper Changwu Formation.

Material.  Four ventral external, 18 ventral internal, five dorsal external, and 23 dorsal internal moulds; upper Changwu Formation, Chun’an.

Diagnosis.  Relatively large shells of Chunanomena with well-developed dorsal median ridge (myophragm) and subparallel side septa.

Description.  Shell relatively large, with adult shells exceeding 20 mm in width, semi-elliptical in outline, about three-quarters as long as wide (Table 1); profile biconvex with dorsal valve slightly deeper; maximum width at hinge line or slightly anterior to it; cardinal extremities acute to subrectangular. Ventral interarea apsacline, with planar surfaces, attaining height equivalent to 13 per cent shell length; dorsal interarea anacline, notably lower. Pseudodeltidium and chilidium well developed, variably convex (Pl. 1, fig. 9; Pl. 2, fig. 6). Unequal parvicostellae of two main sizes (Pl. 2, fig. 7; Pl. 4, figs 6–12), with 3–7 fine costellae separated by coarse ones anteriorly. First-order coarse costellae start just in front of umbonal area, second-order begin at about one-quarter length, and third-order at mid-length of shell. Concentric fila very fine (10–12 per mm), evenly spaced over entire shell surface (Pl. 4, fig. 11). Three or four growth lamellae normally best developed anteriorly. Several weak concentric rugae may be present on posterolateral parts of shell (Pl. 4, fig. 10).

Table 1.   Shell measurements (in mm) of Chunanomena triporcata gen. et sp. nov.
 LWL/WL1L1/LW1W1/WL2L2/LW2W2/WL3L3/LW3W3/WL4L4/L
22 ventral valves
 AVG18.8525.920.738.350.445.530.312.230.1324.110.93
 MIN15.3421.610.586.170.3910.930.251.380.0917.380.79
 MAX20.6431.090.8810.650.538.160.392.950.1729.341.0
27 dorsal valves
 AVG17.6423.900.741.930.117.250.307.400.427.330.3122.380.930.900.05
 MIN13.4520.050.561.450.075.050.255.080.346.330.2516.010.760.610.03
 MAX21.5328.460.932.560.148.320.379.520.539.010.4128.461.01.280.07

Teeth small, triangular; dental plates thin, diverge at about 90 degrees from each other, extending beyond hinge line as posterolateral bounding ridges of muscle field. Diductor muscle field flabellate to subrhomboidal in outline, scalloped with radial ridges, about 44 per cent length and 30 per cent width of shell; adductor muscle scars elongate-oval, confined to posteromedial part of muscle field, delimited by low lateral ridges, enclosed laterally and anteriorly by diductor scars. Vascula media saccate; vascula genitalia well impressed. Crenulations reflecting coarse costellae clearly marked in anterior part of both valve interiors (Pl. 1, figs 3, 7, 9; Pl. 2, figs 9, 12; Pl. 3, figs 7, 10).

Cardinalia small, about 10 per cent length and 30 per cent width of shell; cardinal process lobes small, divergent at narrow angle, with swollen, triangular crest, projecting posteriorly beyond hinge line; notothyrial platform poorly developed; socket ridges undercut anterolaterally, originating from bases of cardinal process lobes, divergent from each other anterolaterally at 75–110 degrees and then curving laterally or posterolaterally to hinge line; sockets relatively deep, open anterolaterally (Pl. 2, fig. 6). Adductor muscle field clearly impressed, about 30 per cent width of shell, subcircular in outline, with weak myophragm; median ridge and pair of side septa subparallel to one another, thin, sharply defined. Vascula media saccate; vascular genitalia well impressed on both lateral slopes, bearing prominent, anterolaterally tilted tubercles in some specimens (Pl. 2, figs 13–15).

Remarks.  Observation of the 49 specimens assigned to the new species revealed a number of infraspecific variations in external as well as internal morphology.

  • 1
     Shell outline and cardinal extremities. Most of the shells have a length:width ratio of 3:4, but in some the ratio approaches 1:2, making the outline semicircular (Pl. 2, figs 8–9; Pl. 3, fig. 13). The cardinal extremities are typically subrectangular, but may be acute or rounded in a few specimens. It is not clear to what extent this variation is attributable to preservation.
  • 2
     Convexity of dorsal valve. In general, the dorsal valve is gently and evenly convex, but in a few specimens it is only weakly convex or nearly flat (Pl. 3, fig. 4).
  • 3
     Divergence of dental plates. In most ventral valves, the dental plates diverge at a right angle, but the angle may be only 65–75 degrees in some specimens (Pl. 1, figs 7–8).
  • 4
     Socket ridges. Normally, the socket ridges originate from the base of cardinal process, diverge at 75–110 degrees anterolaterally, and then curve laterally to posterolaterally (Pl. 2, figs 5–6). In a few specimens, however, the ridges are mostly linear, extending laterally subparallel to the hinge line (Pl. 3, figs 3–6, 10–12).

Compared with other strophomenoids of the study area, C. triporcata is unique in its scalloped ventral muscle field with adductor scars completely enclosed by diductors and without anterolateral bounding ridges, anterolaterally undercut socket ridges and well-developed central median ridge and side septa. Its parvicostellae are also rare among biconvex shells of the Strophomenidae. The well-impressed vascular genitalia with prominent tubercles are seen only in gerontic specimens (e.g. Pl. 2, figs 13–15), but such a character is common in the Caradocian Molongcola variabilisPercival, 1991 and the Telychian Pentlandina tartana (Bancroft, 1949). Both species are quite different from C. triporcata in their external and other internal features.

