DSpace at VNU: Late Silurian marine shelly fauna of Central and Northern Vietnam

LATE S I L U R I A N M A R I N E S H E L L Y F A U N A OF C E N T R A L A N D N O R T H E R N V I E T N A M T~ANH TONG-DZUY, ARTHURJ BOUCOT, JIA-YU RONG & ZONG-JIE F A N G TONG-DZUY T., BOUCOT A.J., RONG J.Y & FANG Z.J 2001 Late Silurian marine shelly fauna of Central and Northern Vietnam [Une faune coquilli~re marine du Silurien sup~rieur du centre et du nord du Vietnam] GEOBIOS, 34, 3: 315-338 Villeurbanne, le 31.07.2001 Manuscrit d~pos~ le 20.07.1999; accept5 dSfinitivement le 10.11.2000 ABSTRACT -The Late Silurian (late Ludlow-Pridoli) brachiopods and bivalves from North and Central Vietnam are described and illustrated from the Kien An (North Vietnam) and My Duc (Central Vietnam) localities The biostratigraphic relations and age of the fauna, the so-called Retziella fauna, are discussed The My Duc fauna is the same as that at Kien An, indicating that during the Late Silurian both North Vietnam and Central Vietnam, situated on the South China and Indochina Plates respectively were probably fairly close geographically to each other The Late Silurian is globally a time of moderately high, although not highest, provincialism as regards marine benthic invertebrates A new brachiopod species, Nikiforovaena vietnamensis BOUCOT& RONG, and three new bivalve species Schizodus kienanensis FANG,S ? myducensis FANG,and Modiomorpha paracrypta FANGare described © 2001 Editions scientifiques et m~dicales Elsevier SAS KEYWORDS: BRACHIOPODS, BIVALVES,NEW TAXA, LATE SILURIAN, BIOGEOGRAPHY,VIETNAM RI~SUMt~ - Les brachiopodes et les bivalves du Silurien sup~rieur (Ludlow terminal-Pridoli) des localit~s de Kien An (Nord Vietnam) et de My Duc (Centre Vietnam) sent ddcrits et figur6s L'~ge de la faune RetzieUa et les relations biostratigraphiques sont discut~s La faune de My Duc est la m~me que celle de Kien An, indiquent que pendant la fin du Silurien le Nord Vietnam et le Sud Vietnam, situ~s respectivement sur les plaques Sud-Chine et Indochine, ~taient probablement assez proches l'une de l'autre La fin du Silurien est globalement une p~riode de provincialisme marqu6, bien que n'~tant pas le plus accentu~, pour les invertSbr~s benthiques marins Une nouvelle esp~ce de brachiopodes, Nikiforovaena vietnamensis BOUCOT & RONG, et trois nouvelles esp~ces de bivalves Schizodus kienanensis FANG,S ? myducensis FANG, et Modiomorpha paracrypta FANGsont d~crites © 2001 Editions scientifiques et m~dicales Elsevier SAS MOTS-CLt~S: BRACHIOPODES, BIVALVES, NOUVEAUX TAXONS, SILURIEN SUPI~RIEUR, BIOGI~OGRAPHIE, VIETNAM INTRODUCTION The Retziella fauna has been known for some time from South China, North China, Central Asia, and Australia, based on specimens weathered out of calcareous shales for the mostpart The occurrences in northern Vietnam have not previously been illustrated or described in detail The Vietnamese brachiopods described here occur as casts and molds which substantially supplement the earlier descriptions of the interiors based mostly on serial sections The paleoecological significance and overall biogeographic significance of the Retziella fauna were considered by Rong Jia-yu et al (1995) The bivalves accompanying the Retziella fauna brachiopods have not previously received much attention GEOLOGICAL SETTING Silurian rocks with Retziella weberi have been known in North and Central Vietnam for some time First, Duong Xuan Hao and'Nikiforova (1963) published on the My Duc (Quang Binh Province, Central Vietnam; 17°14'N, 106°41'E) occurrence of Retziella weberi, and later occurrences were found in the downstream region of the Da River, and at Kien An (20°48'N, 106°35'E) near Hai Phong in North Vietnam The Retziella weberi faunas described in this paper were collected by Tong-Dzuy Thanh and A.J Boucot in 1994 at My Duc (Quang Binh Province, Central Vietnam) and at Kien An near Hai Phong (North Vietnam) (Figs 1A-D) KIEN AN AREA Patte (1926, 1927) first described the Paleozoic faunal assemblage at the Tien Hoi, Xuan Son and Phu Lien Mountains of the Kien An area, some five kilometers, as the crow flies, from Hai Phong City, as Late Devonian with Spirifer cf ziczac ROEMERand Rhynchonella sp A I Jamoida (in Dovjikov 1965) discovered brachiopods in the Xuan Son Mountain that Duong Xuan Hao and Nikiforova (1963) identiffed as Retziella weberi, Eospirifer cf lynxoides, and corals (Nipponophyllum sp., Xiphelasma sp.) 316 FIGURE - A Map showing locations within tle Kien An area (Xuan Son, Phu Lien, Kho Lain and Cuu Vien Mountains) The fauna from the Xuan Son Mountain is described in this paper B Stratigraphic column for the Xuan Son Mountain locality, indicating where the Retziella weberi fauna was collected that is described in this paper C Map showing locations within the My Duc area, Central Vietnam, and the spot where the Retziella weberi fauna described in this paper was collected D Stratigraphic column for the My Duc area, indicating where the Retziella weberi fauna was collected that is described in this paper All figured specimens are from My Duc The specimens described in this paper are deposited at the Hanoi Geological Museum, Collection Number BT 178 All figured specimens of brachiopods in Figs 2-5 are from My Duc The others are noted where appropriate in the figure legends A Carte des localitgs dans la rggion de Kien An (Montagnes de Xuan Son, Phu Lien, Kho Lain et Cuu Vien) La faune de la montagne de Xuan Son est ddcrite dans cet article B Colonne stratigraphique de la localitd de Xuan Son montrant la position de la faune & Retziella weberi C Carte des affleurements de la r@ion de My Duc, Vietnam central et localisation du gisement & Retziella weberi D Colonne stratigraphique de la r@ion de My Duc avec le positionnement de la faune & Retziella weberi Tous les spgcimens figures proviennent de My Duc Les spgcimens dgerits dans cet article sont d@osgs au Mus~e Gdologique de Hanoi, sous le numgro de collection BT178 Tousles brachiopodes des figures 2-5 proviennent de My Duc Les autres localitgs sont indiqudes dans les lggendes des figures B UPPER ~ , , , ~ , L~ DEVONIAN , ~~ ~ , , E~ , , , ~ ( KIEN AN / Ash-graylimestonebearing Famennian Foraminifers, Amphipora laxeperforata Marl, dark gray limestone lenses: Mesofavos/lessp., - 1O0 m Ho/mophy//umsp., N/pponophy//umsp., Re#/e//a weber/; [ 'i i"ii NikEorovaenafefqanensis Intercalation of quartz sandstone and mudstone: 400 m, Howe//e//aaff.bra£ensis FORMATION' " i ' " "1' " '1' ' Cai'careous mudstone, limestone lenses, thin beds of I - - I * I ~120 m shale: Micfoplasmasp., Nik/forovaenafergana, y ~ , ~ 7.~I (Relz/e//a weber/"in Phu Lien Mt) D , CuBa/ IiIill I Formation~ I I I Darkgraylimestone Marlatbase 3~section.Stromatoporoids,Corals, Brachiopods Sandstone,red or wine colored JTan Lain 300 m Formation -_ ~?,~,,,.~_ mudstone with Linqula , ~ ~ Long Dai Formatbn (Upper Ordovician-Lower Silurian) mu~etoneand darkgrey sandstone Dai Oiang Formation (Silurian} intercalation of mudstone and sandstone with marl lenses and limestone at base -: ~ ^ limesloneat upper of section DaiGiang 1~5urn.,Brachio.p~s, Tribb~es, Cora.ls,Ve~ebrales CuBaiFormatbn(Givetiani Formation ~ 450- Sandstone, mudstone UpperDevonian)darkgray La ){beFonnatlen(Lower , : :- ::.]500 m Brachiopods (first Retziella weber~ limestone,intercalationof Carboniferous) intercalat(on Long Dai ; -_ v-'- -.; Formation Sandstone, shale Graptolites limestone mudstone siliceous of limestone, mad,and mudstone limestoneat b a s e ~ In the Xuan Son Mountain the tripartite rock sequence is as follows: Lower part consists of bluegray marl, mudstone and yellowish-gray sandstone bearing Eospirifer cf lynxoides and indeterminate rugose corals The thickness is about 120 meters; following are gray sandstone and quartz sandstone with dark purplish-red mudstone interbeds having about a 320 meter thickness These mudstones yielded Retziella weberi, Nikiforovaena ferganensis and SacSonFormation (Parmo-Carbonifarous) light gray Limestone ~ Pliocene-OuatemaryBasalt Ouatemaryandrecent alluvium Nguyen Quang Hap (1967) named these rocks the Kien An Suite (Formation), while Hoang Ngoc Ky et al., and Ngo Quang Toan et al (Vu Khuc & Bui Phu My 1989) renamed this unit the Xuan Son Formation Priority rests with the term Kien An Formation Ten Lain Formation (Lower Devonian) sandstone and red or ~ne colored mudstone Fossillecafity Nowellella sp The upper part of the Section on the North slope of Xuan Son Mountain consists of thick bedded dark gray limestone with shale and marl interbeds in the uppermost layers, where we collected an abundant Retziella weberi assemblage; the thickness of this unit us about 100 m At the same level on the north slope of Tien Hoi Mountain the following brachiopods were noted: Retziella weberi, Eospirifer cf lynxoides (= Nikiforovaena ferganensis), Howellella bragensis, Howellella sp (Vu Khuc & Bui Phu My 1989) Additionally, corals are abundant, including Favosites admirabilis, Xiphelasma su., Nipponophyllum sp., and recently Mesofavosites was identified by Tong-Dzuy Thanh Commonly the upper part of the Kien An Formation consists of 317 dark gray, thick-bedded limestones with some ashgray shale and marl interbeds, reaching a thickhess of about 320-400 meters 1) Lower part consisting of interbedded sandstone and mudstone which reach a thickness of 550 meters At Phu Lien Mountain the cross-section is shorter, with only two beds of the formation present, as follows: brownish-yellow sandstone, siliceous shale and yellowish, purple-red, cross bedded mudstone at the top, with a thickness of about 200 meters, yielding poorly preserved brachiopods including 2) A middle part consisting of dark gray, thin bedded marl and calcareous mudstone with some limestone interbeds, with a thickness of about 220450 meters Retziella weberi, Nikiforovaena ferganensis, Eospirifer ? sp., Howellella sp., and Camarotoechia sp (= unidentified rhynchonellid) Intercalations of yellowish sandstone and gray marl with calcareous mudstone having a thickness of about 50 meters, with poorly preserved fossils (Retziella weberi, Eospirifer ? sp., Howellella sp and rhynchonellids) have been noted (Vu Khuc & Bui Phu My 1989) The majority of the fossils cited above indicate a Late Silurian age, but some are close to the Lower Devonian, for example, Favosites admirabilis No conodonts have been found Based on the brachiopods described here the Kien An area Retziella weberi bearing rocks are dated as Late Silurian, Late Ludlow or Pridoli THE DOWNSTREAM DA RIVER BASIN In the downstream Da River Basin, western North Vietnam, the Retziella weberi assocation has been found in the Bo Hieng Formation This formation consists of marl, calcareous shale and thin bedded, dark gray limestone with a thickness of about 500 to 900 meters It lies between the Sinh Vinh Formation (Ordovician-Silurian) and the Song Mua Formation (Early Devonian) Like the fossil assemblage in the Kien An Formation, the Retziella weberi association in the Bo Hieng Formation consists mainly of Silurian brachiopods (Retziella weberi, Tadschikia