BulletinofGunmaMuseumofNaturalHistory (4): 1-22, 2000 1

OriginalArticleゴーーーヱーゴ=延互ベゴーゴーノー／ベノーゾ，ゴヘゴーーーヱーゴ=延互ベゴーゴーノー／ベノーゾ，ゴヘ

MiddleMiocenedeep-watermolluscsoftheHaratajino

Formationinthelsobedistrict, theAnnaka-Tomiokaarea,

GunmaPrefecture,centralJapan

YukitoKuRHIARA

Doc"て〃Pj･ogm"z"1G"s""z", "zE[ん"”蔀〃Q/Tszｨ片zめα, T3szｲﾙzめα，必α""1 315-85"

Abstract

TheHaratajinoFormation in the lsobedistrict of theAnnaka-Tomiokaarea, Gunma

Prefecture iscomposedmainlyofweakly-beddedsandysiltstone, andyields24molluscan

taxa, including3gastropods, 3scaphopods, 17bivalves, and l cephalopod. The fauna

contains two types of assemblages (protobranch-dominant andAcﾉzα""dominant) and is

inferredtorepresentadeep-watelF (bathyal) faunaonthebasisof its taxonomicstl-ucture.

Similarities ingenericcompositionbetweenthebenthicmolluscanfaunaof theHaratajino

Formationandthatof thebathyal zone inmodernSagamiBaysUggest that themarine

conditionduringtheHaratajinodepositionwassimilar tothatofthe intermediatewaterof

Sagami Bay. Commonoccurrenceofwarmwaterplanktonicgastropods andcephalopod

fromthe formation indicates that the suIfacewaterwasunder the innuence ofwarm

current．

Keywords:deep-watermolluscan fauna,Miocene, HaratajinoFormation, Isobe district,

inte'Tnediatewater, giantA(莇/””x，

HaratajinoFormationwas bylshiwada (1948),who

listedsixspeciesbutneitherdescribednor illustrat-

ed. Subsequent studyon themolluscs fromthe

HaratajinoFormation is representedonlybyKanie

"".(1999),whodescribedandillustratedagiant

species of the solemyid bivalveAc〃αmx fromthe

Isobe district. Therefore, this paper is the first

detailedaccount of themolluscsof theHaratajino

Formation.

Introduction

Chienymarinesedimentaryrocks ofMioceneage

arewidelydistributedintheAnnaka-Tomiokaarea、

situatedat thenorthernmarginof theKantoMoun-

tains (Figurel-A) . Thelsobedistrict is locatedat

thecentralpart of theAnnaka-Tomiokaarea (Fig-

urel-B),wheretheMioceneTOmiokaGroupcrops

out along theUsui-gawaRiVer. TheHaratajino

Formationis the lowermost stratigraphicunit inthe

district and constitutes themiddle part of the

TomiokaGroup. Inthispaper,molluscanfossilsof

theHaratajinoFormatiOn inthe lsobedistrict are

de､ribedand illustrated. The firstpublishedmen-

tionofmolluscs frombeds here assigned to the

Geologicsettingandage

Stratigraphic studies ofMiocene strata in the

Isobedistrict arerelativelyfewincomparisonwith

those intheotherdistrictsof theAnnaka-Tomioka

Receivedl3January2000;Acceptedl5February2000

YukitoKuRIHARAワ白

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Figure l . Indexmapof theAnnaka-Tomiokaarea (A) andsimplifiedgeologicmapoftheAnnaka-Tomiokaarea,modifiedafterNakano鉦α/.(1998) (B) .

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MiddleMiocenedeep-watermolluscsoftheHaratajinoFormationinthels()bedistrict ３

Oishi&Takahashi

（1990）ThispaperKanehara(1938) |shiwada(1948)

ｊｄｅ

Ｅ‐ｂ

Ｓ

ａ

ｄ

ｎ

ｅ

ａ

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AnnakaBeds ltahanaFm ltahanaFm

HaraichiFmBedsD HaraichiMs.Beds HaraichiFm

UpperUpperNiwayaFmBedsC ShomyojiSs.BedsNiwayaFm

LowerIsobeAlt.BedsBedsB

normapped

TsukaharaMs.BedsBedsA HaratajinoFm

Figure3. StratigraphicrelationoftheMiocenestrataof thelsobedistrict.MsMudstone; Ss., Sandstone;Alt.,Alternation; Fm.,Formati()11.

area. The geol()gicmap and the comparison of

stratigraphicdivisionsof theMiocene strata in the

Isobedistrict are shown inFigures 2Aand 3,

resDectivelv.

The first detailedgeologicmapof the lsobedis-

trictwaspublishedbyKanehara (1938), whodivid-

edtheMiocene intofiveunits; BedsAtoE. Sub-

sequently, Ishiwada (1948) studiedthesamedistrict

andcame toanearlvsameconclusionwiththat of

Kanehara (1938). Ishiwada (1948) namedfiveunits,

inascendingorder, theTsukaharaMudstone, Isobe

Alternation, Shomyoji Sandstone， HaraichiMud-

stone, andAnnakaBed． Themolluscs treated in

this paper are from the TsukaharaMudstone.

Recently,Oishi andTakahashi (1990) revised the

stratigraphicdivisionof thewholeTomiokaGroup

onthebasisof theirdetailedfieldsurvevmainlvin

theTomioka district. According t() them, the

group is divided into seven units, in ascending

order, theUshibuse, Obata, Idozawa, Haratajino,

Niwaya,Haraichi, and ltahanaFormations. Al-

thoughOishi andTakahashi (1990) didnot show

thegeologicmapof theareawhere theTsukahara

Mudstonecropsout, theTsukaharaseems tocorre-

sDond to theHarataiinoFormationon thebasis ofO ,更』 、

its lithology and stratigraphic succession (written

com. fromM・ Takahashi). In this paper, Iuse

thenameof theHaratajinoFormation insteadofthe

TsukaharaMudstone, followingOishi andTaka-

hashi'sdivision.

TheHaratajino Formation (proposed byMat-

sumaru, 1967; redefinedbyOishi andTakahashi,

1990) inthelsobedistrictcropsoutalongtheUsui-I■

d l

gawaRiver and consistsmainlyofweakly-bedded

sandv siltstonewithminor siltstone and thin tuff

beds・Dip isgenerallyabout lO｡, andstrike iscon-

siderablyvariable. Bioturbati()n is commonlyrecog-

nized.Aspointedout byKaniee/ αﾉ. (1999), tube

shapedc()ncretionsarecommol]lyfound.

Thegeologic ageof theHaratajinoFormation is

assigned to earlyMiddleMiocene (upper part of

planktonic foraminiferal zoneN. 8 ofBIow), be-

cause theunderlying formations yield foraminiferal

assemblagesassignedtoN.8, andbecausetheO7伽"‐

'"datum(N.8/N.9boundary) is recognizedinthe

overlyingNiwayaFormation (Oishi andTakahashi,

1990) ． Inthisstudy, several sampleswereexamined

fortheagedeterminationbymeansofdiatomfossils,

but itunfortunatelvfailed invain.

Fossi l local itiesandpreservation, and

associatedfauna

Molluscan fossils collected from four localities

(Figure2B)werestudiedinthispaper. Inaddition,

H.NakajimaCollectionstored illGunmaMuseumof

Natural History (with the abbreviationHN)was

alsoexamined. LocalitydataofNakajimaCollection

usedareasfollows;HNO1, collectionfromthesame

localitvwithTomO2;HNO2, collectionfromseveral

localities of theHarataiinoFormation in the lsobe

district.

Preservationofmolluscanshells intheHaratajino

Formation isgenerallypoor. Theyareusuallymore

ol- less deformed, and their shellmaterial is dis-

solvedorexfoliated.Anexceptionis thegastropod

O/'2ciOS"", which isalwaysreplacedbyamosaicof

secondarycalcitecrystals.