Chunanomena sembellina sp. nov. Plate 4, figures 13–15; Plate 5, figures 1–10

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Figure EXPLANATION OF PLATE 5.  Figs 1–10. Chunanomena sembellina gen. et sp. nov. 1–3, holotype, NIGP142048; ventral external mould (1) and its latex cast (3) with local enlargement of mould (2) showing details of costellae and concentric fila. 4–5, paratype, NIGP142049; dorsal internal mould and local enlargement showing details of cardinalia and muscle field. 6, 9, paratype, NIGP142050; dorsal internal and external moulds. 7–8, 10, paratype, NIGP142051; dorsal internal (7) and external (10) moulds with local enlargement of mould (8) showing details of cardinalia and muscle field.Figs 11–15. Cheramomena subsolana gen. et sp. nov. 11–12, paratype, NIGP142052; ventral view of partial internal mould of conjoined shell and partial dorsal external mould (11) and local enlargement (12) showing details of dental plates and muscle field. 13–14, paratype, NIGP142053; dorsal internal mould and local enlargement showing details of cardinalia and muscle field. 15, paratype, NIGP142054; dorsal internal mould. Scale bars represent 2 mm except where noted.

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Derivation of name.  Latin, sembella, small coin, referring to the small, subcircular shell of the new species.

Types.  Four specimens: holotype, NIGP142048 (Pl. 4, figs 13–15; Pl. 5, figs 1–3); paratypes, NIGP142049–142051; upper Changwu Formation.

Material.  One ventral external, one ventral internal, two dorsal external, and three dorsal internal moulds; upper Changwu Formation.

Diagnosis.  Commonly medium-sized, subcircular, weakly biconvex shells of Chunanomena; central median ridge and side septa usually weak.

Description.  Shell subcircular, about four-fifths as long as wide (Table 2), weakly biconvex; maximum width attained slightly anterior of hinge line; cardinal extremities rounded. Interareas and pseudodeltidium same as in type species. Unequal parvicostellae of two sizes, with 2–5 fine costellae separated by coarser ones in anterior part of shell. First order coarse costellae start at apex, second order at one-third length, and third order at two-thirds length of shell (Pl. 5, figs 1–3). Concentric fila and intermittent coarser lamellae best preserved anteriorly.

Table 2.   Shell measurements (in mm) of Chunanomena sembellina gen. et sp. nov.
 LWL/WL1L1/LW1W1/WL2L2/LW2W2/WL3L3/LW3W3/WL4L4/L
1 ventral valve
 17.8021.200.848.050.457.410.352.910.1618.770.89
5 dorsal valves
 AVG11.7114.790.791.030.094.560.314.200.364.960.3412.110.820.530.045
 MIN10.5613.170.760.900.074.540.283.830.344.610.3211.190.790.470.042
 MAX12.4516.340.821.280.104.580.354.700.395.490.3513.700.850.570.048

Teeth delicate, wedge-shaped; dental plates thin, low, diverge from each other at about 90 degrees, extend anteriorly beyond hinge line as posterolateral bounding ridges of muscle field (Pl. 4, figs 13–15). Diductor muscle field flabellate in outline, with rounded, unbounded anterior margin, scalloped with faint radial ridges anteriorly, occupying 45 per cent length and 30 per cent width of shell; adductor scars small, elongate-oval, located in posteromedial part of muscle field, enclosed laterally and anteriorly by diductor scars. Cardinalia small, about 9 per cent length and 30 per cent width of shell; cardinal process lobes small, projecting posteriorly beyond hinge line, with subtriangular, swollen crests; base of cardinal process merging anteriorly with weak median ridge; notothyrial platform not developed; socket ridges originate from bases of cardinal process lobes, diverge anterolaterally at about 115 degrees and then bend posterolaterally towards hinge line; sockets shallow, open anterolaterally. Adductor scars subcircular in shape, divided by weak median ridge (myophragm), but lacking lateral bounding ridges. Crenulations on inner surface similar to those of type species (Pl. 4, figs 13, 15; Pl. 5, figs 4, 6–7).

Remarks. Chunanomena sembellina differs from the type species of the genus in having a smaller, subcircular, flattened ventral valve, more posteriorly projecting cardinal process lobes, and slightly divergent side septa.

strophomenid gen. et sp. indet. 1 Plate 6, figures 7–11

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Figure EXPLANATION OF PLATE 6.  Figs 1–6. Cheramomena subsolana gen. et sp. nov. 1–2, paratype, NIGP142055; dorsal external mould and local enlargement showing details of costellae and concentric fila. 3–6, holotype, NIGP142056; dorsal internal mould (3) and its latex cast (4) with two local enlargements (5–6) showing details of cardinalia and muscle field, particularly the deep notothyrial cavity.Figs 7–11. Strophomenid gen. et sp. indet. 1. 7, NIGP142057; ventral internal mould. 8–9, NIGP142058; dorsal internal mould and local enlargement showing details of cardinalia and muscle field. 10–11, NIGP142059; dorsal external mould and local enlargement showing details of costellae.Figs 12–15. Leptellina qianjiangensis (Liang, inLiu et al. 1983). 12, topotype, NIGP142060; dorsal external mould. 13–15, topotype, NIGP142061; dorsal external mould (13) and its latex cast (15) with local enlargement of mould (14) showing details of ventral interarea and delthyrium. Scale bars represent 2 mm except where noted.

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Material.  One ventral external, one dorsal external, and one dorsal internal mould; upper Changwu Formation.

Description.  Shell medium to large, subsemicircular, with length:width ratio of 0.75, strongly ventribiconvex. Ventral and dorsal interareas apsacline and anacline, respectively. Unequal parvicostellae of two main sizes; coarse costellae consisting of three orders, separated by 3–5 fine ones. Dental plates tilted medially and extending anteromedially to be muscle bounding ridges. Ventral muscle field elongate-oval in outline, about 45 per cent length and 23 per cent width of shell; adductor scars small, slender, enclosed by diductor scars. Cardinal process sits on gently elevated notothyrial platform; cardinal process lobes divergent with swollen myophore, projecting posteriorly beyond hinge line; socket ridges very short, curved. Dorsal muscle field transversely subrectangular (Pl. 6, figs 8–9). Median ridge and side septa short, weak.

