Bull.KitakyushuMus.Nat.Hist.,18:105-136,pis.26-32.March31, 1999 Permian Brachiopods from the Khao Hin Kling Area near Phetchabun, North-central Thailand JuichiYanagida1 andNikorn Nakornsri2 'izumi3-60,Kasuga-shi,Fukuoka-ken816-0853,Japan 21004/3SoiUdomsuk56,Sukumvil103Road, Bang Na,Bangkok10260,Thailand (ReceivedDecember10, 1998) Abstract ThispaperdealswithPermianbrachiopodscollectedfrom7localitiesinthe TakFaFormationoftheRatBuriGroup,developedintheKhaoHinKlingarea,about 50 kmsouthwest of Phetchabun. Twentyone specieswithin seventeen genera are describedand discussed. Of them four species,Acosarinakanmerai, Orthotetina ruchae, HaydeneUagrantiand Nolothyrissakagami, are newlyestablished ones. The Khao Hin Klingbrachiopod fauna ranges from the Middle to early Late Permian. The faunal elementscontain closeaffinitiestothoseofthecentralandsouthernTethyanrealms. Keywords Perimian brachiopods,North-centralThailand,TakFaFormation,Central andSouthernTethyanRealms. Introduction In 1963Yanagida fortunately had an opportunitytostudyasmallcollection of Permian brachiopods from north-central Thailand. Itwasprovidedbythe late Dr. Teiichi Kobayashi, ProfessorEmeritus of the University of Tokyo, to whom the materials were submitted bythe Depertment of Mineral Resources of Thailand to knowtheirgeologicage. Thespecimenswereverywellpreservedinblackmudstone often with natural luster of the shell surface. Yanagida (1964) described seven speciesamongsixgeneraandreferredtheageofthebrachiopodfaunatothelower partofthe Yabeina-Lepidolnazoneofthefusulinezonation. Thelocalityofthisfauna iscompletely included in the presentsurveyed area, but unfortunatelythe exact localitiesare not confirmed,owingtoinsufficientfielddata. In 1979 we had an occasion ofvisiting the Khao Hin Kling areawith Dr.S. Sakagami and Mr.A.Hatta, where the brachiopod materialswerecollected. In 1986 Yanagida could have a project team for the biostratigraphic studyof the Paleozoic andMesozoic incentral andnorthern Thailand, financially supported by theOverseasScientificResearchFundofMinistryofEducation,Scienceand Culture oftheJapanesegovernment. Theinterim reportoftheresearch projectwasmade bytheResearch Group (Yanagida (ed.), 1988). Thisstudy covers description ofbrachiopods from the Khao Hin Kling area, 106 JuichiYanagidaand NikornNakornsri about50 km SSWofPhetchabunwith Highway21at about 15km Eofthe surveyed area. Thisisa partofthe results ofstudyofourresearch project. GeologicOutlineoftheKhao Hin KlingArea TheKhao HinKlingareaiscoveredbythe TakFaFormationofthePermianRat Buri Group (Nakornsri, 1976, 1981) or the Saraburi Limestone of the Saraburi Group (Bunopas,1981). Geologicallythisareaholds apartofthe Loei-Phetchabun fold belt which is regarded as a late Paleozoic orogenic belt developed along the western margin ofthe IndochinaBlock(Bunopas, 1981). In the surveyedarea the strata are fossiliferousand theyconsistmainlyofbeddedtomassivelimestonesin the upper part, and alternation of dark limestonesand blackmudstones, and black to brown shale intercalatedwith fine sandstonesin the lower part. The lithofacies in thelowerpartisvariablebothlaterallyandvertically. Thegeneraltrendofthestrata isalso variable. In southern hills ofthe surveyed area, the general trend ofstrata showsNE-SWdirectionwithnorthwestwarddip. In northernarea, to the contrary, itisrepresented bynorthwestwardstrikeand southwestwarddip. BriefNotes on Localities,Accompanied FossilsandAgesofBrachiopods Fossillocalitiesin the KhaoHin Klingarea are shownby23pointson the accom panied map (Fig. 1) withalphabeticalsymbols (A-W). Of them the brachiopods occurat 7localitiesasfollows (Originallocalitynumberisshownin parentheses). LocalityA (860809-01): About7.3kmwestof Highway 21;abundant brachio pods in muddypart of dark impurelimestone; Orthotetina ruchae, n. sp., O. sp., Cleiothyridinasp.,Permophricodothyris?sp.AandPermophricodothyris?sp.Baccompanied