Besidesmolluscs,variousmarineinvertebrateand

vertebrate fossilsoccur fromtheHaratajinoForma-

tion・ Themost conspicuous fossils arean irregular

echinoid (a7ssoPs/S sp.),whichis sporadicallybut

YukitoKuRIIlARA4

commonlyfound throughout the formation. ノ吻灯y"-

"Z"Sp. , which isrecentlyconsideredtobeanagglu-

tinatedforaminifer (HaseandKondo, 1999),occurs

densely at some places.Other representatives in-

cludebenthicandplanktonicforaminifers, adecapod

(乃(z(PIzy"ﾉ℃"l"s sp.), a crinoid (ISsE"cγ加況s sp.) ,

squalidsharks, turtles andmarinemammals.These

arenotyet formallyreportedexcept for theprelimi-

narvresultof thesharkteeth (Takakuwa, 1999) .

autochthonousorparautochthonous.Thecharacteris-

ticsofmodeofoccurrenceandtaxonomiccomDosi-

tionofeachassemblagearedescribedbelow.

Typel: protobranch-dominantassemblage

This assemblage is characterizedby thepredomi-

nanceofprotobranchbivalvesand is foundatLocs.

TomOl andToml9. The shells are sporadically

distributed in a weaklybedded and bioturbated

sandvsiltstone.Most of bivalves aredisarticulated

except forACﾉz""" andPe"〃O脚α species.Commis-

sure planes ofmost bivalves are parallel to the

bedding.

At Loc. TomO1, the protobranch PO汀/〃城α

(ﾊ化gzzyo/(力") /hγα""il)/w"S isdominant andaccounts

forabout 50%of thespecimens.AtLoc.Tom19,

ontheotherhand, P． 〃zγα"""""Sdoesnot occur

Mol luscanassemblages

Twentv-fourm()lluscan taxawere discriminated

fromtheHaratajinoFormation, and twotypes of

assemblages are recognized (Table l) . The shells

generallydon()t showsignsofpostmortemwear,

breakageorbiologicalmodification. Theseevidences

suggest that themolluscanassemblage isessentially

Tablel.Listof them()lluscanfossilsof theHaratajinoFormationinthelsobedistrict (R=1-2,F=

3-4, C=5-9, A=10 19, innumberofspecimens) .

IocalitiesTomO1Toml9TomO2Tom23HNO1 HNO2

GASTROPODA

Orectosp"ashﾉmokawara/Urata

Veg/"e"a？sp、

Diacro//"/aau"ia(Bel lardi)

SCAPHOPODA

F1Ss/denia"umcf."unomeae(Takeda)

F7Ssﾉde"ra""mcfwa埴"abe/(Kanno)

Gad"a？sp・

BIVALVIA

Acharaxgりas(Kanno)

AC/7aﾉaxaff.rokunaga/(Yokoyama)

Ac"asp.

E""Uc"/asp.

Ⅳe"One/値/Sens/SShibata

Ⅳe"one/bisukbawaensjsKurihara

Ma//e垢me"刀/s(Yokoyama)

MJcu/ana(Cﾉasso/e")pennu/a(Yokoyama)

Tenu"e"cf. /kebe/(SuzukiandKanehara)

Po"ね"d旧(Megayo/dia)的個c旧eわ"刀心(Storer)

ROpea"7uss/u"7iafe/wa/Kanehara

Ropeamuss/"m/Uga叩e"sEYamana

L"C"70maSp.

Ax"7u/us？sp･

Ca"pioge"a？sp・

Pe"/omam/isUganoenseAraki

Myoneﾉaosawa"oens/s(Tsuda)

CEPHALOPODA

R 目

~C

Ｒ

ＲR

Ｒ

Ｒ

Ｒ

R

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C

~A

Ｆ

Ｒ

Ｒ

Ｆ

Ｒ

Ｆ

Ｒ

Ｒ

Ａ

Ｒ

3

~~~

Ｒ

Ｒ

Ｒ

~ ~

~

~~~

R

~F ~R ~

Ｒ

Ｒ

~ ~

F

~R ~~~

R

~曰

AmO"aLﾉia？sp R~

MiddleMiocenedeepwatermolluscsoftheHaratajinoFormati()11 inthelsobedistriclＰへ』

andnoremarkabledominant species isrecognized community type,WUﾉ“"画L"〃710"I"-SO/27""Commu-

nitiesofHickman (1984) , thoLIgh thepredominance

ofagiantAc向αﾉ"x lsunlque･ InNeogeneofU.S.A.

andJapan, thereareafewrecordsofAc加噸x-domi-

nant fossil assemblages (Campbell, 1992; Research

Group forgiantClamCommunities of theHayama

Group, 1995), both of which are interpreted as

chemosynthetic communities related to methane

seepage. Although living solemyid bivalves are

known t() have sulfide-oxidizing symbiotic bacteria

intheirgillsandt() inhabitar()undcoI(I seepageand

in various reducing environments (2.9, Metivier

andCosel, 1993), it isuncertainwhethel- thegiant

Ac/Z""x fromtheHaratai inoF()rmationwas related

tomethane seepage. Inorder toclarify thepaleo-

ecologyof thegiantA(Ph〃･"x, geochemical analyses

areneeded.

Climatically, theHaratajino fauna is inferred to

have lived inrelativelycoolwater. This interpreta-

tion is basedon itsgeneric compositioncharacter-

izedbvamixtureof the southern, northern, and

Typell: Achaﾉaxgﾉgasassemblage

This assemblage is characterizedby thepredomi-

nance of thegiant solemyid bivalveAC"γα兀部gns

andisfoundatLoc.Tom02.Pﾉ℃”α"剛ss"〃z /α花加几zj

and P"ip/0脚α "2"s"9m""zs2 are associated. The

shells occur sDoradicallv frommassive sandv silt-

stoneofverynarrowstratigraphic interval (belowl

min thickness).Large specimens ofAC血αγ“are

mostlv contained in concretions. The concretions

arepresumablysil iceous, becausetheydonot react

tohydrochloricacid intensively. Theshellmaterial

ofAc""".x isdissoIved()rexfol iated, althoughperios-

tracumispartlypreservedinsome specimens.The

majorityof specimens ofAcImmx are articulated,

andnarrowlyorwidelyopenvalves are common

thanclosedones. Althoughasmall livingsolemyid

species is said to inhabitwithinY-shapedburrow

(Stanley, 1970),noburrow-likestructuresobserved

intheassemblagebearinghorizon. LatitudeN. 30 32 34 36 38 40 42

： ｜鞘 ｜: ：

幽 ’

Myone/・a

PropeamussﾉU〃）

Ⅳe〃one〃a

ぐぐぐ

０

０

０

S

PaleoenvironmentSJ OreCrOSpﾉra ー： ’

AcharaX

Megayo/ぴﾉa

７

２

５

７

一歩

bPb

燭Themolluscanfaunaof theHaratajinoFormation

inthelsobedistrict is inferredtohave lived indeep

water (bathyal zone; greaterthan200mindepths)

on the basisofits taxonomic structure.The taxo-

nomic structureof theHaratajinobivalve fauna is

characterized by the remarkable predominance of

protobranchs (about 60%),whichis indicativeof

deepwatel- (Hickman, 1984) . This interpretation is

concordantwiththat fromthecompilationsofmod-

ernbathymetricrangesof theconstituentgeneraof

theHaratajinofauna.Amongtheconstituentgenera,

”"""e",My(77f"", C"JJﾉ〃OgP1”？ andA獅加zz"zs？ are

restrictedtothebathyal orbathyal toabyssal zones

(T""/2", 700-1,030mdeep;Myo"9m, 400900m

deep;Qz/y"0雛"α, 500-5,700mdeep; A.x加況/"s, 700

mdeep), andtheothergenel-ahavearangetaking

inthesublittoral tobathyal zones (HigoandGoto,

1qQql一一′､ノレノ ・

Judgingfromtheviewpoint ofassemblagetypes,

Type-I isreferabletotheProtobranchCommunities,

oneof thedeep-watermolluscancommunity types

recognizedbyHickman (1984) .Ontheotherhand,

Type-II is comparablewith another deep-water

N

LatofSagamiBay｣LLatofthestudyarea

Figure4. Latitudinal rangeof theselectedgeneraand

subgenera of theHaratajin() fauna in themodernnorthweStemPacilic. S, southel-n

element; SJ, soL'thernJap()nicelements; N,''orthemelemellts. Distributi()n data are

based ()I]Kur()(laandHabe (1952),Okutani

(1968) , andHig() alldGot() (1993) .