Remarks.  The strongly ventribiconvex profile and a transversely subrectangular adductor muscle field suggest that this indeterminate strophomenid represents a new genus and species of the Strophomenidae but more specimens are needed to provide a detailed generic and specific description.

strophomenid gen. et sp. indet. 2 Text-figure 4D–E

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Figure TEXT-FIG. 4..  A–B, Leptellina qianjiangensis (Liang, inLiu et al. 1983), topotype, NIGP142073, dorsal internal mould and local enlargement showing details of cardinalia and bema. C, Mabella sp., NIGP142074; dorsal internal mould. D–E, strophomenid gen. et sp. indet. 2, NIGP142075; ventral internal mould and its lateroventral view. F, Rongambonites sp., NIGP142076; a broken dorsal internal mould. G–L, Sowerbyella (Sowerbyella) sinensis Wang, inWang and Jin 1964. G, NIGP142077; ventral internal mould. H, NIGP142078; ventral internal mould. I, NIGP142079; dorsal internal mould. J–K, NIGP142080; dorsal internal mould and its latex cast. L, NIGP142081; a tiny dorsal internal mould. Scale bars represent 2 mm except where noted.

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Material.  Two ventral internal moulds.

Description.  These two ventral valves are strongly convex, and dorsally geniculated. The figured valve is 14.2 mm long and 17.3 mm wide, with the length of the disc area being approximately the same as the height of the geniculated trail (Text-fig. 4D–E). The muscle field is subrhomboidal in outline, with strong lateral-bounding ridges and slender, highly elevated adductor scars. The diductor scars are prominently bilobed at the anterior margin forming a deep anteromedial notch. Several gentle, irregular undulations are present in the medial part of the trail.

Remarks.  The two specimens are assigned to the Strophomenidae on the basis of the subrhomboidal outline of ventral muscle field, which shows some degree of narrowing anteriorly, resembling the ventral muscle field of some strophomenids (e.g. Furcitella and Bellimurina). Precise generic and specific identification is difficult at present because of the limited material available, particularly the lack of dorsal valves. Furthermore, the strongly convex and geniculated ventral valve of this indeterminate form is rather rare in the family, although some strophomenids may have a moderately convex ventral valve.

Family GLYPTOMENIDAE Williams, 1965

Genus CHERAMOMENA gen. nov.

Derivation of name.  Greek, cheramos, hole, referring to the deep nothothyrial cavity of the new genus.

Type species. Cheramomena subsolana sp. nov.

Species included.  The type species only.

Diagnosis.  Shell large, concavo-convex with dorsal geniculation and medial-posteriorly developed, irregular, concentric rugae. Dental plates extend anteriorly as bounding ridges of rhomboidal muscle field. Cardinal process lobes project posteriorly, separated by narrow, deep nothothyrial cavity that expands anteriorly into suboval depression. Notothyrial platform absent. Socket ridges curved; dorsal adductor muscle scars fan-shaped, divided by median ridge originating from floor of notothyrial cavity.

Remarks. Cheramomena is characterized by having a concavo-convex shell and cardinalia with features intermediate between Types A (e.g. Strophomenidae) and C (e.g. Glyptomenidae). Its Type A characters include posteriorly projecting cardinal process lobes and curved socket ridges (Rong and Cocks 1994). Compared to the typical cardinalia of the Strophomenidae, however, the cardinal process lobes in Cheramomena do not converge anterobasally onto a notothyrial platform. Rather, the two lobes are separated by a deep groove (notothyrial cavity) that expands anteriorly beyond the cardinal process into a suboval depression. The median ridge (myophragm) originates from the anterior floor of the depression. In the Strophomenidae, the median ridge originates directly from the anterior margin of a notothyrial platform. In this respect, the cardinalia of Cheramomena are somewhat similar to the Type C cardinalia of glyptomenids. For example, separated cardinal process lobes may be present in Mid–Late Ordovician glyptomenids such as GlyptomenaCooper, 1956, BystromenaWilliams, 1974 and ParomalomenaRong, 1984, although none of them apparently have a notothyrial cavity and a depression in front of it.

Cheramomena subsolana sp. nov. Plate 5, figures 11–15; Plate 6, figures 1–6

Derivation of name.  Latin, subsolanus, eastern, with reference to the occurrence of the type species in eastern China.

Types.  Five specimens: holotype, NIGP142056 (Pl. 6, figs 3–6); paratypes, NIGP142052–142055; upper Changwu Formation.

Material.  Four ventral external and 18 internal, five dorsal external and 22 internal moulds; upper Changwu Formation, Chun’an.

Diagnosis.  As for genus.

Description.  Shell large, subsemicircular, about three-quarters as long as wide (Table 3), concavo-convex with short dorsal geniculation; maximum width along hinge line; cardinal extremities acute to rectangular. Ventral interarea apsacline, attaining height of one-tenth length of shell; dorsal interarea anacline, much lower. Pseudodeltidium poorly preserved; chilidium strongly arched. Unequal parvicostellae of two main sizes, with 2–4 fine costellae separated by coarse ones. First-order coarse costellae start at apex, second-order at one-third, and third-order at two-thirds length of shell. Concentric fila c. 6–7 per mm, evenly spaced over entire shell surface. Irregularly concentric rugae present (Pl. 6, fig. 1).

