DSpace at VNU: Lower Devonian chonetoidean brachiopods from Bac Bo, North Viet Nam

LOWER DEVONIAN CHONETOIDEAN BRACHIOPODS F R O M B A C B O , N O R T H V I Eà T N A M by PATRICK R RACHEBOEUF and T O N G - D Z U Y THANH ABSTRACT Recent investigations of the Lower Devonian fauna of North VieÃt Nam have provided abundant invertebrates, among which chonetoidean brachiopods are especially common Their good preservation has allowed the revision of eight of the nine species described in the literature The North Vietnamese chonetoidean fauna is mainly characterized by the diversity of representatives of the Family Strophochonetidae (strophochonetines and parachonetines), which includes nine species Three new genera, namely Tulynetes, Bacbonetes and Cyrtochonetes, and two species, namely Bacbonetes janvieri and Chlupacina nariensis, are described The occurrence of Perichonetes mirabilis, Chlupacina nariensis, and plicanoplitid brachiopods establishes the extension of the south-west China pelagic Nandan Facies to eastern Bac Bo The Lower Devonian chonetoidean fauna of eastern Bac Bo is closely allied to that of south-west and central China belonging to the Yangtze microcontinent, whilst the fauna of western Bac Bo appears to be more closely allied with that of the northern Gondwanaland margin One new additional chonetoidean genus, Orthochonetes, is described in a note added to the systematic section KEY WORDS: Chonetoidean brachiopods, Devonian, Viet Nam, taxonomy D EV ONIAN chonetoidean brachiopods from South East Asia (e.g VieÃt Nam, Laos) were ®rst described by Mansuy in several papers published between 1908 and 1921 Mansuy recognized a total of 12 species of chonetoidean brachiopods, among them eight new species, all assigned to the genus Chonetes The new species were: Chonetes zeili Mansuy, 1908 (p 16, pl 7, ®g 13), Chonetes longispina Mansuy, 1912 (p 57, pl 10, ®g 6a±d), Chonetes magnini Mansuy, 1912 (p 58, pl 10, ®g 7a±b), Chonetes hoabinhensis Mansuy, 1914 (p 58, pl 6, ®g 10), Chonetes indosinensis Mansuy, 1916b (p 47, pl 7, ®g 5a±b), Chonetes lacroixi Mansuy, 1916b (p 46, pl 7, ®g 6a±b), Chonetes lantenoisi Mansuy, 1916b (p 46, pl 7, ®g 7a±c), and Chonetes nongpoensis Mansuy, 1919 (p 26, pl 5, ®g 4a±b) The four remaining taxa were assigned to previously described species: Chonetes striatella Dalman, 1828 (Mansuy 1914, p 53, pl 5, ®g 11a±d), Chonetes cf margaritacea Whidborne, 1898 (Mansuy 1916a, p 11, pl 1, ®g 10a±b), Chonetes cf striatella Dalman, 1828 (Mansuy 1916a, p 11, pl 2, ®g 1; 1916b, p 46, pl 7, ®g 8), and Chonetes hardrensis Phillips, 1841 (Mansuy 1921, p 18, pl 2, ®g 5a±c) Later Patte (1926, pp 61±65) redescribed and re-illustrated Chonetes zeili Mansuy, 1908 (p 61, pl 4, ®g 5), ?Chonetes lantenoisi Mansuy, 1916 (p 63), and Chonetes indosinensis Mansuy, 1916 (p 64, pl 4, ®gs 1±4) Patte was the ®rst to establish the synonymy between Strophonella inversa Mansuy, 1921 (p 18, pl 2, ®g 6a±c; pl 3, ®g 1), Plectambonites yenlacensis Mansuy, 1916 (p 49, pl 7, ®g 3a±b (pars), Chonetes cf margaritacea, and Chonetes zeili Patte also suggested that some specimens of Plectambonites yenlacensis were synonyms of Chonetes lantenoisi, and he described Chonetes mansuyi as a new species (1926, p 64, pl 4, ®g 6.), and Chonetes sp (p 65) None of these species has been revised since their description, and they still remain poorly known, especially with regard to their internal features More recent references in the literature only refer to new generic assignments as well as to their stratigraphical range within the Devonian succession of Bac Bo One of us (Tong-Dzuy Thanh, 1993) established that Chonetes mansuyi Patte, 1926 is restricted to the Bac Bun Formation (upper Lochkovian±lower Pragian), while both Chonetes lacroixi Mansuy, 1916, and Parachonetes zeili (Mansuy, 1908) occur in the Mia-Le Formation (Pragian) of north-eastern Bac Bo In north-western Bac Bo, Strophochonetes hoabinhensis (Mansuy, 1914) was said to occur in the Song-Mua Formation (Lochkovian), while Parachonetes zeili was said to be restricted to the Pragian Ban Nguon Formation [Palaeontology, Vol 43, Part 6, 2000, pp 1039±1068, pls] q The Palaeontological Association 1040 PALAEONTOLOGY, VOLUME 43 List of Devonian chonetoidean brachiopods described from Bac Bo (North VieÃt Nam), revised assignments, and new taxa TABLE Species described and/or illustrated by H Mansuy Proposed new assignment 1908 Chonetes zeili sp nov Chonetes sp.? Chonetes cf striatella 1912 Chonetes longispina sp nov Chonetes magnini sp nov 1914 Chonetes hoabinhensis sp nov Chonetes striatella Dalman 1916a Chonetes cf margaritacea Whidborne Chonetes sp.? Chonetes cf striatella Dalman 1916b Chonetes cf striatella Dalman (pl 7, ®g 8) Chonetes indosinensis sp nov Chonetes lacroixi sp nov Chonetes lantenoisi sp nov ?Plectambonites yenlacensis sp nov (pl 3, ®g 9) 1919 Chonetes nongpoensis sp nov 1921 Strophonella inversa sp nov Chonetes hardrensis Phillips Parachonetes zeili Parachonetes zeili Tulynetes hoabinhensis `Strophochonetes' longispina originals not found Tulynetes hoabinhensis Tulynetes hoabinhensis Parachonetes zeili ?Cyrtochonetes indosinensis Chlupacina nariensis sp nov Cyrtochonetes indosinensis Cyrtochonetes indosinensis ?Parachonetes lantenoisi Parachonetes lantenoisi Parachonetes zeili Tulynetes nongpoensis Parachonetes zeili originals not found Species described and/or illustrated by E Patte 1926 Chonetes zeili Mansuy ?Chonetes lantenoisi Mansuy Chonetes indosinensis Mansuy Chonetes mansuyi sp nov Chonetes sp Parachonetes zeili ?Parachonetes lantenoisi Cyrtochonetes indosinensis Cyrtochonetes indosinensis ? New taxa from VieÃt Nam described in this paper Perichonetes mirabilis Xu, 1979 Chlupacina nariensis sp nov Bacbonetes janvieri gen et sp nov Other new taxa described Orthochonetes gen nov Although abundant, Lower Devonian chonetoids from Bac Bo are not easy to study Shells are always decalci®ed, preserved as external and internal moulds, and mainly occur in muddy sediments which are often strongly affected tectonically Such an unfavourable context partly explains the number of species in the literature Indeed, most species have been described from a single specimen only, often incomplete and distorted (see Mansuy, 1914, p 58; description of C hoabinhensis for example), and most external characters (e.g outline, density of costellae, development of a ventral sinus) are directly affected by tectonics This fact, plus some misinterpretation, is partly responsible for the 13 chonetoidean species described ®rst by Mansuy, then by Patte, between 1908 and 1926 However, owing to the ®ne-grained nature and quiet environmental conditions of most Lower Devonian chonetoidean-bearing beds, many important characters, such as spine morphology and spine distribution, and ventral and dorsal interiors, are suf®ciently well preserved to allow complete descriptions for each identi®ed species This led us to propose signi®cant synonymy lists, and to reduce to six species the number of previously described Lower Devonian chonetoidean brachiopods from Bac Bo (see Table 1, together with new generic and speci®c assignments) Two more species are described for the ®rst time The main dif®culty in this study lay in ®nding the originally described specimens Specimens described and illustrated by Mansuy in 1908 and 1912, were deposited in the collections of the EÂcole des Mines de RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1041 Paris before the opening of Vietnamese collections in Ha NoõÈ in 1912 These specimens are now housed in Lyon Original specimens of Mansuy's species described later, as well as Patte's originals, were housed in Ha NoõÈ until 1954 when they were moved to Saigon (now Ho Chi Minh City) Recently these collections were returned to the Ha NoõÈ Geological Museum Unfortunately several type and illustrated specimens of chonetoidean brachiopods could not be found when one of us (PRR) visited the Museum in November 1998 As well as the inability to ®nd several original specimens, another dif®culty was the fact that both Mansuy and Patte gave no precise data about the geographical location of most type localities This implies that the search for topotypes will require time and be dif®cult Moreover these two authors did not describe any ventral or dorsal interiors, although they had materials at hand, at least for some species; either they did not recognize interiors, or they could not prepare corresponding specimens Hence, the species they described, mainly on ventral exteriors of distorted shells, can hardly be recognized However, delicate and lengthy preparation of the available type specimens allowed the description of most of the inner features, as well as detailed comparison with the newly collected material All types and specimens described and illustrated in this paper are deposited in the collections of the Ha NoõÈ Geological Museum, Pham Ngu Lao Street, Ha NõÈ (pre®xed BT for Bao Tang ˆ Museum), and in the collection of the Universite Claude-Bernard ± Lyon I, 43 bd du 11 novembre 1918, F-69622Villeurbanne cedex (pre®xed FSL for Faculte des Sciences de Lyon) Plastotypes of original specimens housed in France have been deposited in Ha NoõÈ During the preparation of the present paper, the systematic study involved comparisons with chonetoidean faunas from other regions As a consequence, one new chonetoidean genus is proposed in the last part of this paper, in an additional systematic note GEOLOGICAL BACKGROUND The Lower Devonian of North VieÃt Nam Extensive data