southernJaponicelements in thesenseofKurihara

(1999) (Figure4) . InthePacificcoastofJapan, co

occurrenceof theseelements foLInd in theHarataji-

nofauna isn()wrestrictedtodeepwaterofSagami

Bay (see Figure l-A).According toOkutani' s

(1968) study of deep-watermolluscan fauna in

SagamiBay, theco-occurrence ()f thethree types is

typicallyrecognizedat thedepthsof400to lOOOm,

where thevwould be bathed in the intermediate

waterof6to8℃, andwhereall of theconstituent

benthicgeneraof theHaratajinofaunaoccul-. Such

similarities in thegenericcompositionbetweenthe

benthicmolluscanfauna ()ftheHaratajinoFormation

and of the bathyal zone inmodern Sagami Bay

suggests that the marine condition duril]g the

Haratajino depositionwas similar to that of the

YukitoKuRIIIARA６

intermediatewaterofSagamiBay・ Onthecontrarv､

commonoccurrenceof suchwarmwater planktonic

generaasZ)/"C/'()"〃α, 1/"~"･7惚"α?and :47'gひ"α"/α？from

theHaratajinoFormation indicates that the surface

waterwasundel‐ the influenceofwarmcurrent.

Rcw2"As.-All the specimens areincomplete and

replacedbysecondarycalcite crystals. The largest

specimen (GMNH-PI2008; p1 ． 1, figs. la, b) is 19.6

+mmhighand 14.0mmwide andwell exhibits

shell outline and surface sculpture" The present

specimensagreewellwiththeholotypeofOﾉ唖加s〃m

Sh""0"""mノUratafromtheEocenePoronaiForma-

tion、 Hokkaido, though the shell size is rather

small (about2/3) .

ThissDecies isvervsimilartoO)'cC/0S〃γα/""/t)""s

(Watson), aPliocene toRecent species of south-

central Japan, but the tubercles aredistinct on the

laterwhorls.0"cIOs""sp.illustratedbyKurihara

(1999) fromtheArakawaFormation, SaitamaPrefec-

tureisconspecificwiththisspecies.

Occ〃γ2"C2. Locs.Tom01,Tom21andHNO2.

Z)is/"6〃"0〃.

Eocene: PoronaiFm.,Hokkaido.

Lowel-MiddleMiocene: ArakawaFm., Saitama

Pref.

SystematicPaleontology

Taxonomic remarks andsynonymies aregiven in

this section for representative taxa. If svnonvmies

are too volummous, the original description plus

subsequent descriptions that dealwith the species

most extensively are cited.All the specimens de-

scribed in thispaperarestored inGunmaMuseum

ofNaturalHistorv・ withtheabbreviationGMNH.

ClassGastropoda

OrderMesogastropoda

FamilyOrectospiridae

GenusOrectosP/raDall, 1925

Orecfosp/ras/7/mokawaﾉ.aノUrata, 196] OrderThecosomata

FamilyCavoliniidae

GenusD/acro/in/aJanssell,

D/acro//n/aa""ra(Bellardi、

Plate l， figures la-2b 1995

1873）

O姥〃0s"ms〃"zOh"(wWU1-ata, 1961,p. 13,pl. 4,

figs. 2a, b.

Oﾉで(､rOS”'αsp. Kurihara, 1999, figs.6-5-6b.

Plate4, figure26

Hy"/"""""aBellardi , 1873, p. 26, p1 . 3, fig. 6

［β血Janssen, 1995].

Cα”"7”ノ･”"α"sNomuraandZinb6, 1935,p.19,pl.

15, figs、 25, 26.

C"0/"""cf.m7,"α"S (NomuraandZinbo)[SiC]. Shi-

bata, 1970, p1. 4, figs. 14, 15; Shibata /"

Itoigawa鉦α/. , 1974, p、 192, p1 ． 60, figs、 5-

8, 12.

Ca""”α”"rα"S （NomuraandZinbo)[Sic]・ Shibata，

1977,pl.13, figs.16-18; Shibata, 1980,pl.3,

figs、 19-21; Itoigawaa〃, , 1981, p1 . 47, figs.

12-15; Itoigawa""/., 1982,p. 296; Ujihara

andShibata, 1982, p1 ． 6, fig. 22; Shibata,

1983,p.81,pl.2, fig.13;Ogasawara""/.,

1986, p1 . 4, figs、 6, 8, 9.

CaⅨ)"7"α〃sz""mvar.""iα"S (Nomura andZinbo)

[sic].ShibataandUjihara, 1989,p.32,pl.3,

figs.6-8; Shibatag/ "/., 1989, p.39,pl.4,

figs. 17-19.

C"しり/""α〃sz"""(Kittl) ． ？Ujihara2／ α/､ ， 1990, p、

I1"z花〃α/.-The followingdescription is basedon

five specimens (GMNH-PI2001-2005) fromHNO2

and two specimens (GMNH-PI2007, 2008) from

Tom23.

D2sc"p"0列. Shell small tomoderate in size for

genus, turriculate in formwithmoderately-elevated

spire and flattened base; whorls at least seven

(apices broken in all examined specimens) ; earlier

whorls sharply angulated by a peripheral rowof

tuberclesthat is Iocatedat lowertwofifthsofwhorl ,

and that rapidlydescends to the level of suture;

sutureweaklyimpressedandconcealedunderperiph-

eryinlaterwhorls. Surfacesculpturedwithminute,

closely-spaced spiral striae and incremental growth

lines; axial ribs sometimesweakly developing on

uppermost partofwhorls, Detailsof apertu'-almor-

phologynot observable.Umbilicalpart poorlypre-

served, but traceofaverynarrowlyopenedumbili-

cusobservablein thelargest specimen.

MiddleMiocenedeepwatermolluscs ()f theHaratajin()F()rmati()ninthelsobe(listrict

319-320, p1 ． 2, figs.7a,b;Akagig/ (z/.,1992,

p. 3032, p1 ． 1, figs. 2022.

Di""'0/""αα7""a (Bellardi)． Janssen, 1995, p. 111-

119, p1. 9, figs6-8 [containsextensivesyn-

onymy].

NotQzzﾉ0"”αルiSzM/c"" (Kittl).Shibatag/"/., 1986,

p. 49， p1 . 8, figs. 12， 13 [=Dj"(､/'0/""α？2"()／

Janssen].

Lowel-MiddleMioceneYanagawaFm.,Fukushi-

maPref.:HiranitaFm.,SaitamaPref.(Shibataand

Ujihara,1990) ;OidawaraFm. 、 GifuPref, ;Kumano

Gr.,WakayamaPref. ;HigashibesshoFm.,Toyama

Pref.;TakakuraFm. , OkayamaPref.;BihokuGr.,

HiroshimaPref:TottoriGr. 、 TottoriPref.