Table 3.   Shell measurements (in mm) of Cheramomena subsolana gen. et sp. nov.
 LWL/WL1L1/LW1W1/WL2L2/LW2W2/WL3L3/LW3W3/WL4L4/L
2 ventral valves
 22.8831.380.748.330.368.300.272.390.1031.381.0
4 dorsal valves
 AVG24.1129.600.812.980.139.970.348.160.348.230.2829.601.00.890.038
 MIN19.5729.060.672.890.118.890.317.570.316.920.2429.061.00.850.033
 MAX26.7430.540.893.160.1611.260.378.770.3310.80.3530.541.00.950.043

Teeth small, wedge-shaped; dental plates thick, low, extend anterolaterally for a short distance and then bend anteromedially, forming bounding ridges of muscle field. Diductor muscle field rhomboidal in outline, c. 36 per cent length and 27 per cent width of shell; diductor scars slender, elongate-oval, divided by medial groove, open at anterior margin of muscle field forming small notch (Pl. 5, figs 11–12). Vascula media poorly preserved; vascula genitalia lemniscate.

Cardinalia small, about one-eighth length and one-third width of shell; cardinal process lobes small, projecting moderately posteroventrally, separated by narrow, deep notothyrial cavity which expands anterior of cardinal process into suboval depression (fossa); cardinal process bases diverge laterally to merge with socket ridges; socket ridges initially diverge from each other anterolaterally at about 110 degrees, then recurve slightly towards hinge line; inner medial surface of socket ridge crenulated with 3–4 small denticles on both sides (Pl. 6, figs 5–6). Dorsal muscle field fan-shaped, with poorly bounded, rounded anterior margin; medial ridge strong, originating from floor of notothyrial cavity, widening and flattening anteriorly to be replaced by weak central median ridge. Side septa thin, weak, slightly laterally curved forming loose brackets, extending mid-length of shell. Sub-peripheral rim weak. Vascula media saccate.

Remarks.  The ventral muscle field of rhomboidal outline, raised bounding ridges extending all the way to the anterior medial notch, and slender diductor scars extending to the anteromedial margin of the muscle field are characters reminiscent of the ventral muscle field of Strophomena. However, linear adjustor muscle scars, often well impressed along the lateral margins of the ventral muscle field of Strophomena, have not been observed in C. subsolana.

Genus LATERISEPTOMENA gen. nov.

Derivation of name.  Latin, lateris, side, and septum, partition, with reference to the prominent dorsal side septa of the new genus.

Type species. Lateriseptomena modesta sp. nov.

Species included. Lateriseptomena modesta gen. et sp. nov., Lateriseptomena rugosa gen. et sp. nov.

Diagnosis.  Shell small to medium-sized, planoconvex to gently biconvex with variable dorsal geniculation, unequally parvicostellate; irregular rugae may be present. Bilobed ventral muscle field with strong lateral-bounding ridges. Cardinalia small, type C; cardinal process lobes separated by notothyrial cavity; socket ridges curved, with partly crenulated inner surface. Side septa long, prominent, weakly divergent anteriorly.

Remarks. Lateriseptomena is assigned to the family Glyptomenidae based on its Type C cardinalia (Rong and Cocks 1994). Its most distinctive character is the pair of strong side septa that originate posteromedially, extend through the dorsal adductor muscle field, and continue to about the mid-length of the dorsal valve. In their strength and slight divergence angle, this type of side septa is uncommon in the Strophomenoidea, e.g. in FoliomenaHavlíček, 1952 and HercostrophiaWilliams, 1950, both of which differ from Lateriseptomena in several external and internal characters. Hercostrophia has a denticulate hinge line. Foliomena can be easily distinguished in having a smooth shell, a prominent tubular pedicle sheath, and much weaker and shorter socket ridges and side septa.

Within Glyptomenidae, Platymena may have a similar shell outline, profile, ornamentation and cardinalia, but it lacks the characteristically prominent side septa of Lateriseptomena.

Lateriseptomena modesta sp. nov. Plate 7

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Figure EXPLANATION OF PLATE 7.  Figs 1–16. Lateriseptomena modesta gen. et sp. nov. 1–5, paratype, NIGP142062; dorsal, ventral, posterior and lateral views of an internal cast with local enlargement (4) showing details of hinge teeth. 6–9, holotype, NIGP142063; dorsal internal mould (6) and its latex cast (8) with two local enlargements showing details of cardinalia and muscle field. 10, 13, paratype, NIGP142064; dorsal internal mould and local enlargement showing details of cardinalia and muscle field. 11–12, paratype, NIGP142065; dorsal internal mould and local enlargement showing details of cardinalia and muscle field. 14–15, paratype, NIGP142066; dorsal internal and external moulds. 16, paratype, NIGP142067; ventral internal mould and a broken piece of dorsal external mould. Scale bars represent 2 mm except where noted.

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Derivation of name.  Latin, modestus; with reference to the moderate size of the type species.

Types.  Six specimens: holotype, NIGP142063 (Pl. 7, figs 6–9); paratypes, NIGP142062, 142064–142067; upper Changwu Formation.

Material.  Three ventral external, three ventral internal, one dorsal external and seven dorsal internal moulds, and one conjoined internal mould; upper Changwu Formation.

Diagnosis.  Commonly planoconvex shells of Lateriseptomena with short dorsal geniculation and strong side septa. Ventral muscle field large, bilobed anteriorly with medial notch; small adductor scars confined to posteromedial part of muscle field.

Description.  Shell small to medium-sized, subsemicircular, width slightly greater than length (Table 4), planoconvex with short dorsal geniculation; cardinal extremities rectangular to rounded. Ventral interarea apsacline, attaining height of 9 per cent length of shell; dorsal interarea anacline, lower. Pseudodeltidium and chilidium strongly arched. Unequal parvicostellae of two main sizes, with 2–7 fine costellae separated by coarse ones in anterior part of shell. Concentric fila fine, 8 per mm, evenly spaced over entire shell surface. Rugae usually absent, irregular and faint when rarely developed (Pl. 7, fig. 15).