about the Devonian stratigraphy, faunal content, biostratigraphy, lithostratigraphy and palaeobiogeography of North VieÃt Nam have been published earlier by one of us (Tong-Dzuy Thanh, 1993), and only a short overview is given here The Devonian succession includes both lithostratigraphical units and biostratigraphical levels which are grouped together to form regional stages The correlation between these regional stages and the International Global Stratigraphic Chart for the Devonian remains uncertain (Table summarizes the main characters of the Lower Devonian sucession of Bac Bo) Because of signi®cant lithological differences, a distinction is made between the western and eastern parts of North VieÃt Nam The Devonian succession of North VieÃt Nam begins with Red Beds (Si Ka Formation) in the northeastern mountain area (eastern Bac Bo) and with marine deposits (Iridistrophia praeumbraculum fauna) in the north-western area (western Bac Bo) (Table 2) These two units are usually grouped together as the Si Ka Regional Stage The Si Ka Formation overlies unconformably Cambrian or Ordovician deposits It consists of purplish red conglomerates, sandstones, shales and marls in some sections It yields plant remains (Buthotrephis aff antiqua) and ®sh remains which are referred to Yunnanolepiformes and Polybranchiaspis cf gracilis (Tong-Dzuy Thanh and Janvier 1987) The Si Ka Formation is correlated with the Lianhuashan Formation, and with the lower part of the Cuifengshan Formation of South China (Tong-Dzuy Thanh 1980; Tong-Dzuy Thanh et al 1988) It can be compared with the Old Red Sandstone of Western Europe and may be assigned to the Lochkovian Stage The Iridistrophia praeumbraculum fauna represents the lowermost Lower Devonian marine strata in the north-western mountain area of North VieÃt Nam In the lower basin of the Song Da River, black shales of the Song Mua Formation (over 1800 m thick) are poorly fossiliferous Among other fossils, the middle part of the formation yields tabulate corals (Parastriatopora cf rzonsnickajae), brachiopods (Iridistrophia praeumbraculum, Mesodouvillina aff subinterstrialis, Platyorthis cimex), and crinoids (Schyschcatocrinus astericus) The Iridistrophia praeumbraculum fauna can be assigned to the Lochkovian The Silurian/Devonian boundary could probably be situated within the interval between the top of the underlying Bo Hieng Formation (Silurian) and the beds with Parastriatopora cf rzonsnickajae 1042 TABLE PALAEONTOLOGY, VOLUME 43 Lower Devonian lithostratigraphical units and index fossils of North VieÃt Nam The Bac Bun Regional Stage was established on the basis of the correlation of marine deposits yielding the Howittia wangi Assemblage (Hysterolites wangi of previous works) This unit includes the Bac Bun Formation of the north-eastern mountain area, the upper part of the Song Mua Formation, and the middle part of the Nam Pia Formation in the north-western mountain area and other equivalents (Table 2) They consist mainly of black muddy shales with intercalations of ®ne-grained sandstone and marls, and limestone lenses in some sections Most characteristic fossils are brachiopods, bivalves, and corals in the upper part In the eastern area of North VieÃt Nam, the lower part of this unit yields ®sh remains (Tong-Dzuy Thanh and Janvier 1990) Fish fossils of `South Chinese' type (Songdalepis pustolatus) have recently been described from this stage in the downstream Song Da River, probably from a higher level than in the eastern area (Janvier et al 1996) A Late Lochkovian±Early Pragian age is assigned to the Bac Bun Regional Stage yielding the Howittia wangi fauna Because of its abundant fossil content the Mia Le Regional Stage is the most famous unit among the Devonian strata in North VieÃt Nam It includes all beds and formations characterised by the Euryspirifer tonkinensis Fauna, among which are the Mia Le Formation, the Ban Nguon Formation, the upper part of the Nam Pia Formation, and the lower part of the Duong Dong Formation (Table 2) The lithostratigraphical succession consists of shales, ®ne-grained sandstones and marls, sometimes with some local interbedded limestones or calcareous lenses In the north-western mountain area terrigenous components increase in the sequences while carbonate components are more abundant in the north-eastern mountain area In the Ha Lang region (Luoc Khieu Formation), and in the north-eastern coastal area, this unit consists only of terrigenous rocks The typical Euryspirifer tonkinensis Fauna is the most diverse Devonian faunal assemblage in North VieÃt Nam and South China Over 300 species of various benthic groups have been listed and described in North VieÃt Nam, among which brachiopods and corals are the most abundant components, associated with stromatoporoids, bivalves, trilobites, crinoids, and dacryoconarides (Tong-Duy Thanh 1993) Apart from numerous endemic species, many Mediterranean species are found associated with Euryspirifer tonkinensis, such as corals (Favosites styriacus, Heliolites barrandei, RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1043 H praeporosus, Holmophyllum holmi, Roemeripora bohemicus, Squameofavosites cechicus, Thamnopora incerta), and brachiopods (Acrospirifer primaevus, Howellella mercuri, Leptaenopyxis bouei) The dark grey strati®ed limestones of Emsian±Givetian age which crop out widely in North VieÃt Nam (Table 2) have been described under various names such as the Ban Bap, Na Quan, Ha Lang, Bang Ca, Mo Tom, Lo Son, and Trang Kenh units in previous publications They consist of various kinds of limestone, and Tong-Duzy Thanh (1993) has combined them into the Ban Pap Regional Superstage On the whole the succession of this superstage can be divided into three levels The lower level, mainly composed of well-strati®ed bituminous and muddy limestones, which conformably overlie the Mia Le Stage, corresponds to the Pac Nam Regional Stage In several sections, especially in the north near the VieÃt Nam-China frontier, intercalations of thin chert beds occur Corals, stromatoporoids and brachiopods are usually abundant in most sections Dacryoconarids and conodonts are important fossils in the sequences with intercalations of cherts The lowermost beds of the Dong Van± Song Nho Que section yield dacryoconarids of the Nowakia zlichovensis Zone and representatives of Nowakia acuaria; conodonts of the Polygnathus perbonus Zone have also been identi®ed (Ta Hoa Phuong 1994; Tong-Dzuy Thanh and Ta Hoa Phuong, 1994) In the lower part of the Dong Van±Song Nho Que section, Ta Hoa Phuong (unpublished) recently recorded from the bottom upwards: (1) Nowakia acuaria; (2) N zlichovensis; (3) N mana, Polygnathus nothoperbonus, and P gronbergi The middle and upper levels consist of fossiliferous limestones which are Eifelian and Givetian in age The main characteristic fossils are corals, brachiopods and other benthic fauna in the shallow-water facies; dacryoconarids and conodonts in the deep-water facies Fossiliferous sections and localities investigated Two sections and several isolated localities were visited and sampled by both of us in November 1995, and again in November 1998, and several hundred specimens of chonetoidean brachiopods were collected (Text-®g 1A) The ®rst section, called the Dong Mo section (Text-®g 1B), is located 30 km south-west of Lang Son, in eastern Bac Bo; it is exposed along the road from Dong Mo to Tu Don, between 3´5 and km from Dong Mo Six fossiliferous levels have yielded chonetoideans The second section (Text-®g 1C) is located north-west of Hoa Binh, in western Bac Bo; Devonian deposits are well exposed along the road from Hoa Binh to Tu Ly (Da Bac district), between and 9´2 km from Tu Ly The top of the section, which corresponds to the Tu Ly section of Mansuy, is just in front of the last house of the village of Xom May from Hoa Binh Four levels have yielded chonetoids Other isolated localities of eastern Bac Bo visited and sampled in 1998, are located north and south of YeÃn Lac; south of Dinh Ca, near Don An (Tran Xat section), and near Na Tuong (south of Na Ri) (Text-®g 1A) PALAEOBIOGEOGRAPHIC SIGNIFICANCE OF THE CHONETOIDEAN FAUNA The most striking characteristic of the Lower Devonian chonetoidean fauna from Bac Bo is the abundance and relative diversity of representatives of the family Strophochonetidae (subfamilies Strophochonetinae and Parachonetinae) It contrasts strongly with the apparent lack of representatives of the families Anopliidae, Chonetidae and Eodevonariidae, which are usually common components of the Lower Devonian benthic fauna worldwide In fact no representatives of these three families were found in the ®eld, and the literature contains no evidence of their occurrence in the Lower Devonian of northern VieÃt Nam Such faunal composition at the family level is reminiscent of several Lower Devonian chonetoidean faunas from other palaeobiogeographic areas, such as the south-eastern part of Australia and South China, which are characterized by the occurrence of strophochonetids (strophochonetines and parachonetines) but include other chonetoideans An exception is the occurrence of the anopliine genus Tuberella in the uppermost beds (Dalejian) of the Tangxiang Formation of the Nandan area in south China (Vogel et al 1989) Tuberella is a preoccupied name; the genus should now be known as Anopliella (Racheboeuf 1998) Within Bac Bo, a distinction has to be established between the western and eastern parts The relative numerical abundance of representatives of the genus Parachonetes in