Permian brachiopods from the Khao Hin Kling area near Phetchabun, north-central Thailand

47 Pages·1999·4 MB·

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.