Table 4.   Shell measurements (in mm) of Lateriseptomena modesta gen. et sp. nov.
 LWL/WL1L1/LW1W1/WL2L2/LW2W2/WL3L3/LW3W3/WL4L4/L
1 ventral valve measured
 13.6416.950.806.230.464.590.271.280.1016.951.0
6 dorsal valves
 AVG9.8913.350.741.090.124.980.363.630.374.330.3112.210.930.430.04
 MIN8.7211.230.690.890.104.150.362.730.312.890.269.050.810.370.03
 MAX12.6516.000.801.210.125.410.414.420.426.200.4115.041.00.520.05

Teeth small, with 6–7 pairs of crenulations on their inner surface (Pl. 7, figs 3–4); dental plates thin, high, diverging from each other at about 90 degrees, extending anteriorly to become parallel lateral-bounding ridges of muscle field. Muscle field relatively large, bilobed anteriorly with medial notch, occupying 44 per cent length and one-third width of shell (Pl. 7, fig. 2); adductor scars small, confined to posteromedial part of muscle field, slightly elevated above muscle field floor. Vascula media lemniscate; vascula genitalia bear small tubercles.

Cardinal process lobes small, discrete, with their bases merging laterally with socket ridges; socket ridges thick, with crenulations (Pl. 7, figs 9, 12) corresponding to those of teeth (Pl. 7, fig. 4), curved. Dorsal adductor scars small, divided by median ridge and side septa radially into four lobes. Side septa strong, originate posteriorly near base of cardinal process, diverge anteriorly at 15–25 degrees, extend to about one-third to one-half of shell length, highest around middle parts. Palial markings digitate; vascula media originate from anterior ends of inner adductor scars, diverge anteriorly; vascula myaria begin around medial part of side septa; vascula genitalia tubercular (Pl. 7, figs 1, 6–7, 14).

Remarks.  Among the available material, observed variations include the divergent angle between two side septa (15–25 degrees), the degree of dorsal geniculation (sharp to gentle), and the convexity of the dorsal valve (its disc area is usually flat but rarely shows a gentle concavity or convexity).

Lateriseptomena rugosa sp. nov. Plate 8, figures 1–7

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Figure EXPLANATION OF PLATE 8.  Figs 1–7. Lateriseptomena rugosa gen. et sp. nov. 1–3, holotype, NIGP142068; dorsal internal mould (1) and its latex cast (3) with local enlargement of mould (2) showing details of cardinalia and muscle field. 4, paratype, NIGP142069; dorsal external mould. 5–6, paratype, NIGP128079; dorsal internal and external moulds. 7, paratype, NIGP128078; ventral internal mould.Figs 8–15. Glyptomenid gen. et sp. indet. 8–9, 11–12, NIGP142070; dorsal internal mould (8) and its latex cast (11) with two local enlargements showing details of cardinalia and muscle field. 10, NIGP142071; ventral external mould. 13–15, NIGP142072; ventral internal mould and its latex cast with local enlargement showing details of teeth, dental plates and muscle field. Scale bars represent 2 mm except where noted.

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1998 indet. teratelasmine gen. et sp. nov. Zhan and Cocks, p. 46, pl. 7, figs 1–3.

Derivation of name.  Latin, rugosus, wrinkled, with reference to the wrinkled shell surface of the new species.

Types.  Holotype, NIGP142068 (Pl. 8, figs 1–3); paratypes, NIGP142069; upper Changwu Formation.

Material.  Two dorsal external moulds, one dorsal internal mould; upper Changwu Formation, Chun’an County. Additionally, one ventral internal mould (NIGP128078) and one paired dorsal external and internal mould (NIGP 128079) have been illustrated by Zhan and Cocks (1998) from the upper Changwu Formation of the Dianbian section, Jiangshan County, western Zhejiang.

Diagnosis.  Planoconvex to gently biconvex shells of Lateriseptomena with irregular rugae, subcircular ventral muscle field with faint lateral-bounding ridges, and weak side septa.

Description.  Shell small, subcircular to semi-elliptical, width slightly greater than length (Table 5), planoconvex to gently biconvex, with short and weak dorsal geniculation; cardinal extremities rectangular to rounded. Interareas, pseudodeltidium, chilidium and parvicostellae same as those of type species. Concentric fila very fine, c. 22–24 per mm (Pl. 8, figs 4, 6). Irregular rugae on entire shell but best developed posteriorly (Pl. 8, figs 1–6).

Table 5.   Shell measurements (in mm) of Lateriseptomena rugosa gen. et sp. nov.
 LWL/WL1L1/LW1W1/WL2L2/LW2W2/WL3L3/LW3W3/WL4L4/L
1 ventral valve
 7.338.280.892.500.342.620.320.750.106.890.83
2 dorsal valves
 7.658.910.880.990.132.660.302.570.342.410.278.500.940.270.035

Dental plates thin and high, divergent at about 90 degrees, extend anterolaterally for a short distance, then bend (and weaken) to form bounding ridges of muscle field. Muscle field subrhomboidal with faint lateral-bounding ridges and rounded, unbounded anterior margin, about one-third length and width of shell; adductor scars poorly impressed.

Cardinal process lobes small, projecting posterior of hinge line, separated by a narrow groove, continuous laterally with socket ridges (Pl. 8, figs 2–3, 5); socket ridges well-developed, slightly curved, each bearing 5–6 crenulations in posterior outer part (Pl. 8, figs 2–3). Dorsal adductor scars and side septa similar to those of type species.

Remarks.  Compared to the type species, Lateriseptomena rugosa sp. nov. has several unique characters, such as a gentle biconvex profile, wrinkled shell surface, less curved and narrower socket ridges, and subrhomboidal ventral muscle field. Its somewhat more delicate side septa, shallower muscle scars and stronger reflections of rugae on inner shell surfaces are probably related to generally thinner shell walls.

glyptomenid gen. et sp. indet. Plate 8, figures 8–15

Material.  One ventral external and internal, and one dorsal internal mould.