byabundantbryozoans,smallerforaminifersandsomegastropods. Ageofbrachio podsreferabletomiddleGuadalupiantoearlyLopingian. Locality H (790807-02): Thickbedded fossiliferous limestonesexposed near junior schoolat northwestern margin ofsurveyed area. Brachiopods completely silicified; Acosarina kanmerai, n. sp., Schuchertella cf. cooperi Grant and Marginifera drasticaGrant. Ageofbrachiopods referabletolateGuadalupian. Locality L (860810-03): Bedded black limestones with thin intercalations of blackmudstonesnear top ofsmall hilllocatedinsoutheastern marginofsurveyed area; Tyloplectacf. nankingensisaccompaniedbybryozoansandfusulines (Nankinella? sp.). Ageofbrachiopods referabletolateMaokouan. Locality N (860810-01): Black limestones inalternation with black mudstones on eastern slope of small hill along up stream of Khlong Khon Kaen river at southeasternmarginofsurveyedarea;Orthotichiasp.A,Orthotichiasp.BandMeekeUa aff. arakeljani (Sokolskaja). Age ofbrachiopods referable tolateGuadalupian to early Lopingian. PermianBrachiopodsfrom theKhaoHinKlingAreanearPhetchabun,North-centralThailand 107 Fig.1. Mapshowingthelocalitiesforthebrachiopodandotherfossilcollectionsandgeneralstrike anddipoftheTakFaFormationintheKhaoHinKlingarea(aftertheResearchGroup,1988). LocalityO (860811-03,05): Calcareousfinesandstonesat footofhill, Khao Nam SapKhwae, about700mwestoflocalityN;Eolyttoniasp.(860811-05) andHaydenella granti, n.sp.(860811-03) accompanied bybryozoans. Age ofbrachiopodspossibly referable to middleGuadalupian (Wordian). Locality R (860813-01): Bedded dark fossiliferous limestones often with nodu lose chertdistributedonhill atabout3km southofKhao HinKling hill; Orthotichia sp.A,HustediaratburiensisWaterhouseandPiyasin,Callispirinaaff. austrinaGrant, Araxathyris cf. araxensis Grunt and Notothyris sakagami, n. sp. accompanied by bryozoans, fusulines (including Schubertella sp.) and coral. Age of brachiopods referable to late Guadalupian to earlyDzhulfian. Locality T (860813-02): Bedded dark fossiliferous limestones distributed at western marginofsurveyed area; Orbicoeliaaff. extima (Grant), Marginifera drastica Grant, Linoproductus sp. and Tyloplecta sp. accompanied by bryozoans and fusulines (schwagerinids and Nankinellasp.). Age ofbrachiopods referable tolate Guadalupian. 108 JuichiYanagidaandNikornNakornsri As far as a small brachiopod fauna formerly described by Yanagida (1964) is concerned, the exact localities were not confirmed. However, it is strongly suggested that the localities may be at slightly northwest ofthe present locality O. The small brachiopod fauna is composed of Tyloplecta yangtzeensis (Chao), T. nankingensis (Frech), Haydenella kiangsiensis (Kayser), Marginifera banphotensis Yanagida, OrthotetinaphetchabunensisYanagida, OrthotichiajavanaphetiYanagidaand Linoproductussp.Theage ofthe fauna wasreferred to the earlyDzhulfian. Table 1. Distribution ofthe brachiopodfossilsinthe KhaoHinKlingarea. Localities Species A H L N o R T Acosarinakanmerai,n.sp. o Orthotichiasp.A. o o Orthotichiasp. B. o Schuchertellacf.cooperiGrant o MeekeUaaff.araheljani(Sokoi^kaja) o Orthotelinaruchae,n.sp. o Orthotetinasp. o HustediaratburiensiWaterhouseandPiyasin. o Callispirinaaff.austrinaGrant. o Cleiothyridinasp. o Araxathyriscf.araxensisGrunt o Permophricodothyris}sp.A o Permophricodothyris?sp.B o Orbicoeliaaff. extima(Grant) o Haydenellagranti,n.sp. o MarginiferadrasticaGrant o o Eolyttoniasp. o Linoproductussp. o Tyloplectacf.nankingensis(Frech) o Tyloplectasp. o Notothyrissakagami,n.sp. o Charactersofthe KhaoHin KlingBrachiopodFauna Affinitieswithin Thailand: TheKhao HinKling Permian brachiopods have large similarities to those at the seven localities in the Rat Buri Limestone ofsouthern Thailand. Theyweredescribedanddiscussed byWaterhouseandPiyasin (1970) andYanagida (1970)from KhaoPhrik,westofRatBuri,and byGrant (1976)from the sixlocalities, from Ban Kao,about 30km westof Kanchanaburi, down south to the KoMuk Island on the AndamanSeaalongsouthern peninsula. Orthotichiasp.AisveryclosetoO. waterhouseiGrantfromKhaoChang,about15 kmsouthofRatBuri. Grantnoticedthat0. waterhouseicloselyresembles Orthotichia corallina (Waagen) from the Kalabagh Memberof theWargal Limestone, the Salt PermianBrachiopodsfromtheKhaoHinKlingAreanearPhetchabun, Noruvcentra!Thailand 109 Range. Schuchertellacf. cooperiiscomparable to S.cooperiGrant. Thisspecieswas originallydescribedfrom KoMuk. MeekeUaaff. arakeljanialso resembles M.addicta Grantfrom KoMuk. Hustediaratburiensis,originallydescribedfrom Khao Phrikby Waterhouse and Piyasin, is also common from Ko Muk and Khao Tok Nam near Khao Phrik (Grant,1976). Grant noticed that Hustedia ratburiensis strongly resembles Hustedia sulcataReed and some specimens ofHustedia indica(Waagen) from the Amb Formation of the Salt Range. Callispirina aff. austrinais closely comparablewith C.austrinaGrantfrom KoMukandPhangnga. Permophricodothyis} sp.AissimilartoAnomaloriaglomerosaGrantfrom KoMuk. Permophricodothyris}sp. B resembles P. notialasiatica Grant from Phangnga. Grant noticed similarity between thelatterspeciesandP.lineata(Martin) byWaagenfrom theAmb Forma tion, the Salt Range. Marginifera drastica Grant is well known from Phangnga. Eolyttoniasp. isrelated to E.?sp. from KoMuk. It was well examined and noticed by Waterhouse and Piyasin (1970) and Grant (1976) that the Permian brachiopod faunas from several localities in southernThailandembrace manyspecificelementswhicharecloselyrelated tothose of the Permian of the SaltRange, WestPakistan. Grant (1976) referred the age of the faunasfrom southern Thailand to the Artinskianbased on the opinion that theyare closely comparable with those of the AmbFormation of the SaltRange. Yanagida (1970) also considered the age of the Khao Phrik brachiopods to the Artinskian. Waterhouse and Piyasin (1970) showed a different consideration on the age ofthe KhaoPhrikbrachiopods, referring to the Kazanian. Accordingto the recent knowledge on biostratigraphyofthe ZaluchGroup of West Pakistan, it became apparent that the conodonts from the Amb Formation clearlyindicate a Wordian (middle Guadalupian,Kazanian) age (Wardlow and Pogue, 1995). Takingthe faunal characterofthe conodontsfrom theAmb Forma tionintoconsideration,theageofbrachiopodsfromsouthern Thailand ispossibly referable to the middle Guadalupian. Waterhouse (1983)describedalatePermian lyttoniidfaunafrom theHuaiTak Formation, northwest Thailand. Of the brachiopods following four speciesare common in generato the Khao Hin Klingfauna: AcosarinaantesulcataWaterhouse, MeekeUakueichowensisHuang, Orthotetinasp.,Araxathyriscf.bisulcataLiao. Acosarina antesulcataisdistinctfromA.kanmeraiinhavinganelongateformandanteriorsulcus in bothvalves. MeekeUa kueichowensis istoopoorly preserved tocompare with the Khao HinKlingspecies. Orthotetinasp. ismuchsmallerthanO. ruchaeand O.sp.of the Khao Hin Klingfauna. Araxathyris cf. bisulcata is easilydistinguishable from A.araxensisby thesize, outlineand anteriorcommissure. Affinities outside Thailand: The Khao Hin Kling fauna containsin itsspecific elements somestronglyrelated speciesto thoseofthe south China fauna. The occurrence of3speciesof Tyloplectashowsa closefaunal relation between the central Thailand and southChinese province. In the Khao Hin Kling area 110 JuichiYanagidaand Nikorn Nakornsri Tyloplectayangtzeensisand T.nankingensisarealready known (Yanagida, 1964), and this time Tyloplectacf. nankingensisand T.sp. areconfirmedagain from the localities (respectivelyfrom LandT) veryclose to the formerlocalities. Tyloplectasp. isfrag mentarybutwellshowsan elongatedsubquadrateoutlineandstronglycostateventer with nodes on costae. It isindicated that a close relation is recognizable between T.sp.and T.costiferinoidesfrom the Maokouan ofGuizhou (Fong, 1978). According toYang andothers (1997), Tyloplectanankingensisisoneofthe representativespecies oftheupperMaokouanand T.yangtzeensisisoneofthemostimportantspeciesofthe Upper Permian Wuchiapingian. Liang (1990) described T.yangtzeensis from the upper Maokouan Lengwu Formation in the Zhejiang province. Summarizing the occurrencesofTyloplectainthe KhaoHin Klingarea,the ageof3specieswillprobably be referable to the late Maokouan. Haydenellagrantihasresemblancetothecostategroupof//,kiangsiensis(Kayser), the typespeciesofthisgenus, from the "Lyttonia"bed ofthe Lopingian,southChina. Exact age of H.grantiisnot confirmed at present. Orthotetina ruchaeis related to O. emaciatusChing andYefrom the UpperPermianofthe Chinhai province, north westChina. Orthotetinasp.issimilarto O. mutabilisLiangfrom the upperMaokouan Lengwu Formation, Zhejiang province, southeast China. Araxathyris araxensis Gruntiswellknown from the lower UpperPermian LontanFormationofGuizhou, south China (Liao, 1980) and the Upper Permian of northwest Chinhai province (Chingetat, 1979). Itisalso known from theupperMaokouanLengwuFormation ofthe Zhejiangprovince (Liang, 1990). Cleiothyridina sp. is similar to CL? saraiensis Reed from the Middle Productus Limestone(WargalFormation)oftheSaltRange(Reed,1944). Orbicoeliaaff.extima iscloselyrelated to O. extimaGrantfrom the Upper Permian Chhidru Formation, West Pakistan. Notothyris sakagami iscloselyrelated to N.praelecta Reed from the MiddletoUpper PermianoftheSaltRangeandN.ghundiensisREEDfromtheMiddle PermianofWestPakistan (Reed, 1944). Orthotichia sp. B well resembles O. avushensis from the Middle Permian Gnishikian ofArmenia (Sokolskaja,1965). MeekeUaaff.arakeljaniiscloselyrelated toM. arakeljani(Sokolskaja) fromtheupperMiddlePermianHuchikian,Armenia. Araxathyriscf.araxensisiscloselycomparablewithA.araxensisGruntfromtheUpper Permian Dzhulfian (Araxilevis zone) of the Caucasus. It is also known from the UpperPermian NesenFormation ofnorth Iran (Sestini, 1966). SystematicDescription SuperfamilyEnteletaceaWaagen, 1884 FamilySchizophoriidaeSchuchertand LeVene, 1929 GenusAcosarinaCooperandGrant, 1969 PermianBrachiopodsfromtheKhaoHinKlingAreanearPhetchabun, North-centralThailand 111 Type-species: AcosarinadorsisulcataCooperandGrant, 1969 Acosarinakanmerai^ n. sp. PI.26,Figs.1-7 Material and Locality: Lots of complete and incomplete specimens are at hand. The holotype, KMNHIvP610,001 (PI.26, Fig.6), showsa slighdy younger stage ofgrowth. Internalstructuresare wellshown bysomedisarticulated orpartly brokenarticulatedvalves(Locality H). Description: Average size for genus, subcircular to subquadrate in oudine, slighly wider than long with largest width at midlength; hinge much shorter than largest width; lateral profile slighdy dorsi-biconvex. Anterior commissure slightly sulcate. Surface multicostellate, about 4 to 5 costellae in distance of 1 mm on anteriorhalf. Pedicle valveless convex than brachial one with largest convexity at slightly posterior to midvalve; median anterior half nearly flat. Umbonal region slightly swollen with projected beak. Interarea slightlyconcave with apsacline to nearly catacline profile to commissuralplane. Hinge line about a half length of largest width ofvalve. Delthyriumopen andconspicuous. Brachialvalvestronglyand evenlyconvexinlateralprofilewithlargestconvexity atmidvalve;anteriorprofiledomedwithmedianpartflattenedorslightiyand broadly sulcated; flanks swollen and rather steep-sided; sulcus broad, shallow but distinct; notothyriumsmall andopen. Pediclevalve interior withshort, flaringdental plates;median septum lowbut long,extendinganteriorlyforabout midlength ofvalve. Brachialvalveinteriorwith shortdivergent brachiophores,smallsocketsand brachiophoresupports. Cardinal processsmall. Dimensionsof7specimensasfollows(in mm): length length lengthof width thickness (ped.v.) (br.v.) hingeline KMNH IvP 610,001 11.1 11.1 13.1 7.0 7.2 (holotype) 610,002 13.2 13.1 16.0 8.0 610,003 11.6 12.0 13.9 7.6 7.5 610,004 9.5 9.7 11.5 5.8 6.2 610,005 9.1 9.2 11.1 5.2 5.8 610,006 ca. 12 ca. 12 14.0 7.0 8.0 610,007 14.6 5.9 8.5 112 JuichiYanagidaand Nikorn Nakornsri Remarks: Acosarinakanmerai,n.sp. ischaracterizedbysubcircularto transversely subelliptical outline and by having a distinct and shallow sulcus in the brachial valve. Thereforetheanteriorcommissurerevealsaslightlysulcateform. Fromthe viewpointofthe latter character this species issimilar to Acosarina dorsisulcatafrom the Lower Permian Bone Spring Limestone.western Texas (Cooper and Grant, 1969). However, itdiffers from the latterbyitswider outline,lessinflatedvalvesand stonglyinclined interareaofthe pediclevalve. In Thailand Waterhouse (1983) described Acosarina antesulcata from a mud- stone ofthe Huai TakFormation in the Doi Pha Phlungarea, northwestThailand. The figured specimen of the holotype shows elongate oval outline and other Figuredspecimensare moreorlessdeformedand almost allofthemare the internal moulds. Waterhouse paid attention to the presence of a ventral sulcus in A. antesulcata. Therefore, it is clearly distinguished from the present species. OrthotichiawaterhouseiGrantfrom the MiddlePermianoftheRatBuri Limestone in KhaoChangand KhaoTok Nam,the southernpeninsulararea ofThailand (Grant, 1976), issimilarto Acosarinakanmeraiin itsgeneral characters. The most conspicu ous difference between them, however, is the existence ofa dorsal sulcus in the latter. The Salt Range species, Orthis indica Waagen, is often treated as Acosarina. Grant (1976), however,emphasizedthe importanceofthe ventralsulcus in the Salt Rangespecies, Orthisindica. HeexamineditbythetopotypematerialsfromtheAmb Formation. However, Waagen (1883) clearly described existence of the dorsal sulcusand hisfiguredspecimenswell reveal the character. Therefore the generic position of O. indicaisreferable toAcosarinawithout doubt. Liang (1990) described a speciesunder the name ofA.indica (Waagen) from the upper Middle Permian Lengwu Formation in the Zhejiang province, south China. Although the Zhejiang specimen isrepresented byan internal mould of conjoinedshell,itshowsashallowandbroaddorsalsulcusand thegeneralcharacters are similarto A.kanmerai. The Zhejiangspecies,however, maybe distinguishable fromA.kanmeraibyitsmoreinflatedandlargershell. Yanagida (1964) describeda newspecisofOrthotichia, O.javanapheti(=nowitisreferredtoAcosarina) fromablack mudstone in the surveyedarea. Thatspecieshasan elongate ovaloutline, inflated valves,andabroadshallow sulcus in the dorsalvalve. Thesecharacterseasilydistin guishA.javanaphetifrom A.kanmerai. The newspeciesisnamedafterDr.Kametoshi Kanmera, ProfessorEmeritusof Kyushu University, whogreatlycontributedtoestablish thefusuline biostratigraphy ofthe RatBuri Limestonewith the late Dr.Toriyama. Genus OrthotichiaHalland Clarke, 1892 Type-species: Orthis? morganianaDerby, 1874 PermianBrachiopodsfrom theKhaoHinKlingAreanearPhetchabun,NoruVcentralThailand 113 Orthotichiasp.A PI.26,figs.8and9 MaterialandLocality: Three conjoinedandsilicifiedshells,KMNH IvP610,011, 610,012, 610,013areat hand (Locality Nand R). Descriptive remarks: Shell medium for genus, slightly wider than long with subrounded outline; hinge much shorter than width, largest width at midvalve. Pediclevalveslightiyconvex,flattened or broadlydepressedon mediananteriorhalf and narrowly swollen posteriory; beak weakly projected on slightly concave low interareawithapsacline profile tocommissural plane; delthyriumopen;valvesurface ornamented byfine costellae, increasingin numberbyintercalation,about4to5in distanceof1mm nearanteriormargin; anteriorcommissurerectimarginatewithvery slight arch. Brachial valve smoothly and slighdymore convex than opposite valve longitudinally, beak region broken, neithersulcusnor depression distinguished on median surface; surface ornamentationassameaspediclevalve. Pedicle valve interior with partly observed median ridge and dental plates. Brachialvalveinteriorwith partlypreservedbrachiophoresupportingplates,extend ingat abouta third length from beak. Dimension of better preserved specimen, KMNH IvP 610,011, as follows (in mm):length (ped.v.), ca 14;length (br. v.),ca 14;width, 10;thickness,8.8;lengthof hinge line, 5.9. The Khao Hin Kling specimens with conjoined valves are characterized by having slighdy less convex pedicle valveswith nearly flattened anterior half, nearly rectimarginate or slightly arched anterior commissure without any suggestion of dorsaldepression. In thesecharacters the presentspeciesseems to be veryclose to Orthotichiawaterhouseidescrived byGrant (1976) from the MiddlePermian ofKhao Chang, southern Thailand. The Khao Hin Kling species, however, may be distinct from O.waterhouseiin havingthe more transverse outline. Orthotichiasp. B PL26,fig.10 MaterialandLocality: Apartlybrokenconjoinedspecimen,KMNH IvP610,014, isavailablewith the following dimension (in mm): length (br.v.), 17.5;width, ca 18; thickness, ca 12 (LocalityN). Descriptiveremarks: Shell large forgenus,roundedsubtriangulartosubpentagonal in oudine with widest part at slightly anterior to midvalve; both valvesmoderately convex, brachialvalveslightlylargerthanpediclevalveinconvexity. Surfaceofboth valvesornamentedbycostellae, about5costellaein 1mmon anteriorhalf,increasing in numberanteriorlybyintercalation,largeronesdisposedin intervalofabout1mm. Anteriorcommissure rectimarginate. 114 JuichiYanagidaandNikorn Nakornsri Conspicuouscharacters of the present speciesare in itssubtriangular outline, moderatelyconvexbrachialvalveandrectimarginatecommissure. Thesecharacters ofthe Khao Hin Klingspecieswellresemble those of Orthotichiaavushensisdescribed by Sokolskaja (in Ruzhentsev and Sarycheva, 1965) from the Middle Permian Gnishikianin Armenia. However, the Thailand speciesisslightlylarger than the latter. SuperfamilyOrthotetaceaWaagen, 1884 Family SchuchertellidaeWilliams, 1953 SubfamilySchuchertellinaeWilliams, 1953 GenusSchuchertellaGirty, 1904 Type-species: StreptorhynchuslensWhite, 1862 Schuchertellacf.cooperiGrant, 1976 PI.27,figs.1-8 cf. 1976. SchuchertellacooperiGrant, p.42,pi.4,figs.1-41, pi.6,figs.1-12. Material and Locality: Most of the available specimens are fragmentary and silicified ones rangingfrom youngertoadultstages ofgrowth. (Locality H). Description: Shell average size for genus; outline transversely subquadrate; hinge line slightly shorter than largest width which normally locates at midvalve, hinge marginsometimesextendsslightly. Pedicle valve very shallowly conical posteriorly on anterior half, however, it rapidly becomes flattened; interarea low with profile ofapsacline to commissural plane; pseudodeltidium slightly arched; pedicle valvesurface covered by costellae, increasingin numbergenerallybyintercalation,veryrarelybybifurcation,about9to 11costellae in 5 mm on anterior half; growthwrinkles rather common arranged in irregulardistancesandfine growth linessometimesvisible. Pediclevalveinteriorwith stoutteethsupportedbylowdentalridgesalonginner marginsofpseudodeltidium;medianridgeisverylowandshort,onlyrecognizablein beakregion; muscleareaobscure,valvefloor ornamentedbyradialstriation, reflect ingexternalcostellae,generallystressednearanteriormargin. Brachial valve interior with low and wide cardinal process, myophores low; musclearea narrowandobscurelymarked;socketsratherdeepwith recurvedsocket plates, cruralplatesshortandslightlyprojectanterolaterally;ornamentationon valve floorassameasopposivevalve.