xuanbaoi, Lissatrypa sp (probably an Atrypoidea), Fardenia ? sp.) and bivalves (Modiomorpha brevis and others) In addition, some corals ordinarily considered to be of Devonian age such as Favosites kunjakensis, Squameofavosites ex gr cechicus (Sqf bohemicus), Tryplasma ex gr karcevae and others are present, although their age here is Late Silurian MY DUC AREA In the My Duc area (Quang Binh Province, Central Vietnam) the Retziella weberi association was collected from the upper part of the Dai Giang Formation A.M Mareishev and Tran Duc Luong (Dovjikov ed 1965) first described the Dai Giang Formation, and then Nguyen Xuan Duong et al (1996) studied it in detail The formation consists mainly of fine-grained sandstone, mudstone and shale, which crop out widely in Quang Tri and southern Quang Binh Provinces, Central Vietnam (Fig 1) In 1977 Nguyen Xuan Duong described the best section of this formation, along the Dai Giang River Three parts of the formation are cited here from the eight members described by Nguyen Xuan Duong 3) An upper part consisting ofmudstone with sandstone interbeds with a thickness reaching 250 meters The total thickness of the formation is more than 1,000 meters Abundant fossil associations have been collected from different horizons at different localities Among them the most characteristic are graptolites (Monograptus sp., Bohemograptus bohemicus, Monoclimacis sp., Pristiograptus ludlovensis), brachiopods (Retziella weberi, Nikiforovena ferganensis, Howellella nucula), trilobites (Metacalymene sp., Cromus beaumonti, Encrinurus sinicus) and corals (Multisolenia cf formosa, NipponophyUum anmaense), indicating a Silurian, mostly Late Silurian age In the My Duc area, near An Ma Mountain and the Cam Ly Reservoir, west of the My Duc railway station (Fig 1C), the sequence consists of a lower member which is composed of fine-grained sandstone and mudstone, that becomes coarser upwards, with a thickness of about 450-500 meters, and an upper member which is largely arenaceous, but becomes somewhat carbonaceous in its uppermost part, with a thickness of about 400-450 meters (Fig 1D) It is possible that these two members correspond to the above mentioned lower and middle parts of the formation They were formerly dated as Middle Devonian (Fromaget 1927; Dovjikov ed 1965) Later, thanks to the collection of RetzieUa weberi assemblage brachiopods, such as Retziella weberi, Nikiforovaena ferganensis, Howellella nucula, trilobites (Encrinurus cf sinicus) and corals (Multisolenia cf formosa, Nipponophyllum anmaense) these beds in the My Duc area were assigned to the Late Silurian Dai Giang Formation (Tran Van Tri et al 1977; Vu Khuc & Bui Phu My 1989; Nguyen Xuan Duong et al 1996) The age of the Dai Giang Formation has been the subject of debate in the Geology of Central Viet Nam Dovjikov ed (1965) and Tran Van Tri et al (1977) assigned it to the Silurian, whereas Nguyen Xuan Duong et al (1996, 1977, in lit.), Vu Khuc and Bui Phu My (1989) dated it as Late Silurian-Early Devonian The Late Silurian-Early Devonian assignment was supported by the 'majority of fossils collected in the Dai Giang Formation which indicate a Late Silurian age; but apart from these Late Silurian fossils, in some cross-sections Early Devonian fossils are also noted' (Vu Khuc & Bui Phu My 1989) The authors did not provide a list of 'Early Devonian fossils', while all the fossils cited in their description, including graptolites, trilobites and brachiopods not support an Early Devonian age for even the top of the formation It is notable that in the top of some cross-sections the collected fossils indicate a Late Silurian age only including, for example, trilobites (Encrinurus cf sinicus), 318 graptolites (Bohemograptus bohemicus, Pristiograptus ludlovensis), and brachiopods (RetzieUa weberi and others) Thus, the Retziella weberi bearing rocks of Central Vietnam must be correlated with those in North Vietnam (Kien An area and the downstream part of the Da River Basin); all yield Late Silurian fossils AGE Although no conodonts are found in the studied areas in Vietnam, based on regional stratigraphic correlation and the range of the brachiopod species, in particular, Retziella weberi, R alaica 'HoweUella' lynxoides, and Nikiforovaena, our conclusion for the age of this Vietnamese fauna is that it is of late Ludlow to Pridoli age Additionally, the presence of earlier Ludlow graptolites below the Retziella fauna in the My Duc area is consistent with a later Ludlow regional shallowing, i.e., upward replacement of the deeper water graptolitic facies by the BA 2-3 shelly facies in coarser classics, followed in the earlier Devonian by nonmarine beds In the Kien An area graptolitic beds, unfortunately, are unknown, but to the northeast in the offshore islands the upper parts of the Co To Formation have yielded earlier Ludlow graptolites, with all of this being consistent with the assignment of the Kien An and My Duc shelly fauhas to the later Ludlow-Pridoli The Co To Formation, with citations to it's Ludlow graptolites, has been described by Nguyen Huy Mac and Pham The hien (1972) and Tran Van Tri et al (1972) No conodonts have yet been found from the Retziella-bearing strata in Central Asia The most abundant species in the fauna in North Vietnam is Retziella weberi NIKIFOROVAwhich occurs in Ludlow to Pridoli rocks in Central Asia, although the type specimens came from the Isfara Horizon of Pridolian age In the western part of South China Retziella-bearing strata are well developed, and their age was determined as late Ludlow to early Pridoli by Rong and Yang (1980, p 264) chiefly based on the study of the brachiopods from the Miaokao Formation, Qujing, eastern Yunnan, Southwest China It should be pointed out that there is conodont evidence; Ozarkodina crispa and others were found in the upper Kuanti, Miaokao, and Yulungsuu Formations indicating late Ludlow to early Pridoli age (Wang 1980, 1981; Walliser & Wang 1989) REMARKS The occurrence of the Retziella weberi fauna at the three localities noted in this paper, two (Kien An area and downstream part of the Da River Basin) are north of the Song Ma Suture on the South China Plate, or Guangxi-Yunnan-North Vietnam Block (Wu 2000), and one (My Duc area) south of the Song Ma suture on the Indochina Plate, argues for these two areas having been reasonably close to each other during the Late Silurian The situation for the Early Devonian is more difficult to interpret North of the Song Ma Suture within North Vietnam there is a characteristic South China Region, Old World Realm fauna of marine benthos, as well as vertebrates similar to those present in South China However, south of the Song Ma Suture there is no biogeographically useful information concerning marine invertebrates, although the information about the vertebrates does feature taxa distinct from those of the South China Region in both North Vietnam and South China TongDzuy Thanh has discussed the relation of the known Vietnamese Early Devonian faunas with those present in the Rhenish-Bohemian and Tasman regions (Tong-Dzuy Thanh et al 1985, 1996, 1997) PALEOGEOGRAPHY Trying to work out the paleogeographic and lithofacies relations of the Chinese and Vietnamese Retziella fauna localities is difficult owing to lack of truly compelling data However, we will attempt to provide some insight into the varied possibilities First, it needs to bc recognized that lateral movements on the Song Ma Suture and the Red River Fault Zone may well have significantly displaced the My Duc region, belonging to the Indochina Plate, relative to the Vietnamese and Chinese localitics to the north that all belong to the South China Plate We will first discuss the gross lithological sequence at the localities In the My Duc region, as discussed above, the Retziella fauna is from the relatively shallow water, upper part of the Dai Giang Formation, which is underlain by Silurian graptolitic shales and overlain by uppermost siliciclastics that have yielded Silurian trilobites, which are overlain in turn by relatively unfossiliferous siliciclastics of Old Red Sandstone aspect (Tan Lain Formation) that probably represent the Early Devonian in largest part, overlain themselves by younger Devonian, fossiliferous limestones In the Kien An area, near Hai Phong, there are Silurian graptolitic shales in the small islands northeast of Hai Phong, and earlier Devonian nonmarine beds to the south of the city However, the complex structural relations in the Hai Phong region makc the working out of a detailed lithostratigraphic sequencc difficult In the Da River Basin, well to the west of Ha Noi the Bo Hieng Formation with its Retziella fauna, is overlain by typical South China Region, fully marine, probably Benthic Assemblage 3, fossiliferous, Early Devonian beds of the Song Mua Formation, and underlain by the relatively unfossiliferous Ordovician-Silurian Sinh Vinh Formation In northern Vietnam, in the Lang Son region, nonmarine Early Devonian strata, followed by marine Early Devonian, lie unconformably on Ordovician beds, with fossiliferous Silurian unrecognized 319 These relations are similar to those to the northeast in the nearby Liujing area, Hengxian County, Guangxi where the marine Early Devonian, richly fossiliferous, Benthic Assemblage through Lianhuashan Formation lies unconformably on Cambrian strata Silurian beds with marine fossils are unrecognized in this region Far to the north in the Qujing area of eastern Yunnan, the Retziella fauna of the Miaokao Formation is overlain by the Pridoli, marine Yulungsuu Formation, followed by paralic Early Devonian strata (Wang Nian-zhong 1997, concludes that the lower part of these beds may be of late Pridoli age), and underlain by the early-middle Ludlow Kuanti Formation of marine aspect, which also yields a very low diversity Retziella fauna Trying to tie these very scattered bits of information together paleogeographically suggests the presence of an Early Devonian land area from Qujing on the north, south to Liujing and nearby Lang Son, with an intervening region of marine environments present further south in North Vietnam, while in the My Duc area there is another land area during the Early Devonian In Late Silurian, Retziella fauna time there was shallow sea everywhere except in the Liujing and adjacent Lang Son areas where land may have been present Aul of this is complicated, of course, in terms of how much lateral movement may have taken place on the Song Ma Suture and the Red River Fault Zone The occurrences of the Retziella weberi fauna noted in this paper are located in three localities Two (Kien An area and downstream part of the Da River Basin) are north of the Song Ma Suture, or in other words, are part of the South China Plate, whereas the third (My Duc area) is located on the Indochina Plate The reasonably endemic Late Silurian Retziella weberi fauna occurs on both sides of the important Song Ma S u t u r e - T h e shelly Early Devonian (including the highly endemic Dicoelostrophia faunas of North Vietnam and adjacent Guangxi