eastern Bac Bo, often associated with strophochonetines, contrasts with their apparent absence (or their scarcity) in the western part (Song 1044 TEXT-FIG PALAEONTOLOGY, VOLUME 43 A, map of the localities listed in the text B, location of the chonetoid-bearing levels along the Dong Mo section C, location of the chonetoid-bearing levels along the Tu Ly section RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1045 Schematic reconstructions from camera lucida drawings of Lower Devonian strophochonetid representatives from Bac Bo in ventral view, and longitudinal pro®le of the articulated shell, for comparison All ´ except G which is ´ A, `Strophochonetes' longispina Mansuy B, Tulynetes hoabinhensis (Mansuy) C, Tulynetes nongpoensis (Mansuy) D, Bacbonetes janvieri gen et sp nov E, Chlupacina nariensis sp nov F, Perichonetes mirabilis Xu G, Cyrtochonetes indosinensis (Mansuy) TEXT-FIG Da area, Hoa Binh section) This fact makes the Lower Devonian eastern Bac Bo chonetoidean fauna very closely allied with that of the South China microcontinent, mainly with that of Sichuan in south-west China, and central South China, which yields strophochonetines (`Chonetes' ellipticus, `C.' ganxiensis) and parachonetines (Parachonetes sp 1, P sp 2, P liujingensis) (Yang et al 1977; Xu et al 1979) By contrast, in western Bac Bo the strophochonetids Tulynetes hoabinhensis and T nongpoensis (the latter originally described from the Tran Ninh area of Laos) give the area belonging to the Indochina Block, some Gondwana-like af®nities In fact, the genus Tulynetes gen nov appears to be a south-east Asian equivalent of the Lower Devonian (Lochkovian-Emsian) south-west European and North African genus Ctenochonetes Racheboeuf, 1976, with which it is undoubtedly related both morphologically and phylogenetically However, the lack of any anopliid representative in North VieÃt Nam remains questionable, particularly because they occur in deposits re¯ecting similar palaeoenvironments together with strophochonetids in the Lower Devonian of the Shan ThaõÈ-Malayia Block, Thailand (Boucot et al 1999) and in South China 1046 PALAEONTOLOGY, VOLUME 43 (Vogel et al 1989) A lot of ®eld work needs to be done, and many ancient fossiliferous localities need to be investigated in VieÃt Nam, and in the whole of south-east Asia, to establish the vertical range and the geographical distribution of the chonetoidean taxa, and to test the faunal af®nities and detailed biogeographical relationships between the different structural blocks, mainly on each side of the Song Ma suture SYSTEMATIC PALAEONTOLOGY Order PRODUCTIDA Sarytcheva and Sokolskaya, 1959 Suborder CHONETIDINA Muir-Wood, 1955 Superfamily CHONETOIDEA Bronn, 1862 Remarks Original specimens that were found in Mansuy's collections either in Lyon or in Ha NoõÈ are here assigned lectotype status, or holotype status by monotypy Among the nine chonetoidean species originally described from VieÃt Nam, ®gured originals of Chonetes magnini Mansuy, 1912, and Chonetes hardrensis (in Mansuy 1921) have not yet been found This situation calls for some comments about these species The same is true for the originals of Chonetes mansuyi Patte, 1926, but this species is considered herein to be a junior synonym of Chonetes indosinensis Mansuy, 1916 Chonetes magnini Mansuy, 1912 (p 58, pl 10, ®g 7a±b) This species was described from the Mang-Nho locality (sheet Thanh-Ba), based upon poorly preserved and unprepared specimens Neither the original description on page 58, nor the two ®gures on plate 10 in Mansuy's paper, provide original information suf®cient to diagnose C magnini Original specimens, and further additional material are needed before revising this species Chonetes hardrensis Phillips, in Mansuy, 1921 (p 18, pl 2, ®g 5a±c) This species was recorded from the Po Duong locality (sheet ThaÃt-KheÂ, north-east Bac Bo), and brie¯y described based on ventral valve interiors only Mansuy listed the following characters: shell outline subsemicircular, with maximum with at hinge line or anterior to hinge line in some specimens; costellae number between 80 and 100, or even more; four spines on each side of beak From the illustrations it can be added that internal moulds are deeply impressed by the outer ornament Moreover, posterolateral costae possibly originate along the posterior shell margin, and the specimen shown in ®gure 5c of Mansuy (1921) shows a weak sulcus-like longitudinal depression This form cannot be assigned to any of the species described herein However, it is probably a member of the family Strophochonetidae; it cannot be assigned to the Carboniferous genus Rugosochonetes for which C hardrensis is the type species Family STROPHOCHONETIDAE Muir-Wood, 1962 Subfamily STROPHOCHONETINAE Muir-Wood, 1962 Genus UNCERTAIN `Strophochonetes' longispina (Mansuy, 1912) Text-®gures 2A, 3A±F v 1912 Chonetes longispina Mansuy, p 57, pl 10, ®g 6a±d Lectotype The ventral valve (both external and internal moulds) illustrated by Mansuy in 1912 (pl 10, ®g 6a±c); FSL 424455a±b (Text-®g 3A ± C), is selected here Paralectotypes Five ventral valves and several fragments, as well as two incomplete dorsal valve interiors and two dorsal valve exteriors from the type locality, Mansuy's collection, FSL 424454 and 413838±413840 Type locality Between Lang-Con and Lang-Tien (sheet Thanh-Ba) according to Mansuy 1912 (p 58) Lithostratigraphical unit and age unknown RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1047 `Strophochonetes' longispina (Mansuy) All specimens ´ A±C, FSL 424455; ventral valve, lectotype, original of Mansuy, 1912, pl 10, ®g 6a±c D, FSL 413838; ventral valve external mould E, FSL 413839; latex replica of an immature dorsal valve exterior F, FSL 413838; latex replica of an incomplete dorsal valve interior TEXT-FIG Description Exterior Shell medium sized (maximum length about mm; corresponding width, 13 mm), transverse in outline, and moderately arched Maximum width anterior to hinge line Undistorded specimens exhibit a shallow, relatively wide ventral sulcus, corresponding to a dorsal fold in some specimens This feature may be exaggerated by tectonics Ventral interarea ¯at, apsacline, with small pseudodeltidum Delthyrium opening as wide as high Dorsal interarea hypercline Chilidium not observed Ventral ornamentation with ill-developed median-enlarged costa in the posterior part of the shell only Radial costellae low, rounded, with narrower intervals Ventral costellae ®rst increase by intercalation in the posterior half of the valve, then by bifurcation towards valve margins At mm anterior to the beak, as well as along anterior margin, costellae number 12±14 per mm Dorsal costellae ®rst increase by bifurcation, then by intercalation The lectotype, as well as other syntypes, exhibits four pairs of spines Spines orthomorph perpendicular, and almost symmetrically displayed, right spines developing before left ones The spine distribution in the lectotype is as follows: 4´7 (4'), 3´7 (3'), 2´3 (2'), 1´0 (1')±0´8 (1), 1´8 (2), 3´3 (3), 4´6 (4) Ventral valve interior Interarea relatively thickened for the size of the shell Stout, thick, anteriorly rounded teeth parallel to the interarea Short and relatively thick myophragm, about 1´5 mm long, dividing an ill-de®ned muscle ®eld Short, straight, low, wide, poorly developed posterior muscle-bounding ridges anteriorly divergent at about 90 degrees Diductor scars indistinct Adductor scars well differentiated, elliptical to semi-elliptical in outline, about three times longer than wide, their anterior margin at about 2´0 mm from beak Vascula media present, originating between adductor scars Visceral cavity well de®ned The whole inner surface of the valve, including the diductor ®eld, is deeply impressed by the outer radial costellae This character is indicative of a relatively thin valve, and contrasts strongly with the thickenings of the posterior part of the shell Dorsal valve interior Low, short, straight, and rounded inner socket ridges, anteriorly divergent at about 130 degrees Proximal part of sockets with small horizontal expansions overhanging the inner part of sockets Cardinal process laterally widened and short, extending slightly beyond the valve margin Cardinal process weakly bilobed internally, with a narrow, high, dorsally directed myophore Median septum low, widening posteriorly, fused with proximal part of anderidia Anteriorly, median septum low and narrow, not extending beyond two-thirds valve length Anderidia relatively well developed, long, thickened, anteriorly divergent at 60±70 degrees Valve interior strongly impressed by the outer ornamentation Endospines scarce, weakly elongated, and relatively stout, located on radial ridges only Remarks Chonetes longispina Mansuy undoubtedly belongs to the family Strophochonetidae as attested 1048 PALAEONTOLOGY, VOLUME 43 by its shell outline and morphology with a ventral median-enlarged costa (although reduced), by its spine arrangment and morphology, and by the interior of the dorsal valve However, owing to the lack of additional material, the generic position of Chonetes longispina cannot be precisely established Original specimens differ externally from species assigned to Tulynetes by their poorly differentiated medianenlarged costa, and by their spine arrangment (almost symmetrical whereas species of Tulynetes exhibit two more spines on the right side of the ventral valve) In the interior of the dorsal valve the geniculated pro®le of the cardinal process, which characterizes Tulynetes, cannot be established, and