ClassBivalvia

Ordel-Solemvoida

FamilySolemyidae

GenusAcI7araxDall、 1908

R2ﾉ""hs. Fourmold specimens (GMNH-PI2009

2011)wereobtained.All thespecimensareoblique

lydepressed， and thelargest one (GMNH-PI2011;

p1. 4, fig. 26) showingthedorsal viewis 9.3mm

high and9.0mmwide.The characteristic three

broadribs separatedbytwoshallowradial grooves

andcommarginal undulatiol]s on thedorsal sideof

thesespecimensagreewellwiththoseofZ)i"cm/""〃

α"""(Bellardi). InJapan, this species had been

knOwn asQZ"/伽ね”γ"α"S (Nomura andZinl)6) ,

whichwasrecentlyregardedasajuniorsynonymof

D.""汀a (Bellardi) byJanssen (1995) .

Ocα"7'f7zcE.-Locs.TomOlandToml9.

DIs"ﾂ〃"0〃.－This specieshasbeenrecordedfrom

theMioceneofHungary, Italy, Turkey, Japanand

theCaribbean (Janssen, 1995)Japanesel-ecordsof

thespeciesaresummarizedbelow.

UDDelrLowerMiocene: Oi Fm． ,MiePref. ; Ayu-

gawaGr. , ShigaPref. (Shibata, 1977) .

Ac/7araxgﾉ'gas (Kanno, 1960)

Platel, figures35; Plate2, figuresl-2b

Plate3、 figures la－2;Figures5-1 3

S()〃"ly" (Ar""") 919"sKanno, 1960, p. 187-188,

p1 ． 50, figs, 1， 2．

Acﾉz""""s (Kanno)Kanie2/"/, , 1999, p. 1820,

figs. 31-2b.

ハ樅z/"/"/, The followingdescription is basedon

eight specimens (GMNHPI338344,2()00) fromLoc.

HNOl and two specimens (GMNHPI2050. 2051)

fromLoc.T()m02,

Z)"""""1.-Shell moderate to very large for

genus, common]y exceeding 200mmin length,

~ ~睡礎散mold (GMNHPI343),X0．6, Loc. HN01. 2.

X0．6,Loc.Tom02． 3.RubberCastfromrightACImmXgignSKanno、 l.Rubbercast fromleftexternalRubbercast frOmrightextemalmOld (GMNH-PI2050),externalmold (GMNHPI2051),Xl.2,Loc.TomO2.

Figure5

YukitoKuRIHARA8

transverselyelongatedwithalmost truncatedanteri-

ormarginandnarrowly-roundedposteriormargin,

presumably thin, andmoderatelyinnated; ventral

margin subparallel to dorsal margin, and long;

umboplacedposteriorly, about65to70%of length

fromanteriorend, and lesselevated; postero-dorsal

marginwidelyconcave.Anteriorportionofexternal

surfacewith four or fiveverv shallowandwide

radial grooves; middleportionalmost smooth; poste-

riorDortionwithafewverVfaintradial ornaments;

internal surface almost smooth but sometimes in

correspondencewithexternal sculpture.Hingeplate

edentulous , but thickened with strong radial

grooves; chondrophore-likeridges present at front

andrearofumbo; anterioradductor scarobscure,

posterioradductor scarelongateovatewithnumer-

ousradial striations.

R""""s.-The specimens examined aremostlv

internal molds partly possessing exfoliated shell

material.Thelargestspecimen (GMNH-PI338; pl.3,

fi9. lb) iswell-preservedinternalmoldof260.0mm

long and 85.0mmhigh,whichis probably the

largest recordoffossil andRecent solemyidbivalves

as far as l am aware. The smallest specimen

(GMNHPI2051; Figure5-3) is 46.0mmlongand

21.5mmhigh.Thepresent specimens arereferable

toAcIZ""gigZzS (Kanno), becausetheiroutlineand

su㎡acecharacterarealmost identicalwiththoseof

theholotype andparatypes fromthe lowerMiddle

MioceneHiranitaFormation, SaitamaPrefecture.

Especially, aparatype (TKD6187) of the species,

whichwas not illustrated byKanno (1960) and is

nowstored in theUniversityofTsukuba, isvery

similar toaHaratajinospecimen (GMNHPI2000) in~戸 1 で

slze, torrnandsculpture.

This species resemblesACIz"""yohos"舵砿isKanie

fromthelowerMiddleMioceneHayamaFormation,

KanagawaPrefectureinshellsizeandform.Howev-

er,A.yohos"膨"sis clearlydiffers fromthis species

inhavingverythickshell .

Oc""で"".-Locs.TomO2andHNOl.

Dis〃わ""0〃.－

LowerMiddleMiocene: HiranitaFm. , Saitama

Pref.

Aが伽"y､－

So/2772yα加hz""gniYokoyama, 1925a, p. 31, p1. 6,

figs. 1-3.

Re加"hs.-Four internal molds of articulated

valves (GMNH-PI2016-2019)were obtained. One

illustratedspecimen(GMNH-PI2018; p1. 4, fig. 13)

is less deformed internal mold andwell exhibits

outlineandscLIIpture. Theother specimens includ-

inganother illustratedone (GMNH-PI2016; p1. 4,

fig. 9) havemore elongated shells than the first

specimen, thoughtheyaremoredeformed.However,

theyallmust beconspecific, judgingfromthesimi-

larshell sizeandthesurfacesculpturecharacterized

byabout sevendistinct radial groovesontheanteri-

orportlon.

This speciesdiffers fromA. gigrZS (Kanno) in its

smaller shellwithdistinct radial grooves.Most of

previousworkers have referred JapaneseMiocene

specimensofAChαγαXwithdistinct radial grooves to

A. /0"""gIzi (Yokoyama).However, theMiocene

specimens includingthepresentonesmaybedistin-

guishablefromthePliocenespecimens includingthe

lectotypeand topotype intheirdominantmomholo-

gywithmoreelongateform. Taxonomicrevisionof

theso-calledAcﾉz”α虻/0"""gZZjisneeded.

Ocα"陀池2.-Locs.TomOlandToml9.

OrderNuculoida

FamilyMalletiidae

GenusNe//one//aDall, 1881

Ne//one//aノsens/sShibata, 1970

Plate4, figurel

唖"0'泥"α is"zsIs Shibata, 1970, p. 59-60, p1. 1,

figs. 7a, b; Shibata加Itoigawa毎α/・ , 1974,

p， 47， p1 ． 1， fig、 17； ？UjiharaandShibata，

1982, p1. 5, fig. 5; Yamaoka, 1993, p1. 1,

fig. 1;Kurihara, 1999, figs. 6-7a, b, 12.

M""hs・－Thisspecies ishererepresentedbyfour

internalmolds (GMNH-PI2020).All the specimens

arelessthan4mminlength. Fromthesmall size,

ovate outline with prominent umbo and com-

marginal ribsonsurface, thepresent specimens are

referabletoNe"0池〃αise7zsisShibata.

Achaﾉaxaff. rokunaga/ (Yokoyama, 1925)

Plate4, figures9, 13

MiddleMiocenedeepwatermolluscsoftheHaratajinoFormationinthelsobedistrict 9

inshelloutline, inwhichthepresent specimensare

included.The smallest specimen (GMNH-PI2023;

9.5mmlong, 7.6mmhigh; p1. 4, fig. 3) 1ooks

similar toBajhW"α"g"αC""cWsIs ShikamaandKase

fromtheMioceneMorozakiGroup,AichiPrefecture,

but theposteriorend isnottruncatedbutrounded.

OCC""CMe.-Loc.TomOl.

DiS/"6""".-SeeMoritae/α/. (1996) .

Oca"海"".-Locs.TomOlandToml9.

Disi"6〃"0〃.

UDDerLowerMiocene:MorozakiGr.,AichiPref.;

MitsuganoMemberofOi Fm. ，MiePref. ； ？Ku-

manoGr.,WakaVamaPref.

LowerMiddleMiocene: ArakawaFm., Saitama

Pref. ;OidawaraFm. . GifuPref.