Description.  Shell subcircular, width slightly greater than length (Table 6), strongly concavo-convex with gentle dorsal geniculation; maximum width at about one-third length of shell; cardinal extremities rounded. Ventral interarea apsacline, with planar surface, attaining height of 13 per cent length of shell; dorsal interarea anacline, much lower. Pseudodeltidium not preserved; chilidium strongly arched. Unequal parvicostellae of two main sizes, with 2–3 fine costellae separated by coarse ones. Concentric fila fine, about 20 per mm, evenly spaced over entire shell surface. Some weak, irregular concentric rugae around mid-length of shell (Pl. 8, figs 8, 10).

Table 6.   Shell measurements (in mm) of glyptomenid gen. et sp. indet.
 LWL/WL1L1/LW1W1/WL2L2/LW2W2/WL3L3/LW3W3/WL4L4/L
1 ventral valve
 11.9813.650.884.810.404.270.311.570.139.540.70
1 dorsal valve
 12.6616.070.791.400.116.100.385.320.426.240.3913.080.810.400.03

Teeth stout, wedge-shaped; dental plates thick, extend anteromedially to become muscle bounding ridges (Pl. 8, figs 13–15). Muscle field subcircular to cordate in outline, elevated, about 40 per cent length and 30 per cent width of shell; adductor scars, a pair elongate-suboval, pinched anteriorly. Vascula media saccate. Sparse crenulations reflecting coarse costellae present along peripheral area of valve interior (Pl. 8, fig. 13).

Cardinal process distinctly undercut, projects posterior of hinge line; cardinal process lobes delicate, separated by a narrow groove at base, sitting on small, horizontal, hanging plate (Pl. 8, fig. 12). Socket ridges thin, weak, slightly recurved, medially discontinuous with hanging cardinal process. Adductor muscle field poorly impressed, subcircular on each side, lacks distinct bounding ridges. Median ridge and side septa slender, low, extending to mid-length of shell (Pl. 8, figs 8–9, 11–12). Vascula media poorly impressed. Subperipheral rim between shell disc and trail weakly developed (Pl. 8, figs 8, 11). Shell pseudopunctae well preserved in parts of interior surface (Pl. 8, figs 8–9).

Remarks.  Among the Strophomenida, our material is unique in having a strongly concavo-convex shell, with an undercut, bilobed cardinal process. This type of cardinalia is common in the superfamily Chilidiopsoidea, such as in MorinorhynchusHavlíček (1965). However, Morinorhynchus, like all the other chilidiopsoids, has an impunctate shell, whereas the shell of our indeterminate taxon is pseudopunctate. Its dorsal valve is usually thinner than the ventral valve, as indicated by the strong reflections of costellae in the dorsal interior. The lack of an adequate number of specimens hinders a precise generic and specific identification.

Superfamily PLECTAMBONITOIDEA Jones, 1928 Family LEPTELLINIDAE Ulrich and Cooper, 1936 Subfamily LEPTELLININAE Ulrich and Cooper, 1936

Genus LEPTELLINA Ulrich and Cooper, 1936

Type species. Leptellina tennesseensisUlrich and Cooper, 1936 (illustrated in Ulrich and Cooper 1938); Lenoir Formation (upper Llanvirn = uppermost Darriwilian), Friendsville, Tennessee, USA.

Leptellina qianjiangensis (Liang, inLiu et al. 1983) Plate 6, figures 12–15; Text-figure 4A–B

1983 Qianjiangella qianjiangensis Liang, in Liu et al., p. 275, pl. 95, figs 5–8.

Material.  Two dorsal external moulds and one internal mould.

Remarks. Qianjiangella Liang, inLiu et al. 1983 from the middle Ashgill of western Zhejiang Province has been treated as a junior synonym of Leptellina (Cocks and Rong 1989, 2000). Our specimens are from the same locality and horizon as the type material of Q. qianjiangensis, the type species of the genus. The two dorsal external moulds (NIGP142060, 142061) indicate a large, subsemicircular, concavo-convex shell, with unequal parvicostellae. Its ventral and dorsal interareas are well-developed, planar, apsacline and hypercline respectively (Pl. 6, figs 12–15). Both the pseudodeltidium and chilidium are well preserved. The dorsal internal mould is 5.2 mm long and 8.1 mm wide, with a faint bema and dorsal platform. The specimens described by Liang are mostly large, with a notably stronger bema, median septum, and platform. Thus, our dorsal internal mould is considered to be a juvenile of L. qianjiangensis.

Genus MABELLA Klenina, inKlenina et al. 1984

Type species. Leptellina (Mabella) obtusa Klenina, inKlenina et al. 1984, Taldiboiskaya Formation (upper Katian), Chinghiz Range, Kazakhstan.

Mabella sp. Text-figure 4C

Material.  One incomplete dorsal internal mould.

Remarks. Mabella is characterized by an anteriorly forked dorsal median septum, which separates it from LeptellinaUlrich and Cooper, 1936. WiradjuriellaPercival, 1991 from the Caradoc of New South Wales, Australia, also has a distally bifurcating median septum and has been treated as a junior synonym of the latter by Cocks and Rong (2000).

The Jianglütang specimen has all the diagnostic features of Mabella, but being the only representative, specific identification is precluded. This is the first record of the genus from South China; elsewhere, it is known only from southern Kazakhstan and Australia.

Family HESPEROMENIDAE Cooper, 1956

Genus RONGAMBONITES Zhan and Cocks, 1998

Type species. Rongambonites bellaZhan and Cocks, 1998, p. 34, pl. 4, figs 8–13; upper Changwu Formation, middle Ashgill (uppermost Katian), Dianbian of Daqiao, Jiangshan County, western Zhejiang Province, eastern China.

Rongambonites sp. Text-figure 4F

Material.  One dorsal internal mould.