Province, so characteristic of the South China Region; Hou & Xian 1975; Wang & Rong 1986; Wang et al 1987) and Eifelian, earlier Middle Devonian faunas north of the Song Ma Suture are of South China Region, Old World Realm aspect (Benthic Assemblage 5, deep water, Eifelian faunas were collected in 1997 at Na Ri in North Vietnam; they are similar to faunas of the same age in southwestern Guangxi, near Nanning, and are now being studied) Until rich shelly Early Devonian and Eifelian marine faunas are discovered and collected south of the Song Ma Suture we will be uncertain of the earlier Devonian situation MATERIAL The Late Silurian fossils described here all occur as casts and molds in heavily weathered, arenaceous mudstone They came from collections made at two localities The first includes 95 pedicle valves and 125 brachial valves of species ofbrachiopods from the Xuan Son Formation in a quarry near the town of Kien An, near Hai Phong, northern Vietnam The second, a much larger collection, contains 1777 pedicle valves and 1391 brachial valves, belonging to brachiopod species from the Dai Giang Formation of the same age at a locality near My Duc, north-central Vietnam 679 specimens were collected near Kien An, with 221 brachiopods (32.7 % of the entire association) Among the brachiopods (including one specimen with conjoined valves), the commonest species is Retziella weberi NIKIFOROVA(62.6 % of the brachiopod total) The other brachiopods are 'Howellella' lynxoides (NIKIFOROVA)(18.5 %), Nikiforovaena vietnamensis BOUCOT & RONG, nov sp (9.5 %), and Retziella alaica NI~FOROVA (9.5 %) The brachiopods are associated with many bivalves (total 389 specimens, 57.3 %), the commonest taxon in this association, a distinctive feature of this collection Some gastropods (64 specimens, 9.4 %), trilobites (2 pygidia and free check, 0.044 %), and orthoceratid (0.015 %) are also present No other fossils were noted In the My Duc area, 3459 fossils were gathered Among them there occur 3203 brachiopod valves (including 35 specimens with conjoined valves), 94.13 % of the entire association Within the brachiopods, Retziella weberi is again the most abundant species, including 43.9 % of the entire brachiopod association, much less than in the Hai Phong area collection The other two abundant taxa are Nikiforovaena vietnamensis BOUCOT & RONG, nov sp (23.8 %) and 'Howellella' lynxoides (NIKIFOROVA)(21.0 %), higher percentages than present in the Hai Phong area Retziella alaica NIKIFOROVA (9.8 %) is fourth, and the percentage of this species is close to that in the Kien An area collection Another five species are rare, each less than 30 valves with Atrypoidea (0.9 %), Morinorhynchus (0.1%), Reticulatrypa, Spirinella ?, and gen et sp indet (each 0.03 %) None of these rare species has been found at the Kien An area locality The My Duc area brachiopods occur with various other marine benthic invertebrates, including bivalves (2.54 % of the whole association), gastropods (2.25 %), tabulates (0.03 %), rugose corals (0.12 %), trilobites (0.61%), bryozoans and ostracodes (each 0.14 %), pelmatozoan debris, and vertebrates (0.52 %), and a few other undeterminable fossils (0.06 %) These last forms are relatively rare in number The following fossils are recorded from the locality near Kien An, northern Vietnam Taxa Brachiopoda Retziella weberi NIKIFOROVA Retziella alaica NIKIFOROVA 'HowelleUa' cf lynxoides (NIKIFOROVA) Nikiforovaena vietnamensis BOUCOT& RONO,nov sp Pedicle valves Brachial valves 95 51 10 21 125 86 11 20 13 Conjoined valves Bivalves 389; this count includes broken and incomplete specimens The relatively complete specimens, those used in the taxonomic study numbered 81 Actinopteria mansuyi GRABAU Pterinea sp aft P dianensis Guo Schizodus kienanensis FANG,nov sp 14 50 320 Sanguinolites sp Sphenotus antecedens GRAgAU Goniophora dianensis Guo 1 12 Gastropods 64 Trilobites Orthoceratid Total 679 The following fossils are recorded from the My Duc area in central Vietnam Taxa Brachiopods Morinorhynchus sp At~:ypoidea sp Reticulatrvpa sp Retziella weberi NIFdFOROVA Retziella alaica NIKIFOROVA 'Howellella' cf lynxoides Nikiforovaena vietnamensis BOUCOT& RONGnov sp Spirinella ? sp Gen.and sp indet Pedicle valves Brachial valves Conjoined valves 1777 16 688 175 451 1391 13 35 663 145 234 35 441 335 Bivalves 88; this count includes broken a n d incomplete specimens The relatively complete specimens, those used in the taxonomic s t u d y numbered 44 Pterinea sp aff P dianensis GtJo Schizodus ? myducensis FaNG nov sp Sphenotus antecedens GRABAU Modiomorpha paracrypta FANa nov sp Goniophora dianensis Guo Gastropods Trilobites Tabulates Rugose corals Ostracodes Bryozoans (?) Orthoceratids Vertebrates Indet fossils Total 10 27 78 21 5 18 3459 SYNECOLOGIC ANALYSIS The Late Silurian brachiopods studied in this paper belong to the Retziella F a u n a which is widely distributed in east-central Asia and eastern Australia (Rong et al 1995) It must be emphasized that at many localities in which R weberi NIKIFOROVAor R uniplicata (GRABAU)occur, each of these species is very abundant and dominant, and usually make up more than 30-70 %, or even more, of the total association There are two examples of this situation in which the last two species were recorded 1) R weberi with very abundant individuals on the same bedding plane was recorded from the Late Silurian rocks of the northern slope of the Alay Mountains, southwest Kirghizistan, Central Asia (Nikiforova 1937, pl 12, fig 8; also see Rong et al 1995, Appendix 1) More recently Kim and Sapelnikov (in Sapelnikov et al 1999) recorded Retziella weberi Community from the type locality (Havalbet Mountain, Severnyi Nuratau Range, southern Tienshan) This is a high dominance, low diversity unit consisting almost entirely of the eponymous taxon and a BA or inner position lias been suggested 2) Very abundant specimens of R uniplicata were recorded with Striispirifer sinensis RONG & YANG, and Atrypoidea foxi JONES in the lower part of the Kuanti Formation of the Qujing area, eastern Yunnan, Southwest China (see Rong & Yang 1980; Jones & Rong 1982), a low diversity, high dominance brachiopod association, previously named the Atrypoidea Community The three species are all abundant, and the horizon in which they occur is not far from the base of the formation which is underlain disconformably by Middle Cambrian rocks The local paleogeography and the paleoecology indicate a nearshore, normal, shallow, warm water, level-bottom BA to inner position for this association R weberi from the My Due area locality, north-central Vietnam, herein described, also is the most abundant taxon in the collection The other brachiopod genera associated with R weberi are not as numerous, being parts of a relatively low diversity fauna This probably indicates a similar, nearshore, normal, shallow water environment for the widely distributed Retziella fauna in the LudlowPridoli This fauna may have inhabited a BA to inner BA position We will discuss in detail the environmental evidence for each locality The fossils from both Vietnamese localities are almost in situ This is chiefly based on the following evidence 1) Preservation of fossils is excellent although the matrix is relatively coarse; even micro-ornamentation is sometimes well preserved in this coarse matrix; brachiopod shells are always complete, with no broken valves or signs of abrasion, indicating no strong water currents; 2) Relatively equal percentages of pedicle and brachial valves within most species (with little disparity) among the brachiopods At the locality near My Due the Retziella weberi collection contains 688 pedicle valves and 663 brachial valves; at the Kien An area locality the 'Howellella' of lynxoides collection contains 21 pedicle valves and 20 brachial valve, but things are different for this species in the My Due area where there are 451 pedicle valves and 234 brachial valves of this species; 3) The fossil associations we found in these two localities appear to be relatively in situ, without any evidence of mixing of components of one community with those from another; 4) There is a complete size spectrum, large to small, for the relatively abundant taxa are all preserved in the place where they inhabited with an overall range in shell width from 2-4 mm to more than 20 mm for the species (Ret- ziella weberi, Retziella alaica, Nikiforovaena vietnamensis nov sp., and 'HowelleUa' cf lynxoides) The same thing characterizes the other fossils, including the bivalves and gastropods Based on the statements above, it seems that there is no evidence for significant net directional transportation in these collections Of course, this does not mean that there were no water currents present, because most of the shells are disarticulated The fossils from the Kien An area, indicate a shallower environment than those from the My Due area One of the evidences for demonstrating this conclusion, in particular, is that the bivalves from the My Due area (2.56 %) are much less abundant than those from the Kien An area (57.3 %), indica- 321 ting a shallower water environment for the latter A higher proportion of the gastropods (9.4 %) in the Kien An area than those in the My Duc area (2.27 %) again supports this conclusion A lower diversity (5 different higher taxa of fossils, and only species of brachiopods) and high dominance of bivalves and Retziella weberi, which make up 90 % of the association in the Kien An area again suggests that the locality represents a nearshore, very shallow water environment (most likely BA 2) The My Duc area locality, on the other hand, represents a relatively deeper, normal marine environment than that in the Kien An area, but still is considered a shallow water situation This is mainly based on the higher diversity of the entire faunal association (10 higher taxa), higher brachiopod diversity at the generic level, far fewer bivalves and gastropods, much more abundant brachiopod individuals, and presence of some normal marine, shallow water benthic invertebrates [such as rugose corals, bryozoans (?), tabulates, ostracodes and others which are lacking in the Kien An area] in the My Duc area than in the Kien An area Therefore, an assignment to inner BA for the collection from the My Duc area is suggested This is consistent with all the records eisewhere in Asia and Australia for the Retziella Fauna which has been ascertained to have no deep water representation in BA 4-5 (Rong et al 1995) The new Vietnamese data further support the conclusion that the Retziella Fauna is typicaliy a nearshore, shallow water benthic fauna, mainly BA to shallower BA position, a good environmental indicator for investigation of brachiopod communities in the Sino-Australian Province during the Late Silurian The overall abundance of bivalves at Kien An, as stated above, suggests a very nearshore environment, permissively in agreement with what the ecologically better known brachiopods suggest The taxonomic composition of the bivalve assemblage is similar to that at My Duc, with the