Ⅳe"one//ars"k/gawae"sﾉsKurihara, 1999

GenusMJc"/anaLink, 1807

SubgenusCrasso/edaSavizky, 1972Plate4, figures6, 7

MJc"/ana(C7asso/eda) Penn"/a(Yokoyama, 1925)N"/ow"αts況厳塑加""sisKurihara, 1999, p. 232, figs

6-8a 10b[containssynonymy].

Plate4, figure2

Rew"hs.-Twodisarticulatedvalves and two frag-

mental specimens areavailablefor this studv. One

illustratedspecimen(GMNH-PI2022; 9.8mmlong,

5.4mmhigh; p1． 4, fi9． 6) is an internalmold

withexfoliated shellmaterial andwell exhibits its

elongateovateoutline. Another illustrated specimen

(GMNH-PI2021; 9.3mmlong,5.6mmhigh; pl.4,

fig. 7) isacast fromleft externalmoldandshows

its surfacesculpturecoveredalloverbycommarginal

ribs.Onthebasisoftheirsize, outlineandexternal

sculpture, the present specimens are referable to

jVNc"(we"αtsz"9Zzz(l"7"SKurihara.

Occ"""z".-Locs.TomOlandToml9.

D/sかめ""”.－

LowerMiddleMiocene: ArakawaFm.,Saitama

Pref. ； ？OidawaraFm. 、 GifuPref.

Z,2"'"""/αYokoyama,1925b,p.9,pl.2,figs.7-9.

IVMw/""(7ｿ"sﾊﾉﾉc")"加況/" (Yokoyama) ．Moritag/

"/., 1996,p.130-131,pl.5, fig.22[contains

extensivesynonymy].

Mfcz"αﾂ奴（α"SSOﾉe") aff・ be”郷/a (Yokoyama).Kuri-

hara, 1999, figs. 6-14, 15.

Rew"hs. Internal andexternalmolds of a left

valve (GMNH-PI2027; 11.0mmlong,4.0mmhigh)

wereobtained.Althoughthespecimen is somewhat

deformed, it is referable toMMc〃/α"(CγαssO/gdtz)

”""〃a (Yokoyama) by its transversely elongated

shell, commarginal ribs that aremuchnarrower

thaninterspaces onexternal surface, and smooth

internal suIfaceof therostrum. The lastmentioned

one is adiagnosticcharacterof the subgenusCms-

So/e",accordingtoKafanovandSavizky(1995) .

OcczI"Gwc9.-Loc.Tom01.

Dis"的""0".－SeeMoritag/α/. (1996) .

GenusMa//et/adesMoulins. 1832

Ma//er/a/"e/.m/s(Yokoyama, 1925)

Genus 7~en"//edaHabe, 1977Plate4, figures3-5

γenu//edacf. /kebe/ (SuzukiandKanehara, 1936)p1.2, figs. 1-6.

Morita""/. ,

10､ 11｢contains

Z,gdtzM""sYokoyama, 1925b, p.9,

BB""zy加α"g"α i"""s (Yokoyama) .

1996, p.125-126, p1.5, figs

extensivesynonymy].

Plate4, figurelO

Co""""""z.

MMczz/""c"c""(77"s放酌gi Suzuki andKanehara

1936, p. 182184, p1. 10, figs. 16-18.

MMcz"""娩酌"(Suzuki andKanehara).Okutani

1962, p. 8, p1. 1, figs. 10, 11.

ReW"hS.-Fourinternalmolds (GMNH-PI2023-

2026)wereobtained・Thelargest specimen (GMNH-

PI2025; p1 . 4, fi9. 5) is 18.0mmlongandl1.0mm

high.As illustratedbyYokoyama (1925a)'soriginal

figures, this species shows aconsiderablevariation

YukitoKuR田ARA10

Propeam"ssﾉ"mrareﾉwa/Kanehara, 1936R""""〃S･ Internal and externalmolds of a left

valve (GMNH-PI2028; 10.7mmlong, 4．1mmhigh)

areavailablefor thisstudv.ThissDecimen isnearlv

identical in size and formwithTe""/g"i"6"

(SuzukiandKanehara) illustratedbyOkutani (1962)

fromSagami Bay, but the preservation is insuffi-

cient for thepositive identificationtothespecies. If

thepresent specimen is trulvreferredtoT. i"6",

it represents the lowermost stratigraphicoccurrence

ofthespecies.

Occz"7wzc(P ．－Loc.Tom01.

Plate4, figures l8-20

Pﾉ'0"α加況ssz況加〃〃zs7""加瀬"Otuka, 1935, p1 ． 55, fi9.

145 ["0""72 1W"""7､l , without description; as

Pm"""池SS""〃〃切岱"ゆ""jc"Mochizuki,MS].

P7'op"加況ssi""2 (P7""加況SS""〃) /"/どれ"i Kanehara,

1936, p、 33-35, p1 . 10, figs. 5, 6; Shikama

andKase, 1976,p.19-20,pl.1, figs.16, 17,

p1. 2, figs・ 16, 17; Lee, 1992, p. 75, figs. 27

－6－8．

Pmp"加況ssz況加 ／〃〃"" Kanehara. Matsui and

Urashima, 1950,p.20, textfig. 1;Masuda,

1962, p. 152, p1 . 18, figs、 1－4;Yamana, 1972,

p.8,pl.4, figs.6-7b;UjiharaandShibata,

1982, p1. 5, fi9. 13; ShibataandIna, 1983,

p.39,pl.2, fig.8;NakagawaandTakeyama,

1985,pl. 23, fig. 2; Okamotogi"/., 1986,

pl.20, figs.8-10; ItoigawaandShibata, 1986、

p1. 17, fig. 16;Amano, 1991, figs. 3-1 3, 5

7; Yamaoka, 1993, p1 . 2, figs. 4, 6, 7;

Yamana, 1997,p.85,pl.19, figs・ ’4．

P""α"zzIssi""zcf. /"/"""Kanehara. Saito, 1988, p1 .

33, fig. 5.へ

Pα"α加況ss""7' (FY"'α加況ss""") /""z(ﾉ"27zsIsOmori, 1955,

p. 11-12, p1 . 1, fig. 1.

P'""""ss""" (s. s.)"α"α"sOmori, 1955, p. 16-17,

p1 . 1, figs. 10, 11.

C/cMz加況sz況加（雌"α加ZIss加加）h"S"eWS/S(Takeda).Kan-

no, 1960, p. 212-213, p1. 32, figs 5-7 [not

P"""""ssIz""k"s"027fsis (Takeda)].へ

Pα”α加況SSi""(s. s.) sp. a.0mol･i, 1955, p. 12, p1.

1, fig. 2.へ

P"""2"ssj〃"I (s. s.) sp. b. Omori, 1955, p. 13-14,

p1 . 1, fi9. 3.

GenusPorr/and/aM6rch, 1857

SubgenusMegayo/diaVerrill andBush, 1897

PoIT/and/a(Megayo/d/a) r/7/ac/aeわﾉm/s(Storer, 1838)

Plate4, figures l6, 17

』V"c"/α／〃αα“んγ"SStorer, 1838,p.122， 1 textfig.

Pα"α"伽a (MMeg上zyo城α) /〃α""/bγ""s (Storer) ． Uozu-

mi, 1957, p, 574-576, p1 ． 1, figs. 5, 5a, 7-8a,

p1. 7, figs. 23, 28.

Yo城a （ﾊ化gnyO“α) //z"ααeルノ'""S (Storer).Moore,

1983, p・A26-A27,pl.3, figs.17, 18.

PO"/"城a （A化gnyo/("α) "zmC/"""ziS (St6rer)[SiC].

Noda“αﾉ . , 1993, p. 129-130, figs. 12-6, 21.

A化gnyo/dm/〃γ"""/b"7"S (Storer) ．Moritaaα/. , 1996,

p、 142-144,pl. 6, figs. 15, 18-20 [contains

extensivesynonymy].