Remarks. Rongambonites is characterized by a triangular dorsal platform with straight anterolateral ridges, as seen in our dorsal valve, which, however, differs from it in having a more anteriorly located triangular platform that nearly touches the anteromedial part of the peripheral rim. It may represent a new species but more material is needed to elucidate the morphological variation, particularly of the triangular platform.

Family SOWERBYELLIDAE Öpik, 1930

Genus SOWERBYELLA (SOWERBYELLA) Jones, 1928

Type species. Leptaena sericea J. de C. Sowerby, 1839. Horderley Sandstone, lower Caradoc (Sandbian), Whittingslow, Shropshire, England.

Sowerbyella (Sowerbyella) sinensis Wang, inWang and Jin 1964 Text-figure 4G–L

1964 Sowerbyella sinensis Wang, in Wang and Jin, p. 46, pl. 13, figs 9–11.

1983 Sowerbyella lanxiensis Liang, in Liu et al., p. 276, pl. 99, figs 1–3.

1998 Sowerbyella (Sowerbyella) sinensis, Zhan and Cocks, p. 40, pl. 5, figs 8–13.

Material.  Two ventral internal moulds, one dorsal external mould, and five internal moulds.

Remarks.  Our collection includes both juvenile and adult forms of the species, with a range of shell sizes from barely 2 mm (Text-fig. 4L) to 20 mm in width. All of the dorsal valves have a pair of long, strong side septa, which extend to four-fifths of the length of the shell. Eochonetes and Thaerodonta may also have a pair of very long dorsal side septa (Reed 1917; Wang 1949; Howe 1965; Havlíček 1967; Amsden 1974; Dewing 1999), but these forms differ in having dorsal denticles.

Sowerbyella is a cosmopolitan plectambonitid brachiopod of Mid–Late Ordovician age (Cocks and Rong 1989, 2000). It has been reported from both shallow and relatively deep water benthic assemblages on many palaeocontinents (Rong et al. 1999), and is widespread in the Upper Ordovician of South China (Wang in Wang and Jin 1964; Zhan and Cocks 1998; and various regional atlases). It is abundant and even dominant at some localities and horizons in the border region of Zhejiang and Jiangxi provinces (Zhan and Rong 1995b; Zhan et al. 2002), but in the Chun’an area, Sowerbyella sinensis is only a rare element of the brachiopod fauna.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Brief notes on regional geology
  4. Faunal development of ordovician strophomenides in south china
  5. Palaeobiogeographic affinities
  6. Systematic Palaeontology
  7. Acknowledgments
  8. References
  9. Appendix

Acknowledgements.  Yan Kui (NIGP) provided assistance in the field. Dave Harper (Copenhagen) kindly provided data ‘in press’ for our faunal affinity analysis. Research funding has been provided by the Chinese Academy of Sciences (KZCX3-SW-149), the Ministry of Science and Technology of China (2006CB806400, 2006FY120300-5), the National Natural Science Foundation of China (40532009), and the Natural Sciences and Engineering Research Council of Canada (JJ). This paper is a contribution to the IGCP Project 503, ‘Ordovician Palaeogeography and Palaeoclimate’.

References

  1. Top of page
  2. Abstract
  3. Brief notes on regional geology
  4. Faunal development of ordovician strophomenides in south china
  5. Palaeobiogeographic affinities
  6. Systematic Palaeontology
  7. Acknowledgments
  8. References
  9. Appendix
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Appendix

  1. Top of page
  2. Abstract
  3. Brief notes on regional geology
  4. Faunal development of ordovician strophomenides in south china
  5. Palaeobiogeographic affinities
  6. Systematic Palaeontology
  7. Acknowledgments
  8. References
  9. Appendix

Localities and faunas on which the multivariate analyses were based (Text-figure 3)

GIR: Drummuck Group (Cautleyan–Rawtheyan, middle Ashgill), Girvan District, Scotland (Harper 1989, 2006); Katastrophomena, Hedstroemina, Leptaena, Pomeromena, Christiania, Eopholidostrophia, Origostrophia, Fardenia, Strophomena, Gunnarella, Drummuckina, Scotokiaeromena, Palaeocarrickella; Palaeostrophomena, Anoptambonites, Diambonia, Rurambonites, Sowerbyella, Anisopleurella, Rugosowerbyella, Eochonetes, Eoplectodonta, Kozlowskites, Bimuria.

WAL: Dolhir Formation (Rawtheyan), Glyn Ceiriog District, North Wales (Hiller 1980); Strophomena, Gunnarella, Luhaia, Katastrophomena, Kjaerina, Mjoesina, Christiania, Leptaena, Limbimurina, leptaenid gen. et sp. indet. 2, Fardenia; Diambonia, Leangella, Sampo, Sowerbyella, Kozlowskites, Chonetoidea.

DAL: Boda Limestone (middle Ashgill), Siljan area of Dalarna, Sweden (Cocks 2005); Strophomena, Gunnarella, Holtedahlina, Costistrophomena, Luhaia, furcitellinine gen. et sp. indet., rafinesquinine gen. et sp. indet., Leptaena, Ygdrasilomena, leptaenid gen. et sp. indet. 1, Kiaeromena, Trondomena, Ungulomena, Christiania, Eostropheodonta; Bimuria, Craspedelia, Leangella, Aegiria, Anoptambonites, Rugosowerbyella, Eochonetes, Anisopleurella, Eoplectodonta, Ptychoglyptus, plectambonitoid gen. et sp. indet.

IKB: Killey Bridge Formation (Cautleyan, middle Ashgill), Pomeroy, County Tyrone, Ireland (Mitchell 1977); Strophomena, Actinomena, Gunnarella, Luhaia, Kjerulfina, Mjoesina, Platymena, Christiania, Leptaena, Kiaeromena, Rhactomena, Pomeromena, Eostropheodonta, Brachyprion, Origostrophia; Leptellina, Anoptambonites, Trimurellina, Leptestiina, Leangella, Sampo, Sowerbyella, Rugosowerbyella, Viruella, Anisopleurella, Eochonetes, Eoplectodonta, Kozlowskites, Aegiria, Chonetoidea, Bimuria.