relative abundances also being not too different from each other (Goniophora and Schizodus are the abundant taxa, with Actinoptena absent at My Duc) The very rare, disarticulated vertebrate plates (Thanh et al 1997) found in the My Duc area probably were transported into the Retziella weberi Community there, although whether from a marine or nonmarine fauna elsewhere is unknown with a possible occurrence in North Korea), South China Plate (eastern Yunnan, eastern Guangxi, northern Vietnam, western Sichuan, and western Qinling), Tarim Plate (including southern Tienshan, Central Asia), Indochina Plate and Australian Plate in the Late Silurian In addition, there are some possible or doubtful occurrences of the genus Retziella in Central Pamir, Eastern Afghanistan, Eastern Iran, and the northwest corner of South Island, New Zealand (Rong et al 1994) All of the definite areas are characterized by the presence of the shallow water, normal marine, Retziella Fauna, indicating a possibly close biogeographic relationship among them in the Late Silurian, and a Sino-Australian Province has been proposed for the above regions that include the fauna (Rong et al 1995) Both the Retziella Fauna and the Tuvaella Fauna have been recognized as two major biogeographic units within the Uralian-Cordilleran Region (Boucot 1975; Rong et al 1995) As one result of this study it has become apparent that those howellellids with one or more plications in the sulcus and corresponding grooves on the fold, a group of species that we suspect will end up in the genus Nikiforovaena (see taxonomic discussion of this genus), provides one more piece of evidence strengthening the concept of the Sino-Australian Late Silurian Province by providing a better understanding of the distribution and morphology of that genus 1) Relation to Central Asia It is remarkable that Central Asia and Indochina possess the same species group of Retziella with the most abundant, common species, R weberi The more interesting situation is that R weberi is associated with R alaica NImFOROVA [= Retzia (Retziella) weberi var alaica NIKIFOROVA,1937] in both Central Asia (Nikiforova 1937) and Vietnam (this paper) Moreover, both regions have similar constituents not only at the generic, but also at the specific levels for the brachiopod fauna in which RetzieUa occurs According to Nikiforova (1937, p 7), Retziella weberi is one of the most important species of the Isfara fauna (Pridolian) of Central Asia in which is Eoreticularia tschernyschewi NALIVKIN (probably Spirinella), Nikiforovaena ferganensis NIKIFOROVA, and Lissatrypa camelina BUCH (should be Atrypoidea) As mentioned above R weberi is associated with R alaica in Central Asia where diversity of BIOGEOGRAPHIC RELATIONSHIPS the fauna is changeable: only a single species (R weberi) (sec Nikiforova 1937, pl 12, fig 8) at one extremity, or at the other extremity more than taxa as exemplified by an association at outcrop number 1552 collected by Weber in 1910, including R weberi NIKIFOROVA,Eoreticularia tschernyschewi mattschensis NIKIFOROVA (probably Spirinella), Eospirifer cf togatus (BARBANDE),Atrypoidea damelina (BUCH), and Atrypa aspera aff squamosa (SoWERBY)(probably Gotatrypa) in 1552 m, and Schizophoria (Eoschizophoria) ferganensis NIKIFOBOVAin 1552i, and Nikiforovaena ferganensis (NIt~FOROVA) in 1552 (with no T or 'm' marked after '1552') (Nikiforova 1937) The Retziella Fauna occurs in the North China Plate (Central Jilin and southern Inner Mongolia, The majority of these genera in the fauna in Central Asia are known from the My Duc area on The My Duc area fauna is assigned to the Retziella weberi Community, but the Kien An area fauna belongs to a bivalve-Retziella weberi unit, which might represent a mixture between a somewhat deeper water, Retziella-dominated fauna and a shallower water, nearer shore, bivalve-dominated fauna; in the absence of more samples from other localities we leave the Kien An area fauna unnareed 322 the Indochina Plate, and some are known in the Kien An area of the South China Plate Both Central Asia and Vietnam have R weberi and R alaica; 'Howellella' cf lynxoides (NIKIFOROVA);Nikiforovaena vietnamensis nov sp from the Kien An area and the My Duc area are also very similar to H lynxoides and N ferganensis respectively from Central Asia It should be kept in mind that the latter four species are most abundant in the collections from the Kien An area and the My Duc area Moreover, Tadschikia, a distinctive genus of rhynchonelloid in Central Asia, has also been recorded in Vietnam (Duong 1980, p 68, pl 34, figs 8a-d) Although some genera (such as Eospirifer, Eoschizophoria, Atrypa) occurring in Central Asia have not been found in Vietnam, and some [such as Morinorhynchus, Reticulatrypa and an undetermined taxon (gen and sp indet, in this paper)] present in Vietnam have not been discovered in Central Asia, this probably reflects different lithofacies or collection bias It seems to the authors that the similarities between these two regions are more important than the differences 2) Relation to South China There are two types of Retziella in eastern Yunnan, South China, one with a single rib, and another with two or more ribs in the pedicle sulcus, namely R uniplicata (GRABAU) and R minor (HAYASAKA)[ R plicata (MANsUY)and many other synonyms] respectively Remarkably, they are similar to R weberi and R alaica respectively from Central Asia and Vietnam, but they are different evolutionary stocks within the genus This led us to conclude t h a t the Retziella fauna described in this paper from Vietnam is closer to that of Central Asia than to South China, although, R weberi and R uniplicata are very similar to each other if they are not conspecific, even though different tectonic plates are involved while keeping in mind that the Tarim Plate may represent a former northwestern portion of what is now the South China Plate with the Indochina Plate close to both This conclusion is further supported by the following evidence There are genera (Eoschizophoria, Aesopomum, Atrypa, Protathyris, and Striispirifer) in South China that have not been found in Vietnam, and Reticulatrypa and an undetermined taxon (gen and sp indet, in this paper) from Vietnam that have not been discovered from South China Additionally, abundance of some common genera is different in the two regions: Atrypoidea and Spirinella are common in South China but very rare in Vietnam Moreover, specific constituents of the fauna in Vietnam are evidently different from those of South China All of this suggests that the discrimination between them may have been related to slightly different environments, chiefly different substrates on which they lived We are aware that both regions have many genera in common (Morinorhynchus, Atrypoidea, Retziella, 'Howellella', Nikiforovaena and Spirinella), indicating that they belonged to the same biogeographic province in the Late Silurian, even to the same subprovince (R0ng et al 1995), in spite of occurring in different lithofacies Most recently, Rong et al (1995) recorded an occurrence of a very low diversity, high dominance Ret- ziella Fauna with a single species of Retziella from Late Silurian rocks at Chengxi, eastern Guangxi, geographically closer to the Kien An area of Vietnam, but considered to be within the Yunkai block (or terrane) rather than in the South China Plate, far from the eastern Yunnan region in the Late Silurian It is notable that the bivalve species from both Kien An and My Duc have much in common (4 out of and out of respectively) with those from the Qujing area of eastern Yunnan, which further reinforces the evidence provided by the brachiopods The other species are either new, not known from elsewhere, or not identifiable specifically 3) Relation to eastern Australia Since Molongia elegans capricornae MCKELLARfrom Queensland, New South Wales, Victoria and the Australian Capital Territory has been moved to Retziella (Rong et al 1994), the occurrence of the Retziella Fauna in eastern Australia has been confirmed It should be pointed out t h a t R capricornae (MCKELLAR)possessing a single median rib in the sulcus is very similar to R weberi or R uniplicata if they are not conspecific Besides, the Australian and Vietnamese faunas have some common genera including Retziella, Morinorhynchus, Atrypoidea, Atrypa, 'Howellella" Nikiforovaena, and Spirinella All these facts suggest a faunal relationship between Vietnam and eastern Australia during the Late Silurian However, the relation of Vietnam to eastern Australia was significantly less than that to Central Asia and South China This is because many genera present in eastern Australia have not been discovered in Vietnam, including Aeginia, Pholidostrophia, MitchelleUa, Protochonetes, Aliconchidium, Notoconchidium, Molongia, and Striispirifer The overall abundance of Notoconchidium in the Tasman region and its absence in Asia emphasizes the difference between these two geographic entities The occurrence of some endemic forms led Rong et al (1995, p 48) to establish a new subprovince within the Sino-Australian Province for eastern Australia A separate biogeographic unit for the Australian Retziella faunas may eventually be needed Iu summary, we position the Indochina Plate, including the My Duc area, between the Tarim (including Central Asia) and South China Plates, and closer to the Tarim Plate than to South China particularly in terms of the same species group of Retziella in both the Tarim and Indochina Plates Genera* Eoschizophoria 'Leptostrophia' Aesopomum Morinorhynchus Gypidula (Gashaomiaoia) Stegerhynchus Linguopugnoides Tadschikia Atrypoidea 10 ReticulatrTpa 11 Atrypa 12 Retziella 13 Molongia Central Asia X S Inner Eastern Mongolia Yunnan X X ? Kien An Vietnam My Duc Eastern Vietnam Australia X X X X X X X X X X X X XXX XXX X XXX XXX XXX X XXX X 323 14 Protathyris 15 Eospirifer 16 Striispirifer 17 Howellella 18 Nikiforovaena 19 Spirinella X X ? X X X X X X X X X X X X X X X X X X *The data came from Nikiforova (1937) for Central Asia; Rong et al (1985) for southern Inner Mongolia; Rong & Yang (1980) and Fang et al (1985) for eastern Yunnan; this paper for Vietnam; and McKellar (1969), Strusz et al (1984) for Australia Some data are from Rong et al (1995) Other genera, such as Aegiria, Pholidostrophia, Mitchellella, Protochonetes, Aliconchidium, and Notoconchidium, which only occur in Australia in the Late Silurian, are not included here XXX means the most common species in the collection 1) Morinorhynchus sp.; 2) Atrypoidea sp.; 3) Reticulatrypa sp.; 4) Retziella weberi NImFOROVA,1937; 5) Retziella alaica NImFOROVA, 1937; 6) 'Howellella' cf lynxoides (NIKIFOROVA, 1937); 7)Nikiforovaena vietnamensis BOUCOT& RONGnov sp.; 8) Spirinella ? sp.; and 9) Gen and sp indet BRACHIOPODA Order STROPHOMENIDA Superfamily ORTHOTETOIDEAWaagen, 1884 Family CHILIDIOPSIDAEBoucot, 1959 Genus Morinorhynchus HAVLICEK, 1965 Morinorhynchus sp REGIONAL RELATIONS The regional paleogeographic and lithofacies relations of the Retziella Fauna are complex The South China