POγ"伽峨asp.Kurihara, 1999, figs.6-18, 19.

R2"1""S.-Foul- articulatedand fourteendisarticu-

latedvalves (GMNH-PI2029-2032) are available for

this study. The largest specimen (GMNH-PI2032;

p1. 4, fig. 17) is34．8mmlongand21.5mmhigh.

The characteristic broad outline and somewhat

truncated posterior end of the present specimens

agreewiththoseofP(M.) /〃γα""ib7'"S (Storer),

although the blunt ridge fromthe umbo to the

postero-ventral corner is indistinct.

Occz"γ27M2.-Loc.Tom01.

Dis加如"0".－SeeMoritag/ (Z/・ (1996) .

R"z"hS. Sixdisarticulatedvalves (GMNH-PI2033

-2038) are available in this study. The largest

specimen (GMNH-PI2037; pl. 4, fig. 20) is 10.2

mmlongand10.0mmhigh,Thisspeciesischarac-

terizedby itsmoderate-sizedandsemi-circular shell

withnine or tennarrowlyelevated internal ribs.

Accordingto themeasurement datagivenbyKane-

hara (1936) andShikamaandKase (1976); theratio

oflength/height ranges fromO.95 to1.16．Marginal

apronof rightvalveof fossil propeamussids is said

to be rarely preserved (Hayami, 1988), and an

OrderPterioida

FamilyPropeamussidae

GenusPropeamLﾉSSﾉUmdeGregorio, 1884

MiddleMi()cenedeep-watermolluscs ()ftheHaratajinoFormation inthelsobedistrict 11

illustratedspecimen (GMNH-PI2035; p1. 4, fig. 18)

isreferabletosuchacondition.へ

Pγ0P“加況ss""ﾉz (s. s. ) cic"/α"s Omori was svn-

onvmizedwith this sDecies bvShikama andKase

(1976, p、 20) ． Inaddition, P"""畑ssiz"" (""'"7zz4ssi-

~""2) 2."z""fwsisOmori is hereinmade iunior svn-

onvmof this sDecies for the first timebecauseP.

i"b2""fWs/s is indistinguishable fromrightvalvesof

thisspecies lackingthemarginal apron.

Occz"7で"". Locs. TomOl,Tom02,T()ml9 and

HNO2.

DIs/"6"〃0〃.－

Upper LowerMiocene: Nenokami Sandstone,

Saitama Pref.; Komagome Fm.,Nagano Pref.;

ShidaraandMorozakiGs.,AichiPref.; IchishiG.,

MiePref.

LowerMiddleMiocene: KonomaiGl-. , Hokkaido;

YanagawaFm.,FukushimaPref.iAwashimaFm.,

NiigataPref.; IdozawaFm.,GunmaPref.; Bessho

Fm． 、 Nagano Pref. ; Nawashiroda Fm., 1baraki

Pref. (Nikaido andKikuchi , 1983) ; Higashibessho

Fm． , ToyamaPref. ; Nanamagari Fm． , Ishikawa

Pref.; ShimoFm.,FukuiPref.; MorozakiGr.,

AichiPref.;KumanoGr.,WakayamaPref.; Bihoku

Gr.,Shimane Pref.; TottoriGr.,TottoriPref.;

Ennichi ShaleandHagjeonandDuhoFms, Korea.

R"1"/bS.-Asingle deformed internal mold of

right valve (GMNHPI2039, 27.0mmlong, 35.4

mmhigh) partlypossessing the shellmaterialwas

obtained・ The shell is higher than longwithnine

narrowlvelevated internal ribs. The shellmaterial

preserved near theventralmargin shows that the

external surface is coveredwith fine commarginal

lamellae.Judgingfromthesecharacters, thepresent

specimen is referable toP"鉦α"畑ssz況加血gmfji97zsis

Yamana fromthe lowerMiddleMioceneTottori

Group｡ TottoriPrefecture.As shownintheabove

synonym list, the species name /"gIz72/"7zSis has

becomeavailableaccordingtothelnternationalCode

of ZooIogical Nomenclature sinceYamana (1997)

gave adiagnosis for thespecies.P・血gIz72/i"zsiS iS

characterizedbytherelativelylargesize (commonly

larger than20mmhigh andoften attainingmore

than 55mmhigh) , higher shell outline (ratioof

length/height ranging O.78-0.92), right external

surface coveredwith commarginal lamellae， left

external surfacewith a cancellatepatternof com-

marginal lamellae and radial striations, and nine

narrowinternal ribs that are shorterinleftvalve

than inrightvalve (Yamana, 1972, 1997) .

This species often occurs in associationwith

P""α"岬sS”"”〃だiMWKanehara, but the latter is

easilydistinguishable fromtheformer in its smaller

shell size (commonly less than l2mminheight)へ

and nearly circulal- outline. P. /ahaS2WSIS OmOri

(1955, p. 12-13, p1 . 2, fig. 1) fromtheMioceneof

YamagataPrefecture resembles this species inhav-

ingahigher shell outlinewithnine internal ribs.

However,P. /αhascws/s is basedonasmall poorly

Preserved specimen, thus its detailed comparison

withthisspecies isnowdifficult.

The speciesmost similar to the present one is

Pγ0〆α"卿SS?〃洲ル"/SOﾉｶ (Smith) , aRecent lndoPacific

species. These twospecies resemble inshell size,

outlineandexternal sculpture, butdiffer indegree

of the development of the internal ribs between

right and leftvalves. Lengthof the internal ribsof

P･ ル"/s(7/27. is nearly same between right and left

valves, whereas that ofP. ji4gZz"/ie'7zsis is consider-

ablvdifferent as illustratedbyYamana (1972) .

OCc"""zc2.-Loc.HNO2.

Dis/河加"0”.

UpperLowerMiocene: ShidaraandMorozakiGrs.,

AichiPref.

Propeam"ss/"mfugan//ens/sYamana, 1997

Plate4, figure22

A'"〃S加加sp.Yamana, 1972,p.4-8,pl.1, figs・ 1-6,

p1 . 2, figs・ la6, p1 ． 3, figs. la-2, p1 . 4,

figs, 1a-5b.

Pα”'α"畑ss/""1 sp. ItoigawaalldNishikawa, 1976, p1 .

33, fig. 3;Okamotog/"/・ , 1986, p1 ． 19, figs.

11-14,･ Yamaoka, 1993, p. 66, p1 . 2, figs. 8a-

Qジc

"P"""加況ss加加" sp. Shibataandlna, 1983, p. 39,

pl . 2, fig. 9,

P701"加況ssiz""/Wgmz/i27zs/sAkagig/"/., 1992,pl.1,

fig. 1 ["0"z"加砒加加, without description; as

Pﾉ””加況SSz"加血9W"7"2sis Omori and lnoue

(MS)I

Pﾉ””加況ssz況加血gZz7fルフ燭jsYamana, 1997, p. 88, p1 .

21, figs. la-3, p1 . 22, figs. 1-6 [asP'"""1"s-

S""77ji'9m"だ"SisOmori andlnoue].

YukitoKuRmARA12

MyOﾉ7eﾉaosawaﾉ7oens/s(Tsuda, 1959)LowerMiddleMiocene:TottOriGr. 、 TottoriPref

~BihokuGr.,HiroshimaPref.

Plate4, figurel5

OrderVeneroida

FamilvVesicomvidae

GenusCa/yprogeﾉ7aDall, 1891

C"s"(/t""0""""ewsisTsuda, 1959,p. 73,pl. 2,

figs.2a， b.

My""" 0s""'"""s (Tsuda).Kurihara, 1999, p

232, figs. 6－25-27[containssynonymy].Ca/)/progena？sp

Plate4, figures ll, 12 RcP洲α疏S. Internal andexternalmoldsof asingle

leftvalve (GMNH-PI2048, 6.5mmlong, 5.4mmhigh)

are easily recognized asMy()"mos""""27fs/S by

having a small shell, sharp sulcus separating the

disc from the rostrum, and rough commarginal

undulationsontheanteriorDortionofthedisc.