the inner socket ridges are less developed than in the new genus All of these characters can be considered `primitive', and would possibly suggest a Silurian age for this species, but no chonetoid-bearing Silurian deposits are known in this region In this way C longispina could possibly be regarded an ancestral form of representatives of the genus Tulynetes, but more material and further information about the age of the species are needed before it is possible to be sure about this hypothetical phyletic relationship None of the newly collected specimens can be assigned to this species Its outline, external ornament, spine arrangment, and its dorsal interior make it easily distinguishable from all of the species described below Genus TULYNETES gen nov Type species Chonetes hoabinhensis Mansuy, 1914 Derivation of name From the so-called Tu Ly section, north-west of Hoa Binh, western Bac Bo Diagnosis Strophochonetidae with a prominent, strongly bilobed and geniculated cardinal process; shell exterior costellate with median-enlarged costa variably developed, in ventral valve only, or in both valves; spines orthomorph-perpendicular, with the two proximal spines lacking on the left side; ventral valve interior with relatively short, laterally elongated, subrectangular hinge teeth; dorsal valve interior with a breviseptum-like, often spinose, median ridge; wide, narrow, posteriorly bent, inner socket ridges Remarks External morphological characters (e.g shell shape and pro®le, ornamentation with a variably developed median-enlarged costa, orthomorph-vertical spines), as well as internal features, make Tulynetes a member of the subfamily Strophochonetinae Tulynetes differs from all previously described strophochonetid genera in the characters of the interior of its dorsal valve Typical features are the short, markedly knee-shaped, deeply bilobed and laterally elongated cardinal process, the presence of welldeveloped cardinal crests, the morphology and disposition of the inner socket ridges, the breviseptum-like morphology of the median septum, as well as the development of stouter endospines in the anteromedian part of the valve Together these characters make `adult' representatives of the genus Tulynetes easily recognizable Comparison has to be made with the genus Ctenochonetes Racheboeuf, 1976 from the Lower Devonian of western Europe and north-western Africa Externally, representatives of both genera share a similar shell outline and pro®le, and similar spine distribution, but specimens of Tulynetes are smaller (maximum observed width about 16 mm for T hoabinhensis, 40 mm for C aremoricensis), and they often exhibit a weakly developed ventral sulcus which has never been observed in any species of the genus Ctenochonetes Internally Tulynetes shares with Ctenochonetes a knee-shaped cardinal process, but the former can be distinguished by its shorter, less developed median septum and narrower, more posteriorly located and anteriorly, more divergent, inner socket ridges Tulynetes hoabinhensis (Mansuy, 1914) Plate 1, ®gures 1±14; Text-®gure 2B 1908 1914 1993 Chonetes cf striatella Dalman; Mansuy, p 37, pl 7, ®g 14 Chonetes hoabinhensis Mansuy, p 58, pl 6, ®g 10 Strophochonetes hoabinhensis; Tong Duy, ®g Lectotype Although the original and unique specimen illustrated by Mansuy in 1914 has not yet been found in the Mansuy collection housed in Lyon, or in his collection in the Geological Museum in Ha NoõÈ, there is no doubt about the 1054 PALAEONTOLOGY, VOLUME 43 Remarks Although it exhibits some morphological peculiarities, this new genus undoubtedly belongs to the family Strophochonetidae The familial assignment is warranted by the ventral median-enlarged costa, as well as by inner features of both valves, mainly the interior of the dorsal valve Most external morphological characters of the new species ®t with the diagnosis of Tulynetes gen nov except for the morphology of spines, which are typically of cyrtomorph extraverse type instead of orthomorph perpendicular as in T hoabinhensis (Mansuy) and T nongpoensis (Mansuy) The cyrtomorph extraverse morphology of spines cannot be related to tectonics because this character is constant in all available specimens Among strophochonetids such spine morphology was previously only described in representatives of the genus Chlupacina HavlõÂcÏek and Racheboeuf, 1979 (Racheboeuf 1981) However shell-size, outline and distribution of spines on both sides of ventral valve clearly distinguish Bacbonetes from Chlupacina Internally, the new genus can be differentiated by the poorly developed dorsal median septum and inner socket ridges, as well as by its low cardinal process anteriorly bounded by a faint cardinal process pit in the dorsal valve Both outer and inner morphological characters make Bacbonetes an unusual Lower Devonian strophochonetid genus Bacbonetes janvieri gen et sp nov Text-®gures 2D, 4A±K Holotype Ventral and dorsal external moulds of a complete, articulated shell; BT 229/32, Text-®gure 4C±D Locality and horizon Sloping outcrop along road 305, 3´2 km south of YeÃn Lac, on the right side of the road from YeÃn Lac, Mia Le Formation Derivation of name To honour Dr Philippe Janvier, MuseÂum National d'Histoire naturelle, France Material Sample 98V5: 34 decalci®ed, weakly tectonically affected specimens: ®ve external and internal moulds of articulated shells; 13 ventral valve exteriors and nine interiors; three dorsal valve exteriors, and four interiors Illustrated specimens, BT 229/32±229/41 Diagnosis As for the genus Description Exterior Shell medium-sized (maximum observed length, 8´2 mm; corresponding width, 11´3 mm), transverse, subsemicircular in outline Length/width ratio about 0´66 for 15 ventral valves, more than mm long Maximum width at hinge line Postero-lateral commissures perpendicular to hinge line Ventral valve markedly convex, regularly arched, without developed sulcus Median part of ventral valve sometimes ¯attened or very weakly depressed Dorsal valve moderately concave Ventral interarea apsacline and ¯at, concave in its posterior part, with a large, prominent triangular pseudodeltidium Dorsal interarea hypercline, ¯at, with reduced but well-differentiated chilidium Medianenlarged costa reduced and barely perceptible on smallest shells only Radial costellae rounded, sub-semicircular in cross section, with much narrower, deep interspaces In ventral valve, costellae increase ®rst by implantation in the median part of the shell, then by bifurcation towards periphery of the valve In dorsal valve, costellae increase ®rst by bifurcation, then by implantation Along anterior margin, costellae number 3±4 per mm Costellae number 44±58 for shells between and 7´2 mm long Spines of cyrtomorph extraverse type, and asymmetrically arranged Spine diameter is relatively strong (0´25±0´3 mm) for shell size In their proximal part, spines bend medially, then they progressively bend outwards and tend to parallel the plane of symetry A maximum of ®ve spines was observed on the right side of the shell, and only two on the left side Their distribution is: 4´08 (4'), 2´63 (3')±0´3 (1), 0´88 (2), 2´13 (3), 3´56 (4), 5´15 (5) Spine 5' was not observed but its presence would be expected in largest shells Ventral valve interior Hinge teeth relatively large, subrectangular and markedly transverse in outline, extending parallel to hinge line Valve internally arched longitudinally Posterior bounding muscle ridges poorly differentiated, wide, low, rounded, and anteriorly divergent at about 100 degrees Myophragm very thin and elevated, not extending anteriorly beyond one-sixth of the valve length Diductor scars indistinct Adductors scars very long and narrow, inserted obliquely along the base of the myophragm Vascula media present but faint No visceral cavity differentiation Inner RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1055 à n Lac All specimens are latex replicas, TEXT-FIG Bacbonetes janvieri gen et sp nov., outcrop 3´2 km south of Ye except H, and all ´ A, BT 229/33; ventral valve exterior B, BT 229/34; dorsal side of an immature articulated shell C±D, holotype, BT 229/32; articulated shell, ventral and dorsal views E, BT 229/35; ventral valve exterior F, BT 229/ 36; ventral valve exterior G, BT 229/37; immature ventral valve with dorsal valve partly conjoined H, BT 229/38; ventral valve, internal mould I, BT 229/39; ventral valve interior J, BT 229/40; dorsal valve interior K, BT 229/41; dorsal valve interior surface strongly impressed by the external ornamentation, including the diductor ®eld Strong, sparse endospines in the posterolateral parts of the valve Other endospines very tiny, isolated and radially displayed Dorsal valve interior Cardinal process internally bilobed, low, short and laterally widened Myophore widely separated medially, and laterally bounded by strong cardinal crests Outer socket ridges wide and narrow Inner socket ridges low, rounded, relatively wide, anteriorly divergent at about 150±160 degrees, medially fused with the cardinal process Anterior edge of the cardinal process weakly elevated above valve ¯oor, anteriorly bounded by a poorly developed cardinal process pit Anterior adductor scars clearly marked and divided by a low, wide, septum-like median 1056 PALAEONTOLOGY, VOLUME 43 ridge Posterior adductor scars ill-de®ned Anderidia blade-like, anteriorly divergent at about 60 degrees Shell surface impressed by the outer ornament Endospines, sparse, radially displayed, exhibiting a stronger development in the antero-median part of the valve Remarks Externally, Bacbonetes janvieri gen et sp nov can easily be distinguished from other Lower Devonian Vietnamese strophochonetids by its shell outline and pro®le, by its outer ornament, by its spine morphology as well as by its spine diameter, which is unusually large (up to 0´30 mm) Genus CHLUPACINA HavlõÂcÏek and Racheboeuf, 1979 Type species Chlupacina longispina HavlõÂcÏek and Racheboeuf, 1979 Chlupacina nariensis sp nov Text-®gures 2E, 5A, I±J v 1916a ? 