Plate includes northern Vietnam, and probably the Kien An locality A central, eastern Chinese locality yielding a very low diversity Retziella assemblage in eastern Guangxi (Chengxi) is considered to be within the Yunkai block (or terrane), ratier than in the South China Plate in the Early Paleozoic It might have been related to the Indochina Plate, but this remains to be decided In southern Guangxi, and the Qujing area of eastern Yunnan, one finds Late Silurian or Early Devonian beds resting with angular unconformity on the Cambrian or Ordovician The RetzieUa F a u n a occurning in eastern Guangxi and in eastern Yunnan is interpreted to be present in 'bays' extending inland into an overall nonmarine region The Early Devonian faunas of this region are present in the Old Red Sandstone facies, locally interpreted as being nonmarine, and overlain by marine beds canying the Emsian, Early Devonian Rostrospirifer tonkinensis Fauna In none of these areas is graptolitic earlier Silurian recognized either above or below the angular unconformity In the Hai Phong region, which includes the Kien An area, on the contraly, there is good evidence in the islands present to the northeast for graptolitic pre-Retziella Fauna, with nonmarine Devonian also occurring in this region To the south, in the My Duc area, central Vietnam region on the Indochina Plate, one also finds graptolitic, older Silurian overlain by the shallower water Retziella Fauna, overlain in turn by Old Red Sandstone facies beds that have flot yet yielded dated fossils The overall faunal similarities between the Kien An area Retziella Fauna and that to the south in the My Duc area suggests that they were not far apart geographically during the later Ludlow-Pridoli A unifying theme here is that latest Silurian Pridoli, Downtonian) to Early Devonian Old Red Sandstone facies is present almost everywhere Fig 2.1-2, 15 M a t e r i a l - Only specimens consisting of pedicle valves with internal and external molds and brachial valve with both molds D e s c r i p t i o n - Shell small, 2.5-6.4 mm in length and 3.6-9.7 mm in width, transversely subrectangular in outline, gently biconvex in profile; shells not always symmetrical Pedicle valve interarea high, catacline or slightly hypercline; brachial valve interarea anacline, much lower than pedicle valve Ornament of fine costellae, increasing mainly by insertion, costellae sharp, finer than interspaces; a few concentric growth lamellae developed near the anterior margin Pedicle valve interior with short and very thin dental plates, widely divergent Brachial valve interior with short socket ridgcs, widely divergent at about 120 degrees; they connect with cardinal process which is bilobed, separated and extending evidently posteriorly above the hingeline; no muscle scars seen M e a s u r e m e n t s - Dimensions of the figured specimens of Morinorhynchus sp (in ram) N° of specimen Internal pedicle mold Internal pedicle mold Internal brachial mold Length Width 2.6 3.9 6.4 3.6 5.6 9.7 Height of interarea 1.5 ? ? C o m p a r i s o n - The assignment of this undetermined species to Morinorhynchus is considered to be better than to assign it to Aesopomum since it possesses dental plates, although they are thin and short, and its cardinalia are much more like those of Morinorhynchus This species is also characterized by rather small individual size, whereas other species attributed to the genus are larger than the valves described here Order ATRYPIDA Superfamily LISSATRYPOIDEATwenhofel, 1914 Family LISSATRYPIDAETwenhofel, 1914 Genus Atrypoidea MITCHELL• DUN,1920 SYSTEMATIC PALEONTOLOGY R e p o s i t o r y - The specimens figured and described here are deposited at the Hanoi Geological Museum, Collection Number: BT 178 brachiopod species are described in this paper Atrypoidea sp Fig 2.9-14, 18-19 M a t e r i a l - 16 internal pedicle valve molds and 13 internal brachial valve molds 324 325 D e s c r i p t i o n - Shell small, width and length measured less than 10 mm (see below), elongately oval in outline, gently d0rsi-biconvex in profile; pedicle valve shows a very shallow median depression near the anterior margin of the shells; shell surface smooth No dental plates in the pedicle valve Brachial valve interior with separate hinge plates and widely divergent socket ridges Muscle scars in both valves not observed M e a s u r e m e n t s - Dimensions of the figured specimens of Atrypoidea sp in mm N ° of specimen Internal pedicle mold Internal pedicle mold Internal pedicle mold Internal brachial mold Internal brachial mold I n t e r n a l brachial mold Length Width 6.1 ? 7.2 3.9 6.1 9.3 5.9 7.0 7.9 4.2 6.6 9.9 R e m a r k s - This taxon is assigned to Atrypoidea based on its smooth surface, its cardinalia, and the absence of dental plates There are 'many species which have been attributed to Atrypoidea up to date It is difficult to compare our Vietnamese specimens with those of other species since 1) there are probably some synonyms within the genus and even different species which possess similar shell shape at the early stages; 2) there are no large individuals of Atrypoidea sp in the collection we studied herein for comparison Superfamily ATRYPOIDEAWaagen, 1881 Family ATRYPIDAE Waagen, 1881 Genus Reticulatrypa SAVAGE,1970 Reticulatl:ypa sp Fig 2.3,4 M a t e r i a l - Only one pedicle valve with both external and internal molds D e s c r i p t i o n - Shell small, 4.8 mm long and 5.4 mill wide, subcircular, pedicle valve gently convex with a median crest like a low fold; ornament of fine costeliae with about regularly spaced concentric lamellae Pedicle valve interior with thin, short, divergent (about 80 degrees) dental plates, and muscle scars discernible R e m a r k s - Many features, such as outline, convexity and ornamentation of the shells, of this u n d e t e r m i n a b l e species are consistent with those proposed by Savage (1970) for the genus Reticulatrypa We not give a species name for the material in this paper because of the presence of only a single pedicle valve Order ATHYRIDIDABoucot, Johnson & Staton, 1964 Superfamily RETZIELLOIDEAModzalevskaya, 1996 R e m a r k s - The retziellid group was assigned to Athyrisinacea in the 1965 Treatise on Invertebrate Paleontology Braehiopoda Volume which was followed by many paleontologists Recently, Rong et al (1994) thought t h a t it is essentially different from the athyrisinids which are similar to athyridids and they attributed it to the Meristelloidea Waagen, 1883 Most recently, Alvarez, Rong and Boucot (1998) have further pointed out that the retziellids are peculiar both in their external and internal structures and agree with Modzalevskaya (1996) in promoting this group to superfamily rank There is only one family, Retziellidae, involved in this superfamlly It includes five genera: Gissarina MENAKOVA • NIKIFOROVA, 1986; Metathyrisina RONG & YANG, 1981; Molongia MITCHELL, 1921; Qinlingia RONG, ZHANG& CHEN, 1987; Retziella NImFORGVA, 1937 The biogeographic significance of this pecullar group has been discussed in Rong et al (1995) and its f u r t h e r implications are evaluated above Family RETZIELLIDAERhzonsnitskaya, 1974 (nom transl Rong, Strusz, Boucot, Fu, Modzalevskaya & Su, 1994 ex Retziellinae Rzhonsnitskaya, 1974, p 54) (= Metathyrisinidae WANG, RONG & YANG, in Rong & Yang, 1981, p 245) Genus Retziella NH~FOROVA,1937 T y p e S p e c i e s - Retziella weberi NIKIFOROVA, 1937, p 57, pl 12, figs 8, pl 14, figs 1-4; from U p p e r Isfara Horizon (Pridolian), Isfara River, n o r t h e r n slope of Alay Mountains, southwest Khirghizistan, Central Asia The holotype specimen of this species h a s been re-illustrated by Rong et ah (1994) Diagnosis - Retziellidae with variably developed ventral sulcus and dorsal fold, both usually plicate (ribbed), with I to (a few even or 5) plicae in the sulcus and to on each flank, with thin, short dental plates and very narrow lateral cavities in the pedicle valve, and with a well-doveloped apical septalium supported by a short, thin median septum in the brachial valve Emended R e m a r k s - Having studied the internal structures, Rong et al (1994) concluded that Protathyrisina ZHu, 1974, from South China, Gannania Fu, 1982 and Stegospira Fu, 1982 from Western Qinling should be regarded as junior subjective synonyms of Retziella Some species formerly assigned to Athyrisina and Molongia should also be attributed to Retziella All species of the genus Retziella have been listed in Rong et al (1994) RetzieUa can be distinguished from Molongia in having a ribbed pedicle sulcus and well developed septatium supported by FIGURE - 1-2, 15 Morinorhynchus sp 1, ventral external impression; 2, ventral internal impression; 15, dorsal internal impression; all specimens x 5.3, Reticulatrypa sp., ventral external and internal impressions, x Spirinella ? sp., ventral internal impression, x 3.6-8, gen et sp indet 6, ventral internal impression 7-8, ventral external and internal impressions, × 3.9-14, 18-19 Atrypoidea sp., 9-11, 19, internal dorsal impressions, x 3.12-14 (11, 13, same specimen), 18, 19, internal, external, ventral impressions, x 3.16-17, 2035 Retziella weberi NIKIFOROVA,16-17, two dorsal internal impressions, x 2.20, 23, 27-28, steinkern, anterior, lateral, ventral, dorsal views, x 3.21, 29-31, steinkern, anterior, dorsal, lateral, ventral views, x 3.22, ventral internal impression, x 2.24, dorsal internal impression, × 2.25, dorsal external impression, x 26, ventral internal impression, × 3.32-34, three dorsal internal impressions, x 35, dorsal external impression showing coarse, concentric growth lamellae, x 5.1-2, 15 Morinorhynchus sp 1, moule externe ventral; 2, moule interne ventral; 15, moule interne dorsale; tous × 3, 4, Reticulatrypa sp moules externe et interne ventraux x 5, Spirinella ? sp moule interne ventral 6-8, gen et sp indet 6, moule interne ventral; 7, 8, moules externe et interne ventraux 9-14, 18-19 Atrypoidea sp 9-11, 19, moules internes dorsaux x 12-14 (11, 13, m~me spgcimen); 18, 19, moules interne et externe ventraux x 16-17, 20-35 Retziella weberi NIKIFOROVA.16, 17, deux moules internes dorsaux x 20, 23, 27-28, moule interne en vues antdrieure, latgrale, ventrale et dorsale × 3; 21, 29-31, moule interne en rues antgrieure, dorsale, latgrale et ventrale × 3; 22, moule interne ventral x 2; 24, moule interne dorsal × 2; 25, moule externe dorsal x 2; 26, moule interne ventral x 3; 32-34, trois moules internes dorsaux x 3; 35, moule externe dorsal montrant les fortes lamelles de croissance concentriques x 326 327 a median septum, whereas Molongia has a smooth pedicle sulcus, and no septalium in the brachial valve Age a n d D i s t r i b u t i o n - Late Wenlock to Pridoli; Kirghizistan and Tadzhikistan, Central Asia, N o r t h e r n Tarim, S o u t h China, N o r t h China, N o r t h Korea (?), n o r t h e r n Vietnam, Central Vietnam and E a s t e r n Australia Retziella weberi NIKIFOROVA, 1937 Figs 2.16-17, 20-35; 3-18-20, 24-25 Retziella weberi NIKIFOROVA, 1937, p 57, pl 12, fig 8, pl 14, figs 1-4; Nikiforova 