BFS: Fosse Formation (middle Ashgill), the region of the Sambre and Meuse rivers, Belgium (Sheehan 1987); Christiania, Foliomena, Strophomena, Luhaia, Costistrophomena, Katastrophomena, Leptaena, Kiaeromena, Fardenia, Diambonia, Leangella, Sampo, Sowerbyella, Rugosowerbyella, Anisopleurella, Ptychoglyptus, Chonetoidea.

AMC: Elgin Limestone (Richmondian), Maquoketa, Iowa (Wang 1949), and Waynesville Formation (Richmondian), Cincinnati, Ohio (Davis 1985); Leptaena, Strophomena, Tetraphalerella, Holtedahlina, Megamyonia, Oepikina, Thaerodonta.

ANT: Vaureal Formation (Rawtheyan, middle Ashgill), Anticosti Island, eastern Canada (Dewing 1999); Strophomena, Mjoesina, Megamyonia, Tetraphalerella, Nasutimena, Furcitella, Thaerodonta, Archeochonetes.

MAN: Selkirk Member and Fort Garry Member, Red River Formation (middle–upper Maysvillian, middle Ashgill), north-eastern Williston Basin, southern Manitoba, Canada (Jin and Zhan 2001); Strophomena, Tetraphalerella, Nasutimena, Megamyonia, Oepikina, Kjaerina, Holtedahlina, Thaerodonta.

KAZ: Dulankara Formation (upper Caradoc), Chu-Ili range, southern Kazakhstan (Popov et al. 2000; Popov and Cocks 2006); Strophomena, Holtedahlina, Rhipidomena, Glyptomenoides, Platymena, Christiania, Karomena, Dzhebaglina; Bandaleta, Glyptambonites, Nikitinamena, Dulankarella, Shlyginia, Leangella, Anoptambonites, Metambonites, Sowerbyella, Rugosowerbyella, Gunningblandella.

NSW: Malongulli Formation (Caradoc), Gunningbland, central western New South Wales, Australia (Percival 1979a, b); Infurca, Oepikina, Durranella, Kassinella, Dulankarella, Sowerbyites, Sowerbyella, Gunningblandella, Sericoidea, Leptellina.

SCH: Changwu Formation (middle Ashgill), western Zhejiang and eastern Jiangxi provinces, eastern China (Wang in Wang and Jin 1964; Liang in Liu et al. 1983; Zhan and Rong 1994, 1995a; Zhan and Cocks 1998; Rong et al. this paper and in prep.); Strophomena, Leptaena, Christiania, Fenomena, Holtedahlina, Katastrophomena, Tashanomena, Eopholidostrophia, Chunanomena, Cheramomena, Lateriseptomena, Foliomena, glyptomenid gen. et sp. indet., strophomenid gen. indet. 5, strophomenid gen. indet. 6, strophomenid gen. indet. 7, Leptellina, Anoptambonites, Kassinella, Bimuria, Sowerbyella, Rugosowerbyella, Metambonites, Synambonites, Rongambonites, Mabella, indet. xenambonitid gen. et sp. nov.

Numerical code for the genera recorded in Text-figure 3

1, Actinomena; 2, Aegiria; 3, Anisopleurella; 4, Anoptambonites; 5, Archeochonetes; 6, Bandaleta; 7, Bimuria; 8, Brachyprion; 9, Cheramomena; 10, Chonetoidea; 11, Christiania; 12, Chunanomena; 13, Costistrophomena; 14, Craspedelia; 15, glyptomenid gen. indet.; 16, Diambonia; 17, Drummuckina; 18, Dulankarella; 19, Durranella; 20, Dzhebaglina; 21, Eochonetes; 22, Eopholidostrophia; 23, Eoplectodonta; 24, Eostropheodonta; 25, Fardenia; 26, Fenomena; 27, Foliomena; 28, Furcitella; 29, furcitellinine gen. indet.; 30, Glyptambonites; 31, Glyptomenoides; 32, Gunnarella; 33, Gunningblandella; 34, Hedstroemina; 35, Holtedahlina; 36, indet. xenambonitid gen. nov.; 37, Infurca; 38, Karomena; 39, Kassinella; 40, Katastrophomena; 41, Kiaeromena; 42, Kjaerina; 43, Kjerulfina; 44, Kozlowskites; 45, Lateriseptomena; 46, Leangella; 47, Leptaena; 48, leptaenid gen. indet. 1; 49, leptaenid gen. indet. 2; 50, Leptellina; 51, Leptestiina; 52, Limbimurina; 53, Luhaia; 54, Mabella; 55, Megamyonia; 56, Metambonites; 57, Mjoesina; 58, Nasutimena; 59, Nikitinamena; 60, Oepikina; 61, Origostrophia; 62, Palaeocarrickella; 63, Palaeostrophomena; 64, Platymena; 65, plectambonitoid gen. indet.; 66, Pomeromena; 67, Ptychoglyptus; 68, rafinesquinine gen. indet. 1; 69, strophomenid gen. indet. 7; 70, Rhactomena; 71, Rhipidomena; 72, Rongambonites; 73, Rugosowerbyella; 74, Rurambonites; 75, Sampo; 76, Scotokiaeromena; 77, Sericoidea; 78, Shlyginia; 79, Sowerbyella; 80, Sowerbyites; 81, Strophomena; 82, strophomenid gen. indet. 5; 83, strophomenid gen. indet. 6; 84, Synambonites; 85, Tashanomena; 86, Tetraphalerella; 87, Thaerodonta; 88, Trimurellina; 89, Trondomena; 90, Ungulomena; 91, Viruella; 92, Ygdrasilomena.