Occ""'師".-Loc.Tom01.

Dis〃的""ひ〃.－

LowerMiddleMiocene: ArakawaFm., Saitama

Pref.;HigashibesshoFm.,ToyamaPref.; Oidawara

Fm. 、 GifuPref.

Rew"hS. Four internalmolds (GMNH-PI2040-

2043)wereobtained・ Thelargest specimen (GMNH-

PI2043; pl.4, fig.12; deformed) is16.7+mmlong

and9.2mmhigh.Theirelongate-ovateoutlineand

somewhat prosogyrated umbo located nearly two

fifthsofthelengthfromtheanteriorendremindme

Cα/"rogrl"or its closelyrelated genera, but the

preservation is toopoortoallowpositive identifica-

tiontothegenus.

Oca"γ271".-Loc.TomOl.

ClassCephalopoda

OrderOctopodida

FamilyArgonautidae

GenusArgo"auraLinnaeus, 1758

OrderPholadomyoida

FamilyPeriplomatidae

GenusPe"P/omaSchumacher, 1817

Pe"p/omam/rsLﾉganOenSeAraki, 1959 ArgonaL"a？sp

Plate4, figure21 Plate4, figure25

Pβ"〃O脚α加"s"gzzwogwsGAraki, 1959,p.163,pl.18,

figs、 2a, b.

Pe"p/0加α畑"szzgIzIzOSCIZSiS [SiC]Araki.Moritag/ (z/.,

1996, p. 167-168, p1. 11, figs. 6-8, 11 [con-

tainsextensivesynonymy].

Re"1""s.-A small depressed internal mold

(GMNH-PI2049,maximumdiameter33.4mm)was

obtained. It looks similartoA'郡?""(zandIZ況加07”"‐

"z inhavingrounded sigmoidal ribs on the lateral

side, but is insufficient for the positive generic

determinationdue to thedepression・ Therefore, it

is tentativelyidentifiedhereinwithA増りう睡鰄α？sp・

There are anumber of reportedoccurrences of

A増ひ/"""andIZZ""07"""fromtheLower andMid-

dleMiocene strata ofHonshu, but themost are

fromthe JapanSea side (Yanagisawa, 1990) . The

fossil recordof thesegenera in thePacificsideof

Honshuis representedonlybyA増りう”z"αcf. /0hz""-

9ZzI (Yokoyama) from the lowerMiddleMiocene

SakachiFormation, IbarakiPrefecture (Ohyamaand

Sakurai, 1966), and thepresent occurrenceis the

secondone.

Oca"7"""2.-Loc．HNO2.

R""/'hs,－Twospecimens (GMNH-PI2046, 2047)

were obtained. Illustrated slightlydisplacedvalves

(GMNH-PI2046; 22.5mmlong, 18.5mmhigh)well

exhibit outline and sculpture. This specimenwell

agreeswiththeholotypeofPe""0脚α ﾉ""SZzgZZWO27ZSe

Araki, thoughtheshell sizeisnear・lvhalf.

Oc""で砿9.-Locs.TomO2andTom19.

aS/"6""07z.-SeeMorita“α/. (1996) .

T言 ･1 〆、

上'arnllyしuspidariidae

GenusMyo"eraDall, 1886

MiddleMiocenedeep-waterm()lluscsoftheHaratajilloFormationinthelsobedistrict 1qユJ

Japan.n℃z71s"""zsa湿乃w"""gso/"zgP"/"""/091"/

SOc"ryoノノ"加邦， 』V@"S""s, (36) :161-167, p1. 4.

Bellardi,L.

1873 1mOlluschidei terreni terziari delPiemonteedella

Liguria, 1． Cephalopoda, Pteropoda, Heteropoda,

Gastropoda (Muricidae et Tritonidae). A化加~ 尺．

Ac"". Sc. 7bﾉ伽0, 2 (27) :1-264i、 pls. 1-15. ["0/

s""1. , ｣

Acknowledgments

Iwould like toexpressmydeepappreciation to

Prof. Hiroshi Noda (University ofTsukuba) and

Dr.YoshikazuHasegawa (DirectorofGunmaMuse-

umofNaturalHistory) for theirhelpful adviceand

encouragement throughout thepresent study.Ialso

thank Prof. Kenshiro Ogasawara (University of

Tsukuba) forhiscritical readingof themanuscript.

Acknowledgments are extended to the following

persons: Mr・ HajimeNakajima (AnnakaCity) for

hisdonationofgiantAc/@"""andotherfossil speci-

mens; Mr. YujiTakakuwa (GunmaMuseumof

NaturalHistory) forarrangingthe loansofGMNH

collection; Dr. YukioYanagisawa (Geological Sur-

veyofJapan) forhis examinationofdiatomfossi1s;

Dr・MasakiTakahashi (GeologicalSurveyofJapan)

for the discussion of stratigraphic problem; Mr.

YoshibumiKikuchi (UniversityofTsukuba) forhis

identificationof echinoid fossils; andMr.IwaoYa-

mana(TottoriCity) forprovidingthe informationof

P70pe""zzssj"加血g""""sis.

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1999 Taxonomicpositionof A独z〃胆加α： Re－examlnatlon

based on the elementmapping andmomhologic

analvsis of sDines. A6s""/s of"z2 1999Aﾉが鯉α／

/I"""29, TyZg Paﾉ“切加ﾉ畷"/Soc"yO/""z; IO2.

Hayami, 1.

1988 Functional and taxonomic implications of internal

ribsofP""α"加諏"柳．乃迩蛎伽加旙""Pmc"dmg9 (7/

"MP""(wI(7I(7gi"J Soc花〃0ゾル"2 ,N"ノ Se"",

（150) :476-490．

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1974Molluscan fossils of theMizunamiGroup. B"〃c/加

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V

1981 Miocene fossils of theMizunami Group, Central

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1982 Miocene fossils of theMizunamiGroup,Central

Postscript

After submitting thismanuscript, Hir()ki Hayashi (Tohoku

Univ.) sent me the preliminary result ()f planktonic

foraminiferal analvsisof theHaratai inoFormati()n in the lsobe

district.Accordingtohim,anassemblageobtained fromLoc.

TomO2isreferablet()BIow'supperN.8orl()werN.9Z()nein

containingPme("伽/"雌c加z"α”s、

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MiddleMiocenedeepwatermolluscsoftheHaratajinoF()rmationinthelsobedistrict 17

Plate l

2a

1a

b

3

ExplanationofPlate l.

Figure

la-2b.O7･"/os"msﾉz"”んα抄"miUrata…･ ･ ･…･ ･ ･ ･…･ ･ ･ ･…“………“…………………. ．…｡． ．…l.Lateralview(a) andumbilicalview(b) (GMNHPI2008),X2,Loc.Tom232.Lateralview(a) andumbilicalview(b) (GMNHP-PI2001), X2, Loc.HNO2

3 5.Ac/i""gignS (Kanno) ･ ･……“……･…･…･……･ ･ ･ ･…･…“･………”…･…“･ ･…･ ･ ･……”3． Internalmold(GMNH-PI2000),X0.55,Loc.HNO1.4.InternalmOld(GMNHPI342),X0.55,Loc.HNO1.5． Internalmold(GMNHPI343),X0.55,Loc.HNO1.

p.6

p. 7

YukitoKuRIHARAl8

Plate2

2a

ExplanationofPlate2.Figure

1-2b. Ac"""gigns (Kanno) ･ ･ ･ ･…“. ．…･ ･ ･ ･…･………･……

1.Internalm()ld (GMNH PI340),X0.55,Loc.HNO1

2. Rubbercast fromright internalm()ldsllOwingtheMNH-PI339),Loc.HNOl.

the

p，7

hingeplate,X0.8 (a) andinternalmold, X0.55 (b) (G

MiddleMi()cenedeepwaterm()lluscsoftheHaratajinoFomlati()n il' thels()bedistrici l9

Plate3

1a

ExplanationofPlate3.Figure

la 2.Ac〃αﾉ'αxgigns (Kann()) ･ ･p.7

(GMN1.Rubbercastfromleftinternalmoldshowingthehingeplate,Xl (a) andinternalmold,X0.55 (b)H-PI338),HNO1.2.Internalmold(GMNH-PI341),X0.55,HNOl.