1949, p 19, p] 7, fig 4; Rzhonsnitskaya 1974, p 61, pl 11, fig 8; Duong 1980, p 68, pl 34, figs 4-7; Rong et al 1994, p 566, pl 2, figs 9, 12-19, 21-27; pl 4, fig 12; Rong et al 1995, p 41, Fig 1, L,P,Q,V M a t e r i a l s - All specimens of this species are preserved in a coarse sandy matrix as external a n d i n t e r n a l molds 1777 pedicle internal molds and 1391 brachial internal molds from the My Duc area and 51 pedicle a n d 86 brachial molds from the Kien An area Most of t h e m are disarticulated, but 35 conjoined valves were recovered The i n t e r n a l structures of both pedicle a n d brachial valves are well preserved with the exception of spiralia We only obtained a single specimen with spiralia directed laterally, indicating its assignment to the ribbed, impunctate athyridids D e s c r i p t i o n - Shell medium to large in average size (the minimum width of the shell only attains mm, and the maximum more than 15 mm); changeable in outline, usually round to roundly pentagonal, wider than long, and vice versa as well; gently subequally ventri-biconvex in lateral profile; ventral beak prominent and relatively high, with a mesothyrid foramen and conjoined small deltidial plates underneath the foramen; shallow ventral sulcus and low brachial fold present, the sulcus expanded widely anteriorly Ornament of prominent, usually rounded plications well preserved, interspaces between two plications wider than the latter; usually plications, sometimes and on the flank area, only a single plica present in the sulcus and on the fold; all plications start from the beak of the shells; widely located, strongly concentric lamellae well developed on the whole shell surface, in particular on the anterior half of the shells, one specimen (lenght 11.5 mm, width 12.5 mm) with 16 concentric lamellae, the lamellae crowded near the anterior marginal area Pedicle valve interior with thin, short, widely divergent dental plates, attaining 1/7-1/10 of shell length; lateral cavities very narrow and small; muscle scars usually discernible, possibly limited to the pedicle chamber area Brachial valve interior with thinner outer hinge plates supported dorsally by a pair of plates convergent onto a thin median septum to form an apical septallum which is very small and shallow (see discussion below); the median septum short, extending anteriorly, gradually thinning, and attaining about 1/5-1/4 the length of the shells; spiralia oriented laterally M e a s u r e m e n t s - Dimensions of the figured specimens of Retziella weberi NIKIFOROVA, 1937 (in mm) Abbreviations are length (L), width (W), thickness (T), n u m b e r of lateral plications (LP) and n u m b e r of plications in the sulcus (SP) or fold (gP) N°.of specimens Internal brachial mold Conjoined valves Internal brachial mold Internal brachial mold Conjoined valves Internal brachial mold Internal pedicle mold Internal pedicle mold Internal pedicle mold 10 Internal brachial mold L W 3.1 7.4 9.5 9.8 10.0 10.8 12.9 12.2 12.6 16.1 3.2 7.8 10.7 14.2 11.7 14.0 13.1 12.3 12.0 13.2 T 2.9 7.0 LP 4 3-4 4-5 3-4 4-5 SP 1 FP 2 2 2 1 Comparison - Two species of the genus Retziella, R weberi NIKIFOROVA,1937 from the Pridolian rocks of Central Asia and R uniplicata (GRABAU, 1931) from late Ludlow to early Pridoli strata of southwest China, are very similar to each other Externally they have the same shape and size range, plications well developed on flanks, and only plication in the pedicle sulcus and on the brachial fold, and the latter two variably developed in both species They have great variation in shell shape and size in each population For example, in addition to the shape of the shells, numbers of plications are also variable in R weberi: we have measured both pedicle and brachial valves of 1) the holotype of the species (Nikiforova 1937), 2) two topotype specimens housed in the Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing (Rong et al 1994), and 3) 13 specimens of this species from Central Asia housed in the U.S National Museum, Washington, altogether 18 specimens with 36 valves: 19 valves with plications (including the holotype and all other topotype specimens), with 4-5 plications, with plications, with plications, and one each with 3, 3-4, and 5-6 But, we can see that the majority of the species possess plications on each flank But, for R uniplicata, we measured the neotype (NIGP 46666: length 9.0, width 9.1, and thickness 5.7 mm) and another FIGURE - 1-3, 6-7, 12-15, 21-23, 26-27 RetzieUa alaica NII~FOROVA,1, dorsal internal impression, x 3.2-3, two ventral internal impressions, x 3.6-7, two ventral internal impressions, x 2.12-13, two ventral internal impressions, × 14, dorsal internal impression, x 15, ventral internal impression, x 2.21, dorsal internal impression showing septallum, × 8.22, dorsal internal impression, × 3.23, ventral external impression showing fine filae, x (on same specimen as bivalve holotype) 26-27, ventral external impressions showing fine flac, x 18-20, 24-25 Retziella weberi NIKIFOROVA,18-20, 24, steinkern, dorsal, lateral, ventral, anterior of same specimen, x 3.25, dorsal internal impression, x 2.4-5, 8-11, 16-17 'Howellella' cf lynxoides (NIKIFOROVA),4, ventral internal impression, x 3.5, rubber replica of ventral external impression, x 3.8, 9, two dorsal internal impressions, x 10, dorsal external impression, x 11, ventral external impression, x 16, 17, rubbcr replica of ventral external impression, x 1-3, 6-7, 12-15, 21-23, 26-2Z Retziella alaica NIKIFOROVA 1, moule interne dorsal x 3; 2-3, deux moules internes ventraux x 3; 6-7, deux moules internes ventraux × 2; 12-13, deux moules internes ventraux x 2; 14, moule interne dorsal x 2; 15, moule interne ventral x 2; 21, moule interne dorsal x 3; 23, moule externe ventral montrant les fines filae x (sur le rn~me dchantillon que l'holotype); 26-27, moules externes ventraux montrant les filae × 18-20, 24-25 Retziella weberi NIKIFOROVA 18-20, 24, rnoule interne, rues dorsale, latdrale, ventrale et antdrieure x 3; 25, moule interne dorsal 4-5, 8-11, 16-1Z 'Howellella' cf lynxoides (NIKIFOROVA).4, moule interne ventral X 3; 5, empreinte en latex d'un moule externe ventrale x 3; 8, 9, deux moules internes dorsaux × 3; 10, moule externe dorsal x 3; 11, moule externe ventral x 3; 16, 17, empreinte en latex d'un moule externe ventral x 328 topotype (NIGP 46667: length 12.5, width 12.9, and thickness 8.0 ram) which have and in each of the valves This feature can be used for distinguishing this species from R uniplicata Moreover, the interspaces between plications in R weberi are usually wider than those in R uniplicata The Vietnamese specimens identified as R weberi were originally described briefly and illustrated by Duong (1980) and are studied in detail in this paper They are more like R weberi of Central Asia than R uniplicata from southwest China We have measured lateral plications on the flanks of 10 figured specimens (two conjoined valves, pedicle valyes, and brachial valves) with the following results: and 3-4 plications on valves, plications on valves, 4-5 plications on valves and plications on one valve The majority of the valves have 3-4 plications on each flank, a feature different from R uniplicata Moreover, the interspaces between two plications are wider in the Vietnamese specimens than in the Chinese specimens ofR uniplicata Retziella weberi NIKIFOROVAis also similar to R minor (HAYASAKA,1922) in many characters, including general shell size, shape, profile, and plications on the lateral areas R minor can be differentiated from R weberi by having or more (3-5) plications in the pedicle sulcusi whereas Retziella weberi possesses only a single plica in the sulcus, and moreover R weberi has wider rib interspaces than R minor RetzieUa alaica NIKIFOROVA,1937 Fig 3.1-3, 6-7, 12-15, 21-23, 26-27 Retzia (Retziella) weberi v a t alaica N1KIFOROVA,1937, p 58, pl 14, figs 5-7 M a t e r i a l - 175 pedicle i n t e r n a l v a l v e m o l d s a n d 145 b r a c h i a l i n t e r n a l m o l d s from t h e M y D u c a r e a , a n d 10 pedicle a n d 11 b r a c h i a l i n t e r n a l m o l d s f r o m t h e K i e n A n area D e s c r i p t i o n - Shell small to medium (the minimum width of the shell only attains mm, and the maximum more than 16 ram); outline changeable, round to roundly pentagonal, wider than long or vice versa; usually gently subequally biconvex; yentral beak relatively high, pedicle sulcus shallow, narrow, or sometimes discernible during the whole ontogeny, and brachial fold low or sometimes indistinct Ornament of prominent, usually low, rounded plications, interspaces between two plications prominantly wider than the latter; usually 14-16 plications on the whole shell surface, or more plica present in the sulcus and or more on the fold; all plica originate at the beak; numerous fine concentric fila well developed on the whole shell surface, a few strongly concentric growth lamellae only seen at the anterior margin Pedicle valve interior with a pair of thin, very short, widely divergent dental plates, lateral cavities very narrow; muscle scars usually discernible, possibly limited to the pedicle chamber area Brachial valve interior with outer hinge plates supported dorsally by a pair of plates convergent onto a thin, short median septum to form an apical sep- talium which is very small and shallow; the median septum attaining about 1/5 the shell length Measurements - D i m e n s i o n s of t h e f i g u r e d s p e c i m e n s of RetzieUa alaica NIKIFOROVA, 1937 (in ram) A b b r e v i a t i o n s a r e l e n g t h (L), w i d t h (W), n u m b e r of l a t e r a l plications (LP), a n d n u m b e r of plications in t h e pedicle s u l c u s (SP) or b r a c h i a l fold (FP) N ° of specimens Internal pedicle mold Internal brachial mold Internal pedieie mold Internal pedicle mold 5.Internal brachial mold Internal pedicle mold Internal pedicle mold L W LP SP 9.6 10.2 10.4 15.6 15.6 16.1 16.4 11.3 10.8 10.5 13.8 15.4 14.7 14.5 4-5 4-5 4-5 5 (4) 3 (3) 2 FP C o m p a r i s o n - We promote Retzia (Retziella) weberi var alaica NIKIFOROVA, 1937, to specific level because alaica can be easily distinguished from R weberi by the following characters: finer and more costae, much less developed (usually almost discernible) sulcus and fold, and more than I costa in the sulcus and more than on the fold Moreover, we examined the Vietnamese specimens of R alaica studied in this paper which possess very fine, concentric fila on the whole shell surface, which are absent in R weberi, and the concentric lamellae well developed in R weberi are almost lacking or only located at the anterior marginal area of the shells in R alaica Retziella minor (HAYASAKA) from the Miaokao Formation (late Ludlow-early Pridoli) of the Qujing area, southwest China, also has plicae in the sulcus, a character similar to R alaica They differ from each other in the following: R minor possesses smaller shell size on average, much more developed pedicle sulcus, and much less wide interspaces between two plicae than R alaica Regarding