1979 ? 1989 Chonetes cf striatella Dalman; Mansuy, p 11, pl 2, ®g Strophochonetes cf ®listriata (Walcott); Xu, p 371, pl 3, ®g 29 Strophochonetes cf ®listriata (Walcott 1884); Vogel, Xu and Langenstrassen, pl 3, ®gs 4±5 Derivation of name From the Na Ri district Holotype Both moulds of a dorsal valve; BT 229/2, Text-®gure 5I±J Type locality and horizon Outcrop along the track between Na Tuong and Na Lu, about km north-east of Na Tuong and 10 km south of YeÃn Lac (Na Ri district, Bac Can province), Na Tuong Formation, associated with Nowakia holynensis, Costulatostyliolina peneaui and Styliolina sp.; uppermost Emsian±lowermost Eifelian The original of Mansuy (1916a, p 11) was collected along the road from Cao-Bang to Ta Sa Material Sample 98V7: decalci®ed isolated valves, both external and internal molds, and the dorsal side of an articulated shell, among which both moulds of a ventral valve on the same slab as the holotype, and probably belonging to the same shell (BT 229/2, Text-®g 5I±J) Mansuy's original specimen of Chonetes cf striatella is a small slab (4 ´ cm) with 15 incomplete, distorted, and decalci®ed isolated ventral valves and articulated shell exteriors; BT 229/1 Diagnosis Small shell, weakly concavoconvex and transverse in outline; length vs width ratio between 0´60 and 0´65; 6±8 costellae per mm; two spines on the right side of ventral valve, respectively at 0´3 mm and 1´7 mm from beak; unusually long and narrow cardinal process pit; long, straight and narrow inner socket ridges anteriorly divergent at about 160 degrees Description Exterior Shell very small (maximum observed length, 5´0 mm; corresponding width, 8´2 mm), transverse in outline, with a length vs width ratio between 0´61 and 0´65 Longitudinal pro®le weakly concavoconvex Both interareas are very short, ¯at, the ventral one being apsacline, and the dorsal one hypercline, both lying in the same plane Median enlarged costa poorly developed in ventral valve, relatively narrow and poorly differentiated, originating at the beak, and reaching the anterior margin Shell surface radially costellate Costellae number 6±8 per mm along the anterior shell margin; they increase both by intercalation and bifurcation in both valves Costellae low and wide, rounded, with narrower intervals Two spines on the right side of ventral valve only, respectively at 0´3 mm (1), and 1´7 mm (2) The ®rst spine is short, orthomorph perpendicular, whilst the second one is long, cyrtomorph intraverse in its proximal part, becoming parallel to the plane of symmetry distally Ventral valve interior Hinge teeth very short but laterally markedly elongated, subrectangular in outline Myophragm very thin, low and short, not extending beyond one-®fth of valve length Interior impressed by the external ornamentation Muscle ®eld indistinct Isolated, sparse endospines bounding the visceral cavity Periphery of the valve well-impressed by the outer ribbing RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1057 Dorsal valve interior Inner socket ridges exceptionally well developed, long, straight, elevated, and narrow, anteriorly divergent at about 160 degrees In their proximal part, inner socket ridges support the cardinal process Cardinal process short, extending slightly beyond the hinge line, laterally elongated, and deeply bilobed internally Cardinal process elevated above the valve ¯oor; anterior bounded by a relatively long, deep and narrow cardinal process pit Anderidia very low and thin, anteriorly divergent at about 70 degrees No median septum Muscle ®eld not impressed on the valve ¯oor Inner surface impressed by the external ornament, with sparse isolated endospines Remarks Despite the small number of available specimens, their good preservation and characteristic features are suf®cient to allow a new species name to be proposed All outer and inner characters are in good agreement with the diagnostic characters of the genus Chlupacina The occurrence of the genus Chlupacina in the upper Emsian±lowermost Eifelian pelagic facies of Bac Bo is indicative of strong palaeobiogeographic relationships with the western European part of the Old World Realm Shell outline and morphology, ornamentation and spine distribution testify to the conspeci®city of Chonetes cf striatella (sensu Mansuy 1916a), and the new species from Na Tuong Chlupacina nariensis differs from other species assigned to the genus by its tranverse outline, ornamentation, and distribution of spines, but the most distinctive character is undoubtedly the morphology and development of inner socket ridges The dorsal valve inner features are very similar to those of Strophochonetes cf ®listriata as illustrated by Xu Han-kui (1979), and Vogel et al (1989) from the Nandan facies of Guangxi However, specimens from Guangxi exhibit less numerous radial costellae (4±5 per mm instead of 6±8) along the anterior margin; the second right spine is inserted at 1´2 mm from the beak instead of at 1´7 mm, and the ventral median costa is somewhat less developed than in C nariensis Additional well-preserved specimens from the Nandan facies are needed to establish more detailed comparison between the Vietnamese and the Chinese forms Genus PERICHONETES Xu, 1979 Type species Perichonetes mirabilis Xu, 1979, from the Tangxiang Formation of SW China Perichonetes mirabilis Xu, 1979 Text-®gures 2F, 5B±H Locality and horizon Outcrop along the track between Na Tuong and Na Lu, about km north-east of Na Tuong and 10 km south of YeÃn Lac (Na Ri district, Bac Can province), Na Tuong Formation, associated with Nowakia holynensis, Costulatostyliolina peneaui and Styliolina sp.; uppermost Emsian±lowermost Eifelian Material Sample 98V7: 15 decalci®ed isolated valves, both external and internal moulds; ®gured specimens, BT 229/3±9 Description Shell very small (maximum observed length, 3´0 mm; corresponding width, 3´8 mm); smallest shells almost isometric (0´8 mm long; 0´9 mm wide), becoming moderately transverse during ontogeny, with a length vs width ratio decreasing from 0´95 to 0´62 with growth for shells between 0´8 mm and 3´0 mm long Shell very thin, with a weakly concavoconvex to planoconvex (probably owing to ¯attening?) longitudinal pro®le, the ventral valve being very weakly convex Both interareas are very short, ¯at, and catacline; they lie in the same plane Median enlarged costa well developed in ventral valve, originating at the beak, and always reaching the anterior margin Shell surface smooth, devoid of radial costae up to a length between 1´5 and mm Radial costae originating after a strong concentric growth line corresponding to an ontogenetic morphological change First developed costae number 8± 10 per mm; along the anterior margin of the largest specimen (3´6 mm long), costae number per mm Costae low, rounded, with narrower intervals Two orthomorph perpendicular spines on the right side of ventral valve only, respectively at 0´25 mm (1), and 1´02 mm (2) (mean distances for eight specimens) Ventral valve interior Hinge teeth reduced, short and laterally elongated, subrectangular to trapezoidal in outline Myophragm very thin, low and short, not extending beyond one-eighth of the valve length Muscle ®eld indistinct Isolated, sparse endospines in the antero-median part of the valve 1058 PALAEONTOLOGY, VOLUME 43 A, I±J Chlupacina nariensis sp nov All specimens are latex replicas and ´ A, BT 229/1; ventral valve exterior with a long right spine, Mansuy's original of Chonetes cf striatella (1916, vol 4, pl 2, ®g 1) I, holotype, BT 229/2a; dorsal valve interior of an adult J, BT 229/2b; ventral valve inerior, and part of the dorsal valve exterior of the holotype, adult specimens B±H Perichonetes mutabilis Xu All specimens are latex replicas, except G, and all ´ B, BT 229/3; ventral valve C, BT 229/4; ventral valve exterior with well-preserved right spine D, BT 229/5; ventral valve exterior with well-preserved right spine E, BT 229/6; ventral valve, external mould F, BT 229/7; ventral valve exterior G, BT 229/8; ventral valve, internal mould H, BT 229/9; ventral valve exterior TEXT-FIG Dorsal valve interior Inner socket ridges very small, short and narrow, parallel to hinge line and supporting a short, laterally elongated, internally bilobed, cardinal process Cardinal process elevated above the valve ¯oor; anterior bounded by a relatively large, deep and elongated cardinal process pit No median septum Muscle ®eld not impressed on the valve ¯oor Remarks When describing the genus Perichonetes, Xu (1979, p 380) emphasized the development of what he called a `ridge surrounding the delthyrial cavity' Later Vogel et al (1989) noted that the ventral semicircular ridge was missing in their material from the Tangding to Tangxiang formations (1989, p 35) This ridge probably corresponds to the ®rst strong concentric growth line observed on the Vietnamese specimens This concentric line is interpreted here as an ontogenetic morphological change; it is well marked on both the ventral exteriors and interiors Moreover, the available latex molds of the Chinese material show that