YukitoKuRIHARA20

ExplanationofPlate4

Figure

1 . 1VW./0"〃/"IS(wsﾉsShibata･･…･ ･ ･…･ ･ ･ ･ ･…･…･…･……. ．…･…. .…． .…･ ･ ･…･ ･ ･ ･ ･…･ ･ ･…･……． ．…･ ･ ･ ･ ･

LRight interllalmold (GMNHPI2020), X4, L()c.Tom19.

2.MI(･"/α"a (O'αssO/f(/tr) """"/" (Yokoyama) "･…“…． .……･ ･ ･…･……･……･……･…･…･ ･ ･……”

2.RLlbbercastlr()mleltexternalm()ld (GMNH-PI2027),X2.9,Loc.TomO1.

3-5. A伽"c"α〃I”""･s (Yokoyama) ･ ．…･ ･ ･…･ ･ ･…･ ･ ･ ･ ･ ･ ･ ･ ･…･ ･ ･ ･ ･”･…･………一 ･ ･ ･ ･ ･ ･…･ ･ ･ ･……･………

3.LeItinlcmalmold (GMNH-PI2023),X2,L()cTomO1.

4.Right internalm()l(l (GMNH-PI2024),X2,Loc.T()m01.

5.Rightintemalmold (GMNHPI2025),X2,L()c.Tom01.

6, 7. IVf'//0"('"αIs""g""""sKurihara･ ‘ ‘ ･ ･ ･…． ．…･……･ ･ ･ ･ ･ ･ ･ ･……………． ．…･…………･ ･ ･ ･ ． ．…･ ・

6. Right internalm()ld(GMNH-PI2022), X2.9, Loc.TomOl

7.Rubbercast fromleftexternalmold (GMNH-PI2021),X3,Loc.Tom01.

8. L"(､/"(""asP、

8.RLlbbercast fromrightexternalmold (GMNH-PI2044),X3,Loc.Tom19.

9-13. 』産l(畑ﾉmf aff. /0ﾙ""α9"(Yokoyama) ･…………･ ･ ･ ･ ･…………･……………･…･ ･ ･…． ．……………

9.Rightinternalm()ldanddeformedleftvalve (GMNH-PI2016),X1.1,Loc.TomOl

13.Leftinter''almold(GMNHPI2018),X1.2,Loc.Tom01.

10. 7､2ﾉ""/('(/"cI. ノル的fノ (Suzuki andKanehara)……･……･ ･ ･ ･…………･…･………． ．……･……………

10.LeItintemalmold(GMNH-PI2028),X2.6,Loc.Tom01.

11, 12' Ca/J1"()雛ﾉ〃？sp、 …･ ･ ･…･ ･ ･…･…･……･…･ ･ ･ ･ ･…………･…･………． ．…･ ･ ･ ･…………･ ･ ･ ･ ･ ･ ･ ･…・

l1. Right internalmold (GMNHPI2042), X2.5, Loc.Tom01.

12. Right intemalmold (GMNH-PI2043), X2, Loc.Tom01.

14.Ax/""//パ？sp、

14. Lelt interllalmold (GMNH-PI2045), X5, Loc. Tom19.

15.M)'0""W(ﾉs(zI""""SiS (Tsuda)………･……………･ ･ ･ ･…………･…･………………･……･…………･…

15.Leftintemalmold (GMNH-PI2048),X3,Loc.T()m01.

16, 17. j)0ﾉﾌ/α"(/『a （A企g"yO〃"） 〃"通α~"/bﾉ7ﾉ"S (Storer)･･……･ ･ ･ ･ ･…･…………･ ･…･…”…………･ ･ ･ ･ ･…

16.RLlbbercast fromleftexternalmold (GMNH-PI2030),Xl.5,Loc.Tom01.

17． Rightinternalmold(GMNH-PI2032),X1.2,Loc・Tom01.

18-20.Pﾊﾉ"αﾉ""ss""〃/"""""Kanehara． ,……“･ ･ ･ ･ ･ ･ ･……“…･…･ ･ ･……． ．…･ ･ ･ ･ ･…･………． ．…. ･ ･ ･

18.Rightintel-nalmold(GMNH-PI2035),X4,Loc.Tom19.

19.Lefti'1ternalmold (GMNH-PI2036),X3,Loc.Tom19.

20.Le[tintemalmold (GMNH-PI2037),X3,Loc.Tom19.

21. />f/･//)/(ﾉﾉ"αノ""s"9mz""sFAraki …･……･ ･ ･ ･…･…･ ･ ･ ･ ． ．………･…･…･…･……･ ･…． ．………. ･ ･…. ．…

21.Lenexternalm()ldandrightirlternalm()ld (GMNH-PI2046),X1,Loc・ Tom19.

22, Pﾉ･0""""“""〃／"“"ﾉ/"zsIsYamana･ ･…………･ ･……………･…･…………． ．………． ．……･…………

22.Right valve (GMNHPI2039),X1,L()c.HN02.

23. j7Yssﾉ〔ん"/α/""〃cf・ ノ畑ﾉ""泥"(Takeda)

23.Externalmold (GMNH-PI2012),X2,Loc・Tom01.

24.Ca""α？sp、

24.Extemalmoldwithafragmentalinternalmold(GMNH-PI2015),X2,Loc.Tom01

25． A増U"α"/α？sp． ･ ･ ･ ･ ･ ･ ･ ･ ･ ･ ･ ･ ･ ･ ･…． ．…｡ ．………･………･ ･ ･……･ ･…･…･…･ ･ ･ ･ ･ ･ ･ ･ ･ ･ ･ ･ ･……･ ･ ･ ･……. .…. . 、

25.Internalmold (GMNH-PI2049), sideview,Xl,Loc.HNO2.

26.D/"ﾉ･0/""αα"ﾉ'"a (Bellardi)…“…･ ･ ･ ･………………･…･ ･ ･………･ ･….…. .………･………………. . .…．

26. Rubbercast fromexternalmold (GMNH-PI2011), dorsalview, X3, Loc.Toml9.

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p. 9

p. 9

p， 9

p.8

p.9

p.12

p・’2

p.10

p.10

p.12

p，11

p、12

p， 6

MiddleMiocenedeepwatermolluscsof theHaratajin()F()rmati()n inthelsobedistricl 21

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和文要旨

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原田篠層産中期中新世深海性貝類

栗原行人

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る計24種の貝類を産する． 原川篠III{加減I化ｲi群は2タイプの群鮠（原鯏如卓越型とA(T"""x

卓越型）を含み， 群熊榊造の竹徴から深i耐IJI化石郡であるとち･えられる． 本化石群と現在の相

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それに類似していたことを示唆する. *)'i'1からは|暖水'|ｿliの浮遊|ｿ|311m足類および頭足類の産出がま

れではないことから， 、'1時の表"i水はll愛流の影郷ドにあったと考えられる．

栗原行人筑波大学大学院地球科学研'究科：〒305-8571 茨城ﾘi '：つくば'|j犬| ;台1-1-1．YukitoKuRIHARA

Doct()ralPrograminGeoscience, lheU11iversity ()ITsukuba:Tsukuba, Ibaraki, 305-8571, Japa''