the synonymy question of species assigned to Retziella from South China there is a complicated story What Grabau (1931) identified as Athyrisina plicata (MANsUY), Rong & Yang (1980) as Protathyrisinaplicata, and Rong et al (1994) as Retziella plicata, can be differentiated from minor chiefly by having plications in the sulcus However, in Chinese specimens, those with or plications (or even more) in the sulcus occur in the same populations, and may be better regarded as different phenotypic forms of the same species Based on the same reasoning, those with plications in the sulcus and identificd as Retziella quadriplicata (GRABAU) from the Miaokao Formation of the Qujing area (Zhu in Fang & Zhu 1974; Rong & Yang 1980) should also be assigned to Retziella minor (HAYASAt(A) It would be better to consider those forms with 2, 3, or plications in the sulcus of various forms of the genus Retziella from South China as different phenotypes of the same species occurring in the same population However, it should be pointed out that the holotype of Retzia plicata MANSUY,1922, came from an unknown horizon at Lunan, Central Yunnan and is lost Since its exact locality and horizon are unknown the topotype specimens of this species cannot be restudied It is also uncertain whether or not the internal structures of Retzia plicata MANSUY are the same as those in Retziella minor Meanwhile, the holotype 329 specimen ofAthyrisina quadriplicata GRABAU,from the Middle Devonian Wangjia Beds of southern Gansu, North China (Grabau 1931), cannot be investigated as well because the holotypes have not been located Therefore, it is also unknown whether or not A quadriplicata GRABAUand that identified as A quadriplicata GRABAU(in Rong et al 1974) and Protathyrisina quadriplicata ZHU (in Fang & Zhu 1974) from the Miaokao Formation of the Qujing area are conspecific~ Further investigation of these specimens is warranted O r d e r S P I R I F E R I D A Waagen, 1883 Superfamily DELTHYRIDOIDEAPhillips, 1841 Family DELTHYRIDIDAEPhillips, 1841 Genus Howellella KOZLOWSKI,1946 'Howellella' cf lynxoides (NIKIFOROVA,1937) Fig 3.4-5, 8-11, 16-17; 4-6, 18, 22-28 cf Spirifer (Eospirifer) lynxoides NALIVKINn o m e n n u d u m , in Nikiforova, 1937, p 50, pl 10, figs 7-1 n o n Eospirifer lynxoides NALIVKIN, D u o n g , 1980, p 68, pl 34, figs 3a-d M a t e r i a l - 21 pedicle a n d 20 b r a c h i a l i n t e r n a l m o l d s f r o m t h e K i e n A n area, a n d 451 pedicle a n d 234 b r a c h i a l v a l v e m o l d s from t h e My D u c area All p r e s e r v e d as i n t e r n a l a n d e x t e r n a l molds D e s c r i p t i o n - Small to medium in size, transverse rhomboidal in outline, subequally biconvex in lateral profile; wider than long, the maximum width at the hingeline, with acute extremities Pedicle valve gently convex, interarea low, beak not higher, overhanging the hingeline very much, umbo gently curved, not swollen; sulcus well developed, expanding anteriorly widely, occupying approximately 2/5 of the shell width Brachial valve also gently convex, the most convex part of the shell near the mid line, median fold carinate, prominently above the flanks of the shells Megascopic-ornament of about 3-5 (mostly or 5), occasionally 6, simple, strong plications on the flanks, and a short, median rib in the pedicle sulcus with a corresponding median furrow on the brachial fold, in the smaller specimens the rib is absent, in a single specimen examined in the collection there are twQ weak, low plications present in the sulcus, in addition to the median one, there is another one lateral to the latter, indicating an irregular phenomenon; microornament is not usually well preserved in the collection, but a few specimens of this species clearly show concentric growth ]amellae upon which are superimposed capillae that become fimbriate at the anterior margin of the growth lamellae Pedicle valve interior with short, thin, narrowly divergent dental plates, disposed just at the outside of the two strongest plications delimiting the sulcus, the latter extending anteriorly to expand widely and relatively deep; no muscle field seen Brachial valve interior with a pair of widely divergent sockets, subparallel to the hingeline, crural plates almost lacking, striated cardinal process located at the end of small delthyrial platform; muscle fields discernible Measurements - D i m e n s i o n s of t h e f i g u r e d s p e c i m e n s of 'Howellella' cf lynxoides (NI~FOaOVA, 1937) (in m m ) Abbrev i a t i o n s a r e l e n g t h (L), w i d t h (W), n u m b e r of l a t e r a l plications (LP), a n d n u m b e r of plications in t h e pedicle s u l c u s (SP) or b r a c h i a l fold (FP) N ° of specimen Internal pedicle mold Internal pedicle mold Internal pedicle mold Internal pedicle mold Internal ped~cle mold Internalpedicle mold Internal brachial mold Internal brachial mold Internal brachial mold 10 Internal brachial mold 11 Internal brachial mold L 5.5 6.4 5.8 8.2 11.7 7 0.21+/- 13+/- 0.93 0.21 12 0.86 H H/L Comparison - The present specimens are nearly identical to Pterinea dianensis Guo from the Upper Silurian of eastern Yunnan, China, except that the character of the posterior margin is not clear in the Vietnamese specimens In addition, the shell sculpture ofP dianensis is unknown, since the type, and only specimen is an internal mold A more detailed comparison is therefore difficult to make Genus Actinopteria HALL, 1884 T y p e s p e c i e s - Avicula decussata HALL, 1843, p 203; by s u b s e q u e n t d e s i g n a t i o n of B a s s l e r 1915, p 16 Subclass HETEROCONCHIAHertwig, 1895 Order TRIGONIOIDADall, 1889 Superfamily TRIGONIACEALamarck, 1819 Family SCHIZODIDAENewell & Boyd, 1975 Genus Schizodus DE VERNEUIL • T y p e s p e c i e s - Axinus obscurus J SOWERBY, 1821, p 12, pl 314; by s u b s e q u e n t d e s i g n a t i o n of de V e r n e u i l 1845, p 308 Schizodus kienanensis nov sp FANG Fig 5.18, 20 M a t e r i a l - T h e r e a r e 50 s p e c i m e n s , 33 of w h i c h are left valves, r e p r e s e n t e d by i n t e r n a l a n d e x t e r n a l molds All of t h e m a r e from t h e K i e n A n area T h e p r e s e r v a t i o n u s u a l l y is n o t v e r y good a n d t h e h i n g e s t r u c t u r e is poorly k n o w n Only in a few s p e c i m e n s a r e f a i n t t r a c e s of one c a r d i n a l tooth in e a c h v a l v e visible, b u t no f u r t h e r d e t a i l s a r e p r e s e r v e d Diagnosis - Subelliptical, with elongated posteroventral extremity; umbonal ridge strong Description - Shell medium sized, moderately inflated, inequilateral, subelliptical, posteroventrally elongate; longer thas high with H/L ratio 0.7 or so; umbo located at about the anterior one-fourth of shell length, with prosogyrate beak; anterior margin well-rounded, continuing gradually into broadly rounded ventral margin; posterodorsal margin slightly convex, merging with ventral margin through sharp curve; umbonal ridge well developed, becoming rounded distally; surface nearly smooth Measurements in mm Actinopteria mansuyi GRABAU,1926 Fig 5.7, Pterinea lineata - M a n s u y , 1912, p 44, pl 7, figs 2a-c (non Pterinea lineata GOLDFUSS, 1840) Actinopteria mansuyi - G r a b a u , 1926, p 44, pt 3, figs 3-5 Ptychopteria (Actinopteria) mansuyi - Liu, 1976, p 133, ph 2, fig 10; Guo 1985a, p 100, pl 24, figs 7-9 M a t e r i a l - T h e r e a r e 14 left v a l v e s f r o m t h e K i e n A n locality, r e p r e s e n t e d by i n t e r n a l a n d e x t e r n a l molds M o s t of t h e m a r e i n c o m p l e t e or f r a g m e n t a r y , a n d m o r e or less s e c o n d a r i l y deformed Description - Shell small to medium in size, prosocline, left valve strongly inflated; hinge margin nearly straight, shorter than the length of shell; umbo salient above hinge margin, located near the anterior end; anterior ear small, subtrigonal, welldefined; posterior wing large, depressed; surface marked by reticulate sculpture (observed only in well-preserved external molds) made up of prominent radiating ribs and more obscure concentric ornament, radials somewhat irregularly spaced, from to ribs in mm, near the ventral margin, with interspaces to times the width of the ribs, finer ribs sometimes intercalated; posterior wing with or ribs and a small number of intercalated finer ribs Measurements in mm L Left composite mold Left composite mold Left internal mold 17 21 25 MURCHISON, 4 Left internal mold (holotype) Left internal mold Right internal mold L La La/L H H/L 31 30 24 0.26 0.23 0.25 23 22 17 0.74 0.73 0.71 Comparison - The present specimens show the external morphological features ascribed to Schizodus by Newell and Boyd (1975, p 95) Externally this species is much like Schizodus truemani JOHNSTON [1993, p 111, fig 79, and the juveniles of S oweni (JOHNSTON,1993, fig 78D)] from the Lower Devonian of southeastern Australia, but the Australian specimens have an obliquely truncated posterior margin, forming an obtuse angle with the dorsal margin An Upper Silurian species, Schizodus ? sp from the Lower Ludlovian of Wales (Newell & Boyd 1975, p 97, fig 33) can be readily distinguished by its subquadrate shape, absence of posteroventral elongation, obscure umbonal ridge and poorly defined corselet Schizodus ? myducensis nov sp FANG Fig 5.14, 16 M a t e r i a l - All s p e c i m e n s of t h i s species a r e from t h e M y D u c a r e a a n d p r e s e r v e d in a coarse s a n d y m a t r i x as e x t e r n a l a n d i n t e r n a l molds T h r e e left v a l v e s a n d s e v e n r i g h t v a l v e s on hand Dentition and muscular impressions are not preserved La La/L H H/L Diagnosis - Subcircular shell outline, umbonal ridge weak 7 0.29 0.33 0.28 18 20 26 1.06 0.95 1.04 Description - Shell small to medium in size, slightly inequilateral, subcircular; length slightly exceeding height by a ratio of about 0.9; umbo loca- 334 335 ted at about the anterior one-third of shell length, with prosogyrate beak; all margins of shell wellrounded, umbonal ridge weak; surface nearly smooth Measurements in mm Left internal mold (holotype) Right internal mold Right internal mold L La La/L H H/L 16 19 14 6.5 0.38 0.34 0.36 15 18 12 0.94 0.95 0.86 - The present specimens are tentatively placed in the genus Schizodus because they look like shortened Schizodus kienanensis nov sp FANGwithout posteroventral elongation Comparison Subclass ANOMALODESMATADall, 1889 Order PHOLADOMYOIDANewell, 1965 Superfamily PHOLADOMYACEAKing, 1844 [nom transl Newell, 1965] Family SANGUINOLITIDAEMiller, 1877 Subfamily SANGUINOLITINAEMiller, 1877 [nom transl Morris et al 1991] Genus Sanguinolites Mc'CoY, 1844 T y p e s p e c i e s - Sanguinolites discors MCCOY, 1844, p 49, pl 8, fig 4; by subsequent designation of Stolizcka 1871, p XIX Sanguinolaria ? angustata PHILLIPS, 1836, p 208, pl 5, fig 2) Hind (1900, p 367) and Morris et al (1991) concluded that S discors 1844 is a junior subjective synonym of S angustatus (PHILLIPS, 1836) Sanguinolites sp Fig 5.12 M a t e r i a l - Only a single left composite mold from Kien An is