specimens are tectonically affected, and it is not possible to be sure about the nature of the `surrounding ridge' According to the material at hand, Vietnamese specimens from Na Tuong cannot be distinguished from the Chinese specimens from Guangxi In a ®rst attempt, specimens assigned to Perichonetes mirabilis can be confused with specimens of Chlupacina nariensis sp nov However externally the two strophochonetids can be easily distinguished by the outline of their shells, ornament, and spine implantation In P mirabilis the outline is less transverse; RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1059 the length vs width ratio varies between 0´73 and 0´95 for shells between 0´8 mm and mm long, while it is between 0´60 and 0´65 for shells of C nariensis between 2´6 mm and 5´5 mm long In P mirabilis radial costae originate between 2´5 and mm from the beak, whereas in C nariensis they originate at about 1´0 mm In P mirabilis spines and are respectively at 0´25 mm and 1´02 mm from the beak; in C nariensis they are at 0´3 mm and 1´7 mm from it Internally, the main difference lies in the lateral development of inner socket ridges, which are always short and very reduced in P mirabilis but straight, narrow and long in C nariensis At the Na Tuong locality Perichonetes mirabilis is associated with an abundant fauna including dacryoconarids (Nowakia, Costulatostyliolina, Styliolina), ostracods, small trilobites (among which is Plagiolaria), goniatites, pteriomorph and buchioline bivalves, nautiloid cephalopods, small and rare solitary corals, and brachiopods (Linguliformea and Rhynchonelliformea) Among Rhynchonelliformea, besides plectambonitoideans and chonetoideans, the relative abundance of Costanoplia faceta Xu, 1977, and to a lesser extant that of Tangxiangia delicata Xu, 1977, is of particular interest This faunal identity at the species level reinforces the very close similarities between the Na Tuong fauna and the fauna of the Nandan facies in Guangxi, south-west China (see Xu 1977, 1979; Vogel et al 1989) Genus CYRTOCHONETES gen nov Type species Chonetes indosinensis Mansuy, 1916b Diagnosis Strophochonetidae externally characterised by cyrtomorph intraverse, symmetrically arranged spines; weak ventral median-enlarged costa in juveniles, becoming obscure with growth; dorsal valve interior with an internally subglobose, deeply bilobed cardinal process Remarks The spine morphology and distribution associated with the shell outline and ontogenetic changes of the median-enlarged costa, allow easy distinction of the new genus among other genera of the family Strophochonetidae General features, as well as the interior of the dorsal valve, place the new genus within the subfamily Strophochonetinae Species assigned Type species only Cyrtochonetes indosinensis (Mansuy, 1916b) Text-®gures 2G, 6A±N v 1916b v 1916b 1926 1926 Chonetes Chonetes Chonetes Chonetes indosinensis Mansuy, p 47, pl 7, ®g cf striatella Dalman; Mansuy, p 46, pl 7, ®g indosinensis Mansuy; Patte, p 64, pl 4, ®gs 1±4 mansuyi Patte, p 64, pl 4, ®g Lectotype The original ventral valve illustrated by Mansuy (pl 7, ®g 5) is selected as the lectotype (BT 229/ 61), and reillustrated here (Text-®g 6M) The second specimen (BT 229/62) is designated as a paralectotype (Text-®g 6N) Locality and horizon `Schistes de Khao-jen', sheet Pho Binh Gia, according to Mansuy (1916b, p 47); eastern Bac Bo Originals of C mansuyi are from Lang Cha (sheet Pho Binh Gia) Material More than 50 specimens, internal and external moulds of isolated valves as well as articulated shells, have been collected; samples 95V1, V2, V8 and V9 from the Dong Mo section, along the road from Dong Mo to Tu Don, 1060 PALAEONTOLOGY, VOLUME 43 eastern Bac Bo Other specimens have been collected from a small quarry along the roadside, north of YeÃn Lac, c 2´5 km north of the bridge on the Song Bac Giang river; sample 98V2 BT 229/49±229/60 Description Exterior Shell small (maximum length, mm; corresponding width, 13 mm), transverse, sub-semicircular in outline with maximum width at or closely anterior to hinge line Lateral margins almost perpendicular to hinge line Longitudinal pro®le moderately concavoconvex Ventral valve interarea ¯at, relatively short, and apsacline, with welldifferentiated, tranversely elongate pseudodeltidium Dorsal valve interarea ¯at, hypercline, almost in the same plane as the ventral one, with small, prominent chilidium Median enlarged costa variably developed in ventral valve only Median enlarged costa relatively narrow, but well differentiated in juvenile shells (up to mm long), then commonly becoming obscure with growth Costellae narrower than interspaces, rounded and relatively prominent, increasing by bifurcation in ventral valve and by intercalation in dorsal one Costellae number up to 82 in a shell, which is mm long Costellae number 16±18 per mm along the anterior margin Spines of cyrtomorph intraverse type, and symmetrically arranged Spines originate at about 30±40 degrees with posterior margin before they progressively bend medially to parallel the plane of symmetry At least six pairs of spines on largest shells Ventral valve interior Teeth short, anteriorly rounded Short myophragm dividing an ill-de®ned muscle ®eld with obscure adductor and diductor scars Posterior muscle bounding ridges anteriorly divergent at 130 degrees Visceral cavity relatively wide Interior of valve, including the muscle ®eld area, deeply impressed by the outer radial ornament Endospines well developed and radially arranged on the valve border around the visceral cavity only Dorsal valve interior Cardinal process sub-globose, deeply bilobed internally, moderately elevated above valve ¯oor, and supported by both the median septum and relatively short, straight, narrow, inner socket ridges that are anteriorly divergent at 130 degrees Median septum low and narrow, seldom extending beyond midline Anderidia posteriorly fused with the median septum and anteriorly divergent at 50 degrees Anterior adductor scars deeply impressed Interior of the valve strongly impressed by the outer radial ornament Strong, radially arranged endospines mainly developed in the anteromedian part of the valve Remarks Externally, the morphology of spines associated with shell outline, the lack of a ventral sulcus, and the ornamentation, make this species easily recognizable from other Vietnamese strophochonetids When he described Chonetes indosinensis, Mansuy (1916b, p 47) provided no clear diagnostic information for the species Patte (1926, p 64) gave no further information, but he noted that its ornamentation was variable, and specimens he illustrated differ markedly from Mansuy's original ®gures, two of them (pl 4, ®gs 1±2) exhibiting a distinct ventral median-enlarged costa, and one of them (pl 4, ®g 2) showing posteriorly divergent spines Patte (1926, pp 64±65) also described Chonetes mansuyi, which he said is mainly characterized by spines that are typically posteriorly divergent in their proximal part and bend progressively medially to become almost perpendicular (i.e cyrtomorph intraverse spines) Newly collected specimens from the lower beds of the Dong Mo section as well as from outcrops north of YeÃn Lac, all exhibit cyrtomorph intraverse, symmetrically arranged spines In this way they can be assigned to the species mansuyi with which they share a similar ornament (about 32 costellae per 10 mm) Juvenile specimens and some rare large shells from the same localities and fossiliferous beds, exhibit a median enlarged costa which ®ts well with Chonetes indosinensis (sensu Patte 1926, pl 4, ®gs 1±4), suggesting that this form and C mansuyi are conspeci®c At least, the two specimens of C indosinensis in Mansuy's collection exhibit the same kind of ornamentation as specimens assigned to C mansuyi, namely about 32 costellae, narrower than their interspaces, per 10 mm All these elements make Chonetes mansuyi Patte, 1926 a junior synonym of Chonetes indosinensis Mansuy, 1916b Subfamily Genus PARACHONETINAE PARACHONETES Johnson, 1970 Johnson, 1966 Type species Chonetes macrostriata Walcott, 1884, from the Lower Devonian of Nevada RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1061 Cyrtochonetes indosinensis (Mansuy) gen nov., Dong Mo section, except C, G, K and L from section N of YeÃn Lac, and M±N from Khao Jen All specimens are latex replicas except G, and all ´ A, BT 229/49; ventral valve exterior B, BT 229/50; ventral valve exterior C, BT 229/51; ventral valve exterior with preserved cyrtomorph spines D, BT 229/52; ventral valve exterior with preserved spines E, BT 229/53; dorsal side of an articulated shell F, BT 229/ 54; dorsal valve exterior G, BT 229/55; ventral valve, internal mould H, BT 229/56; exterior of partly exfoliated dorsal valve I, BT 229/57; dorsal valve interior J, BT 229/58; juvenile dorsal valve interior K, BT 229/59; dorsal valve interior L, BT 229/60; dorsal valve interior M, lectotype, BT 229/61; ventral valve interior, Mansuy's collection N, paralectotype, BT 229/62; ventral valve interior, Mansuy's collection TEXT-FIG 1062 PALAEONTOLOGY, VOLUME 43 Parachonetes zeili (Mansuy, 1908) Text-®gure 7A±G v 1908 v 1908 v 1908 non 1908 1916 1916 1921 1993 Chonetes Zeili Mansuy, p 36, pl 7, ®g 13 Chonetes sp.?; Mansuy, pl 7, ®gs 15±17 Strophomena cf ivanensis Barrande; Mansuy, pl 3, ®g Strophomena cf ivanensis Barrande; Mansuy, p 25 Chonetes cf margaritacea Whidborne; Mansuy, p 11, pl 1, ®g 10a±b Plectambonites yenlacensis Mansuy, p 49, pl 7, ®g 3a±c Strophonella inversa Mansuy, p 18, pl 2, ®g 6a±c Parachonetes zeili (Mansuy); Tong Duy, p 6, ®g 2, ®g Lectotype The external mould of the dorsal side of an articulated shell, illustrated in the upper part of plate 7, ®gure 13 in Mansuy (1908), is selected here and reillustrated (Text-®g 7A±B); coll Mansuy, FSL 413841a Syntypes The dorsal shell exterior on the same slab as the lectotype, FSL 413841b, internal mould of a ventral valve; one external mould of a dorsal valve, and two moulds of dorsal side of articulated shells from the same locality, FSL 413842, coll Mansuy Type locality The lectotype and the ®ve syntypes in Mansuy's collection are from the locality Pien-Doc, Na Ri district, Bac Can province New material More than 50 specimens, internal and external moulds of isolated valves, as well as articulated shells, have been collected; samples 95V2, V3, V8, and V10, Dong Mo section, along the road from Dong Mo to Tu Don, eastern Bac Bo; ®gured specimens, BT 229/42±229/45 Description Exterior Shell medium to large (maximum length about 15 mm; corresponding width about 25 mm), transverse in outline with maximum width at hinge line in small specimens, and anterior to hinge line in largest shells Pro®le strongly arched Ventral beak, small, inconspicuous and strongly incurved Ventral interarea orthocline to anacline, concave and anacline medially, ¯at and almost orthocline laterally Pseudodeltidium relatively small and weakly arched Dorsal interarea ¯at, and weakly hypercline Chilidium weakly arched, short and wide Radial ornamentation of stout, low, rounded costellae, with narrower interspaces Lateral costellae originating along posterior margin of the shell Radial ribbing crossed by numerous variably developed, concentric growth lines Ventral costellae increase by bifurcation First bifurcations appear at a distance of between and 10 mm from beak Dorsal costellae increase by intercalation only Costellae number 10±13 per 10 mm at 10 mm in front of the beak, and 12±14 per 10 mm along the anterior margin of the shell Spines cyrtomorph extraverse, relatively slender compared with shell size and morphology, becoming almost parallel to hinge line distally A maximum of ®ve spines, symetrically inserted, has been observed on each side of beak Ventral valve interior Hinge teeth not observed Myophragm long and narrow, not extending beyond one-third of valve length Muscle ®eld indistinct in immature shells Posterior bounding ridges very faintly developed In largest valves, adductors subtriangular, elongated, deeply impressed in the valve ¯oor Diductor scars hardly perceptible, radially grooved by the outer ornamentation Vascula media indistinct The whole inner surface is deeply impressed by the external ornamentation Endospines, few, relatively small, radially elongated, and widely spaced Dorsal valve interior Ten incomplete, variably distorted internal moulds were available for study Cardinal process internally bilobed, elevated above the valve ¯oor, and supported by short, straight, inner socket ridges Sockets relatively small Myophore high, narrow, and dorsally directed, with two narrow, deeply grooved, lobes Large, elongated cardinal process pit laterally bounded by the proximal part of strong, long, elevated anderidia, anteriorly divergent at about 40 degrees Median septum very poorly developed, differentiated in the posterior half of the valve only Adductor scars indistinct Inner surface with small, radially elongated, and widely spaced endospines Remarks All specimens ®gured by Mansuy and listed in the synonymy are housed in the collections of the Universite Claude-Bernard ± Lyon After thorough examination, no differences could be established; RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1063 Parachonetes zeili (Mansuy), Dong Mo section All ´ A±B, holotype (bottom) and syntype (top), FSL 413841a and b; dorsal exteriors of two articulated shells, external moulds and latex replicas C, BT 229/42; ventral valve exterior, latex replica D, BT 229/43; ventral valve, internal mould with spine bases E, BT 229/44; two ventral valve exteriors with preserved spines, latex replicas F±G, BT 229/45; dorsal valve interior, internal mould and latex replica TEXT-FIG hence we assume they all belong to the previously described Chonetes zeili species The newly collected material from the Dong Mo section shows no signi®cant differences from Mansuy's species Morphological variability is small and that occurring results from both tectonic deformation and the nature of deposits This explains the differences between specimens from mudstones (samples 95V8 and 95V10) on the one hand, and siltstones (samples 95V2 and 95V3) on the other According to Mansuy, and to specimens in his collection, as well as to the synonymy established herein, the species is known to occur at the following localities: Ban-Lan, Ban-Djua (Strophomena cf ivanensis), 1064 PALAEONTOLOGY, VOLUME 43 Ban-Hao, Kim-Lu (Plectambonites yenlacensis), YeÃn-Lac Parachonetes zeili occurs in Pragian beds of the Mia Le Formation in north-east VieÃt Nam, and in Pragian beds of the Ban Nguon Formation in northwest VieÃt Nam (Tong Duy, 1993) Shell outline and ornamentation, especially the postero-lateral costellae originating along the posterior margin of the valves, as well as dorsal inner features, allow assignment of Chonetes zeili to the genus Parachonetes Johnson, 1966 Parachonetes zeili (Mansuy) can be easily distinguished from P verneuili (Barrande) by having stouter, less numerous costellae (10±13 per 10 mm, 10 mm in front of the beak, instead of 15±21), as well as by less numerous, and cyrtomorph extraverse spines instead of orthomorph perpendicular spines The characteristic spines were reported by Patte (1926, p 62) The morphology of spines, added to the nature of the radial ornamentation with narrow, elevated, costellae, justify the erection of a new genus, Orthochonetes, for Barrande's Bohemian species (see below) External morphology, ornamentation and spine morphology make P zeili more closely allied to the type species P macrostriatus (Walcott) However, externally P zeili differs from P macrostriata (Walcott) by its more regular ornamentation with lower costellae P zeili exhibits less numerous spines (®ve instead of eight pairs) for a similar size of shell Chonetes baragwanathi Gill, 1949, Chonetes? suavis Talent, 1963, and Chonetes? foedus Talent, 1963 from south-eastern Australia undoubtedly belong the genus Parachonetes, along with Parachonetes ¯emingi Chatterton, 1973, and P konincki Chatterton, 1973 from the `Receptaculites Limestone' of the Murrumbidgee Group of New South Wales P ¯emingi Chatterton, 1973 exhibits 10±11 costellae per 10 mm, with few intercalations and bifurcations, while P konincki has 15±20 costellae per 10 mm, instead of 10±13 costellae in P zeili Comparison with the three other Australian species is made more dif®cult owing to the lack of similar information, and a global revision of Australian Devonian chonetoideans is urgently needed In South China Parachonetes lamella Xian, 1988, P liujingensis Yang, 1977, P nasutus Wang, 1974, P tewoensis Zhang, 1983, and P zhusilengensis Zhang, 1983, have been described However these species are incompletely known, and are in need of further study Parachonetes lantenoisi (Mansuy, 1916b) Text-®gure 8A±F v 1916b ? 1916b 1993 Chonetes lantenoisi Mansuy, p 46, pl 7, ®g 7a±b Chonetes lacroixi Mansuy, p 46, pl 7, ®g 6a±b Chonetes lacroixi Mansuy; Tong Duy, p Lectotype Ventral valve, original of Mansuy (1916b, pl 7, ®g 7a); BT 229/46, reillustrated herein (Text-®g 8A) Paralectotypes One dorsal valve interior, the internal mould of an articulated shell and two incomplete ventral valve exteriors, all preserved on the same slab as the lectotype Type locality Kim Lu according to Mansuy (1916b, p 47) The species is restricted to the Mia Le Regional Stage, where it is associated with Parachonetes zeili (Tong-Duy Thanh, 1993) Additional material Sample 98V5: decalci®ed specimens, internal and external moulds of one ventral valve, BT 229/47, and one dorsal external mould; sloping outcrop along road 305, 3´2 km south of YeÃn Lac, on the right side of the road from YeÃn Lac, Mia Le Formation Description Exterior Shell of medium size The two available ventral valves are respectively mm long (estimated) and 12 mm wide (lectotype), and 13 mm long and 18 mm wide Umbo large, prominent Longitudinal pro®le markedly concavoconvex, with a strongly arched umbo Ventral interarea well developed, apsacline, concave, with large delthyrium and poorly developed pseudodeltidium Dorsal interarea unknown Radial ornamentation of rounded, regular, well-differentiated costae About 20 costae originate at the umbo Three to four lateral costae originate along RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1065 posterior margin on each side of beak Along the valve margin, the total number of costellae is 54 They number 11±13 in a mm interval in the anteromedian part of the valve Costellae appear by intercalation only, the ®rst bifurcation appearing very early, in the umbonal area Cardinal extremities commonly lack ribbing Dorsal costellae increase by implantation only Four spines are partly preserved on each side of the ventral valve, respectively at 3´4 mm, 5´9 mm, 7´5 mm and 8´9 mm from beak Their proximal part is orthomorph oblique, at 50±60 degrees from hinge line Ventral valve interior The anterior margin of the interarea supports a well-differentiated short ridge which extends all along the hinge line, and supports the hinge teeth Hinge teeth wider than long, subtrapezoidal in outline Inner surface poorly preserved, strongly impressed by the external ornamentation, which even partially obscures the diductor ®eld Endospines radially displayed, sparse and oblique, anteriorly elongated Dorsal valve interior Valve longitudinally depressed anteromedially Low median septum supporting the cardinal process, narrowing anteriorly and not extending beyond midlength Cardinal process relatively small, only slightly extending beyond the hinge line, supported by narrow, rounded, short, and straight inner socket ridges anteriorly divergent at about 115 degrees Inner socket ridges overhang narrow, laterally elongate sockets Narrow outer socket ridge extends all along hinge line Myophore not observed Cardinal process weakly elevated above valve ¯oor, not anteriorly bounded by a cardinal process pit Anderidia low, and relatively small, anteriorly divergent at 40±45 degrees Anterior adductors narrow, triangular, and well impressed in the valve ¯oor Surface of valve deeply impressed by the external radial ornament, except for the posterolateral margins of the valve, which are moderately convex and smooth Endospines sparse, and radially arranged on radial ridges Remarks The species lantenoisi is provisionally assigned to the genus Parachonetes on the basis of the outline of the shell and its ornamentation and spine morphology It lacks the typical cardinal process pit which is always well developed in Parachonetes macrostriatus, the type species Parachonetes lantenoisi can be easily distinguished from Parachonetes zeili by its smaller size, and thinner radial ribbing More material of this apparently uncommon form is required for better identi®cation When he described Chonetes lacroixi from YeÃn-Lac, Mansuy (1916b) illustrated two specimens which he indicated as being ventral valves (pl 7, ®g 6a±b) However, according to the description, one of these (®g 6a) appears likely to be a ventral valve with bifurcating costellae; the other (®g 6b), with costellae increasing by intercalation, is most probably an external mould of a dorsal valve Only the latter specimen could be found in Mansuy's collection in Ha NoõÈ It has obviously been strongly distorted tectonically (laterally elongated) and is of no help for identifying the species lacroixi However, despite the distortion, the size of the shell, the morphology and increase in number of radial costellae, as well as their total number (55±60), strongly suggest that Chonetes lacroixi is no more than a tectonically distorted `morphotype' of Chonetes lantenoisi Owing to the better preservation of original specimens of the latter species, C lacroixi is provisionally considered herein to be a synonym of C lantenoisi ADDITIONAL NEW TAXA In the course of this study, comparisons with morphologically closely allied chonetoidean genera and species from other regions allowed us to identify previous errors or misidenti®cations In this way Chonetes verneuili Barrande, 1847 can no longer be assigned to the genus Parachonetes Johnson, 1966; hence, a new genus is proposed below Subfamily PARACHONETINAE Genus ORTHOCHONETES Johnson, 1970 gen nov Type species Chonetes verneuili Barrande, 1879 from the Pragian of Bohemia Derivation of name With reference to the orthomorph morphology and perpendicular orientation of spines Diagnosis Parachonetinae with transverse, markedly arched, shell; spines numerous, orthomorph perpendicular and symmetrically displayed; radial costellae relatively narrow, elevated, with vertical ¯anks 1066 PALAEONTOLOGY, VOLUME 43 Parachonetes lantenoisi (Mansuy) All specimens are latex replicas, and ´ A±C, specimens on a slab from Kim Lu (Mansuy's collection); D ± E, specimen from the outcrop 3´2 km south of YeÃn-Lac A, lectotype, BT 229/ 46a; ventral valve exterior B, BT 229/46b; dorsal valve interior C, BT 229/46c; interior of an articulated shell D±E, BT 229/47; ventral valve, exterior and interior with spine bases F, BT 229/48; original of Chonetes lacroixi Mansuy (1916b, pl 7, ®g 6b), exterior of probable dorsal valve TEXT-FIG Remarks The new genus proposed herein can be easily distinguished from Parachonetes Johnson, 1966 by its external morphology (see Johnson 1966, and HavlõÂcÏek and Racheboeuf 1979) The outline of the shell is more transverse in Orthochonetes, having a moderately convex anterior margin; Parachonetes is less transverse in outline, with a well-rounded anterior margin Orthochonetes bears typical orthomorph perpendicular spines, while they are of cyrtomorph extraverse type in Parachonetes Radial ornamentation also differs; costellae are usually narrower in Orthochonetes verneuili, with vertical ¯anks, whereas they are relatively wide, sinuous, rounded, and with rounded intervals in species of Parachonetes Moreover costellae are much more regular in Orthochonetes than in Parachonetes Internally both genera exhibit similar features which unquestionably allows Orthochonetes to be assigned to the subfamily Parachonetinae Species assigned Chonetes verneuili Barrande, 1879 RACHEBOEUF AND TONG-DZUY THANH: LOWER DEVONIAN BRACHIOPODS 1067 Geographic distribution The type species Orthochonetes verneuili was initially described from Pragian beds of the Czech Republic It has also been recorded from Central Asia, the Ural Mountains and Novaya Zemlya (see Johnson 1966) Acknowledgements We are greatly indebted to Prof Dr Trinh Dzanh who is in charge of the collection of the Geological Museum in Ha NoõÈ, for his help in the search for original specimens and for preparing latex casts Tong Dzuy Thanh thanks the Vietnamese Programme for Fundamental Research in Earth Sciences for its support We gratefully acknowledge the help of Drs A J Boucot (Oregon State University, Corvallis), who sent us additional specimens that he had collected in VieÃt Nam, and D L Strusz (Australian National Museum), who sent us photographs and latex casts for comparison Drs D J Batten (University of Wales, Aberystwyth), P Copper (Laurentian University, Sudbury), and D A T Harper (Geological Museum, Copenhagen) are greatly acknowledged for their help in improving the ®nal version of the manuscript The photographs were taken by NoeÈl Podevigne, FRE 2158 of the Centre National de la Recherche Scienti®que, Lyon REFERENCES and RACHEBOEUF, 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(Ha Giang Province, Vietnam) Proceedings of the International Symposium Stratigraphic Correlation of Southeast Asia, Bangkok, 62±68 TALENT, J 1963 The Devonian of the Mitchell and Wenworth rivers Geological Survey of Victoria, Memoir, 24, 118 pp., 78 pls à t Nam with remarks on palaeobiogeography TONG-DZUY THANH, 1993 Major features of Devonian stratigraphy in Vie Journal of Geology, Geological Survey of VieÃt Nam, B, 1±2, 3±18 ÐÐ and JANVIER, PH 1994 Early Devonian ®shes from Trang Xa (Bac Thai, Vietnam), with remarks on the distribution of the vertebrates in the Song Cau Group Journal of Southeast Asian Earth Sciences, 10, 235±243 ÐÐ and TA HOA PHUONG 1994 New data for correlation of Early Devonian bearing the Euryspirifer tonkinensis fauna in Vietnam and South China Subcommission on Devonian Stratigraphy, Newsletter, 11, 69 ÐÐ DANG TRAN HUYEN, NGUYEN DINH HONG, NGUYEN DUC KHOA, NGUYEN HUU HUNG, NGUYEN THE DAN, TA HOA PHUONG, PHAM KIM NGAN and DOAN NHAT TRUONG 1988 Stratigra®a i tselenteraty Devona Vietnama [Devonian stratigraphy and Coelenterata of Vietnam] I Stratigra®a Nauka, Novosibirsk, 184 pp [In Russian] VOGEL, K., XU HAN-KUI and LANGENSTRASSEN, F 1989 Brachiopods and their relation to facies development in the Lower and Middle Devonian of Nandan, Guangxi, South China Courier Forschungsinstitut Senckenberg, 110, 17±59 VU KHUC and BUI PHU MY (ed.) 1989 Dia chat Vietnam I Dia tang [Geology of Vietnam I Stratigraphy] Tong cuc Mo, Dia chat Vietnam [General Geological Department of Vietnam], Ha NoõÈ, 378 pp XU HANKUI 1977 Early Middle Devonian plicanoplids from Nandan facies of Guangxi Acta Palaeontologica Sinica, 16, 59±70, pls ÐÐ 1979 Brachiopods from the Tangxiang Formation (Devonian) in Nandan of Guangxi Acta Palaeontologica Sinica, 18, 362±380, pls XU QINGJIAN, WAN ZHENQUAN and CHEN YUANREN 1978 Phylum Brachiopoda In Atlas of fossils of southwest China, Sichuan volume, Part 1, from Sinian to Devonian Geological Publishing House, Beijing, 617 pp., 185 pls YANG DELI, NI SHIZHAO, CHANG MEILI and ZHAO RUXUAN 1977 Phylum Brachiopoda In Palaeontological atlas of the central and southern regions, Part 2, Late Palaeozoic Geological Publishing House, Beijing, 856 pp., 253 pls PATRICK R RACHEBOEUF UFR Sciences de la Terre Universite Claude-Bernard, Lyon 43, bd du 11 novembre 1918 F-69622 Villeurbanne Cedex France e-mail patrick.racheboeuf@cismsun.univ-lyon1.fr TONG-DZUY THANH Typescript received 10 November 1999 Revised typescript received 25 March 2000 Department of Geology VieÃt Nam National University, HanoõÈ 334, Nguyen Trai Street Thanh Xuan, Ha NoõÈ VieÃt Nam e-mail duythanh@hn.vnn.vn ... Genus BACBONETES gen nov Type species Bacbonetes janvieri gen et sp nov Origin of the name From Bac Bo, Vietnamese name for northern VieÃt Nam Diagnosis Strophochonetidae with faintly differentiated... 1989 Dia chat Vietnam I Dia tang [Geology of Vietnam I Stratigraphy] Tong cuc Mo, Dia chat Vietnam [General Geological Department of Vietnam], Ha NoõÈ, 378 pp XU HANKUI 1977 Early Middle Devonian. .. TA HOA PHUONG, PHAM KIM NGAN and DOAN NHAT TRUONG 1988 Stratigra®a i tselenteraty Devona Vietnama [Devonian stratigraphy and Coelenterata of Vietnam] I Stratigra®a Nauka, Novosibirsk, 184 pp [In