available, nearly complete No internal shell characters are preserved ~Shell medium in size, elongate elliptical; longer than high with H/L ratio of 0.55; umbo low, lying at less than one-third of shell length from the anterior end; dorsal margin nearly straight, ventral margin broadly convex; anterior end rounded, posterior end obliquely truncated; umbonal ridge well defined, post-umbonal area marked by one radial ridge, antero-umbonal sulcus faint; comarginal ornament fine, varying in strength, no granulation of shell surface observed Description i n m m - Length (L), 33; anterior length (La), 9; La/L, 0.27; height (H), 18; H/L, 0.55 Measurements - The author does not know any species comparable with the present specimen in the described Silurian and Devonian infaunal burrowing bivalves It has external shell characters similar to those of Sanguinolites and may represent a new species Discussion Family GRAMMYSIIDAEMiller, 1877 Genus Sphenotus HALL,1385 T y p e species - Sanguinolites arcaeformis HALL & WHITFIELD, 1869 (see Hall 1885, pl 65, figs 7-11), by subsequent designation of Miller 1889, p 513 Sphenotus antecedens GRABAU,1926 Fig 5.17 Sphenotus antecedens GRABAU,1926, p 52, pl 3, figs 15a, b Goniophora maritima Gvo, 1985a, p 104, pl 24, fig 10 Goniophora maritima socialis Guo, 1985a, p 104, pl 24, fig 11 M a t e r i a l - Two left valves are available from the My Duc and Kien An areas respectively, represented by internal molds Nothing is known of the internal structures - Shell small, inequilateral, elongate subrectangutar, length somewhat less than twice height; umbo salient above hinge margin, located at the anterior one-fourth of shell length; anterior margin rounded, posterior margin slightly convex or somewhat truncated; ventral margin broadly arcuate, subparallel to dorsal margin; umbonal ridge angular dorsally, becoming rounded and dying out ventrally; antero-umbonal sUlcus weak and only variably present Description i n m m - Length (L), 17; anterior length (La), 4; La/L, 0.24; height (H), 9; H/L, 0.53 Measurements - Guo (1985a) proposed a new species and a new subspecies for two specimens which agree closely with Grabau's species The author cannot find any important differences between them Guo (1985a, b) often proposed new species based on individual specimens and left no room for intraspecific variation Discussion FIGURE5 - 1-3, 13, Goniophora dianensis Guo, all x 2.1, internal mold of left valve, Kien An 2, internal mold of left valve, My Duc; 3, 13, internal mold of right valve, side view (3), dorsal view (13), My Duc 4-6 Pterinea sp aff P dianensis Guo 4, internal mold of right valve, x 5, My Duc; 5, internal mold of left valve, x 3, My Duc; 6, internal mold of left valve, x 3, Kien-An 7-9 Actinopteria mansuyi GRABAU,all x 3.7, composite mold of left valve, Kien An; 8, composite mold of left valve, Kien An; 9, internal mold of left valve, KienAn 10-11 Modiomorpha paracrypta nov sp FANG,all x 2.10, internal mold of right valve, paratype, My Duc; 11, internal mold of left valve, holotype, My Duc 12 Sanguinolites sp., composite mold of left valve, x 2, Kien An 14-16 Schizodus ? myducensis nov sp FANG, all x 3.14, internal mold of left valve, holotype, My Duc; 15, internal mold of right valve, paratype, My Duc; 16, internal mold of right valve, paratype, My Duc 17, Sphenodus antecedens GRABAU,internal mold of left valve, x 3, My Duc 18-20 Schizodus kienanensis nov sp FANG,all x 18, internal mold of right valve, paratype, Kien An; 19, internal mold of left valve, paratype, Kien An; 20, internal mold of left valve, holotype, Kien An 1-3, 13, Goniophora dianensis Guo, tous x 1, moule interne d'une valve gauche, Kien An; 2, moule interne d'une valve gauche, My Duc; 3, 13, moule interne d'une valve droite, vues latdrale (3) et dorsale (13), My Duc 4.6 Pterinea sp aff P dianensis Gvo 4, moule interne d'une valve droite x 5, My Duc; 5, moule interne d'une valve gauche x 3, My Duc; 6, moule interne d' une valve gauche x 3, Kien An 7-9, Actinopteria mansuyi GRABAU,tOUSX 3; 7, moule composite d'une valve gauche, Kien An; 8, moule composite d'une valve gauche, Kien An; 9, moule interne d'une valve gauche, Kien An 10-11, Modiomorpha paracrypta nov sp FANG, tOUS X 2; 10, moule interne d'une valve droite, paratype, My Duc; 11, moule interne d'une valve gauche, holotype, My Duc 12, Sanguinolites sp., moule composite d'une valve gauche x 2, Kien An 14-16, Schizodus ? myducensis nov sp FANG, tous × 3; 14, moule interne d'une valve gauche, holotype, My Duc; 15, moule interne d'une valve droite, paratype, My Duc; 16, moule interne d'une valve droite, paratype, My Duc 17, Sphenodus antecedens GRABAU,moule interne d'une valve gauche x 3, My Duc 18-20, Schizodus kienanensis nov sp FANG, tous X 2; 18, moule intenre d'une valve droite, paratype, Kien An; 19, moule interne d'une valve gauche, paratype, Kien An; 20, moule intenre d'une valve gauche, holotype, Kien An 336 FIGURE - Diagram showing the measurements of Pterinea Abbreviations are length (L), length of anterior (La), height (H), ratio of anterior length (La) to length (L) (La/L), ratio of height (H) to length (L) (H/L) Diagram showing the measurements of Modiomorpha Diagramme prdsentant les mesures de Pterinea I L I I L I l La -I l-La I T Abrdviations: longueur (L), longueur antdrieure (La), hauteur (H),; rapport entre longueur antdrieure et longueur (Lr/L) et rapport entre hauteur et longueur (H/L) Diagramme prdsentant les mesures de Modiomorpha Superfamily MODIOMORPHINEAMiller, 1877 emend Fang & Morris, 1997 [nom transl Newell, 1965] Family MODIOMORPHIDAEMiller, 1877 (= Permophoridae VANDE POEL, 1959, pro Pleurophoridae DALL, 1895) Subfamily MODIOMORPHINAEMiller, 1877 (nom, transl Fang & Morris, 1997) (= Permophorinae VANDE POEL, 1959, nora transl Chavan, 1969) Genus Modiomorpha HALL ~%WHITFIELD, 1869 T y p e s p e c i e s - Pterinea concentrica CONRAD,1838, p 116; by subsequent designation of Hall, 1885, p XXIV Modiomorpha paracrypta nov sp FANG Fig 5.10, 11 M a t e r i a l - This species is at present represented by only two right valves and one left valve All of them are from the My Duc area and preserved as external and internal molds Internal shell characters are not visible Diagnosis - Obliquely elliptical, with nasute anterior end, posteriorly expanded; antero-umbonal sulcus prominent D e s c r i p t i o n - Shell medium in size, very inequilateral, obliquely elliptical, posteriorly expanded; longer than high with H/L ratio of about 0.7; umbo salient above hinge margin, located at about te anterior one third of shell length; hinge margin straight; anterior end nasute, regularly rounded into ventral margin which shows a prominent concavity near the center of the length; posterior margin broadly arcuate,' rounding more abruptly into ventral margin; umbonal ridge scarcely deftned; antero-umbonal sulcus very prominent, causing the median concavity of ventral margin; surface nearly smooth Measurements of m m Left internal mold (holotype) Right internal mold L La La/L H H/L 31 30 10 0.32 0.27 22 20 0.71 0.67 C o m p a r i s o n - Externally this species is very similar to Modiomorpia crypta (GRABAU,1926, p 47, pl 3, figs 7-11) from the Upper Silurian of eastern Yunnan, China, but in the latter, the antero-umbonal sulcus is very faint and the anterior end is more rounded Modiomorpia paradoxa (ZHANG) Pojeta et al 1986, p 72, pl 13, figs 1-7; pl 14, figs 7, 10) from the Lower Devonian of Guangxi, China resembles the new species in posteriorly expanded and a prominent antero-umbonal sulcus, but it has stronger comarginal ornament and a more rounded anterior end Genus Goniophora PHILLIPS, T y p e s p e c i e s - Cypricardia cymbaeformis Murchison 1839, p 602, pl 3, fig 10) 1848 SOWERBY,1839 (in Goniophora dianensis Guo, 1985 Fig 5.1, 3, 13) Goniophora dianensis Guo, 1985b, p 168, pl 3, fig 16 M a t e r i a l - There are 39 specimens represented by internal and external molds, 19 left valves and right valves from the My Duc area and specimen of each valve from the Kien An area All of them are disarticulated and have been more or less crushed secondarily Internal shell features are not preserved D e s c r i p t i o n - Shell medium in size, inequilateral, subtrapezoidal, posteriorly elongated; longer than high nearly two times; umbo salient above hinge margin, lying at about one-fourth shell length from anterior end; anterior end rounded, posterior margin obliquely truncated with an obtuse posterodorsal angle; umbonal ridge strong, angular, extending from umbo to posteroventral extremity; sometimes post-umbonal area provided with a radial ridge near the dorsal margin (Fig 5.3, 13); ventral margin slightly concave caused by the anteroumbonal sulcus Measurements in mm Left internal mold Left internal mold Right internal mold L La La/L H H/L I 34 35 30 8 0.26 0.23 0.20 17 17 17 0.50 0.49 0.57 10 C o m p a r i s o n - The Vietnamese specimens are almost identical in external features with the type specimen of this species, except for the radial ridge in the post-umbonal area which only occurs in some specimens and is not a stable character A c k n o w l e d g e m e n t s a n d R e s p o n s i b i l i t y - Tong-Dzuy Thanh acknowledges the support of the Vietnamese Program on Fundamental Research in the Field of Natural Science and Boucot the National Geographic Society's Research Fund and the National Science Foundation In 1994 Boucot made the My Duc and Kien An Retziella fauna collections under Tong-Dzuy Thanh's guidance, followed by preparation, sorting and preliminary identification in Corvallis Rong Jia-yu then visited Corvallis in 1997 to check the identifications and make revisions based on his knowledge of the similar Qujing, South China RetzieUa fauna Boucot then spent time in Nanjing in 1997 working with Rong Jia-yu on the brachiopod descriptions, at whidh time Fang Zong- 337 jie prepared the bivalve descriptions based on the materials previously prepared and sorted by Boucot Tong-Dzuy Thanh is responsible for the account of the local geology and stratigraphy We all collaborated on the overall paleogeographic and lithofacies relations, as well as on varied aspects of the environments involved Boucot and Rong Jia-yu are responsible for the synecological and biogeographic treatment Boucot is responsible for the gastropod determinations Gonjet and Janvier (Tong-Dzuy Thanh et ah 1997) are responsible for the vertebrate information and determinations This work was also supported by the Major Basic Research Project of MTS, China (G2000077708) to Rong Jia-yu and Fang Zong-jie REFERENCES ALVAREZF., RONGJIA-Yu & BoucoT A.J 1998 - 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Qinling), Tarim Plate (including southern Tienshan, Central Asia), Indochina Plate and Australian Plate in the Late Silurian In addition, there are some possible or doubtful occurrences of the genus... Long Dai Formatbn (Upper Ordovician-Lower Silurian) mu~etoneand darkgrey sandstone Dai Oiang Formation (Silurian} intercalation of mudstone and sandstone with marl lenses and limestone at base -: