Transactions and Proceedingsof thePalaeontological Society of Japan
New Ser ies

No. 139

Pa laeontologica l Society of Japan
September 30, 1985

Co-Editors

Hisayoshi IGO and Takashi HAMADA

Officers for 1985-1986
President: Toshimasa TANAI
Honorary President: Teiichi KOBAYASHI
Councillors:

Kiyotaka CHINZEI, Takashi HAMADA, Tetsuro HANAI, Yoshikazu HASEGAWA,

Itaru HAYAMI, Hisayoshi IGO, Junji ITOIGAWA, Tadao KAMEl, Tatsuaki KIMURA,
Tamio KOTAKA, Kei MORI, Ikuwo OBATA, Tsunemasa SAITO, Yokichi TAKAYANAGI,
Toshimasa TANAIMembers of Standing Committee:

Kiyotaka CHINZEI (Membership), Takashi HAMADA (Co-

Editor of Transactions), Yoshikazu HASEGAWA (Foreign Affairs), Itaru HAY AMI(Planning), Hisayoshi IGO (Co-Editor of Transactions), Tatsuaki KIMURA (Finance),
Ikuwo OBATA (General Affairs), Yokichi TAKAYANAGI (Editor of "Fossils"), Juichi
YANAGIDA (Editor of Special Papers)
Secretary:

Hiroshi NODA (Editor of Transactions)Auditor: Yoshiaki MATSUSHIMA

The fossil on the cover is Unuma (Spinunuma) echinatus ICHIKAWA and YAO, a
Middle Jurassic multisegmented radiolaria from Unuma, Gifu Prefecture, central
Japan (photo by A. Y AO, x 260).

All communication relating to this journal should be addressed to the

PALAEONTOLOGICAL SOCIETY OF JAPAN
c/o Business Center for Academic Societies,
Yayoi 2-4-16, Bunkyo-ku, Tokyo 113, Japan

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 139, pp. 149-179, pis. 22-23, September 30, 1985

799. RECURRENT MOLLUSCAN ASSOCIATIONS OF THE OMMA-MANGANJIFAUNA IN THE GOJOME-OGA AREA, NORTHEAST HONSHU,
PART 1. GENERAL DISCUSSIONS OF FAUNA AND SYSTEMATICNOTES ON GASTROPOD AND SCAPHOPOD SPECIES*
SEIICHIRO MATSUI Department of Earth Science, Faculty of Education, Utsunomiya University,
Utsunomiya 321, Japan

Abstract. Six recurrent associations are recognized in Pliocene to early Pleistocene marine molluscan assemblages in the Gojome-Oga Area, northeast Japan. The
distribution of these associations are interpreted to be controlled by physicalenvironmental factors such as bottom character and water depth. The Palliolum
Association occupied the deepest basin bottom, where the turbidite deposits wereaccumulated. The Nuculana Association inhabited in deep muddy environments
but shallower than the Palliolum Association. The Acila-Turritella Association
appeared on muddy and sandy bottom, which was intermediate in water depth.
The Macoma tokyoensis and the Protothaca Associations were the shallowest
inhabitants. The Thyasira bisecta Association occurs in various lithofacies types
and seems to have wide tolerance to sediment types. In the Acila-Turritella Association, stratigraphically alternative occurrence of Acila nakazimai and Turritellasaishuensis is recognized. The alternative occurrence of the two species well corresponds with occurrences of right-coiling and left-coiling forms of a planktonic
foraminiferal species Neogloboquadrina pachyderma. The occurrence seems to becontrolled by sea level fluctuation induced by climatic change. Thirty-two speciesof gastropods and three species of scaphopods are described.

this area are described, and discussed in relation
to their environments. Origin of some minor
differences in composition within an association is also discussed. The environmental background of these associations are reconstructedby means of a detailed examination of lithologic
characters of fossil-bearing sediments, as wellas their stratigraphical and geographical distributions.
The Omma-Manganji Fauna has been repeatedly studied since Yokoyama (1923a),and has been known in the Japan Sea coast
areas from Cheju Island, south of the Korean
Peninsula, far north to Hokkaido. Chinzei(1978) noted that the Omma-Manganji Fauna

Introduction
The Pliocene-lower Pleistocene marine strata
in the Gojome-Oga Area, northeast Honshu,
Japan provide excellent materials for the paleoecological analysis of the Omma-Manganji
Molluscan Fauna, which is a representative of
cold water fauna in the northeast Japan during
Pliocene and Pleistocene times. These deposits
ubiquitously contain rich autochthonous molluscan fossils, in which recurring species associations can be recognized. In this paper, therecurrent molluscan associations recognized in*Received JUly 2, 1984.
149

Seiichiro MATSUI

150

is composed of Pliocene-.early Pleistocene cold
water dwellers and is roughly time-equivalent
to the embayment Tatsunokuchi Fauna in the
Pacific coast of northeast Japan and to thewarm water Kakegawa Fauna in southwest
Japan_
Previous works on the faunal analysis of thisfauna have often treated sand-dominated strata(e.g. Kaseno and Matsuura, 1965; Ogasawara,
1977). It is relatively difficult to reconstruct
the original compositions of molluscan associations in those sandy facies, because in mostcases fossils enclosed in the sandy deposits havemore or less experienced post-mortem transportation. Studies of off-shore muddy molluscus
are relatively scarce. Chinzei (1973) recognized
four association types based on the autochthonous molluscan fossils in the northern Akita
district, of which two are the muddy associations and the other two are sandy associations.
In the Gojome-Oga Area muddy deposits prevail
throughout the Pliocene to lower Pleistocene
formations, which contain abundant autochthonous molluscan fossils. Thus the area is adequate
to study nature of muddy bottom associationsof the Omma-Manganji Fauna.

Stratigraphical framework
The Gojome-Oga Area is located in theenvirons of Akita City, northeast Honshu (Textfig. 1). The area is divided into two subareas:
the Gojome Area and the Oga Area. The lateCenozoic marine strata of the two subareas
are isolated from each other by younger alluvial
deposits. The marine late Cenozoic strata arecomposed of, in upward sequence, basal volcanic
rocks ("Green Tuff"), sandstone and siltstone(Nishikurosawa Formation), fine-grained mudstone (Onnagawa and Funakawa Formations),
siltstone, sandy siltstone and sandstone. The
rocks last mentioned are the subjects of thisstudy and will be noted below in detail. The
succession (Text-fig. 2) is interpreted to represent a sedimentary cycle beginning with
rapid transgression followed by slow regression.
Molluscan fossils abundantly occur both in theinitial trasnsgressive deposits and in the later
regressive deposits. This study is focused on
the molluscan faunas in the regressive stage.
The stage is represented by fossiliferous muddy
and sandy deposits, which are divided into two
formations in each subareas, the Tentokuji
and Sasaoka Formations in the Gojome Area,
and the Kitaura and Wakimoto Formationsin the Oga Area. A detailed description ofthese strata was given by Matsui (1981).
The Tentokuji Formation is composed ofgray, massive, fine- to coarse-grained siltstone.
It overlies the fine-grained mudstone of the
Funakawa Formation and continues upward
into the Sasaoka Formation. The Sasaoka Formation includes various rock types, which
laterally and vertically grade into each other,and is divided into following seven members:
Minamizawa Sandy Siltstone, Tofuiwa Alternation, Machimura Sandy Siltstone, Terasawa
Sandstone, Odai Sandstone, Sodenosawa Sandstone, Tomita Volcanic Sandstone, among which
the Machimura Member occupies the main partand represents lithofacies of the formation.
The Kitaura Formation consists of finegrained siltstone and intercalating graded sandstone. It is covered by the Wakimoto Formation
which consists of greenish gray siltstone andoccasional intercalations of pebbly sandstone.
These four formations are intercalated bymany fine- to medium-grained acidic tuff beds,
which are effective to trace isochronous horizons
and to correlate these formations (Mitsunashi
et al., 1963; Kitazato, 1975; Matsui, 1981).
Matsui (1981) recognized that several tuff
layers are continuous between the Gojome andOga Areas and that the Tentokuji and Sasaoka
Formations in the Gojome Area are respectively
correlative with upper part of the Funakawa
Formation to middle part of the Kitaura Formation and with middle to upper parts of the
Funakawa Formation in the Oga Area. Microbiostratigraphical and magnetostratigraphicaldata (Kimura, 1974; Kitazato, 1975; Nakamura
and Matoba, 1978; Matsui, 1981) support thiscorrelation, and suggest that the PliocenePleistocene boundary is drawn in the base of
the Kitaura Formation.

799. Omma-Manganji Fauna in Gojome-Oga

151

t ions1"-1/ Secexam
ined

G2J Sasaoka Fm.
IillI Wakimoto Fm.

O'2~

GOJOME
AREA

Text-fig. 1.
tions.

Locations of stratigraphic sections examined, and exposures of fossiliferous forma-

Lithofacies and depositional environments
The Tentokuji and Sasaoka Formations in
the Gojome Area and the Kitaura and Wakimoto
Formations in the Oga Area are variable inlithology both in vertical and horizontal directions. Six lithofacies types are recognized inthese formations. Each of them may represent
a characteristic depositional environment andis useful for reconstruction of Pliocene-early
Pleistocene paleoenvironments.

(1) Turbidite facies. The facies is represented
by alternation of massive or thinly laminatedfine.grained siltstone and tuffaceous fine-grainedsandstone, which often shows graded bedding.
The facies is typically seen in the Kitaura Formation in the southern coast of the Oga Area
and includes the Kitaura and Wakimoto For·mations of the southern coast. No turbidite
facies is recognized in the Gojome Area. The
turbiditic sandstone beds become coarser-grained
and thicker upward. Molluscs are rare in the152

Seiichiro MATSUIAGE

GOJOME AREA

OGA AREA
Wakimoto Fm.

Sodenosawa Sandstone

OJ

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Tomi ta •Volcanic
Sandstone~

Ma ch i mu ra
Sandy Si ltstone

Tofuiwa
Al ternation
Tentokuji Fm.

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Funakawa Fm.

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Minamizawa
Sandy Siltstone

Funakawa Fm.
Onnagawa Fm.
OJ

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Nishikurosawa
Fm.

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Onnagawa Fm.

GreenTuff"

Text-fig. 2.

Summary of the stratigraphy of the upper Cenozoic strata in the Gojome-Oga Area.

siltstone.
(2) Silt facies. The facies is represented bymassive greenish fine- to coarse-grained siltstone.
The facies is very homogeneous, but in the upperhorizons the silt becomes more coarser-grained
and more frequently exhibits obscure parallel
laminations than in the lower part. The facies
includes the Tentokuji Formation in the Gojome
Area, and the Kitaura and Wakimoto Formationsin the northern coast of the Oga Area. Molluscs
are sparse in the silt facies, and are more abundant in the upper coarser-grained part than in
the lower finer part.
(3) Sandy silt facies. The facies is lithologically rather variable and is divided into the following five lithological types. (a)· Massive sandy
siltstone, 35-55% in sand content, with tubulous
or irregular shaped burrows of a few to ten mm
in diameter. (b) Massive sandy siltstone similar
to (a) but with "Houki-zuna". "Houki-zuna"(Hase and Hirayama, 1970) is a cross-laminatedblock in the massive sandy siltstone or finegrained sandstone. The block is 10-30 cm
wide and 10-50 cm thick. The lamination isalways concave-upward. (c) Alternation ofmassive sandy siltstone similar to (a) and massive
siltstone of 18-30% in sand content. In thealternation, each bed lithologically merges into
overlying and underlying ones and is ten to a
few tens cm, rarely a few m, in thickness. (d)Alternation similar to (c) but with "Houkizuna" in the sandy siltstone. (e) Massive sandy
siltstone with tubulous burrows of 1-2 cm indiameter and 10 cm in length, which are filledwith horizontally laminated very fine-grained
sand and are nearly vertical to the bed.
The sandy silt facies is generally poor incurrent-generated sedimentary structures. It is
intensively bioturbated. The facies occurs in the
Machimura, Minamizawa and Terasawa Membersof the Sasaoka Formation. Molluscs are widely
found throughout the facies, and are moreabundant in the sandy beds than in the muddy
beds. Fossils also appear in the "Houki-zuna".
(4) Alternation facies. This facies is characterized by irregular alternation of fine-grainedsandstone and sandy siltstone, the latter ofwhich is coarser-grained and better sorted than
the sandy siltstone of the sandy silt facies. The
mud content of sandstone is 15 to 20%. A single

799.

Omma-Manganji Fauna in Gojome-Oga

bed of the alternation ranges from a few tens
cm to a few tens m in thickness. The facies
occurs in the Tofuiwa Member. Both muddy
and sandy beds often contain molluscan shells.
(5) Fine-grained sand facies. The facies isrepresented by massive fine-grained sandstone of
15 to 35% in mud content. The fine-grainedsandstone is often intercalated by coarser-grainedsandstone and conglomerate beds. The facies
occurs in the upper part of the Machimura,
Sodenosawa, Odai and Terasawa Members of the
Sasaoka Formation. The sandy silt facies of
the upper part of the Machimura Member isfrequently intercalated by sandstone of thisfacies, which occurs as beds of a few tens cm
to 10 m thick, and is overlain by the sand faciesof the Sodenosawa Member. The Sodenosawa
Member is represented by fine-grained sandstone
with silty tubulous burrows and mud pellets inthe lower part, and by fine- to medium-grainedsandstone with a fossiliferous granule conglomerate bed in the middle part. The upper part ofthe member is composed of cross-laminatedmedium-grained sandstone, which is in tum
overlain by alternation of non-marine pale grayclay and medium-grained sand. Molluscan shells
are common in fine- and medium-grainedsandstone.
(6) Volcanic sand facies. The facies corresponds to the Tomita Member of the Sasaoka
Formation. The facies is composed of coarsegrained volcanic sandstone and fine- to mediumgrained muddy pumiceous sandstone. The facies
is contemporaneous with the middle and lower
parts of the sandy silt facies. Molluscs are often
found in the muddy part, while rare in thecoarser-grained part.
Spatial distribution of the lithofacies:-As
stated in the earlier section, the marine strata
in this area are considered to have been deposited
during a cycle of sedimentation, which begins
with rapid transgression followed by slow regression. The six lithofacies types noted above
represent the later stage of the regression. In
any section in the area, the lithology becomescoarse-grained upward. In the Gojome Area,
the upper strata exhibit an upward gradation

153

from the silt facies through the sandy silt facies,
to the fine-grained sand facies in the northernpart, or to the alternation facies in the southern
part. In the Oga Area, the turbidite facies (thesouthern coast of the area) or the silt facies(the northern coast of the area) is overlain by
fine-grained siltstone. The vertical gradation oflithofacies indicates the gradual shallowing of
the sea. In the northern part of the Gojome
Area, the fine-grained sand facies is covered
with the non-marine deposits, which represent
the final stage of shallowing of the basin.
Lateral gradational relationships of thelithofacies can be recognized by tracing of themarker tephra, as well as the magnetic andmicrofossil datum levels. Among these marker
horizons, four (horizons I-IV) are widely
traceable and are useful in recognizing thegeographical distributions of the lithofacies(Text-figs. 5A, B).
The lithofacies becomes finer westward
and finally grades into the turbidite or silt facies
in the western extremity. At the horizon II
along a E-W section through the northern partof the Gojome and Oga Areas (Text-fig. 5A),
the following lithofacies are recognized fromeast to west: the sandy silt and silt facies in the
Gojome Area; the silt facies in the northerncoast of the Oga Area; the turbidite facies inthe southern coast of the Oga Area. The horizon
IV is represented by the fine-grained sand facies
in the Gojome Area and thinly laminated siltstone of the turbidite facies in the Oga Area.
This areal arrangement of the lithofacies suggests that during the Pliocene and early Pleistocene periods the sea became deeper westward
and ended in a basinal deep.
In the southern part of the Gojome Area,
the sediments are coarser-grained in any horizon
than those in the northern part. For example thehorizon II is represented by the alternation
facies in the southern part, while it is the sandy
silt facies in the northern part. The southernpart of the Gojome Area was considered to beshallower than the other areas.
The lithofacies often changes in minor scale
within these general tendencies. For example,

Seiichiro MATSUI154

the alternation facies is composed of sandy
silt beds and fine-grained sand beds both ofwhich are thinner than 10 m thick, and theupper part of the sandy silt facies is frequently
interbedded with fine-grained sandstone of
30 cm to 10 m thick. These minor variations
can not be attributed to depth changes of thesea, but are interpreted as a result of local variation of hydrodynamic conditions of the sea
bottom.
In the central part of the Gojome Area,
fine-grained mudstone of the Onnagawa andFunakawa Formations and siltstone of the
Tentokuji Formation abut against a tectonic
high of the Miocene volcanics, the Odai Swell(Matsui, 1981) and fine-grained sandstone of the
Sasaoka Formation directly overlies the swell(Text-fig. 5B). The swell was a submarine
topographic high, on which no deposits areaccumulated until the latest Pliocene. It iscovered by fine-grained sandstone and sandy
siltstone of the upper part of the Sasaoka Formation. The dominance of the sandy deposits
around the Odai Swell suggests much supply
of coarse-grained clastics from the swell andits hinterland.
Molluscan samples and modes ofmolluscan occurrence
Two sets of faunal samples were preparedfor ecological analysis of the molluscan fauna.
One is a set of about 300 assemblages from 75
localities (Text-fig. 3), which cover all fossiliferous horizons in the area studied. The"assemblage" here used means collection ofindividuals from stratigraphically defined interval of exposure. This set is used to establish
faunal association types. Faunal compositionsof the strata change in various scale. In somecases the change occurs within one meter orless in thickness. In order to detect these minorchanges of composition, each assemblage islimited to include individuals of molluscs foundin 10 cm to 1 m stratigraphical interval of an
exposure. The other sample set is prepared toanalyze a finer structure within the Acila-Turritella Association, the most prevailing associ a-tion in the area. This set is composed of thestratigraphically successive assemblages. Two
set of successive samples were obtained fromthe sandy silt facies of the Sasaoka Formation(M-series and GR-series).
Megafossils abundantly occur in the bioturbated sandy silt facies and the fine-grained
sand facies of the Sasaoka Formation, andare rather rare and sparse in the silt facies of the
Tentokuji, Wakimoto and Kitaura Formations.
The metafossil fauna in this area is composedof gastropods, bivalves and scaphopods accompanied rarely by echinoderms. Microfossils suchas foraminifers, ostracods and sponge spicules
are commonly found both in muddy and sandy
sediments.
The bivalve shells are usually complete,
although disarticulated valves are common.
Their delicate surface ornamentations are wellpreserved. The gastropods often have the protoconchs.
In the sandy silt and silt facies, the shells
are randomly oriented, sporadically disseminatedin the sediments and show wide range of size.
The bivalves are commonly disarticulated.
The intensively bioturbated sediments withrare current stratification suggest that burrowing animals or weak current stirred the shells,
so that the shells are disarticulated and have notretained their life positions. The assemblages
in these facies are essentially untransported
and can be called "disturbed-neighborhoodassemblages" (Scott, 1974). In the muddy sediments, deep burrowing bivalves such as Mya
cuneiform is, Thyasira bisecta and Lucinoma
acutilineata are found in living position. They
are articulated and their direct commissureplanes are nearly perpendicular to the bedding
plane.
In the fine-grained sand facies, large andthick-shelled bivalves such as Anadara, Dosinia,
Protothaca and Mercenaria are usually articulated
but rarely stand upright to the bedding plane.
The smaller bivalves are also often articulated.
The assemblages are also regarded as the disturbed-neighborhood assemblages. At loco 24-1b,
the fine-grained sand facies contains well preserved specimens of Turritella saishuensis and799. Omma-Manganji Fauna in Gojome-Oga
Macoma tokyoensis below a fine-grained whitetuff of a few centimeters thick. The individualsof Macoma are articulated, lying on the bedding
plane of about 10 cm below the tuff, while theindividuals of Turritella occur just below the
tuff. Fossils are rare in the neighboring sedimentsof the two fossiliferous horizons. It may beconcluded that the two species were contemporaneously killed by the rapid accumulationof the volcanic ash. The assemblage can be called"fossil census community" (Fagerstrom, 1964).
. At loco 6-1, a granule conglomerate bed of
1.5 m thick contains abraded and broken molluscan shells. The assemblage contains Glycymeris
yessoensis, Mizuhopecten poculum and Clinocardium fastosum in common with the assemblages in the fine-grained sand facies, but Cyclocardia aomoriensis and Peronidia sp., which
exclusively appear at the locality, are mostabundant in number of individuals. This assemblage was apparently transported and is perhaps
a mixture of shells from two or more different
habitats.
In ecological analysis the allochthonous
assemblages are excluded.

Faunal associations
In this paper, the term "association" isadopted to indicate a recurring suite of species.
Six association types are recognized among 288
assemblages obtained from the Gojome-Oga
Area.
The assignments of three assemblages (Locs.
5-11a, 7-7a, 7-8) to the associations are, however, not decided. In these three assemblages,
molluscus sporadically occur. They are characterized by Limopsis tokaiensis, which neverappears in the established associations. They
are restricted to the lower part of the sandy
silt facies. These three assemblages may represent another association, but the fossil data
are too poor to establish a distinct association.
Palliolum Association:-Polliolum peckhami
is the only constituent species of the association.
The association occurs in the turbidite faciesof the Kitaura Formation in the Oga Area.

155

The shells are densely crowded along the basal
surface of tuffaceous sandstone or in thinly
laminated siltstone. The shells are lying parallelto the bedding plane. In massive siltstone of theturbidite facies, it occurs very sporadically.
Fragile thin shells of the species are well preserved. Conjoined valves are commonly found.
Nuculana Association: -The molluscs of thisassociation occur sporadically in muddy sediments. The association frequently appears
both in the silt facies and the lower part of the
sandy silt facies, which is generally finer-grained
than the upper part. It is characterized by
nuculanid bivalves, buccinid and turrid gastropods, two species of Acila, and Siphonodentalium sp. A. The nuculanids are represented byeleven species (Table 1) and Nuculana robaiis the commonest among them. The buccinid
gastropods are represented by Buccinum cf.
rossicum, B.. spp., Neptunea intersculpta, Clinopegma borealis and some others. Propebela
candida is the commonest turrid. Cryptonatica
clausa commonly appears in the association.
The faunal compositions of the association issomewhat different between the Gojome andOga Areas. In the Gojome Area Acila is represented by A. nakazimai, while in the Oga
Area A. divaricata occurs. Nucula niponica,
Portlandia toyamaensis, Volutomitra alaskensis
and some others appear only in the Oga Area.
Minor morphological differences of M ohnia
cf. yanamii are observed between the specimensof the Gojome and Oga Areas (see Systematic
Notes).
The assemblages at Locs. 7-9a and 7-9b,
occurred in a muddy sandstone bed inserted
in the silt facies are composed of Neptunea
sp., Fulgoraria sp., Cryptonatica clausa andsome others but lack nuculanid species. Twoassemblages (Locs. 17-1 and 23-3) obtained
from fine-grained mudstone of the silt facies
have characteristic species compositions, dominated by Saccella onoyamai. The assemblage
Loc. 41-2, found also in fine-grained mudstone,
is more peculiar in composition. It is composedof Yoldia kikuchii, Acharax tokunagai, Periploma cf. besshoensis and Neptunea sp.

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Text-fig. 3. Sections showing stratigraphic positions of the fossil localities described in the text and tables. Fossil localities are numbered 1, 2, 3, ... in stratigraphically descending order in each section and expressed with prefixed by section number as Locs. 1-1, 1-2. At
localities where two or more assemblages are obtained each assemblage is named a, b, c, ... in stratigraphically descending order (e.g. theuppermost assemblage from Loc. 1-2 is denoted as 1-2a). As Loc. 25-3 contains 73 assemblages, the assemblages of the locality are expressed
as 25-3-n (n = 1 - 7,7.5,8 - 72). The location of the sections is shown in Text-fig. 1. a: Miocene volcanics. b: Miocene diorite; c: turbidite.
d: thinly laminated siltstone. e: boulders of siltstone. f: siltstone. g: sandy siltstone. h: fine-grained volcanic sandstone. i: coarse-grained
volcanic sandstone. j: fine-grained sandstone interbedded with sandy siltstone. k: cross-laminated fine- to medium-grained sandstone. I:
fine-grained sandstone. m: coarse-grained sandstone. n: conglomerate. 0: tuff. p: fault. Ma: Miocene volcanics. Te: Tentokuji Formation.
Ki: Kitaura Formation. Wa: Wakimoto Formation. Sc-Si: Sasaoka Formation (Sc: Minamizawa Sandy Siltstone. Sd: Tofuiwa Alternation.
Se: Machimura Sandy Siltstone. Sf: Terasawa Sandstone. Sg: Odai Sandstone. Sh: Sodenosa,"a Sandstone. Si: Tomita Volcanic Sandstone).

......
01-.J

Table 1. List of molluscan fossils of the Palliolum Association (P. Assoc.), Nuculana Association and Thyasira bisecta Association.
Lithofacies are shown by the following abbreviations. tb: turbidite facies. Is: laminated siltstone of turbidite facies. sl: silt facies.
ss:sandy silt facies. vs: volcanic sand facies. fs: fine-grained sand facies. at: alternation facies.
Association

P. Assoc.

71~~

~~~~~

Thyasira bisecta Assoc.

Associationo~~~~~CDgNN_N~~~ _ _ M~N_M

N71~~1~~~

~~~~
0
000

~~,~~777~~~~~~~~7~~~~~~~~~~~~~~o!~~~~~~~~_________....

~~~-----~~~~~~~~---~~------~-----~------~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~_~~~~~~~~~~---~

Pallio/um peckham;

Nuculana

NM~~~~~~~~~~~~~~~

I-'

01
00

NNNMM~~OOOOOOOO~~Ug~M~MN-­

77~. I~~~~~~
___

~~~~~

NN~

--~~~--~-~~~~~~~~~O~~

Nuculo niponica
Acila qivaricata

Acila nakazimai
Nuculana sodoensis
Nuculana yokoyama;
Nuculana roba;

Saccella on oyama;
Portlandia hirosakiensis

Portlandia toyam aens;sYoldia kikuchii
Yo/dia johann;Yo/dia thraciaeformis
Yo/dio sp.
Nuculanidae gen. et sp.
Acharax tokunagai
Limopsis sp.B
Chlamys islandica
Pandora sp.
P~riploma cf. besshoensis
Lunaria pal/ida
Cryptonarica claus a
Fusitriron oregonensis
Buccinum ct. rossicum
Buccinum sp.
Plicifusus sp.
Mohnia cf. yanamii
Neptunea intllrsculpta
N~ptunlla spp.
Clinopegma borllalis
Fulgoraria sp.
Volutomirra alaskllnsis
Admerll lischke;
Elallocyma braunsi
Antiplanes sancriioannis
Propebela candida
Siphonodentalium sp. A
Cyeloeardia ferruginea
Tridonta borealis
Macoma calcarea
Clinocardium ehikagawaense
Pandora wardiana
Microstelma sp.
Turritella nipponiea
Boreorrophon xesrra
Anriplanes contraria
Turbonilla inscirula
Striodentalium rhabdotum

Thyasira bisecta
Lucinoma acutilineatum
Turritella sa,shuensls

~
i';:
::3-

a'

~
~

S

799. Omma-Manganji Fauna in Gojome-Oga

These fossils are well preserved. The bivalves
are often found as conjoined valves. Some
individuals of Acila nakazimai and Yoldia
thraciaeformis keep their shell perpendicular tothe bedding plane. The valves of smaller species
such as Nuculana spp. are usually disarticulated,or, if not, do not seem to be preserved at theirliving position in most cases. Fragile protoconchsof large gastropods are often preserved.
Thyasira bisecta Association:-The association
is made up of only five species. Thyasira bisecta,
a large lucinacean bivalve, is predominant in
number. Lucinoma acutilineata is common but
less in number of individuals than Thyasira.
In addition to them, Acila nakazimai, Turritellasaishuensis and Cryptonatica clausa are rarely
found.
The association is found from various typesof lithofacies, such as the silt facies of the
Tentokuji Formation, sandy silt facies andpumiceous fine-grained sandstone of the alternation facies in the lower part of the Sasaoka
Formation.
Thyasira bisecta and Lucinoma acutilineata
usually keep the valves conjoined and theircommissure planes stand perpendicular or
oblique to the bedding plane. They are apparently preserved at their life positions, as the occurrence is comparable to the mode of life of living
lucinaceans (Stanley, 1970). In some localities
individuals of Thyasira form a dense aggregation. In pumiceous fine-grained sandstone at
Loc. 21-2, 40 individuals of Thyasira, two
Lucinoma and four Acila are disseminated on
the exposure of 2 m high and 1.5 m wide.
Almost all individuals of the three species in theaggregation are conjoined. The commissureplanes of most Thyasira and Lucinoma standperpendicular to the bedding plane. This occurrence is interpreted as a result of colonial andimmobile life of Thyasira.
Acila-Turritella Association:-The characteristic species of the association are Acila nakazimai, Turritella saishuensis, Macoma calcarea,
Clinocardium chikagawaense, Mya cuneiformis
and Glycymeris derelicta. They are associated byYoldia johanni, Yoldia thraciaeformis, Tridonta

159

borealis, Crenulilimopsis oblonga and someothers. The association is represented by 182
assemblages, about 90% of which were obtained
from the upper part of the sandy silt facies.
Twenty assemblages of this association occur
in the fine-grained sand facies, volcanic sandfacies and mudstone and sandstone beds ofthe alternation facies.
In the sandy silt facies, most constituent
species mentioned above are found. Minorlithologic differences within this facies do notseem to give great influence to the species
composition of· the association. Molluscan
shells are, however, less abundant in silty part
than in sandy part of the sandy silt facies. The
association is less diverse in the fine-grained
sand facies of the Sodenosawa and Terasawa
Members, and is composed only of Macoma
calcarea, Mya cuneiformis and Clinocardium
chikagawaense. The upper part of the sandy
silt facies of the Machimura Member is often
intercalated by sandstone beds of the finegrained sand facies, 30 cm to 10 m thick. Theintercalating sand facies also yields assemblages
belonging to the association. The species foundare Turritella saishuensis, Mya cuneiformis
and Macoma calcarea, but no other representative species of the association (Text-fig. 4).
The species composition in the alternation faciesof the Tofuiwa Member is similar to that in the
sandy silt facies, but Crenulilimopsis oblonga,
Nassarius siquijorensis and some others are
exclusively found here, while Glycymeris
derelicta never appears in the facies. The assemblages both in the muddy and sandy beds of thealternation facies show no remarkable differencein species composition.
The fossils are sporadically scattered in therock. They are often found as loose cluster but
the shells do not touch each other. Protoconchs
of gastropods are usually preserved. Fine sculptures of these shells are mostly preserved andfragmental shells are rare. Mya usually keeps
the valves conjoined and is disposed perpendicular or oblique to the bedding plane withposterior ends pointing upward. Macoma is
usually conjoined and is arranged parallel or......
0>

Table 2a. List of molluscan fossils of the Acila-Turritella Association. See Table 1, for abbreviations of lithofacies. (continued on Table 2b)

Association

~
Ofa

C ies

Species

Turritella saishuensis
Aci 10 nakazimai
Mya cuneiformis""'acoma calcarea
CI inocardium chikagawaense
Glycymeris derelicta
Cryplonalica clausa
Nuculana yokoyama;

Nuculana sp.
Portlandia hirosakiensis
Yo/dia johann;Yoldia fhraciaeformis
Anadara amicula
Limopsis sp.A
Solamen spectabilis
Mizuhopecten poculum
Ltici noma acutilineata
Thyasira tokunagai
Cyclocardia ferruginea
Cyelacardia sp.
Tridonta borealis
Paphia sp.
Pandora ward; ana
Myadora japonicG
Periploma plane
Microstelma sp.
Bittium binodulosum
Trophonapsis kagaensis
Boreatrapho n xes tra
Plicifusus ozawai
Admefe Iischkei
Anli pi ane-s contrari a
SUGvodrillia? sp.B.
Riuguhdrillia? sp.
Ophiodermella pseudopannus
Oenopola kagana
Propebela candida
rurbonJlla inscitula
Crenul iii mopsi s oblonga
Nassarius siquljorensis
Suavadri IIi a? sp.A.
Striodentalium rhebdatum
Siphonodenlalium sp. B.

Acila - Turritella
_N

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Table 2b. List of molluscan fossils of the Acila-Turritella Association. See Table 1, for abbreviations of lithofacies. (continued on Table 2c)

Aci/a - Turrite//a

Association

~
h of

ac·
les

Species

Turritella saishuensis
Acile nakazimai
Mya cuneiform is
Macoma calcarea
C{ inocardium chikagawaense
Glycymeris derelicta
Cryptonatica cl ausa
Nuculana yokoyama;
Nuculana sp.
Portlandia hirosaki ensis
Yo/die johann;Yoldia fhraciaeformis

Anadara amicula
Limopsis

sp.A

So/amenspectabilis

Mizuhopecten pocu/urn

Luci noma acutilineata

Thyasira toJwnogoi
eye I ocardi a ferruginea
Cye/ocardia sp.
Tridonta borealis
Paphi a sp.
Pandora wardi ana
Myadora japonica
Periploma plane
MicrosteJma sp.
Bittium binodulosum
Trophonopsis kagaensis
Boreotrophon xestra
Plicifusus ozawai
Admete Ii schkei
Antiplanes contrari a
Suavodrillia? sp.B.
Riuguhdrilli a? sp.
Ophi odermell a pseudopannus
Oenopota kagana
Propebe/a candida
Turbon" I a inscitula
Crenulilimopsis oblonga
Nassarius siquljorensis
Suavodrillia? sp.A.
Stri odental ium rhabdotum
Siphonodentalium sp. B.

~~

Associationo~u~7~~1~~~~~~71~9~77~~~~~~7~~~~~~7~~~77~77~~119-1~7~1177~,~~~~~~~7~7~777777~77~77~77~777777~77777777~77+~~77~~~~~~~2~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~!~!~~ococ~~~~~~~~~~~~~~~~~~~~~~~2~~~~~~~~~~~~~~~~~~~~~~~~~~~••••••

••• •
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•
•

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•

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....

Table 2c. List of molluscan fossils of the Acila-Turritella Association. See Table I, for abbreviations of lithofacies.

Acila - Turritella

Association

~
°fa

C ies

Species

Turri tell 0 so i shuensis
Acila nakazimai
Mya cuneiform is""'acoma calcarea
CI inocardium chikagawaense
Glycymeris derelicta
Cryptonatica clausa
Nuculana yokoyamai
Nuculana sp.

t-:lAssociation-~~~~~~~~~~~~~~~m~w~~~~~~~mR~~~~~,~~1"""",""""""""",~

a~u~~-~a~a~u~
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au~~~~~~~MM~MMMMMMMMMMMM~M~MMMMMMM-NNM~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~N
NN
NNNNNNNNNNNNNNNNNNNNNNNN
NNNNN
NNNNNNNNNNNNNNNNNNNNN
MMM~~~~~~~~~~~~=~~~mm~~~m~m::~:m~~~~mm~:~m~~~m~~~~m=~~~:mm ~::~:~••• •••••••••• ••• •• • •••••••• •• • •••••• • •• ••••• ••••• • •••• ••• ••• • • • • •
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•

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Portlandia hirosakiensis

Yoldia johanni
Yoldia fhraciaeformis\I:l~Anadora amicu/a
Limopsis sp.A

i'i:

•

Solam~n spectabilis
Mizuh opecten poculum
Lucinoma acutilineafo
Thyasira tokunagai
eyclocardia ferruginea
Cyclocardia sp.
Tridonta borealis
Paphia sp.

:::s-

a·

~

•

sp.

Bittium binodulosum
Trophonopsis kagana
Bor~o t ropho n xestro
Plicifusus ozawa;
Admete lischkei
Antip/anes contrari a
Suavodrillia? sp.B.
Riuguhdril/ia? sp.
Ophi odermell a pseudoponnus
Oenopota kagaens;s
Propebe/a candida
Turbon/I/a inscitula
Crenul ilimopsis oblonga

•

~

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•

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•

Pandora ward; ana
Myadora japonica
Puip/oma plane/vIicrosteima

0)

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•
•

•

•

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Nassarius siquljorensis
Suavodrilli a? sp.A.

Striodentalium rhabdotum
Siphonodenta/ium sp. B.
--------------- -

-

--

-

799.
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10

30

50

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Omma-Manganji Fauna in Gojome-Oga

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_ _ _ 75

Text-fig. 4. Stratigraphical sequence at Machimura, the northern part of the
Gojome Area, showing the distribution of common constituent species of the AcilaTurritella Association, sand contents (break line in the left column) and the ratioof the left coiling forms of Neogloboquadrina pachyderma (solid line in the left
column), 1: fine-grained sandstone, 2: coarse-grained sandstone, 3: massive sandy
siltstone, 4: massive sandy siltstone with "Houki-zuna", 5: alternation of sandy
siltstone and siltstone, 6: alternation of sandy siltstone and siltstone with "Houkizuna", 7: sandy siltstone with tubulous burrows, 8: siltstone, 9: tuff, Sh: Sodenosawa Sandstone, Se: Machimura Sandy Siltstone_

164

Seiichiro MATSUI

slightly oblique to the bedding plane. Almost
all individuals of Acila are randomly oriented
and a half of them are conjoined. The occurrenceof Glycymeris is similar to that of Acila. Clinocardium usually occurs as single valve.
Different preservation of the bivalves seems
to reflect their different life habits, especiallydifferent depth of burrowing. Mya cuneiformis
can be regarded as a very deep burrower, judging
from the life habit of Mya arenaria, a living
analogue of M. cuneiform is. Macoma calcarea
is also probably deep burrower. Such deepburrowers generally keep their shells conjoined,
and the orientation of the shells to the bedding
plane probably shows their life positions. On
the other hand, Acila, Clinocardium, andGlycymeris are shallow burrowers. Clinocardium
possesses short siphons and Glycymeris is nonsiphonate bivalve. Both of them probably exposed their posterior end above the bottom
surface. These three species are often foundas single valve, and the valves are randomly
directed. Dominance of single valve and randomorientation of these three species may be due
to reworking of dead shells by weak current
and/or burrowing animals. Molluscan shells
within the "Houki-zuna" in the sandy silt facies
are disposed along laminae, and are usuallycomposed of shallow burrowers such as Acila,
Glycymeris, Clinocardium and Turritella.
Macoma tokyoensis Association:-The association is characterized by dominant occurrence ofMacoma tokyoensis. Macoma is frequently
accompanied by Turritella saishuensis, and small
gastropods and bivalves (e.g. Ophiodermella
pseudopannus, Axinopsida subquadrata) areoften found. Macoma calcarea coexists with M.
tokyoensis at Locs. 4-lh, 4-2a, 4-2b, 5-la.
This association is confined to the fine-grained
sand facies. Some assemblages of the AcilaTurritella Association are similar to the Macoma
Association in species composition but do notcontain Macoma tokyoensis. For example, theassemblage of Loc. 4-2b in the fine-grained sandfacies contains M. tokyoensis, M. calcarea, andTurritella, and is included in the Macoma tokyoensis Association. On the other hand, sandy

siltstone at Loc. 4-2c, situated at 1.4 m below
4-2b contains M. calcarea and Mya cuneiformis
without M. tokyoensis, being considered tobelong to the Acila-Turritella Association.
The shells are well preserved. Two speciesof Macoma are usually disposed parallel oroblique at low angle to the bedding plane.
Protothaca Association:-This association ischaracterized by large and thick shelled bivalvessuch as Protothaca adams~ Anadara amicula,
Glycymeris yessoensis, Dosinia japonica, Mercenaria stimpsoni and smaller bivalves Felaniellausta. It is contained in the fine-grained sandfacies.
The association occupies horizons stratigraphically very close to those of the Macoma
tokyoensis Association in the fine-grained sandfacies. The sand containing these two associations seems to have no difference in lithology,
although there are few common species between
the two associations.
The large bivalves are mostly well preserved,
articulated and randomly oriented. Shells areusually sporadically disseminated in the sand.
Anadara amicula is often crowded in a bed of
10 cm or less in thickness. The other species
are also contained in the Anadara beds. Felaniellausta is also associated with the large bivalves,
although it forms a dense aggregation of shells
in some cases.
Relationships between association types
and environments
Vertical and horizontal distributions of theassociations are shown on a stratigraphicalprofile (Text-figs. 5A-B). There is rather loose
correlation between the association types andthe lithofacies types, as follows:
Palliolum Association - The turbidite facies.
Nuculana Association - The silt facies andlower part of the sandy silt facies.
Acila-Turritella Association - The upper
part of the sandy silt facies, alternation facies
and fine-grained sand facies.
Macoma tokyoensis Association - The finegrained sand facies.

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r-I..-I..--I..... . . - t N N N N N N N N N N..c1Cl.Q1Il,Q......

~ ~~~~~~~~~~~~~~~~~~~~~~~~•. - 4 N N .....
1111111111111111111'oQ'..:r'<::J''o:I'1I1
~
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1I1 1I1 I.t'\ I.t'\ I.t'\ I.t'\ I.t'\ I.t'\ 1I1 I.t'\ I.t'\ I.t'\ lI1 I.t'\ ~ NNNNNSpecies

Turritella saishuensis• •Macoma calcarea• • • •
Yoldia j o h a n n i .
PI ici (usus ozawa;
Antiplanes contraria•
Ophioderme/la pseudopannus• •Oenopota kogano•
M acoma fokyoensis
Acila sp.
• • •/tit i zuhopecten pocul um•
Axinopsida subquadroto• •Clinocardium fastosum
Thracia kakumana
Homalopoma amussitatum_
Trophonopsis kagaensis•
Boreotrophon xestra
Reticunassa cf. spurca
Paradrillia ct. dainichiensis_
Epitonium e c h i g o n u m .
Anadara a m i c u l a .
Glycymeris yessoensis
Felaniell a usta•
Fulvia mutica
Dosini Q japon;ca
Mercenaria stimpsoniProtothaca adamsi
Cryptonatica claus a
Neverita didyma•••

Association~~~~.

.-4.-lNNN
I
I
I
It

u

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I
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1111111111111..,1.1'\
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N~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

"

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•••
•

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•
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o

;:!
•

•

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•

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5

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• • • • • •
•

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••

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0

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(I)

Macoma tokyoensis

Association

I-'

0.

(I)

Table 3. List of molluscan fossils of the Macoma tokyoensis Association and Protothaca Association. See Table 1, forabbreviations of lithofacies.

...

.....
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01

SeiichiroMATSUl

166

A
IV
III

20mO]

Oga Area5":7;".~OQ"'<

Gojome Area

W<::..... . .... ............... ~~;:hN" COQ"

P/? ............... ~ .....~···'-,-------.

~ .............. :"-'?'..... --.. ·· .. ··· .. ···· .......... ···::""~i:: ......p::::::::::::::. . .:---~° II ~--........
...............
......... ...............•.•...•.... --- ... .....

..

- -=--..................

g• .....~II~~~--~///;-.::.~:.::::~.~........... -............. -.~ ~. ~ .~.~.~. ~.~ ~ -IT! IITllTfutx
Gojome Area

B

N<::

III
- - - --.:: ::::::~-=-...::.:-2 · .... ~~ Iv

v v v v vv v v
Swell v v
v v Odaiv v v v v v v
v~1...... 4 ~5 ~6
lImB 2 ffiI]J3 83
8 7

1':':~8[illJ9 lZJ10 1€YJ111

1---···12

-0

p

13

* 14

--~

0

15

• 16

... 17

Text-fig. 5. Stratigraphic distribution of the associations. A: E-W section from the northern partof the Gojome Area to the Oga Area. B: NoS section along the eastern margin of the Gojome Area. 1:
Miocene volcanics. 2: Onnagawa Formation. 3: Funakawa Formation. 4: turbidite facies. 5: thinly
laminated siltstone of turbidite facies. 6: silt facies. 7: sandy silt facies. 8: alternation facies. 9:
volcanic sand facies. 10: fine-grained sand facies. 11: conglomerate. 12: marker horizons I - IV. 13:
Palliolum Association. 14: Nuculana Association. 15: Thyasira bisecta Association. 16: Acila-Tur·
ritella Association. 17: Macoma tokyoensis Association and Protothaca Association.
changes of the lithofacies may be controlled by
the regressive shallowing of the sea and by
areal differences of water depth, while litho·
logical variations within a lithofacies type areprobably due to local differences of hydrodynamic conditions of the bottom. This suggeststhat the distribution of the associations is primarily controlled by water depth. For example,
the Palliolum Association probably occupied

the deepest part of the area, the Acila-Turritella
Association was living in the area shallower than
the former, and the Macoma tokyoensis and theProtothaca Associations occupied the mostnear·shore and shallowest environments. The
variations of lithology within a lithofacies type
are, however, often correlated with compositional variations within the associations. The
major cause of the compositional variations

799.

MUD CONTENT
muddy

80

60

40

o

~

Macoma tokyoensis Assoc.

tI

Pro to thaca

+
.s::.

167

Omma-Manganji Fauna in Gojome-Oga

%
20

sandy

•••••••••••••••••••••••••••••••••••••••••••........_._._.-

Assoc .

~•••••••9 •••••••••••••

VI

::E:
~

a.
1&.1

o

1&.1

>

a.
CI>
CI>

Pall iolum

Association'0

Text-fig. 6. Relationship between the associations and environmental conditions expressed interms of water depth and mud content of the sediments.
associated with the minor lithological variations
may be ascribable to difference of the substrata.
Facies- and depth-related distribution of theassociations is summarized in Text-fig. 6.
The Palliolum Association is confined to theturbidite facies and to the westernmost partof the area studied. Accordingly it is thougtlt
to represent the deepest biofacies of the area.
The Nuculana Association occurs in muddy
deposits and occupies deep environments but
shallower than the Palliolum Association. Someassemblages of the Nuculana Association (Locs.
7-9a, 7-9b) are found in a muddy sand bed(sand content 63%) interbedded in the silt
facies. The two assemblages found in the sandy
sediments contain Neptunea or Fulgoraria,
which are characteristic in the association, butlack nuculanid bivalves. This fact suggests thatthe prevalence of deposit-feeding nuculanid andnuculid is probably due to high contents of
mud fraction in the substrata. Absence of thedeposit feeding bivalves at Locs. 7-9a and 7-9b
is interpreted as a modification of composition dependent on lithology. Sanders (1958)
showed that concentration of clay fraction ispositively correlated with the distribution ofdeposit-feeders in a bay environment.
The Acila-Turritella Association is widelydistributed in the sandy silt facies. The association in this facies is relatively stable in species
composition, although a minor variation independent of lithology is observed. The variation
is probably due to minor fluctuations of water
depth, as discussed in the next section. The
association modifies its composition in the finegrained sand facies, and Glycymeris derelicta
is absent, while Mya and Macoma calcarea areprevalent. The association in the alternation

168

Seiichiro MATSUI

facies of the Tofuiwa Member have similar
composition to that in the sandy silt facies,
but is modified by the abundant occurrence ofCrenulilimopsis oblonga and Nassarius siquijorensis and by absence of Glycymeris derelicta.
Crenulilimopsis and Nassarius are warm watermolluscs, which are rare in other horizons inthis area. The living form of Nassarius siquijorensis is restricted to shelf environment under
the warm Kuroshio water and is distributed
from subtropical to equatorial Pacific region.
The Tofuiwa Member is older than the otherhorizons yielding the Acila-Turritella Association, and is latest Pliocene to earliest Pleistocene
in age (Matsui, 1981). This horizon is assigned
to be in "pre-glacial Pleistocene" time, when
the Japan Sea coast of Honshu including thisarea was considered to be affected by the warm
surface water, based on faunal analysis of planktonic foraminifers (Maiya et al., 1976). Thesewarm water molluscs were conveyed by the
influx of warm waters from the Pacific regions.
The Macoma tokyoensis Association and
the Protothaca Association are found in theuppermost part of the marine sediments andare distributed in the eastern part of the area.
The two associations are considered to be theshallowest inhabitants among others. They areclosely accompanied by each other, and theenclosing rocks of the two associations show
little lithological difference.
The Thyasira bisecta Association appears
in three lithofacies types, the silt facies, sandy
silt facies and fine-grained sandstone of thealternation facies. In the Taihei Area, southeastof the Gojome Area the association occurs inpebbly fine-grained sandstone of the Sasaoka
Formation (Matsui, 1977). The Thyasira bisecta
Association seems to have wide tolerance tosediment types. The association is characterizedby common occurrence of two lucinacean
species, Thyasira Iijld Lucinoma acutilineata.
Allen (1958) stated that the anatomical featuresof the Lucinacea show their successful adaptation to environments unsuitable for other infaunal species, where the supply of oxygen andfoods is suppressed. This fact is probably related

to the absence of Thyasira and Lucinoma in theother associations and their low selectivity to
sediment type.
Fine structure of Acila-Turritella Associationin the sandy silt facies
As discussed before, the Acila-Turritella
Association is heterogeneous in species composition, and some of these variations in composition are interpreted as a result of the difference of lithology and invasion of warm surface
water.
In the sandy silt facies, the association showsa minor compositional variation independentof lithology. The fine compositional variationof the association in the sandy silt facies isanalyzed in relation to lithology and planktonic
foraminiferal assemblages. Stratigraphical distribution of constituent species of the association at an exposure in the northern part of the
Gojome Area is shown in Text-fig. 4 with thechanges of lithology, sand content and coilingratio of a planktonic foraminiferal species
Neogloboquadrina pachyderma.
Acila nakazimai and Turritella saishuensis,

which are characteristic species of the association, rarely coexist at one assemblage. The two
species respectively occupy the limited stratigraphical intervals and alternatively occur inthis section. Other characteristic species of theassociation seem to be distributed more evenly
than Acila and Turritella.
In order to examine the details of the alternative occurrence, molluscs of two sectionsin the northern part of the Gojome Area weresuccessively sampled. The sampling of molluscs
was made semi-quantitatively (Text-fig. 7).
Molluscs on the exposures are counted andwhole individuals of the surface of 2 m wideand 50 cm thick (i.e., 1 m 2 ) are treated as an
assemblage. In case that exposure is narrower
than 2 m by a cover or thinner than 50 cm bya insertion of tuff, the number of individuals
counted is converted to number per one square
meter of the exposure. Sand contents of theenclosing rocks are measured at about 1 m

M-series

Il,A

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LULULULULULULULULULULULULULULULU

Sampl i ng interval
Stratigraphic level

lower
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Turri tell a sa ishuensis
Mya cuneiformis

6

Lithology
Sand content

30~

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10

Text-fig. 7. Stratigraphic distribtuion of the abundance of characteristic elements of the Acila-Turritella Association in two sections.
M-series covers the assemblages of 25-3-68 to 25-3-75. Columnar section of M-series is shown in Text-fig. 4. GR-series covers the assemblagesof 4-5a to 4-5h. Symbols of lithofacies are noted in Text-fig. 4.

.....
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co

Seiichiro MATSUI

170

interval. Stratigraphically successive samples ofsuch assemblages are obtained from two sections.
The two serial samples are called M-series andGR-series.
The alternative occurrence of Acila andTurritella is evident in Text-fig. 7. In the two
sections, the two species are not completely
exclusive from each other, but in horizons
dominated by one species, the other is veryrare or absent. The alternative occurrence ofthe two species is hardly explained by changeof lithology. In the M-series, the two species
attain their maximum individual numbers inthe sandy silt containing sand fraction of about
50%, below and above the tuff Os-1. In the
GR-series, both species are most abundant in
the silt of about 30% in sand content.
The areal distributions of Acila and Turritellaalong the marker tuff Os-1 and Os-2 are shown
~A
\

\

r
r

H

G

in Text-fig. 8. In the localities A to G, thestratigraphical distribution of the two species
are similar to each other, for example, Acila
is abundant below Os-1, and Turritella takes
over the place above Os-1 in most localities.
In the locality H, however, Acila appears at
two horizons, above Os-1 and below Os-2 where
Turritella occurs in other localities. As thesea at that time was considered to become
deeper at the locality H than the localities A
to G, the distribution of the two species implies
that Acila have inhabited in a deeper sea bottom
than Turritella. This interpretation is consistent
with the fact that Acila occurs in the Nuculana
Association, but Turritella is not associatedwith it.
The stratigraphic distribution of the ratio ofleft-coiling forms of Neogloboquadrina pachyderma has a positive correlation with the occur-

F

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B

A

I
I

,
I

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fB
~C

,0
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I

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I
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Acila
nakazimai

Text-fig. 8. Areal and stratigraphic distribution of Turritella saishuensis and Acila nakazimai
along the marker tuff Os-1 and Os-2 in the northern part of the Gojome Area. Sections of A to G
correspond respectively to the following sections of Text-fig. 1. A: 2. B: 4. C: not shown in Textfig. 1. D: 5. E: 24. F: 25. G: 28.

799. Omma-Manganji Fauna in Gojome-Oga

rence of Turritella (Text-figs. 4 and 9). In Textfig. 9, the occurrence of Acila and Turritella
within 1 m from the sampling horizons of
microfossils is plotted against percentage of theleft-coiling N. pachyderma. Turritella occurs inhorizons only where the ratio is more than
78.5%, while Acila occurs in horizons of theratio less than 61%.
):,.

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The left-coiling fonns of N. pachyderma
inhabit in the colder surface water, and thefluctuation of the coiling ratio is probably
caused by the fluctuation of the surface watertemperature (e.g. Ericson, 1959). The change of
paleooceanographic condition in this area wasthought to be linked with the glacial climaticchanges (Maiya et aZ., 1976). The cooling ofclimate resulted the development of ice sheet
and eustatic lowering of the sea level. Therefore
the dominance of the left-coiling fonns may
indicate the horizons of lowered sea level, andTurritella is found in these horizons. The occurrence of Turritella in the horizons of high ratioof left-coiling N. pachyderma coincides with theassumption that Turritella occupied shallower
bottom than Acila.
Systematic notes
All speciemens examined are deposited in thecollection of the University Museum, Universityof Tokyo (UMUT). Registration numbers of
UMUT are given in parentheses after locality
number. Localities of M-series and GR-series
are expressed by combination of series name(M or GR), number of sampling level and a
letter of A or B. The numbers of samplinglevels are shown in Text-fig. 7. The letters of
A or B are code for identification of two sampling quadrates from the same sampling level,
which are not shown in Text-fig. 7.

-I

0 0)
-'0

3

CD

o

Homalopoma amussitatum (Gould, 1861)

A-19
A-14
A-8
A-13

-70
-34
-15
-29

-74
(5

o

Text-fig. 9. Relationship between
the occurrence of Turritella saishuensis
and Acila nakazimai and the ratio ofleft coiling form of Neogloboquadrina
pachyderma.

PI. 22, Fig. 1.
Homalopoma amussitatum (Gould). Habe,1958b,
p. 5, pI. 1, fig. 13; Kuroda, Habe and Oyama,
1971, p. 51, pI. 15, fig. 6.

Locality: 4-2b (CM16223).
Alvania sp.

PI. 22, Fig. 2.
Description:-Shell small in size, elongatedconical. Protoconch one and a half turns, depressed, surface smooth, homeostrophic, 0.4-

Seiichiro MATSUI

172

0.45 mm in maximum diameter. Teleoconch
four whorls, ornamented by axial ribs andspiral grooves. The first one tum ornamented
by round-topped fifteen to seventeen axial
ribs, and by four or five fine spiral grooves,being apparent only on the interspace of theaxial ribs. Penultimate whorl has nineteen or
twenty axial ribs and four or five spiral grooves.
The axial ribs on the body whorl become low
and irregular. The surface of the body whorl
lower than the periphery has five or six narrow
spiral grooves and no axial ribs. Suture is very
narrowly canaliculate. Peristome continuous.
Aperture circular, and umbilicus not open.
They are somewhat similar to Alvania asura(Yokoyama, 1926), but they have stronger
spiral grooves and less inflated whorl thanasura.
Locality: M1B (CM16224, CM16225).
Microstelma sp.

PI. 22, Fig. 3.
Description:-Shell small, solid, suboval in
outline with abutting whorl. Protoconch one
and a half turns, globose, smooth, hom eostrophic, 0.45-0.55 mm in maximum diameter.
Teleoconch three and a half whorls. The firstone ornamented by round-topped, orthoclinal
axial ribs numbering 14 or 15, and by two or
three spiral cords, which are weaker than theaxial ribs. On the later whorls, the spiral cords
become weaker or almost disappear. Axial ribs
17 to 19 on the body whorl, 15 on the penultimate whorl. On the body whorl, the axial ribs
abapically disappear below the periphery, andbecome low on the last quarter of whorl. There
are three or four very weak and flat spiral cords,
which are equal to or wider than the interspace, below the periphery. Aperture circular,
and outer lip slightly thickened. Umbilicus
narrowly opened.
These specimens are similar to Microstelma
daedala A. Adams, 1863 and M. {lava Okutani,
1964, but daedala has angulate shoulder, and{lava has more arcuate whorl and only weakspirallirae on the earlier whorls.

Locality: 12-2 (CM16226); 25-3-45 (CM16227); 25-3-59 (CM16228).
Turritella (Neohaustator) saishuensis
Yokoyama, 1923

PI. 22, Figs. 4-6.
Turritella saishuensis Yokoyama, 1923a, p. 3,
pI. 1, fig. 2.
Turritella (Neohaustator) saishuensis Yokoyama,
Kotaka, 1959, pp. 76-78, pI. 3, fig. 9, pI. 6,
figs. 2--4, 6, 7, pI. 12, fig. 9, pI. 14, fig. 7,
pI. 15, fig. 7.

More than seventy specimens of turritellid
gastropods are examined. They are divided. in tothree morphologically different types, which
are distinguished by differences in spiral cords,
but are very similar to each other with respect
to the other morphological characters. These
three types are morphologically comparable
respectively with T. saishuensis Yokoyama,.
T. motidukii Otuka, 1935 and T. nipponica
Yokoyama, 1920. Here these types are called
as saishuensis-type, motidukii-type and nipponicatype. The motidukii-type is numerically themost abundant, and ubiquitously occurs fromthe Sasaoka Formation. The saishuensis- andnipponica-types are rarer than the motidukiitype, and are usually associated with the motidukii-type. The following associations of thetypes can be recognized; the distribution in the
Sasaoka Formation are shown in parentheses.
"motidukii" only (lower and middle)"motidukii" + "saishuensis" (middle)"motidukii" + "nipponica" (middle and upper)"nipponica" (lowermost)
Kotaka (1959) examined ontogenetic changeof the spiral cords and regarded the motidukiiand saishuensis-types as morphological variation
within a species. The species composed of thetwo types are called as saishuensis in this paper.
The nipponica-type associated with the motidukii-type perhaps represents a phenon in thespecies of saishuensis.
Locality: 2-1b (CM16229); 2-2a (CM16230);
2-5b (CM16231); 2-5d (CM16232); 4-2a (CM799. Omma-Manganji Fauna in Gojome-Oga

16233); 4-2b (CM16234); 4-5a (CM16235); 4-5d
(CM16236); 4-5f (CM16237); 11-2 (CM16238);
20-1a (CM16239); 20-1b (CM16240); 21-1 (CM16241); 23-1 (CM16242); 24-1a (CM16243); 253-14 (CM16244); 25-3-34 (CM16245, CM16246);25-3-38 (CM16247); 26-5c (CM16248); 26-5g(CM16249); 26-7c (CM16250); M13A (CM16251).
Turritella (Neohaustator) nipponica
Yokoyama, 1920

PI. 22, Fig. 7.
Turritel/a nipponica Yokoyama, 1920, pp. 71,
72, pI. 4, figs. 16-19.

The taxonomic status of the samples composed only of the nipponica-type can not be
concluded, because these samples contain only
a few and poorly preserved specimens. They aretentatively called nipponica.
Locality: 7-8 (CM16252, CM16253).
Bittium binodulosum Yokoyama, 1920

PI. 22, Fig. 8.

Lunatia pallida (Broderip and Sowerby, 1829)

PI. 22, Fig. 9.
Polinices

pal/ida (Broderip and Sowerby).
Oldroyd, 1927, p. 728, pI. 97, fig. 9.
Lunatia pal/ida (Broderip and Sowerby). Shuto,
1964, pp. 288, 289, pI. 42, fig. 12, pI. 43,
figs. 4, 6-8, 11, 13.
Polinices (Euspira) pallidus (Broderip andSowerby). Marincovich, 1977, pp. 278-281,
pI. 25, figs. 1-6, 8.

Locality: Og2-3 (CM16256).
Nevertita (Glossaulax) didyma(R6ding, 1798)

PI. 22, Fig. 11.
Neverita (Glossaulax) didyma (Riiding). Habeand Ito, 1965, pp. 32, 33, pI. 9, figs. 1, 2.

Glossaulax didyma (Riiding). Kuroda, Habe andOyama, 1971, p. 121, pI. 18, fig. 2.

Locality: 4-1e (CM16257).
Cryptonatica clausa(Broderip and Sowerby, 1829)

PI. 22, Fig. 10.

Bittium binodulosum Yokoyama, 1920, p. 68,
p!. 4, fig. 8.

?Bittiumyokoyamai

Otuka. Sawada, 1962,
pp. 46, 47, pI. 2, figs. 10, 11.
?Bittium cf. yokoyamai Otuka. Ogasawara,
1977, pI. 22, figs. 15, 16.

The specimens have two nodular spiral cords
on the lower half of whorl and weaker two or
three spirals on the upper half. These spiralcords become low and flat on the later whorls.
The axial ribs are prominent and about 11 on
the body whorl. The outline of the shell issomewhat cyrtoconoidaI. The apical angle isabout 22 degree, and the mean spire angle isabout 15 degree. They well agree with the typespecimen of Bittium binodulosum. The typespecimen of the species from the Pleistocene
Koshiba Formation perhaps represents an immature form.
Locality: 25-3-35 (CM16254); 26-5g (CM16255).

173

Tectonatica

clausa (Broderip and Sowerby).
Habe and Ito, 1965, p. 30, pI. 8, fig. 4.
Natica (Cryptonatica) clausa (Broderip andSowerby). Marincovich, 1977, pp. 410-418,
pI. 41, figs. 7-10, pI. 42, figs. 1-6.

Locality: 1-2 (CM16258); 2-1a (CM16259);
2-5a (CM16260; 2-8 (CM16261); 4-1a (CM16262); 4-1c (CM16263); 4-1e (CM16264); 4-2c
(CM16265); 5-11b (CM16266); 7-6a (CM16267);
7-6e (CM16268); 7-6f (CM16269); 7-9a (CM16270); 12-2 (CM16271); 14-2 (CM16272);
15-3 (CM16273); 16-1 (CM16274); 20-1b (CM16275); 24-1a (CM16276); 25-2 (CM16277);25-3-7.5 (CM16278); 25-3-34 (CM16279); 253-63 (CM16280); 25-3-70 (CM16281, CM
16282); 26-5c (CM16283); 26-7c (CM16284);
28-2 (CM16285); 34-1 (CM16286); Og2-1 (CM16287); Og2-4 (CM16288).
Fusitriton oregonensis (Redfield, 1848)

Seiichiro MATSUI

174
PI. 22, Fig. 12.

PI. 23, Fig. 2.

Fusitriton oregonensis (Redfield). Takayasu,
1962, pI. 1, figs. 26a·b; Habe and It'o, 1965,
pp. 33, 34, pI. 9, figs. 5, 6.

Raphitoma ozawai Yokoyama, 1927c, pp. 172,173, pI. 47, figs. 3,4.
?Lora yanamii tenuis Hatai and Nisiyama, 1939,
p. 152, pI. 9, figs. 15, 16.

Locality: Og2-2a (CM16289).

Locality: 4-2b (CM16307); 4-5c (CM16308).
Trophonopsis kagaensis(Hatai and Nisiyama, 1939)

Mohnia cf. yanamii (Yokoyama, 1926)

PI. 22, Fig. 13.

PI. 23, Figs. 3-5.

Trophon kagaensis Hatai and Nisiyama, 1939,
p. 153, pI. 9, figs. 8, 9, 13, 14; Ogasawara,
1977 , pI. 21, figs. 5a-b.
Troph on ops is kagaensis Hatai and Nisiyama.
Kaseno and Matsuura, 1965, pI. 3, fig. 3.

cf. Bela yanamii Yokoyama, 1926b, p. 261,
pI. 32, fig. 11.
Lora yanamii (Yokoyama). Nomura and Hatai,
1935, pp. 123, 124, pI. 13, fig. 2.
cf. Mohnia sp. Chinzei, 1959, p. 116, pI. 10,
figs. 19, 20.
Mohnia yanamii (Yokoyama). Hatai, Masudaand Suzuki, 1961, pI. 3, figs. 7a-b; Takayasu,
1962, pI. 1, figs. 19a-b; Sakagami et al.,
1966, pI. 2, fig. 12; Honda, 1978, pI. 2, figs.
1a,b.

Locality: 4-1b (CM16290); 4-2a (CM16291);
5-2j (CM16292); 24-1a (CM16293); 25-3-7.5(CM16294).
Boreotrophon xestra Dall, 1918

PI. 22, Fig. 14.
Boreotrophon xestra DaIl, 1918, p. 232; Kosuge,
1972, pI. 7, fig. 6.

Locality: 5-1a (CM16295); 23-2 (CM16296);25-3-69 (CM16297); Og2-4 (CM16298, CM
16299).
Buccinum cf. rossicum Dall, 1907

PI. 23, Figs. 1,7.
cf. Buccinum rossicum DaIl, 1907, pp. 150,151;
DaIl, 1925, p. 8, pI. 31, fig. 5; Kosuge, 1972,
pI. 18, fig. 1.
Six poorly preserved specimens are examined.
They are characterized by rather thin shell,
inflated whorls, fine spiral grooves on the shellsurface, a wide and shallow channel in frontof the suture, and a weak spiral cord on theshoulder. They are very similar to Buccinumrossicum DalI.
Locality: 5-12b (CM16300); 7-6d (CM16301);
7-6h (CM16302); 7-10a (CM16303); 14-1 (CM16304); 14-5b (CM16305); 34-1 (CM16306).
Plicifusus ozawai (Yokoyama, 1927)

Twenty-six specimens were collected fromfour localities. Two living specimens from sandy
bottom 200 m deep of Toyama Bay, the Sea
of Japan are also examined for comparison.
In general outline, eight specimens from the
Gojome Area (Locs. 3-1, 12-1, 34-1) agree with
Yokoyama's description of Mohnia yanamii,
but they are somewhat different from yanamii
in number and shape of axial ribs and in prominence of spiral furrows. The specimens figured
by Yokoyama (UMUT CM23085) has eighteen
axial ribs on the body whorl, and three others
not figured (CM23086) have 21, 20 and 17
axial ribs on the body whorl respectively. The
number of the axial ribs of the specimens fromthe Gojome Area is about 12 on the average,
ranging from 11 to 14. The Gojome specimens
have more round-topped axial ribs, more obscurespiral furrows and anteriorly less narrowed
siphonal canal than the typical Mohnia yanamii.
Eighteen specimens from the Wakimoto Formation (Loc. Og2-4) also differ in number ofaxial ribs and in shape of the siphonal, canalfrom the typical yanamii, but the other features
well agree with Yokoyama's description. The
number of the axial ribs of these specimens is799. Omma-Manganji Fauna in Gojome-Oga

about 13, ranging from 12 to 15. The Wakimoto
specimens have more slender axial ribs and more
prominent spiral furrows than the Gojome
specimens. Two living specimens from Toyama
Bay (UMUT RM16654, RM16655) are very
similar to the specimens from the Wakimoto
Formation, but they have more slender outline
than the latter. Some of the living and fossil
specimens preserve protoconch. The first one
turn is smooth and depressed. The succeeding
half turn has smooth surface and angulate
shoulder. The next one turn is ornamented by
two prominent spiral cords, which are situatedon the shoulder and on the periphery respectively. The axial ribs appear on the next whorl.
Locality: 3-1 (CM16309); 12-2 (CM16310);
34-1 (CM16311, CM16312); Og2-4 (CM16313,
CM16314).
Neptunea intersculpta (Sowerby, 1899)

PI. 23, Fig. 6.
Neptunea intersculpta (Sowerby). Habe and Ito,
1965, pp. 69,70, pI. 25, fig. 4; Shikama andMasujima, 1969, pI. 5, fig. 31.

Locality: 2-8 (CM16315); 5-13a (CM16316).
Clinopegma borealis Tiba, 1969

PI. 23, Figs. 8a, 8b.
Clinopegma borealis Tiba, 1969, pp. 135, 136,
pI. 7, figs. 1-5; Tiba and Kosuge, 1982, pp.
11,12, figs. 1-6.

Shell has an angulate shoulder forming achannel in front of suture. Siphonal canal shortand twisted. Surface of the shell ornamented
with very weak spiral threads and with very
weak and irregular growth lines. They wellcoincide with Clinopegma borealis from Sea of
Okhotsk, although they have somewhat lower
spire than the living species.
Locality: 5-13a (CM16317, CM16318); 5-13c(CM16319); 14-4a (CM16320).
Nassarius (Zeuxis) siquijorensis(A. Adams, 1852)

PI. 22, Fig. 15.

175

Zeuxis caelatus (A. Adams). Kira, 1959, p. 73,
pI. 28, fig. 16.
Zeuxis siquijorensis (A. Adams). Kuroda, Habe
and Oyama, 1971, pp. 177,178, pI. 48, figs.
9,10.

Locality: 20-1a (CM16321, CM16322); 20-1b(CM16323).
Reticunassa cf. spurca (Gould, 1860)

PI. 22, Figs. 16a, 16b.
Nassarius (Hinia) aff. dominulus (TapparonaCanefri). Kanehara, 1940a, pI. 12, figs. 11, 12.
cf. Reticunassa acutidentata (Smith). Kira, 1959,
p. 73, pI. 28, fig. 12.
cf. Reticunassa spurca (Gould). Kuroda, Habe
and Oyama, 1971, pp. 175, 176, pI. 47, figs.
17-19.

The two specimens agree with Reticunassa
spurca (Gould) in general outline, but they havesomewhat smaller shell and less number of axial
and spiral ribs than spurca. The measurement is
as follows.
1 (Loc. 4-1a) 2 (Loc. 24-]:a)Specimen
Height (mm)
6.65
7.85
4.65
Maximum
3.8
diameter (mm)8
Spiral cords on
7
body whorl
Spiral cords on
3
3
penultimate
Axial ribs on
12
14
body whorl
Locality: 4-1a (CM16324); 24-1a (CM16325).
Volutomitra alaskana Dall, 1902

PI. 22, Fig. 17.
Volutomitra alaskana DaB. DaB, 1921, p. 87,
pI. 11, fig. 3; Sakagami et al., 1966, pI. 1,
fig. 28; Tiba and Kosuge, 1980, pp. 3-5,
figs. 1-5.
Mitra kurakiensis Hatai and Nisiyama. Takayasu,
1962, pI. 1, figs. 18a-b.

Locality: Og2-4 (CM16326, CM16327).
Admete lischkei (Yokoyama, 1926)

Seiichiro MATSUI

176

pI. 55, fig. 10.

PI. 22, Figs. lSa, lSb.

Cancellaria lischkei Yokoyama, 1926b, pp. 264,
265, pI. 32, figs. 16, 17.
Admete lischkei (Yokoyama). Chinzei, 1959,
p.116, pLIO, figs. 5-7.
Locality: 12-2 (CM1632S);
16329); 26-5g (CM16330).

25-3-69(CM

Elaeocyma (Splendrillia) braunsi(Yokoyama, 1920)

The specimens have opisthoclinal prominent
axial ribs, which are 12 in number on the penultimate whorl, and have J-shaped distinct sinus.
The first two turns are polished and somewhat
heterostrophic. They are very similar to the
syntype specimens of the species (UMUT
CM2007S-200S0), although the axial ribs of thepresent specimens are abapically extended thanthe Yokoyama's specimens.
Locality: Og2-4 (CM16331, CM16332).

PI. 22, Figs. 19a, 19b.

Pleurotoma (Drillia) braunsi Yokoyama, 1920,
pp. 40, 41, pI. 1, figs. 25a-c.
Elaeocyma (Splendrillia) braunsi (Yokoyama).
Kuroda, Habe and Oyama, 1971, p. 206,

Paradrillia cf. dainichiensis (Yokoyama, 1923)
PI. 22, Fig. 20.
cf. Drillia dainichiensis Yokoyama, 1923b, p. 6,

Explanation of Plate 22
Fig.1. Homalopoma amussitatum (Gould), x 3, Loc. 4-2b (CM16223).
Fig. 2. Alvania sp., x8, Loc. M1B (CM16224).
Fig. 3. Microstelma sp., x8, Loc. 25-3-45 (CM16227).
Figs. 4-6. Turritella (Neohaustator) saishuensis (Yokoyama), xl, fig. 4, "saishuensis"-type,
Loc. 25-3-38 (CM16247); fig. 5, "nipponica"-type, Loc. M13A (CM16251); fig. 6, "motidukii"-type, Loc. 25-3-34 (CM16245).
Fig. 7. Turritella (Neohaustator) nipponica Yokoyama, xl, Loc. 7-8 (CM16252).
Fig. 8. Bittium binodulosum Yokoyama, x 2, Loc. 25-3-35 (CM16254).
Fig. 9. Lunatia pallida (Broderip and Sowerby), xl, Loc. Og2-3 (CM16256).
Fig. 10. Cryptonatica clausa (Broderip and Sowerby), xl, Loc. 25-3-70 (CM16281).
Fig. 11. Neverita (Glossaulax) didyma (Roding), x2, Loc. 4-1e (CM16257).
Fig. 12. Fusitriton oregonensis (Redfield), xl, Loc. Og2-2a (CM16289).
Fig. 13. Trophonopsis kagaensis (Hatai and Nisiyama), xl, Loc. 4-2a (CM16291).
Fig. 14. Boreotrophon xestra Dall, xl, Loc. Og2-4 (CM16298).
Fig. 15. Nassarius (Zeuxis) siquijorensis (A. Adams), x1.5, Loc. 20-1a (CM16321).
Figs. 16a, 16b. Reticunassa cf. spurca (Gould), x3, Loc. 24-1a (CM16325).
Fig. 17. Volutomitra alaskana Dall, x 2, Loc. Og2-4 (CM16326).
Figs. 18a, 18b. Admete lischkei (Yokoyama), x3, Loc. 25-3-69 (CM16329).
Figs. 19a, 19b. Elaeocyma (Splendrillia) braunsi (Yokoyama), x2, Loc. Og2-4 (CM16331).
Fig. 20. Paradrillia cf. dainichiensis (Yokoyama), x2, Loc. 5-1b (CM16333).
Fig. 21. Antiplanes contraria (Yokoyama), x1.5, Loc. 25-3-38 (CM16337).
Fig. 22. Antiplanes (Rectiplanes) sanctiioannis (Smith), xl, Loc. Og2-4 (CM16340).
Fig. 23. Suavodrillia? sp. A, xl, Loc. 20-1a (CM16342).
Fig. 24. Suavodrillia? sp. B, x3, Loc. 2-5d (CM16343).
Figs. 25, 26. Ophiodermella pseudopannus (Yokoyama), fig. 25, x1.5, Loc. 25-3-35 (CM16355);
fig. 26, x3, Loc. 4-1e (CM16349).
Fig. 27. Oenopota kagana (Yokoyama), x1.5, Loc. 2-1b (CM16356).
Fig. 28. Propebela candida (Yokoyama), x3, Loc. 12-2 (CM16360).
Fig. 29. Epitonium (Boreoscala) echigonum Kanehara, x1.5, Loc. 5-2j (CM16369).
Fig. 30. Turbonilla (Ptycheulimella) inscitula Yokoyama, x3, Loc. 25-4 (CM16373).

MATSUI: Omma-Manganji Fauna in Gojome-Oga

Plate 22

799. Omma-Manganji Fauna in Gojome-Oga

177

pI. 1, fig. 2.
cf. Clauatula patruelis dainichiensis (Yokoyama).
Makiyama, 1927, pp. 102, 103, pI. 4, figs.
14,15.
Clauatula dainichiensis (Yokoyama). Kanehara,
1940a, pp. 131-133, pI. 12, figs. 1-10.
cf. Clauatula (Paradrillia) dainichiensis (Yokoyama). Makiyama, 1940, pp. 133, 134.
Clauatula (Paradrillia) dainichiensis (Yokoyama).
Hatai, Masuda and Suzuki, 1961, pI. 3, figs.
4a-b.
Paradrillia ciainichiensis (Yokoyama). Kaseno andMatsuura, 1965, pI. 5, fig. 4.
cf. Paradrillia dainichiensis (Yokoyama). Powell,1969, p. 316, pI. 244, figs. 1-3.

Pleurotoma ( _ _ _ _ ?) Sancti-Ioannis Smith,
1875,pp.416,417.
Pleurotoma sadoensis Yokoyama, 1926b, p. 259,
pI. 32, fig. 3.
Antiplanes (Rectiplanes) sadoensis (Yokoyama).
Chinzei, 1959, pp. 117, 118, pI. 9, figs. 6, 7.
Rectiplanes sanctioannis [sic] (Smith). Takayasu, 1962, pI. 1, figs. 23a-b.
Rectiplanes sanctaioannis [sic] (Smith). Habeand Ito, 1965, p. 83, pI. 30, fig. 28.

The specimen is very similar to Paradrillia
dainichiensis (Yokoyama), although some minor
differences are found in surface sculptures. The
syntype specimens of dainichiensis (UMUT
CM21736, 21737) have thirteen to fifteen nodes
01;1 the shoulder of the penultimate whorl, andaxial ribs below the shoulder are twice as manyas the nodes. On the penultimate whorl of thepresent specimen both the nodes and ribs are
fifteen in number. Some authors applied thename of dainichiensis to Plio-Pleistocene specimens from northeast Japan. They are identicalwith the present specimen. A living specimen
from Sagami Bay (Powell, 1969, pI. 244, fig. 3)
is typical dainichiensis.
Locality: 5-1b (CM16333).

PI. 22, Fig. 23.

Antiplanes contraria (Yokoyama, 1926)

PI. 22, Fig. 21.
Pleurotoma contraria Yokoyama, 1926c, p. 383,
pI. 44, figs. 2a-b.
Antiplanes contraria (Yokoyama). Itoigawa,
1958, pI. 2, fig. 15; Habe and Ito, 1965,
p. 83, pI. 30, fig. 26.

Locality: 2-2b (CM16334); 4-2b (CM16335);
8-1 (CM16336); 25-3-38 (CM16337); Og2-4(CM16338).
Antiplanes (Rectiplanes) sanctiioannis(Smith, 1875)
PI. 22, Fig. 22.

Locality: 7-6b (CM16339); Og2-4 (CM16340,
CM16341).
Suavodrillia? sp. A

A specimen without body whorl was examined. It has high spire, a strong carina, one ormore strong spiral cords below the carina andtwo very low and wide spiral cords between theupper suture and carina. It is somewhat similar
to Suavodrillia declivis, but it has stronger
carina and spiral cords than the species.
Locality: 20-1a (CM16342).

Suavodrillia? sp. B.

PI. 22, Fig. 24.
Two broken specimens were examined. They
are characterized by a strong carina being more
prominent than that of Suavodrillia sp. A. There
are a spiral cord above the carina and strong two
or more cords below the carina. They are similar
to S. kennicottii (Dall, 1871) and S. oyamai Chinzei, 1959, but they have the stronger spiral cords
above the carina than the two species.
Locality: 2-5d (CM16343); 4-5g (CM16344).
Ophiodermella pseudopannus (Yokoyama, 1922)

PI. 22, Figs. 25, 26.
Genotia pseudopannus Yokoyama, 1922, pp. 37,
38, pI. 1, figs. 27, 28; Yokoyama, 1926b,
p. 260, pI. 32, fig. 2.

The specimens are ornamented with two
spiral grooves narrower than the interspace between the shoulder and lower suture, and by very

Seiichiro MATSUI

178

fine numerous spiral cords above the shoulder.
Axial ribs are about 20 on the penultimate
whorl, and become obscure on the later whorlsof the larger specimens. They well agree with
Yokoyama's description. Some of the specimensshow variation of the spiral ornamentation andshell outline. Three specimens from Locs. 4-1e;
21-1; 25-2 have spiral grooves wider than theinterspace (PI. 22, fig. 26). Five specimens from
Loc. 4-1b show variation of the spiral ornamentation, ranging from fine grooves to grooves
wider than the interspace. The other specimen
from Loc. 21-1 has spiral grooves narrower
than the interspaces, which are secondary
grooved. Height of spire and shape of bodywhorl also varies. PI. 22, fig. 25 shows typicaloutline, and PI. 22, fig. 26 exhibits lower spire,less inflated whorl and less narrowed siphonal
canal anteriorly.
Locality: 2-1a (CM16345); 4-1b (CM16346);
4-1c (CM16347); 4-1d (CM16348); 4-1e
(CM16349); 4-2a (CM16350); 4-2b (CM16351);
21-1 (CM16352); 25-1 (CM16353); 25-2
(CM16354); 25-3-35 (CM16355).

Bela candida Yokoyama, 1926b, pp. 261, 262,

Oenopota kagana (Yokoyama, 1927)

Yokoyama, 1927

PI. 22, Fig. 27.

PI. 22, Fig. 30.

Bela kagana Yokoyama, 1927c, p. 172, pI. 47,

Turbonilla (Ptycheulimella) inscitula Yokoyama,

pI. 34, fig. 1.

Bela candida var. angulata Yokoyama, 1926b,
p. 262, pI. 34, fig. 2.

Locality: 2-1a (CM16358); 5-13b (CM16359);
12-2 (CM16360, CM16361); 14-4c (CM16362);
16-1 (CM16363); 25-3-30 (CM16364); 26-5g(CM16365); 28-1a (CM16366); 34-1 (CM16367).
Epitonium (Boreoscala) echigonum

Kanehara, 1940
PI. 22, Fig. 29.
Epitonium (Boreoscala) yabei echigonum Kanehara [MS], 1940a, pI. 12, figs. 13-16, (March
31,1940).
Epitonium (Boreoscala) yabei var. echigonum
Kanehara, 1940b, pp. 14-16, pI. 4, figs.
6a-b (October 5, 1940).
Epittonium [sic] (Boreoscala) yabei echigonum
Kanehara. Kaseno and Matsuura, 1965, pI. 2,
fig. 6.

Locality: 4-2a (CM16368); 5-2j (CM16369).
Turbonilla (Ptycheulimella) inscitula

1927c, p. 176, pI. 47, figs. 15, 16.

fig. 2.

Locality: 2-1b (CM16356); 4-2b (CM16357).

Locality: 4-5g (CM16370); 23-2 (CM16371);
25-3-65 (CM16372); 25-4 (CM16373).

Propebela candida (Yokoyama, 1926)

PI. 22, Fig. 28.

Striodentalium rhabdotum (Pilsbry, 1905)

Explanation of Plate 23
Figs. 1, 7. Buccinum cf. rossicum Dall, xl, fig. 1, Loc. 34-1 (CM16306); fig. 7, Loc. 7-6h
(CM16302).
Fig. 2. Plicifusus ozawai (Yokoyama), x1.5, Loc. 4-5c (CM16308).
Figs. 3,4,5. Mohnia cf. yanamii (Yokoyama), x1.5, fig. 3, Loc. 34-1 (CM16311); fig. 4, Loc.
Og2-4 (CM16313); fig. 5, Toyama Bay, KT-79-5, St. 1-15D (RM16654).
Fig. 6. Neptunea intersculpta (Sowerby), xl, Loc. 5-13a (CM16316).
Figs. 8a, 8b. Clinopegma borealis Tiba, xl, Loc. 5-13a (CM16317).
Fig. 9. Striodentalium rhabdotum (Pilsbry), x2, Loc. Og2-4 (CM16376).
Fig. 10. Siphonodentalium sp. A, x4, Loc. 34-1 (CM16386).
Fig. 11. Siphonodentalium sp. B, x2, Loc. 20-1b (CM16389).

MA TSUJ: Omma-Manganji Fauna in Gojome-Oga

Plate 23

799. Omma-Manganji Fauna in Gojome-Oga
PI. 23, Fig. 9.
Striodentalium rhabdotum (Pilsbry). Habe, 1964,
p. 22, pI. 2, figs. 17,18.
Locality: 20-1a (CM16374); 20-1b(CM16375);
Og2-4 (CM16376, CM16377).

179

and fine grooves. The growth lines curve to theapex around the ventral side.
Locality: 5-13c (CM16378); 7-1 (CM16379);
14-1 (CM16380); 14-5b (CM16381); 17-1
(CM16382); 23-3 (CM16383); 25-4 (CM16384);
28-2 (CM16385); 34-1 (CM16386, CM16387);
Og2-2a (CM16388).

Siphonodentalium sp. A
Siphonodentalium sp. B

PI. 23, Fig. 10.

PI. 23, Fig. 11.
Many broken specimens are examined. Shell
curved, slightly tapering to apex, circular insection. The apex seems simple, although poor
preservation of the apical part prevents theprecise decision. Surface ornamented withgrowth lines and one to three longitudinal weak

A few fragmental materials are examined.
They are similar to Siphonodentalium sp. A,
but the growth lines do not curved to the apex
around the ventral margin.
Locality: 20-1b (CM16389, CM16390).

Gojome 1L~1'I
Hokkaido ~tifilJ1i
Akita f"rB
Funakawa {!'rill I
Kakegawa tf/-lII
Kitaura ~tlt1l
Machimura illJH
Manganji TJI!ii'i:;!f
Minamizawa fYl1R
Nishikurosawa
iI£i,~1R
Odai 7\.{=;
Oga ~J1[
Omma *~
Onnagawa :KlII
Sasaoka fljli'i)
Sodenosaw a fill / 1R
Tatsunokuchi ~ / 1=1
Tentokuji x.~r.1o!fTerasawa =#1R
Tofuiwa If.JIi!J¥iTomita 7:l71U
Wakimoto 116h*

1LM§-~J1[~.~*.-TJmo!f •• D~n~ED.:Mm*~~~1LM§-~.~.K

7j-;(Jii' G~m-rliflJ!mfVErp~~ {tE~7t;(Jiil~. c~.l:? tJ:~m~llSIl.::.mffjJj~J'L -n, GiI>~t§{iftL.t.:o fl{tE~~ <li/3 1:.-l\Ii/3 1:. c!: ~*- Gl'LG t ~-(', -tn GIi6 "?~;HIH.::.MtGnGo~l!U~fi~~rp"('~Ffi'i"J. :Ifffii'l"JI.::.J'JJ: '? t.:lifl7tI.::.;I; Ghn. *r~1itV'J.t'l1U: (X~.l: ? tdli.il~t'?-c7j-;(JiL-n't':C1tt\E~J'LGo i'tJ:hi:;,

Palliolum 'IIf-.lil'&t~l.,jl-l:::-jl·1 l-~:I1t

l'ilfi'G.l:? tJ:iiiH.t..~1tf:.I.::.;I;Ghn. Nuculana r.r.fUXI.::.f,jiI.':;'--/L-- l-~~lifl7t~di.lb-CI.'t.:oAcila· Turritella 'IIf-!$Efi Nuculana 'IIf-*.l: IJiji; <. it.:.l: I) ffUiLtJ: :;'--/L-- l- -;f,(n*1li'j1JfiJ'::'1:.,~,
L t.:o Macoma tokyoensis 'IIf-* c Protothaca 'IIf-.'i*~I.::.{*tJ: '? -C;l; Ghn. ;j:fa.::.JIl!: t m1.,;j;ffi*lLlijl~lifl7t~di.lb-CI.,t.:o Thyasira bisect a 'IIf-.lif1(ktJ:~l\Iic!gffil.::.I±l:mL. a-I.'~
mjH''£~ t '? -C I. ,t.: G L.1. '0 Adla- Turritella lIU~~tJ:i1>,,(, Acila nakazimai c Turritellasaishuensis (iml'::' LiI>;Jl<ff:-lt-f. ~Ft;B91'::':3~]LI.::..i£:I±li' Go ;: ~ 2 fill:~.i£:~j~ c i1nf¥:t1f:fL!ll.
~ Neogloboquadrina pachyderm~ ~~~~I"H'::'fi~.liliil;;I; IJ. 2 fill:~~][~I±l:m'i~~~{tt.::..l: Gifil*~ll'rll!lJl.::.mfflJj~n -C1.'kG LI.'o 32fifi~)II1Je.mc 3 tl1l~f}'l1JE1m~~e.if'&:Lt.:ot~r.s~-!l~[to be continued]

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 139, pp. 180-195, pIs. 24-27, September 30, 1985

800. PLIOCENE FRESHWATER GASTROPODS FROM THE IGA FORMATION
OF THE KOBIWAKO GROUP, MIE PREFECTURE, CENTRAL JAPANKEIJI MATSUOKA
Department of Earth Sciences, Faculty of Science, Nagoya University,
Chikusa, Nagoya 464

Abstract. The Pliocene Iga Formation of the Kobiwako Group of the Ueno
Basin and the Ayama Hills in Mie Prefecture, central Japan contains abundantremains of viviparid and pleurocerid gastropods. Taxonomic examination of thesegastropods results in recognition of one new genus and four species including three
new species. Igapaludina stricta (Araki), n. gen., Bellamya suzukii, n. sp., Tulotomoides sanaguensis, n. sp., and Semisulcospira (Biwamelania) praemultigranosa, n.
sp. are described herein. The subgeneric name Biwamelania is redefined.

known Pliocene freshwater deposits of Japan.
These molluscs seem to constitute a representative of the Pliocene non-marine fauna ofJapan, and moreover they are good material to
fIll a large gap in knowledge of the freshwatermolluscan fauna between the Miocene and the
Recent. Large collections of molluscs weremade at five localities shown in Text-fig. 1.
The purpose of the present study is to describe four species including three new species
and one new genus from the Ohyamada area
and the Sanagu area where the Iga Fonnation
is widely distributed: Igapaludina stricta (Araki),n. gen., Bellamya suzukii, n. sp., Tulotomoides
sanaguensis, n. sp., and Semisulcospira (Biwamelania) praemultigranosa, n. sp.
This is one of the series of papers describing
invertebrate fossils from the Kobiwako Group.

Introduction
The Pliocene Iga Fonnation is the lower partof the Kobiwako Group, and is distributed
mainly over the Ueno Basin and the Ayama Hills
in Mie Prefecture, central Japan. This formationconsists of lacustrine and fluvial sediments
deposited in the ancient lake, Paleo-lake Iga(Okuyama, 1981c) and its marginal area, andcontains an abundant and diversified molluscan
fauna associated with diatoms, sponges, fish,
tortoises, and crocodiles.
Since Nakamura (1925) first reported theoccurrence of fossil molluscs in the Iga Fonnation, the molluscan remains have been treatedgeologically and paleontologically in several
publications (Nakagawa, 1948; Takaya, 1963;
Kondo, 1968; Yokoyama, 1969; Okuyama,
1981a, b, 1983,1984; Matsuoka, 1983a; Tamura
et al., 1984), but no attempt has been made todescribe them in detail.
Molluscs collected from the Iga Fonnation
are well preserved and show high diversity
compared with molluscan fossils from other

Stratigraphy and occurrence
Stratigraphic studies on the Pliocene Iga
Fonnation have been made by Takaya (1963),
Kondo (1968), Yokoyama (1969), Yokoyama
et al. (1980, 1982), Kawabe (1981), and Okuyama (1981c). The Iga Fonnation unconfonn-

Received October 2,1984.
180

800. Pliocene Gastropods from the Iga Formation

181.Loc,E(26)

) (
L).

!

/

..

.-....

\. ..1

\ 0h
•

,.

b
J

\

'..

.....

ql11

\ E. /fatText-fig.1.

f'

j

q (j

tori

q

34~
138

Index map of sample localities in the Ueno Basin and Ayama Hills.

ably rests on the basement of the Ryoke
metamorphic rocks and is overlain conformably by the Koka Formation or unconformably by Quaternay terrace depposits. The stratigraphy of the Ohyamada and Sanagu areas,eastern and northeastern parts of the Iga tectonic
basin (Kondo, 1968), was studied in full by
Yokoyama et al. (1980). They divided the Iga
Formation into three lithological units, Ohyamada clays, Kashikimura sands, and Aitagawa
alternations, in ascending order, and it has atotal thickness of about 300 meters. Among theseveral volcanic ash layers intercalated in the
Ohyamada clays, the Hattorigawa (abbr., Hattori) II volcanic ash layer was dated to be 4.6 Ma
B.P. by the fission track method (Yokoyama
et al., 1980). The common occurrence of theelements of the Metasequoia and Pinus trifolia
floras, such as Glyptostrobus, Sequoia, Fagus,
Liquidambar, Nyssa, and Carya, has been reported from the Ohyamada area by Miki (1948)

and Shimakura (1966). The occurrence ofStegodon cf. elephantoides (Clift) has been
known from the two localities of the Iga Formation (Yokoyama et al., 1980; Kawaguchi, 1984).
Paleontological evidences mentioned above give
support to the fission track age which suggests
an Early Pliocene age.
The columnar sections at the localities A to
E from which molluscan specimens were collected are shown in Text-fig. 2.
Locality A(I16): Blueish gray and massivebedded silts exposed on the confluence of the
Hattori and Takasu Rivers, Hirata, Ohyamada,
Ayama-gun, Mie Prefecture (lat. 34°45'34" N,long. 136°13'30" E).
The fossiliferous silts exposed at this locality
are stratigraphically situated over the horizonof the Nakamura volcanic ash layer (Yokoyama
et al., 1980) intercalated in the lower part of the
Ohyamada clays. Fossils are abundant on thebedding, but are sparse within the bed. Molluscs

182

Keiji MATSUOKA........ :. ..::-...... .
........
........
f-::..- -=.::;:::::::,:. ~ ,,', : . :; '. ':----- - -."~.·,,,!;·o1.,.

:';' 'tJ: .;, ...;·;.:·;·:. ...:::.sLegend.

J~%!;.;m;Katano II4-==-~-.:­

volcanic ash
IiliI granulegravelvvv~ boulderr-.:.:-_

000---- -

fine[ill]
H~iil coarse sand-- silt~~ clayr-_ -_-.:J •• :.vJ Hattori II

,.

.....

gastropod collection

Katano I-----:
vvvvv

Hattori I

5
2

3

Text-fig. 2. Columnar sections at the fossiliferous exposures in the Ueno
Ayama Hills.
1: Loc. D(1l8), 2: Loc. E(I26). 3: Loc. B(12), 4: Loc. A(1l6), 5: Loc. C(17), f: fault.

collected is composed of Igapaludina stricta,
Semisulcospira (Biwamelania) praemultigranosa,
Unio (Nodularia) sp., Cuneopsis sp., Lamprotulasp., and Anodonta sp. This molluscan assemblage
includes numerous and excellently preserved
juvenile to adult forms of Igapaludina stricta,
and other species are present in small numbers.
Many unionid bivalves are preserved with adisarticulated valve or a broken shell. Other
fossils are cyprinid pharyngeal teeth, bones

Basin andand spines, and spongillid sponges adheringto the surface of molluscs.
Locality B(12): Blueish gray silt on thenorth side of the Hattori River at Hatamura,
Ohyamada-mura, Ayama-gun, Mie Prefecture(lat. 34°46' N, long. 136°12'7" E).
At this locality, light gray silts of the Ohyamada clays are exposed on the north side of
the Hattori River, and the fossiliferous sediments
rest conformably on the Hattorigawa 1 volcanic

800. Pliocene Gastropods from the 19a Formation

ash layer and in turn are confonnably overlain by
the Hattorigawa II volcanic ash layer. The present
beds' yielded the following species of molluscs,
19apaludina stricta, Bellamya suzukii, Semisu lcosp ira(Biwamelania)
praemultigranosa,
Inversidens spp., Cuneopsis sp. 1, Cuneopsis
sp. 2, Unio (Nodularia) sp. 1, Psilunio sp.,
Unionetta sp., and Anodonta sp. iIi addition tosome cyprinid fishes as spines, pharyngeal teeth,
scales and bones, imperfectly preserved plantleaves, and sponges. This molluscan assemblage
is characterized by Igapaludina stricta that issmaller in size than that from the Locality
A(I16). The shells are represented entirely bymolds and casts, and are compressed by pressurein the process of fossilization.
From this locality, Okuyama (1981a, b; 1983;1984) photographically illustrated fossil plantremains, cyprinid pharyngeal teeth, scales, spinesand bones, molluscs, trionychid turtles, andcrocodilian teeth.
Yokoyama et al. (1980) noted the occurrenceof Stegodon cf. elephantoides nearby the pondof Midoro approximately 750 meters southsouthwest of the present locality.
Locality C(I7): Small exposure approximately
two kilometes north of Hojiro, Veno City, Mie
Prefecture (lat. 34°44'50" N, long. 136°13'20"
E).

Fossil molluscs were collected from ill-sorted
silty sands including mica fragments near thebase of the section. The fossil-bearing bed isof the Takayama bed (Yokoyama et al., 1980)
which is equivalent to a marginal facies of
the Ohyamada clays. The molluscan assemblage
is characterized by Bellamya suzukii and a few
Semisulcospira (Biwamelania) sp. and "Unio"
sp. are also present. The calcareous matter of themolluscan shell was partly replaced by ferriferous
material, but most of the remains are imperfectly
preserved and are more or less defonned by postmortem compression. Other fossils diatoms,
spongillid sponges, pharyngeal teeth and bonesof cyprinid fishes, "Xeno cypris " sp. andCarassius sp.are included.
Tanaka and Matsuoka (1983) reported the
freshwater diatoms of 10 taxa from the present

183

locality. Also they stated that the silty sands
including diatoms contain marine silicoflagellate
fossils derived from the Miocene strata.
Locality D(I18): Southwest side of the
Tsuge River, 150 meters downstream of the
Toyama-bashi, Toyama, Sanagu-cho, Veno City,
Mie Prefecture (lat. 34°47'53" N, long. 136°9'
53" E).
This locality may be younger or about thesame age as the locality E(I26), and is the stratigraphic position is the upper part of theKashikimura sands. The poorly sorted silty sands
which contain plant fragments, sponges attaching
to Tulotomoides sanaguensis, pharyngeal teeth ofCarassius are probably of fluvial origin. The
molluscan assemblage is rich in Tulotomoides
sanaguensis, and is common or rare in Semisu lcosp ira (Biwamelania) sp., Inversidens sp.,
Anodonta sp., and Corbicula sp. The shells
are in a poor state of preservation, like
McAlester's (1962) "composite mold", andwere distorted by pressure in the process offossilization. The fossiliferous ill-sorted sands
are overlain by the yellowish gray colored andcoarse to medium grained sands about 50 centimeters thick, which yield unionid bivalves,
Anodonta sp., "lnversidens" sp., and plantleaves.
Locality E(I26): Cliff to the south of Goyo
Paper Co. Ltd., Sanagu-cho, Veno City, Mie
Prefecture (lat. 34°47'39"N, long. 136°10'45"
E).

At this locality, the Kashikimura sands arecomposed chiefly of well-sorted .fine grainedsands, two volcanic ash layers, namely lower
Katano I and upper Katano II, and blackish graycolored massive silts with quartz grains. The stratigraphic position yielding fossil molluscs isabout one meter below the Katano II volcanic
ash layer. This molluscan assemblage is predominantly of Tulotomoides sanaguensis. These
viviparid specimens were much defonned bypost-mortem compression, and are now in poor
state of preservation. Among other fossils areplant fragments and spongillid sponges attaching
to the shell surface of T. sanaguensis.

Keiji.MATSUOKA

184

Systematic paleontology
Specimens used for this study are depositedin the molluscan collections of the Departmentof Earth Sciences, Nagoya University (ESN)and of the Mizunami Fossil Museum, Mizunami
City, Gifu Prefecture (MFM).
Class Gastropoda
Order Mesogastropoda
Family Viviparidae Gray, 1847
Subfamily Bellaminae Rohrbach, 1937
Genus Igapaludina, nov. gen.
Type species:-Viviparus stricta Araki, bypresent designation. Pliocene Wakebe Formation of the Age Group, Kambe, Tsu City, Mie
Prefecture, central Japan.
Derivation of name:-From Iga, the oldplace-name of the Ueno City area and paludina(Latin), feminine.
Diagnosis:-Shell medium to large, broadly
conic, with elevated spire. In the early stageof growth, the shell subglobose, with rounded
periphery; the embryonic shell somewhat depressed but the first whorl submammillated.
The embryonic shell marked by two or morespiral ridges with their intercostal fine spirallines and faint growth ones, but at late stageof growth, the shell generally sculptured byonly growth lines. The later whorls having
wide shoulder with step-like ramp anterior to
the suture, rounded periphery, and whorl side
almost flat or slightly concave.
Discussion:-The viviparid genera which appear to be related to the new genus Igapaludina
are as follows:
Heterogen Annandale, Idiopoma Pilsbry, Tulotomoides Wenz, and Tulotoma Haldeman.
Heterogen is separable from the genus Igapaludina by some differences, namely that it
has flattened whorl side oblique to the shellaxis and the embryonic shell is subcylindrical,
with a spiral rib anterior to the suture, and witha subangular periphery. In Igapaludina, thewhorl side is flat or slightly concave, being
subparallel to the shell axis, and the embryonicshell is subglobose, with a rounded periphery.
The shape of the embryonic shell of Idiopoma
has an obtuse angle at the apex, and the whorlside is rounded as in Igapaludina. This new
genus can be distinguished from Idiopoma
by having the larger shell and wide shoulder
in front of the suture. The Recent species belonging to Tulotoma Haldeman have a solid shellwith nodulous spiral ridges. Their distribution
is restricted to the Alabama River and its tributaries in North America. The fossil forms from. eastern Europe and Asia Minor, however, do
not have tuberculated sculptures, therefore thefossil Tulotoma resembles Igapaludina in shellshape, especially in that of the body whorl.
Igapaludina is similar to the extinct genus
Tulotomoides, which has an elongately tobroadly conic shell with shouldered whorl,
and with whorl side nearly vertical below theshoulder. It is distinguished from Tulotomoides
by possessing a larger embryonic shell, theabsence of spiral lines on the whorl surface
and a spiral ridge anterior to the suture.
Igapaludina stricta (Araki)

PI. 24, Figs. 1,2; PI. 25, Figs. 1a-15b;
PI. 26, Figs. 1-5b.
Viuiparus strictus Araki, 1960, Bull. Lib. Arts
Dep., Mie Uniu., Spec. Vol., no. 1, p. 106107, pI. 9, fig. 8. (holotype), type lost (personal communication, Y. Araki).
Type locality:-Road side cliff in easternpart of Kambe, Tsu City, Mie Prefecture, central
Japan (lat. 34°42'21"N, long. 136°29'12"E).
Wakebe Formation, Age Group. Pliocene.
Original description (Araki, 1960):-"Manyspecimens which are preserved as moulds and casts
are in the collection from the lake deposits of
the Age Group. These specimens all have welldefined sutures, rather straight whorl profile,
more or less orbicular aperture, their whorls arerather sharply defined from the basal part by an
obscure angularity marking the lower part ofthe body whorl above the base. The columellais almost straight but slightly curved. The shell
sculpture consists of obscure, slightly oblique,800. Pliocene Gastropods from the Iga Formation

longitudinal striae becoming more or less sigmoidal near their shoulders which is rather
buldging before passing into the defined suture
separating the respective whorls from one another. The younger whorls are missing in all of
the specimens probably due to decollation.
The present specimens have been comparedwith the fossil fresh-water gastropods hitherto
reported from the Tertiary deposits of Japan,
but they all differ and therefore are considered
to represent a new species, for which the nameof Viviparus strictus Araki, n. sp., is proposed,
the name indicating that the specimens arestrict in their shape."
Material studied:-There are 66 specimensfrom Hirata (Loc. A(I16» and 5 from Hatamura(Loc. B(I2». ESN 40029-40031, 40034, 40040,
40042, 40057, 40058, 40060; MFM 110010,
110012, 110013, 111014, 111017, 111022,
111023, 111031, 111034, 111035, 111056-58.
Diagnosis:-Shell medium to large, broadly
conic in outline, having an elevated spire. The
embryonic shell subglobose, with an inflated
whorl. The postembryonic shell having wide
shoulder on the whorl with advancing growthstage, and the whorl side almost flat, nearlyvertical below the shoulder.
Supplementary description:-Shell medium tolarge, up to about 44 mm long, moderately
thick, broadly conic; the spire elevated consisting of about four whorls, comprising about
two-fifths of the height in a little corroded
specimens; the apical angle 40 to 50 degrees.
The embryonic shell subglobose, 2.5 to 3.0
whorls, low spire with rounded periphery, andbeing not sharply separated from the postembryonic shell; the first whorl, small, submammilated. The surface of the test smooth,but having several microscopic spiral lines andfaint growth striae. The microscopic ornamentation sometimes increasing in prominence. The
embryonic shell and early whorls of the spire
genel"811y corroded. The postembryonic shellincreasing in size regularly; the whorl side flator slightly concave, and having a wide shoulder
anterior to the suture. At adult stage of growth,
the shoulder of the body whorl 3 to 3.5 mm in

185

width, and the upper surface undulated near
the groove of rest marks. The surface of thepostembryonic shell ornamented by fine growthlines and their rest marks at irregular intervals.
The rest marks more strongly impressed than
the growth lines. In younger specimens, weakspiral carinae occasionally present on the whorls.
Suture narrow, distinctly impressed, but sometimes becoming wide like groove. Aperturepyriform, broadly rounded anteriorly andnarrowed posteriorly. Outer lip thin, Columellar
lip oblique, completely sealing the umbilicus.
Operculum corneous, thin, concentric, pyriform;
the outer margin curved through a greater arc,and terminating at the posterior edge, the outerand inner margins forming approximately 80
degrees; the inner edge situated at about twofifths of the operculum length; the basal margin
well-rounded. The exterior surface slightly
concave, with irregularly concentric lines; thenucleus apparently amorphous, situated about
half of the distance from the base to the summit
and drown near the inner margin.
Discussion:-The fossil viviparid gastropod
has been known to occur abundantly in Ohyamada-mura, Ayama-gun, Mie Prefecture. The
viviparid gastropod has been assigned to Viviparus sp., Sinotaia sp., and Heterogen longispira (Smith) by Nakagawa (1948), Takaya(1963), Kondo (1968), Yokoyama (1969),
and Yokoyama et al. (1980). Certainly, thewide shoulder and flattened whorl side ofHeterogen longispira, an endemic species in
Lake Biwa, has a similarity to Igapaludina
stricta from the Iga Formation. This species
differs from it in having slender body whorl,
flat and vertical whorl side, rounded periphery,and subglobose embryonic shell. Tulotoma
abchasica from the Pliocene of Abhazu, south
U.S.S.R., originally assigned to Viviparus by
Taboyakova (1964) and Viviparus argesiensis
from the Pliocene (Daz stage) in Rumania
by Wenz (1942), resemble Igapaludina strictain having smooth surface except for growthlines, wide shoulder, and round periphery.
It differs from the latter in possessing a smaller
embryonic shell, lower spire and perforate

Keiji MATSUOKA

186

umbilicus. Igapaludina stricta shows particularly
close resemblance to Viviparus margaryaeformis
from the Pliocene of Mongtze, Yunnan in China,(Mansuy, 1918). V. margaryaeformis has abroader shell outline, rounded convex whorls,
and ill-defined shoulder (personal communication, Pan Huayhang), but Igapaludina stricta
has a slender shell, flattened whorl side andwide shoulder on the whorls. Yen (1943a)
mentioned that V. margaryaeformis appears
to be closely related to the form of Bellamya
quadrata (Benson). Mansuy's margaryaeformis
has hitherto been referred to the genus Viviparus or "Viviparus" (Yen, 1943b; YU et al.,1963), but it can be assigned to this new genus.
Margarya melanioides obsoleta from the Pleistocene of Yunnan (Dautzenberg and Fischer,1905) resembles Igapaludina stricta in having
shouldered whorls, and almost flattened whorlside, but it differs from the latter by the presenceof a more turreted spire and subconic embryonic shell. Igapaludina stricta resembles
Idiopoma chutsingensis and 1. tingi from the Pliocene of Yunnan (Yen, 1935) in outline of theembryonic shell, but differs from the latter twoin having the wide shoulder and flattened whorl
side.
Measurements (in mm):
ESN 40029
ESN 40030
ESN 40031
ESN 40032
ESN 40033
ESN 40034
MFM 110009
MFM 110010
MFM 110011
MFM 111006
MFM 111007
MFM 111009
ESN 40036

H

W

BH

AH

AA

38.7
37.7
38.6
41.6
35.8
40.0
38.0
34.3
40.2
31.0
36.1
35.9
29.2

24.4
21.9
20.2
23.8
21.2
24.4
22.0
20.2
25.2
19.5
20.2
22.8
18.0

26.1
25.7
25.7
28.8
24.8
28.5
27.6
25.0
29.5
22.2
24.8
27.3
22.0

18.0
18.0
17.4
20.5
17.7
18.0
18.0
17.2
20.3
15.5
18.0
18.0
15.9

50°
40°
41°
49°
44°
46°
48°
47°
51°
53°
46°
47°
45°

H = height; W = width; BH = height of bodywhorl; AH = height of aperture; AA = apicalangle.

Genus Bellamya Jousseaume, 1886
Type species:-Bellamya bellamya Jousseaume,by original designation. Recent. Senegal, west
Africa.
Geologic range :-Jurassic to Recent.
Discussion:-The genus Bellamya is inhabited
widely in rivers and lakes of central and west
Africa, and Southeast Asia. The shell characterized by medium, ovately conic, with roundedor convex whorl; the body whorl enlarged,
with a rounded or subangular periphery; theumbilicus narrowly perforate; the aperture isovate, and the outer lip is thin, with· roundedmargin.
Among the Tertiary viviparid gastropods
from Japan, Viviparus uryuensis Yokoyama
from the Oligocene Uryu Group, V. mabutii
Suzuki from the Oligocene Ishikari Group,
and V. kosasanus Ueji from the Miocene Nojima
Group may belong to Bellamya. Oyama et al.
(1960) placed V. uryuensis and V. mabutii
in Bellamya (Sinotaia). The subgenus Sinotaia
was established for the Recent Chinese species
which is characterized by elongate conic, solid
shell with thick columellar lip, and conspicuous
carinae on whorls at the young and adult stages.
The type species is Paludina quadrata Benson.
Some of the Recent Chinese species andPrashad's (1928) Vivipari dissimiles group havebeen assigned to Bellamya by Yen (1943b),
and Sinotaia has been regarded as a juniorsynonym of Bellamya. Brandt (1974), Pace
(1973) and Popova (1980), however, considered
Sinotaia to be a separate genus, including thefossil species of U.S.S.R. and the living speciesof Thailand and Formosa, with which I do notagree.
.
Bellamya suzukii, nov. sp.

PI. 26, Figs. 6a-14b.
Type locality:-Hojiro (Locality C(I7», Ueno
City, Mie Prefecture, central Japan.
Derivation· of name:-The species is named
in honor of the late Dr. K. Suzuki, who studied
fossil non-marine molluscs of the Japanese187

800. Pliocene Gastropods from the Iga Formation

Islands and north China.
Material· studied:-18 specimens. Figured
specimens, ESN 40026-40064, 40067, MFM
110014,110015,111036,111042.
Diagnosis:-Shell medium, ovately conical;
the spire about 3/10 of the shell height; theapical angle 50 to 60 degrees. The whorl siderounded, with weakly carinate spirals in younger
stage of growth. The body whorl large withwell-rounded periphery.
Description:-Shell medium for genus, up to
25 mm long, thin to moderately thick, ovately
conical; the spire moderately elevated, comprising about 3/10 of the shell height; the apicalangle usually 50 to 60 degrees. The early whorls
including the embryonic shell corroded. The
spire generally preserved four whorls, the whorlside rather convex, increasing in size rapidly.
The periphery rounded near the center of the
body whorl; the basal parts slightly convex or
flat. The later whorls having a very narrow orill-defined shoulder. Suture shallow, but distinctly impressed. Shell surface covered withdelicate growth lines and their rest marks. The
growth lines slightly opisthocline below the
suture. The rest marks being darker in color andmore remarkable than impression of the growthlines. The body whorl sometimes sculptured bya few axial costae with rounded top. At juvenilestage, the surface of the spire covered withweakly carinate spirals. Aperture ovate, broadly
rounded, somewhat extend to the front, andsubangular behind. Outer lip thin, gently
rounded. Columellar lip thin, smooth, oblique,with thick parietal callus. Umbilicus narrowly
perforate.
Discussion:-Bellamya kosasana from theMiddle Miocene Nojima Group of the Nojima
Island, Saga Prefecture, Kyushu is closely related
to Bellamya suzukii, but is assigned to thegenus Viviparus in the original description.
Moreover, this Miocene species has been reported from the Koura Formation in the Shimane Peninsula in Shimane Prefecture (Suzuki,
1949) and the Suzuka Group at the southernfoot of the Suzuka Mountains in Mie Prefecture(Suzuki and Oyama, 1948). It may be distin-

guished from B. kosasana by having a slenderer
shell outline with inflated whorls, round
periphery, and higher shell (20 to 25 mm).
The specimens figured by Kanno (1954) as
Viviparus (Sinotaia) uryuensis from the Early
Miocene Osawa Formation in Fukushima Prefecture resemble the present specimens, but
the former differs from the latter in having
more conspicuous shoulder with a step-like
form, apical angle 70 to 75 degrees, and obtusely
angulated on the anterior two-thirds of the
body whorl. Bellamya suzukii is close to Sinotaia (Sinotaia) deviatkini described by Popova
et al. (1970) from the Eopleistocene Kyzylgir
Formation of Altay Highalnd, U.S.S.R., but
it is distinguished from S. deviatkini in having
a smaller shell size and shallower suture.
Suzuki and Oyama (1948) and Akamine
et al. (1951) have reported Viviparus (Sinotaia)
uryuensis kosasanus from the Plio-Pleistocene
Age Group about 20 kilometers east of thetype locality of B. suzukii. They, however,are probably assigned to B. suzukii.
Measurements (in mm):
BH
15.3

AH
9.5

15.7

16.2

11.2

17.3

13.5

13.5

10.1

MFM 110015(paratype 3)

20.5

14.4

15.4

10.8

MFM 111042

20.1

13.9

15.8

11.2

H
21.3

15.0

ESN 40063(paratype 1)

23 +

17.5

ESN 40067

21.3

MFM 110014(paratype 2)

ESN 40062(holotype)

W

Genus Tulotomoides Wenz, 1939
Type species:-Tulotoma kwangsiensis HsU,
by original designation. Eocene Yongning Formation. Kuanghsi Province, China.
Geologic range:-(Middle Jurassic?) Eocene
to Pliocene.
Discussion:-This species of the genus Tulotomoides first reported from Japan is Tuloto-Keiji MATSUOKA

188

moides japonicus from the Gamo Formationof Kobiwako Group (Habe and Tomoda, 1980).
The species of the genus Tulotomoides
hitherto known from China and U.S.S.R. are as
follows:
Tulotomoides? antiqua Pan . Zhanghe andHuopingyao Formations (Middle Jurassic).
Lufeng and Yangbi, Yunnan Province , China(Pan, 1977).
T.? talatzensis Suzuki. Middle Shale Formation,
Talatzu Group (Early Cretaceous). Sanlaikou,
Jilin Province, China (Suzuki, 1941).
T. k wangsiensis (HsU), T. Iii (HsU) and T. Iii
parva (HsU) . Yongning Formation (Eocene).
Cienyang, Kuanghsi Province, China (HsU,
1935).
T. terrassa Youluo . Shahejia Formation (Early
Oligocene). Kenli , Shantung Province andPanshan , Liaoning Province, China (lnst.
Petrol. Pros. and Develop . Plan and Nanking
lnst . Geol. and Palaeont ., 1978).
T. aspericarinata Youluo. Shaheji Formation(Early Oligocene). Penhsien and Kenli,
Shantung Province , China (op. cit. ).
T. spiralicostata Youluo. Shahejia Formation(Early Oligocene). Kenli, Shantung Province,
China (op. cit.).
T. rehetaiensis Youluo . Shahejia Formation(Early Oligocene). Panshan , Liaoning Province,
China (op. cit.).
T. pagodaeformis (Martinson). Tanhoi Formation(Oligo-Miocene). Near Lake Baikal , U.S.S .R.
(Popova, 1981).
T. cf . tulotomoides (Yen). Ditto.
T. tulotomoides . (Yen). Sijian Formation (Late
Pliocene). QUjing, Yunnan Province, China(Yen, 1935).
Tulotomoides sanaguensis, nov. sp.
PI. 27, Figs. 1-8; Text-fig. 3.

Type locality:-Toyama (Locality D(I18»,
Sanagu-cho, Ueno City, Mie Prefecture, central

Text-fig . 3. Reconstruction of Tulotomoides sanaguensis, n. sp., apertural view . (x 3).
Japan.
Derivation of name:-This name is formed
after the name of place, Sanagu-cho, from which
the type specimens were collected.
Material studied:-14 specimens. Figured
specimens, ESN 40074-40078, 40080, MFM

110016,111049,111051.
Diagnosis:-Shell medium

for the genus,
elongately conic in outline. The embryonicshell and early whorls subglobose, smooth ,and rounded. The later whorls having a flattened
shoulder. The shoulder being ridge-like spiralrib. The surface irregular and undulatory. The
whorl side flat and vertical.
Description:-Shell medium for genus, commonly 20 to 26 mm long, probably thin, elongately conic. Spire moderately elevated, morethan half of the height; the apical angle about
30 degrees. The early whorls including theembryonic shell, less than 5 mm in width ,subglobose, smooth and rounded. The spireconsisting of about four whorls, cylindrical,
with obliquely flattened sutural shelf, increasing

Explanation of Plate 24
Figs. 1, 2. Igapaludina stricta (Araki) from the Ohyamada clays, Locality A(I16).
1 , A swarmed specimen of mature individuals, MFM 111035, x !.
2, A swarmed specimen of juvenile individuals, MFM 111034, X!.

MA TSUOKA: Pliocene Gastropods from the Iga Formation

Plate 24I

800. Pliocene Gastropods from the [ga Formationin size slowly. The whorl side flat and vertical.
The shoulder being ridge-like spiral rib with theirregularly undulated surface which gradually
becoming prominent with advancing years, andjust below the shoulder slightly concave. The
periphery rounded, and the basal part slightly
convex or flat. The suture shallow, but distinctly impressed. Shell surface covered withfine growth lines and with irregularly spaced
rest marks. The growth lines anteriorly curved
near the shoulder. The rest marks sometimes
becoming like longitudinal rib. Aperture elongate ovate, oblique, with continuous roundedmargin in front. Outer lip thin, with moderately
rounded margin. Columellar lip curved, its axial
side concave, not perforate.
Discussion:-All specimens from the type
locality occur as McAlester's (1962) "composite
mold", and have been deformed by post-mortem
compression. This new species is most closely
related to T. japonicus from the Gamo Formation of Kobiwako Group, at Mikumo, Shiga
Prefecture. It differs from T. japonicus by aslender shell with narrower sutural shelf andwith obtusely rounded early whorls. The shells
from the Gamo Formation are large, 33 mm
height in maximum, and have wider sutural
shelf, and distinct shoulder until the younger
shell of 3.2 mm in width. In the Kobiwako
Group, T. sanaguensis occurs in strata older
than those containing T. japonicus. T. sanaguensis may therefore be the direct ancestor of
T. japonicus. T. Iii from the Eocene of Chienyang, Kuanghsi Province of China resembles
this new species in having a rounded whorlside and smooth surface except for growthlines at younger stages of growth, but is distinguished by the presence of three spiral ridges
on each whorl. The slender and elevated spireof T. sanaguensis also resembles T. spiralicostatafrom the Shahejia Formation of Shantung
Province in China, but is distinguished by thepossession of an obtuse apex, and flat andvertical whorl side.
Measurements (in mm):E8N 40074(holotype)
E8N 40075(paratype 1)
E8N 40076
E8N 40077
MFM 110016(paratype 2)

189

H
21.8

12.9

BH
15.7

S/H
0.28

20.2

15.1

15.5

0.23

22.4
24.7
21.2

14.8
15.0
17.0

14.7
18.2
16.1

0.34
0.26
0.24

W

8tH = height of spire/height
Family Pleuroceridae Fischer, 1885
Genus Semisulcospira Boettger, 1886
Type species:-Melania libertina Gould, by
subsequent designation, Annandale and Prashad(1924). Recent.
Geologic range:-(Cretaceous?) Eocene to
Recent.
Discussion:-Boettger (1886) established thisgenus as a section of the genus Sulcospira
Troschel, which includes Semisulcospira libertina(Gould), S. spadicea (Reeve), S. japonica (Reeve),and so on. This genus is restricted to East Asia Amur Basin, Korean Peninsula, China, Formosa,and Japanese Islands.

Subgenus Biwamelania Matsuoka andNakamura, 1981, redefined
Discussion:-The generic name Biwamelania
was first used for species which are endemic in
Lake Biwa, and the Seta and Uji Rivers by Habe
(1978), but descriptions necessary for theestablishment of a new taxon have not beenmade. Matsuoka and Nakamura (1981) havesubdivided the genus Semisulcospira into two
subgenera; Semisu lcosp ira and Biwamelania,
and the two subgenera were correlated with
Davis' (1969) Semisulcospira libertina group
and S. niponica group, respectively. All speciesof Semisulcospira from the Katata Formationof the upper part of the Kobiwako Groupbelong to the subgenus Biwamelania. S. niponica
group consists of species which have chromosome numbers n = 7 to 14, and their adult shells
are conic to elongate conic in outline, possess-Keiji MATSUOKA

190

ing the prominent nodes on the axial ribs, andtwo to six basal cords. The embryonic shell islarger and fewer than that of the Semisulcospiralibertina group in size and number. The subgenus
Biwamelania is revised here to contain some
Recent species, S. decipiens (Westerlund), S.
multigranosa (Boettger), S. habei Davis, S. habei
yamaguchi Davis, S. reticulata Kajiyama etHabe, S. niponica (Smith), and S. nakasekoae
Kuroda. The type of this subgenus placed in thispaper is S. decipiens (Westerlund) which lives in
Lake Biwa. The species of the Semisulcospiracancellata group (Kuroda, 1947) which are
distributed over the Amur Basin, Korean Peninsula, and China presumably belong to this subgenus Biwamelania. The fossil species which may
be assigned to the subgenus Biwamelania are
Semisulcospira spp. from the Kobiwako, Age andTokoname Groups (Matsuoka and Nakamura,
1981; Matsuoka, 1983b, 1985), S. napoensis
from the Eocene Yungning Formation of Guangxizhuangzu (Hsli, 1935), and S. aubryana var.
cancellata, S. aubryana var. spiralis, S. aubryana
var. costellata, and S_ aubryana var. obsoleta
from the Pliocene Cijian Formation in Yunnan,
China (Mansuy, 1912).

Semisulcospira (Biwamelania)
praemultigranosa, nov. sp.

PI. 27, Figs. 9-18.

Type locality:-Hirata (Locality A(I16)), Ohyamada-mura, Ayama-gun, Mie Prefecture, central Japan.
Derivation of name:-This species is named
from prae-(Latin, prefix meaning before) andthe specific name of Semisulcospira multigranosa, feminine.
Material studied:-13 specimens. Figured
specimens, ESN 40023-40026, 40070, 40072,
40073, MFM 110008, 111044, 111048.
Diagnosis:-Shell medium, elongate-conic, six
or more whorls; five prominent nodes on theaxial ribs on the penultimate whorl, but themost anterior node imperfect, sealing suture.
The basal cords distinct, two to three in number.
Description:-Shell medium for genus, moderately thick, elongate conical. Spire high turreted, approximately one-fourth the height ofthe shell, and always lacking the embryonicshell and early postembryonic one; apical angle
18 to 20 degrees. Whorls preserved four to six
in number, increasing in size regularly; whorl
profile flat or slightly convex. Suture shallowly
impressed, undulatory. Sculpture of the spireconsisting of four to five nodes, more or lessregularly spaced, on axial ribs with rounded orsomewhat carinated top, crossed by moderately
raised lirae and feeble spiral lines. The body

Explanation of Plate 25
Figs. 1a-15b. Igapaludina stricta (Araki) from the Ohyamada clays, Locality A(116).
la, apertural view; 1b, abapertural view. ESN 40029, mature specimen, Xl.
2a, apertural view; 2b, abapertural view. ESN 40042, juvenile specimen, XL
3a, apertural view; 3b, abapertural view. MFM 110010, mature specimen, XL
4a, apertural view; 4b, abapertural view. ESN 40031, mature specimen, elongate type, X1.
5a, apertural view; 5b, abapertural view. ESN 40040, juvenile specimen, XL
6a, apertural view; 6b, abapertural view. ESN 40034, mature specimen, XL
7a, apertural view; 7b, abapertural view. ESN 40030, mature specimen, XL
8a, apertural view; 8b, abapertural view. MFM 111014, juvenile specimen, X1.
9a, apertural view; 9b, abapertural view. MFM 111017, juvenile specimen, XL
lOa, apertural view; lOb, abapertural view. ESN 40057, juvenile specimen, X1.5.
11a, apertural view; 11b, abapertural view. ESN 40058, more juvenile specimen, X2.
12a, apertutal view; 12b, abapertural view. MFM 111022, more juvenile specimen, X2.
13a, apertural view; 13b, abapertural view. MFM 111031, more juvenile specimen, X2.
14a, apertural view; 14b, abapertural view. MFM 111023, more juvenile specimen, X2.
15a, apertural view; 15b, abapertural view. ESN 40060, more juvenile specimen, X2.

MATSUOKA: Pliocene Gastropods from the Iga Formation

Plate 25

2b

2a

5b

8b

8a

13b

14a

9a

9b

12a

12b

11b

11a

13a

6b

6a

5a

14b

15a

15b

800. Pliocene Gastropods from the 19a Formation

whorl with rounded periphery, the width about
two-fifths of the height, the spiral cords six,
prominent, more widely spaced than the interspaces, the basal cords strong, two to three,with rounded or weakly carinated top. Axial
ribs on the penultimate whorl 17 to 19, almost
equal to the width of intercostal spaces, orthocline to weakly opisthocline and with fivenodes; the nodes immediately above the suture
imperfect, and the other nodes equal or theuppermost one slightly small. Growth lines
irregularly spaced, very fine, and opisthocline.
Aperture elongate-ovate, oblique with narrowly
rounded basal lip, and angular in posterior.
Outer lip thin. Columellar lip smooth, parietal
callus not thicken, completely sealing the umbilicus. In the juvenile specimen, the early
whorls of the spire narrowly conic, 10.3 mm inheight, and 3.8 mm in width. The shell sculptured by regularly spaced axial ribs with nodes
and crossed by fine spiral cords, and two basal
cords. The width of the axial ribs occupying
one-third to one-fifth of the interspaces. The
embryonic shell about 1.7 mm in maximum
width, and having the axial ribs and spiral cords
with carinated top.
Discussion :-In the adult stage of development, this new species resembles the following
three species, Semisculcospira (Biwamelania)
multigranosa (Boettger), S. (B.) decipiens(Westerlund), S. (B.) habei yamaguchi Davis,
which are found sympatrically in the littoralzone of Lake Biwa. S. (B.) multigranosa shows
close resemblance to S. (B.) praemultigranosa.
It is distinguished from S. (B.) praemultigranosaby having seven to eight numbers of nodes on
the ribs and 23 ribs per penultimate whorl.
Ribs of S. (B.) decipiens are more slender anddelicate than those of this new species and has
seven to eight nodes on them. S. (B.) habei
yamaguchi shows the closest resemblance to the
new species. S. (B.) habei yamaguchi differsfrom S. (B.) praemultigranosa in having thelarge apical angle and generally conspicuous
six nodes on each rib of the whorl in the adultstage. The similarity in shell morphology suggeststhat S. (B.) habei yamaguchi may have derived

191

from this new species.
The fossil specimens reported from theAge Group, under the name of S. cf. multigranosa (Suzuki and Oyama, 1948; Akamine
et al., 1951) are probably identical with S.
(B.) praemultigranosa.
Measurements (in mm):
H
35.6

W
12.8

BH
20.3

AH BC
10.2 3

ESN 40024(paratype 1)

30.2

12.2

17.7

3

ESN 40025(paratype 2)
MFM 110007(paratype 3)
MFM 110008(paratype 4)
ESN 40070
MFM 111044

35.0

12.8

17.6

31.6

15.0

32.9

13.1

19.1

3

29.1
28.0

10.3

11.7
13.9

2
3

ESN 40023(holotype)lOA

3

BC = basal cord
Acknowledgments
I am indebted to Drs. J. Itoigawa and H.
Shibata of Nagoya University for reading themanuscript and offering valuable suggestions.
The author is extremely grateful to Dr. H. Wanof Shanghai Museum Natural History, andDrs. H. Pan and B. Huang of Nanking Instituteof Geology and Palaeontology, for suggestions
and advice on the identification of 19apaludina.
Appreciation is also expressed to Mr. S. Okuyama for supplying specimens of the Iga Formation for this study.
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192

KeijiMATSUOKA

Chekiang Province of China. Proc. Malac.
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Explanation of Plate 26
Figs_1,2. Opercula of Igapaludina stricta (Araki) from the Ohyamada clays, Locality B(12).
1, MFM 110012, X1.5,collected by S. Okuyama.
2, MFM 110013, X2, collected by S. Okuyama.
Figs.3-5b. Igapaludina stricta (Araki) from the Ohyamada clays, Locality B(12).
3, apertural view, MFM 111053, Xl.
4, apertural view, MFM 111057, Xl.
5a, apertural view; 5b, abapertural view, MFM 111056, XL
Figs. 6a-b, 8, 9. Bellamya suzukii, n. sp. from the Ohyamada clays, Locality B(12).
6a, apertural view; 6b, abapertural view. ESN 40062 (holotype), XL
8, abapertural view, ESN 40063 (paratype 1), Xl.
9, abapertural view, ESN 40064, X1.3.
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7, apertural view, ESN 40067, Xl.
lOa, apertural view; lOb, abapertural view. MFM 110015 (paratype 3), X1.5.
11a, apertural view; 11b, abapertural view. MFM 110014 (paratype 2), X1.5.
12, apertural view. MFM 111043, X1.5.
13a, apertural view; 13b, 3bapertural view. MFM 111042, X1.5.
14a, apertural view; 14b, abapertural view. MFM 111036, X1.5.

Plate 26

MATSUOKA: Pliocene Gastropods from the Jga Formation

5a
4

3

6b

7

8
9

10a
11a

11b

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Popova, S. M. (1981): Cenozoic continental
malacofauna from south Siberia and its
neighboring territory. Nauka, Moscow. p. 3188, pIs. 1-40 (in Russian).
- - , Devytkin, E. V. and Starobogatov, Y. I.
(1970): Molluscs Kyzylgir Formation inHighlands Altai. Nauka, Moscow. p. 1-95,
pIs. 1-8 (in Russian).
Prashad, B. (1928): Recent and fossil Viviparidae.
A study in distribution, evolution andpalaeogeography. Mem. Indian Mus., vol. 8,
p. 153-251, pI. 19.
Shimakura, M. (1966): Pollenstratigraphic studies
of Japanese Cenozoic formations IV, The
Paleo-Biwa Group. Jour. Nara Gakugei
Univ. (Nat.), vol. 14, p. 25-39 (in Japanesewith English abstract).
Suzuki, K. (1941): On some freshwater shells
from the Cretaceous Talatzu Series insoutheastern Manchoukuo. Bull. Geol. Inst.

194

Keiji MATSUOKA

Manchoukuo, no. 101, p. 83-91, pI. 1.
--(1949): Development of the fossil nonmarine molluscan fauna in Eastern Asia.
Japan. Jour. Geol. Geogr., vol. 21, p. 91133.
--and Oyama, K. (1948): Freshwater shells
from the coal-bearing Tertiary formationsin Mie-ken, Japan. Venus (Jap. Jour. Malac.),vol. 15, nos. 1-4, p. 36-44 (in Japanese).
Taboyakova, V. Y. (1964): Experience of
biometric study of the Pliocene Viviparusof the south of the USSR. Nauka, Moscow.
p. 5-88, pIs. 1-9 (in Russian).
Takaya, Y. (1963): Stratigraphy of the PaleoBiwa Group and the paleogeography of
Lake Biwa with special reference to theorigin of the endemic species in Lake Biwa.
Mem. Coli. Sci., Univ. Kyoto, Ser. B., vol.
30, no. 2, p. 81-119.
Tamura, M. and Ishiyama High School (1984):
Researches into the fossils of the Kobiwako
Group 1. Sekishinkan Hokoku, no. 8, p.
19-61, pIs. 1-2 (in Japanese).
Tanaka, M. and Matsuoka, K. (1983): Fossil

silicoflagellates from the Pliocene Iga Formation of the Kobiwako Group, Ueno City,
Mie Prefecture, Japan. Bull. Mizunami
Fossil Mus., no. 10, p. 193-198, pI. 54(in Japanese).
Wenz, W. (1942): Die Mollusken des Plioziins
der rumiinischen ErdOl-Gebiete als Leitversteinerungen fUr die AufschluBarbeiten.
Senckenbergiana, vol. 24, nos. 1-6, p. 1293, pIs. 1-71.
Yen, T. (1935): On some Tertiary gastropodsof Yunnan. Bull. Geol. Soc. China, vol. 14,
no. 3, p. 315-336, pIs. 1-3.
-(1943a): Review and summary of Tertiary
and Quaternary non-marine mollusks of
China. Proc. Acad. Natur. Sci. Phila., vol.
95, p. 267-309.
--(1943b): A preliminary revision of the
Recent species of Chinese Viviparidae.
Nautilus, vol. 56, no. 4, p. 124-130.
Yokoyama, T. (1969): Tephrochronology andpaleogeography of the Plio-Pleistocene in theeastern Setouchi geologic province, southwest Japan. Mem. Fac. Sci., Kyoto Univ.,

Explanation of Plate 27
Figs. 1-8. Tulotomoides sanaguensis, n. sp. from the Kashikimura sands, Locality D(118).
1, abapertural view. ESN 40074 (holotype), Xl.
2, abapertural view. ESN 40076, Xl.
3, apertural view. ESN 40080, Xl.
4, abapertural view. ESN 40075 (paratype 1), Xl.
5, abapertural view. MFM 111049, Xl.
6, abapertural view. MFM 110016 (paratype 2), Xl.
7, abapertural view. MFM 111051, Xl.
8, abapertural view. ESN 40078, Xl.
Figs. 9, 10, 17,18. Semisulcospira (Biwamelania) praemultigranosa, n. sp. from the Ohyamada
clays, Locality B(I2).
9, abapertural view. MFM 111044, Xl.
10, abapertural view. ESN 40070, Xl.
17, abapertural view; ESN 40073, more juvenile specimen, X 2.
18, abapertural view. ESN 40072, juvenile specimen, Xl.
Figs. 11-16b. Semisulcospira (Biwamelania) praemultigranosa, n. sp. from the Ohyamada clays,
Locality A(116).
11, abapertural view. ESN 40026, X1.1.
12, abapertural view. MFM 111048, Xl.2.
13, apertural view. ESN 40025 (paratype 2), Xl.
14a, apertural view; 14b, abapertural view. ESN 40023 (holotype), Xl.
15a, apertural view; 15b, abapertural view. MFM 110008 (paratype 4), Xl.
16a, apertural view; 16b, abapertural view. ESN 40024 (paratype 1), Xl.

MATSUOKA: Pliocene Gastropods from the [ga Formation

1

Plate 27

3

2

5

8

7

6

9

4

10

11

13

12

(>.

fj
I

.'

18

14a

14b

15a

15b

16a

16b

17

800. Pliocene Gastropods from the 19a Formation
Ser. Geol. and Mineral., vol. 36, p. 19-85.
- , Makinouchi, T., Takemura, K., Hayashida,A., Sannomiya, T. and Yamamura, H.
(1980): Stratigraphy of the Pliocene IgaAburahi Formation of the Kobiwako Groupat the east of Iga-Ueno City, Mie Prefecture,
Japan. Paleolimnol. Lake Biwa Jap. Pleist.,
vol. 8, p. 45-64.
- , - - , Mori, S., Nakagawa, Y., Tamura,M., Takemura, K., Hayashida, A., Amemori,K. and Mori, H. (1982): Stratigraphy of the
Pliocene Iga-Aburahi Formation of theKobiwako Group around 19a-Ueno City,
Mie Prefecture, Japan. Ibid., vol. 10, p. 4858.
Yii, W., Wang, H. and Li, Z. (1963): Fossil
gastropoda of China. Academia Sinica,
Peking, p. 1 -3 6 2, pIs. 1-66 (in Chinese).

Age ~~
Aitagawa *9])11
Ayama il"TILI
Hatamura 1:lDff
Katano ? Efl!llf (Kouno),
Iga fJl"'Cl.
Hojiro= Hohziro P.ftttfEBmura xxN
Nakamura J:j:JN
Ohyamada :}(ILIEB
Sanagu {t,JJ1lJl<
yama iltllJ
Toyama 7'HlJ
Tsuge fI:iM
Wakebe :$fAA

Hattori n~i1flHirataKashikiKambe fill?
TakaTakasu milill

15lEf!~J\'l\Illf.fjt~~~(7).~ffrlfl:~*lJ=.JIjl~l'Ji : .:::m~'iU~!ff~:ttf!c j)nJUfli.~~·:j;t, ~igfJiJJII

pltJt1i1f~i}\ Gts: Gilf.lj'l!tmJl'\lllf.TAA(7)fJl~~Wi lJ':$fW L.. -C \" Go fJl~~1\¥l Ii, EI *;Jf~Rl/;.if~~(7)*-C:I;tj~Ht=~lifts:~*~4t{t:fi 0=£ ti , wt'il, J'lM, ~m, JI\!:l~M) ~I?!J:.~4t{t:fi (xtt!1MPo, IlIULm) -a-i£:l±l-t Go J'l~Mt:fiIH:=. .,;,.oM, -1.,;,.0 :tl-11l1'i7.J'15 lJ· G~ G.h. -C \, ,t'::lJ',~~tt:5H~~A97Vf~I:tts:
lE2~i?iI1ifmts: C'(7)!ll&fiI!l~li'iJ~tt.h.G;: lJ'~lJ' ") t.::o 4-§),
xllJm.· fti:»!lJl~:It!!~(7)fjt~~JITilJ' G -1 .,;,.0 711 f4(7).=.ttJ'lM c #i£: L.. t.::Dl)~Jli{t:fi-a-~~ L.. t.::RS
l'7\O) 4 ~ (P:ll WT~) 4 fi (pg 3 ~m!) HUI] L.., ~~HT\"~~ /gapaludina Ito J: If!l£.lift Biwamelania -a-.-g. k tll]f,lt:t-o J: VqIj:~~ L.. t.::: /gapaludina stricta (Araki), Bellamya

<,

195

<

c

*,

suzukii (nov. sp.), Tulotomoides sanaguensis (nov. sp.), Semisulcospira (Biwamelania)
praemultigrallosa (nov. sp.). Bellamya NJtf177 9 ,)], JIHW7;;7, *7;;71~, Semisulcospira ~I1*7;;71~7t;fJi-tGo /gapaludina c Tulotomoides 111t~Ji1l-C:~Go ;:.h.
G(7)JIlJEMI;t, EI *(7).ff~I!tH~JEm: (7)mnll;P:I~:btV:9:'~t!!:J;).iltl7)~*~Jll!JEM (7)~~, *~-a­MOO-tGJ:.-c:~~-cm~~.~-C:~Go~~~.=.

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 139, pp. 196-205, September 30, 1985

801. NEW DATA ON URANIUM-SERIES AGES OF HERMATYPIC CORALSFROM THE PLEISTOCENE LIMESTONE ON KIKA!, RYUKYU ISLANDS*AKIOOMURA
Department of Earth Sciences, Faculty of Science, Kanazawa University, Kanazawa 920
and
YOSHIHIRO TSUJI**, KAZUO OHMURA and YUJI SAKURAMOTO
Dia Consultant Co., Ltd., Tokyo 171

Abstract. Twenty-one Pleistocene corals newly collected at fourteen localities
on the island of Kikai were dated by the uranium-series 230Th/234U method. Oneof the most salient observations is that a part of the Pleistocene limestone on theisland was dated to be Middle Pleistocene in age, which may be correlative with
two stages of the high sea stand. The one is corresponding to the stage 7 of themarine oxygen isotopic record (Emiliani and Shackleton, 1974), approximately
200,000 years B.P., and the other may be correlative to the stage 9 (or older one),
250,000 years or more B.P. From the distribution of corals assigned to more than
250,000 years and the lithology of limestone including those corals, the very
shallow environment where hermatypic corals could grow up is inferred to havespread at that time over the area having a diameter of at least 6.5 km. Namely,
the initial coral reef settled directly onto the Pliocene basement (Somachi Formation; Nakagawa, 1969) might be a fairly extensive table reef and the limestone
deposited as such a reef is nowadays composed the basal part of Late Pleistocene
limestone. The other new uranium-series dates also are shown in the present paper.
We point out, based on these new 230ThP34U dates, that the geologic history
itemized by Konishi et al. (1970) should be modified, although it is not necessarily
required to change principally the articles concerning the history since the past
130,000 years.

mainly by employing the uranium-series dating
technique (Komura and Sakanoue, 1967; Konishi
et al., 1970, 1974; Omura, 1983). So far, the230Th/234U and 231pa/23SU coral dates number
between forty and fifty. In addition to them,the ESR (electron spin resonance) dating also
has been applied to some corals on this island(e.g., Ikeya and Ohmura, 1983). The numberof radiometric dates, however, is not necessarily

Introduction
The Pleistocene limestone (Riukiu Limestoneof Hanzawa, 1935) on the island of Kikai has
been chronologically studied in some detail*Received October 15, 1984.
**Presently at Japan National Oil Corporation,
Tokyo 100.
196

801. Uranium-Series Dates of Corals

enough to discuss exhaustively the geologic
history of the island and to correlate the Pleistocene limestone on Kikai with the counterpartsin other areas.
The present paper deals with 230Th/234U ages
for hermatypic corals collected at new localities,
from most of which no radiometric date has
been reported. In this study, we try to examine
the following two problems which remain still
equivocal. (1) Since when has the coral reef
been settled in the place where Kikai is atpresent? How was the scale of such an initial
reef? It is the chief concern of ours to examine
whether the dates assigned to 200,000 years
or more can be obtained for corals from the
Pleistocene limestone on Kikai. Although they
were verified from two islands in the Ryukyu
Islands, Hateruma (Konishi, 1980; Omura,1984) and Toku (Omura, 1982), yet no uraniumseries dates indicative of Middle Pleistocene
have been reported from this island. (2) Whenand how was the uppermost terrace formed?
Konishi et al. (1970, 1974) inferred that theoldest part of the Pleistocene limestone distributing in the highest area of the island was
deposited at the time of the highest sea standthrough the last interglacial from three uraniumseries ages (122,000 ± 2,000 to 128,000 ± 3,000
years) of corals collected at the height of 170 m.
They defined such a stratigraphic unit of reefy
limestone as the Older Member of Riukiu Limestone. The height of the shoreline at that timeof formation of the Older Member was thought
to be more than 200 m in present altitude. In
order to inspect their estimation, we devoted
special attention to collect the datable coral
samples from the localities of the height of
200 m or more.
Samples
Radiochemical analyses were carried out on
twenty-one hermatypic coral samples including
seven genera of Favia, Goniastrea, Porites,
Montipora, Favites, Galaxea and Montastrea.
Among them, five genera except Galaxea andMontastrea are most representative of corals

197

occurred in the Pleistocene limestone on Kikai.
Table 1 lists numbers, taxonomy and elevation
for all samples examined. The localities of themare plotted in Text-fig. 1 together with those ofboth hermatypic and ahermatypic solitary corals
dated previously to be Late Pleistocene in age(see the papers of Konish et al., 1974, andOmura, 1983, for details).
Fossil corals found at the outcrops of Pleistocene limestone were examined very carefully on
their mode of occurrence and mineralogy. The
samples for dating purpose were selected during
the field survey owing to their original positionof growth and to nature of neither pore-filling
nor recrystallization. Three samples (OA053,
A0089 and A0152) listed in Table 1 were apparently not in situ.
Prior to the isotopic analysis, the X-ray
powder diffraction method of Davies and Hooper(1963) was used for each sample in order tocheck the existence of the secondary calcite
and the calcite/aragonite ratio. As the results,
more than 5% of calcite were detected in four
samples (A0091, A0l73, A0085 and A0l75).
Particularly, A0085 and A0175 samples werecomposed of the high percent (25 and 40%,
respectively) of the secondary calcite. The otherseventeen samples were free from calcite orconsisted of more than 95% of the original
aragonite.
Results and discussion
Table 2 summarizes analytical results and230Th/234U ages calculated from the following
equation;
230Th = 238U[1- exp(-Aot)] + 34 U - 238U)[Ao/(Ao - A4)][1- exp(~t - Xot)]
where Ao and A4 are decay constant of 230Th and234 U, respectively.
Known quantities of 232U and 228Th wereused as yield tracers in the analyses of the radioisotopes listed in the table. The quoted errors(one standard deviation) are based on the counting statistical fluctionations only. In calculationof the ages, we assumed that 230Th was initiallyabsent or present in negligible amounts andeAkio OMURA et al.

198

Table 1. List of the dated coral samples from the Pleistocene limestone on the island of Kikai.

Code

SampleNumberNumber

OA053
AOO07
AOO09
A0084
A0085
A0086
A0087
A0088
A0089
AOO90
A009l
A0092
A0150
A015l
A0152
AOl70
AOl71
AOl72
A0173
A0174
A0175

CK-23
75-4-1-3A
75-4-1-3B
K-C-11
K-C-4
K-C-10
K-C-5
K-C-3
K-C-12
K-C-13K-C-14K-C-18K-C-26K-C-27K-C-28K-C-29
K-C-30K-C-31
K-C-32
K-C-33
K-C-34GeneraElevation

Fa vi tes

40 m
170
170
210
210
120
110
25
25
25
25
20
140
140
25
33
135
62

Goniastrea
Goniastrea
Porites
PoritesMontiporaFa vi tesMontipora
PoritesMontipora
Goniastrea
Galaxea
Porites
PoritesMontastrea
Favia
Favia
MontiporaMontiporaMontipora
Favitesthat samples acted as a closed system after incorporation of the radioisotopes. The half-lifevalues used for 230Th and 234U are 75,200 years
and 248,000 years, respectively.
Uranium content in A0175 sample, in which
the high percentage (40%) of calcite was detected, differs significantly from those in thecontemporary corals in the same area (Omura,1976). This fact is thought to be dependent
either on the scantiness of uranium in the calcite
crystallized secondarily or the elution of uranium
from the original aragonitic skeleton during thetime of recrystallization, and/or on the joint
effect of both factors. In any case, the reliableuranium-series age cannot be expected from asample, of which uranium has been reduced thequantity through the diagenetic history.
In the case of A0085, the another sample

72
72

175

CalciteAragonite< 0.0500< 0.010.25< 0.01< 0.02< 0.01< 0.0100.08< 0.0500< 0.01< 0.05< 0.0500.08< 0.050.40

composed of the high percentage (25%) of
calcite, it cannot be asserted from the apparent
isotopic composition that the sample has notbeen preserved as a closed system. Because
uranium content is almost equal to those in thepresent-day corals and 230Th/232Th activity
ratio is very much higher (156 ± 11) than those(1 to 3) in natural waters or sediments. The
existence of the secondary calcite, however,means that this sample does not fulfill one of
the most important criteria for reliable age
determination (Veeh and Burnett, 1982). For
these reasons, the dates of both A0175 andA0085 samples are rejected from the following
discussion.
The others, seventeen samples except A0091
and A0173, can be interpreted to satisfy allof the criteria for reliable dating from both the801. Uranium-Series Dates of Corals

199

r----------~o

I=======-~I----------~------------~~~~~----__4----------~~,"~------~-----------------{~~053'~-,~~--~

h 0 ~ o~e ~t-------I----------t"·(~M ~""L'--~----i_______ -----II

CK-24-~L----__4

S'(\IO({,IG~..r,,/-----1~

SO@O~~I""---------------"1

AOl70
1----------------7"./
I -_____________________~J,

f--------------/--.I

0•~o\<.Oq\l-CK-40,-~====================:;../..,
,

~
A0086

I' .

I,.~'OO\-----

fK- 0,-A 150-A0151

1-------------1..,( J - - - - - - -9 ' ~.A0171

CK-30

-

A
(

t--

¥-.ooo(l L r - - - - - - - - I~L~-------__4r

f-I-~~O1.0\O.AD088

C 11,-12-·CK- ,-14, -25

AOl72
/

A0089 -AD090-

1------...".\'A009I'AOI52
1===~CK-4j'15\.

~(O',(\_AOI73-AOI74

CK-5'-~.

1-1-======-=--=-...::_....'\.~,. . . . ~."\l\.,A\l~O\1092v:

f-------=>."., J(--------------------------------- "?l¥.({'-,,_---~'~"/".
. ~e\s\l...

f-------------~~

~

~

0-

y.o({,I¥.O

\

_

'2-

---=
=_

~~~~-----, ~~/~--------

Text-fig. 1. Map showing the localities of dated corals from the Pleistocene limestone
on the island of Kikai.
(Bigger and smaller black circles show the localities of hermatypic coral samples dated inthis study and reported by Konishi et al_, 1974, respectively: open small circle, the localityof ahermatypic solitary corals by Omura, 1983).

1>:1

o
o

Table 2. Uranium and thorium isotopic composition and estimated 230Th/234U ages of fossil corals from the Pleistocene limestone on theisland of Kikai.
Activity

Isotope Concentration
Code Number238

U (ppm)234.
U(dpm/g)A0092

3.26 ± 0.04

2.73 ± 0.04

A0090

4.16 ± 0.07

3.47 ± 0.06

A0088

4.17 ± 0.03

A0091

3.24 ± 0.05

A0152

3.32 ± 0.03

AO007

232

Th (ppm)< 0.02230

230 Th /232 Th

Ratio
230 Th /234 U

EstimatedAgeTh (dpm / g)

234U/238U

0.866 ± 0.016

1.12 ± 0.01

0.317 ± 0.022

41 ± 446 ± 5(ka)< 0.02

1.20 ± 0.03

1.12 ± 0.02

0.346 ± 0.032

3.53 ± 0.03

< 0.02

1.33 ± 0.02

1.13 ± 0.01

0.376 ± 0.020

51 ± 32.70 ± 0.04

< 0.02

1.02 ± 0.02

1.12 ± 0.01

0.376 ± 0.023

51 ± 42.73 ± 0.03

0.0544±0.0063

1.09 ± 0.02

1.10 ± 0.01

83.9 ± 9.7

0.401 ± 0.007

55 ± 2

3.19 ± 0.10

2.66 ± 0.08

O. 0245±0. 0068

1.60 ± 0.04

1.12 ± 0.03

273 ± 76

0.602 ± 0.039

99 ± 9AOO09

3.23 ± 0.07

2.61 ± 0.06

< 0.02

1.62 ± 0.05

1.08 ± 0.02

0.621 ± 0.038

104 +11 -10

CA053

3.10 ± 0.09

2.38 ± 0.07

0.0361±0.0021

2.03 ± 0.04

1.03 ± 0.04

0.853 ± 0.030

204 +23 -19

A0086

3.80 ± 0.04

2.86 ± 0.03

< 0.022.61 ± 0.03

1.01 ± 0.01

0.911 ± 0.015

259 +19 -17A0089

2.71 ± 0.03

2.08 ± 0.03

< 0.022.02 ± 0.02

1.03 ± 0.01

0.973 ± 0.017

360 +64 -40

A0170

3.44 ± 0.04

2.62 ± 0.03

0.162±0.011

2.54 ± 0.03

1.02 ± 0.01

0.973 ± 0.016

369 +69 -42

A0084

2.71 ± 0.03

2.05 ± 0.03

< 0.022.01 ± 0.02

1.01 ± 0.01

0.981 ± 0.016

409 +120 -55

A0151

3.13 ± 0.03

2.39 ± 0.03

0.0242±0.0044

2.42 ± 0.03

1.02 ± 0.01

AOl72

4.66 ± 0.05

3.53 ± 0.04

O. 0233±0. 0041

3.55 ± 0.04

A0173

4.16 ± 0.05

3.11 ± 0.04

O. 0210±0. 0038

3.13 ± 0.04

AOl71

3.02 ± 0.04

2.32 ± 0.03

0.0284±0.0038

2.37 ± 0.02

1. 03 ± 0.01

A0087

3.08 ± 0.03

2.36 ± 0.02

< 0.022.42 ± 0.02

1.03 ± 0.01

A0174

3.75 ± 0.05

2.83 ± 0.04

O. 0304±0. 0049

2.93 ± 0.04

1. 01 ± 0.01

401 ± 65

1.04 ± 0.02

A0150

2.87 ± 0.03

2.23 ± 0.03

0.0278±0.0040

2.37 ± 0.03

1.04 ± 0.01

354 ± 51

1.06 ± 0.02

234 ± 1465.6 ± 4.4
417 ± 761.01 ± 0.02

> 450

1.02 ± 0.01

634 ± III1.01 ± 0.02

> 450

1.00 ± 0.01

620 ± 1121.01 ± 0.02

> 450

348 ± 46

1.02 ± 0.02
1.03 ± 0.01

A0085

4.55 ± 0.05

3.47 ± 0.04

O. 0235±0. 0016

3.66 ± 0.03

1.02 ± 0.01

156 ± 111.05 ± 0.01

A0175

1.41 ± 0.02

1.08 ± 0.02

0.0636±0.0082

1.08 ± 0.02

1.03 ± 0.02

71.1 ± 9.2

1.00 ± 0.03

> 450

~

;ito

o·

~
~

~

.,......
Q:-

801. Uranium-Series Dates of Corals
mineralogical nature and the isotopic composition of each sample. In other words, the assumptions used in calculating the ages are certainly
supported in these samples by the observations
listed in Tables 1 and 2 (see the paper of Veeh
and Burnett, 1982, for detail and concrete
discussion).
The 230Th/234U dates reported here involvesome useful pieces of information to understandthe geologic history of Kikai. They are as thefollowings:
The estimated ages of twelve samples, from
OA053 through A0l50 in Table 2, are 200,000
years or more, and moreover the ESR dates of403,000 ± 21,000 to 536,000 ± 37,000 years
have been obtained from ten samples except
OA053 and A0170. We may, therefore, reasonably say that a part of the Pleistocene limestone
on Kikai is Middle Pleistocene in age. Such 23oTh/
234U dates are likely to be divided into twogroups. The one is approximately 200,000 years
from one sample (OA053) and the other is morethan 250,000 years. The former is almost equivalent to the age of the penultimate interglacialwhich is corresponding to the stage 7 of themarine oxygen isotope record (Emiliani andShackleton, 1974). In the Ryukyu Islands,
the same dates have been previously reported
from the island of Hateruma by Konishi (1980)
and Omura (1984). Namely, a part of the Pleistocene limestone on this island may be correlativewith the Hateruma I of Ota et al. (1982). The
extent of distribution and the litho- and biofacies of the limestone deposited at this stage,
however, are not clear on Kikai as of now.
The value of the latter is thought to be nearor beyond the limitation of the 230Th/234U
method for dating, although the ages can be
numerically calculated as shown in Table 2. It
can be conclusively said from the 234U/238U
ratios close to the unity that these corals are
too old for the uranium-series method to be
applicable. The value of the 234U/238U activity
ratios of the samples averages 1.019 ± 0.011.
Assuming that the initial 234U/238U ratio was
1.14 (Ku et al., 1977), the mean age is estimatedfrom such an average value of 234U/238U ratio

201

to be 645,000~rg;:ggg years. These facts suggestthat the oldest limestone on Kikai may becorrelative to the deep-sea core stage 9 or thepreceding warm stage. So far, in the Ryukyu
Islands the same extent of 23°Th/234U age has
been obtained from the Kametsu Formation(Nakagawa, 1967), a part of the Riukiu Limestone of Hanzawa (1935), on the island of Toku
(Omura, 1982).
The localities of the samples assigned to morethan 250,000 years are scattered in a extensive
area on the island (Text-fig. 1). Such an area islikely to cover the distribution area of theYounger, Middle and Older Members of Riukiu
Limestone of Konishi et al. (1974). The distancein a straight line between the localities of A0170
and A0l74 samples is about 6.5 km. Tsuji (1979)
mapped geologically the southwestern part of
Kikai and concluded that the oldest limestone
on this island occurs fairly extensively in thisarea and is unconformably overlain even with
the Araki Limestone which is thought to be
the uppermost unit of the Pleistocene limestone
on this island and to have been deposited 35,000- 45,000 years ago by Konish (1967) andKonish et al. (1970, 1974). The very shallow
environment where hermatypic corals could
grow up is thus inferred to have spread at thattime over the area having a diameter of at least
6.5 km. On the whole, the limestone including
corals indicative of the age of Middle Pleistocene
is not typical bindstone or framestone of Embry
and Klovan (1971). However, it is sure that a
considerable number of hermatypic corals arepreserved in the state of their original positionof growth and that the binding structure madeof flat-shaped colonies of hermatypic corals
and crustose coralline algea is observed in someplaces. These facts suggest that the initial coral
reef developed directly onto the Pliocene basement (Somachi Formation; Nakagawa, 1969)
might be a fairly extensive table reef. And then,the limestone deposited as such a reef is considered to constitute the basal part of the Pleistocene limestone on the island.
Two (A0007 and A0009) samples weredated to be approximately 100,000 years,

202

Akio OMURA et al.

which fits in the time of· an interstadial phaseand almost equals the age of the Barbados II
terrace of Mesolella et al. (1969) on Barbados,
West Indies, and the age of the Reef Complex
VI on the Huon Peninsula in New Guinea (Bloom
et al., 1974). Both 23oTh/234U and 231Pa/235U
ages of about 100,000 years have been previously reported for a coral sample (CK-30) collectedon the island by Konish et al. (1974). This datecorresponds with the age of the Hateruma IV(Omura, 1984).
As shown in Table 1, the elevation of both
A0007 and A0009 samples is 170 m and is 30
m higher than that of CK-30 sample of Konish
et al. (1974). Based on the elevation and themode of occurrence of these samples, there isvery little doubt that the sea level of about
100,000 years ago was 170 m or more in present
altitude. It is generally known that the sea level,
through the period of the last interglacial, has
attained to the maximum (say 6 m higher thanpresent) 120,000 to 130,000 years before.
Comparing with it, the sea level during theinterstadial of about 100,000 years ago seems
to have been roughly 20 m lower, from thedata for the uplifted coral reefs on the islandof Barbados and the Huon Peninsula (Broecker
etal., 1968;Bloometal., 1974).
Supposing the depositional depth ("Ld"value of Konishi, 1967) of 0 - 10 m, we caninfer from the present elevation (as a first approximation, regarded as "Le" value) of thesample dated that the sea level was 170 - 180 m
in present altitude. The limestone, from which
both A0007 and A0009 were sampled, consistsof large hermatypic coral heads in growth position and of encrusting coralline algae and foraminifera. For this observation, we suppose that
this limestone was formed as the reef-wallfacies and that its depth was 0 to 10 m. Because
the differences ("LlSL" value) between sea levelat the time of deposition and sea level at present
is -14 m, the amount of vertical displacement("Ll V" value) due to tectonic uplift is calculated
to be 184 - 194 m by the equation of Konish(1967). If the displacement is continuous rather
than episodic, the rate of displacement ("Ll V/

LlT" value) is estimated to be 1.84 -1.94 mm/y.
This Ll V /Ll T value is consistent with that estimated for the Araki Limestone and the Younger
Member of Riukiu Limestone by Konish et al.
(1970). By assuming that such a value of Ll V/
LlT is also valied for the limestone depositedat the time of 120,000 - 130,000 years ago,then we can calculate that the sea level at thattime reaches to the present elevation of 227239 m to 245 - 258 m. This means that thehighest point of 224 m in Hyakunodai has been
submerged during the time of last interglacialas pointed out by Konish et al. (1970, 1974).
In order to vindicate the inference as statedabove, it is the best way to date the appropriate
coral samples occurred in the limestone unit
which makes of the terrace deposit of Hyakunodai, attaining a height of more than 200 m.
Among the samples treated in this study, only
two samples (A0084 and A0085) are collected
at the locality of higher than 200 m. The apparent date of A0085 sample, however, cannot
be used here for above-mentioned reason. Thus,
for the present, we can hardly avoid the conclusion that the limestone of the highest terrace is
Middle Pleistocene in age. It is necessary in thefurther study to search and date the coral samples occurred in the portion close to the surfaceof the terrace.
The date of a coral sample (A0092) was
41,000 ± 4,000 years (Table 2), which is corresponding to the age of the Araki Limestone of
Konish et al. (1970, 1974). This limestone unit
was originally divided as an independent lithostratigraphic unit from the Riukiu Limestoneof Hanzawa (1935) by Schlanger and Konishi(1966) who remained the name of "Riukiu
Limestone" adopted by Hanzawa (1935) anddivided the other part into two, Younger andOlder Members of Riukiu Limestone. The
Araki Limestone is composed mainly of wellsorted and slightly cemented calcarenite. Maincomponents of this unit are tests of Calcarina,
Amphistegina, Marginopora and Baculogypsina,
and disartiCUlated fragments of Amphiroa,
Corallina and Halimeda (Konishi et al., 1970).
A few hermatypic corals in growth position are801. Uranium-Series Dates of Corals

present at the basal part of the fonnation. The
age of the Araki Limestone is thought based on
230Thj234U and 231Paj235U dates of total numbers of fifteen to be 35,000 - 45,000 years
B.P. (Konishi et al., 1974). Tsuji (1979) who
examined the litho- and bio-facies in moredetail made clear that this limestone unit issporadically distributed in the southwesternpart of the island. The locality of A0092 sample is situated approximately 800 m northwestof Kamikatetsu at a height of 20 m, and is included in the area of the Araki Limestone seenin the geologic map of Tsuji (1979). These facts
support, therefore, his conclusion as to the
distribution of the Araki Limestone.
A date of 55,000 ± 2,000 years was obtained
for a coral (A0152) collected at the type localityof the Araki Limestone. This date is correlative
to the age of the Younger Member of Riukiu
Limestone of Konishi et al. (1974). It may,therefore, be said that some corals in the Araki
Limestone are detrital in origin, even though
they appeared to be kept in their original position of growth. An another sample (A0091)
from the same location also may be of detrital
origin, depending on its date (51,000 ± 4,000
years) close to the age of the Younger Memberof Riukiu Limestone.
As stated above, we reported in this papersome additional uranium-series dates of corals
from the Pleistocene limestone on the islandof Kikai. Such dates do not require to change
largely the geologic history since the last interglacial of this island, which was itemized by
Konishi et al. (1970), although the dates assigned
to probably two stages during the time of Middle
Pleistocene were newly obtained. In order togeneralize the geologic history of Kikai, we
propose here to add at least two articles described below between the first (A) and thesecond (B) among the seven items seen in thepaper of Konishi et al. (1970).
(i) Development of a fairly extensive coral
reef (probably, table reef) onto the basement,
Pliocene Somachi Fonnation (Nakagawa, 1969),
more than 250,000 years B.P.
(ii) Fonnation of a small-sized reef (fringing

203

reef?), during the time of the penultimate
interglacial stage, approximately 200,000 years
B.P.
Summary(1) A part of the Pleistocene limestone on
the island of Kikai is Middle Pleistocene in age
and is thought to have been deposited during
two stages of high sea stand. The one is approximately 200,000 years B.P. and the other is morethan 250,000 years B.P.
(2) The fonner can be correlative with theHateruma I on Hateruma Island (Omura, 1984).
The latter is almost near or beyond the limitationof the 230Thj234U dating method but is thoughtfrom the 234U j238 U activity ratio to be correlative with the Kametsu Fonnation (Nakagawa,1967) on the island of Toku.
(3) The distribution of corals assigned tomore than 250,000 years denotes that the very
shallow environment where hennatypic corals
could grow up has spread at that time over thearea having a diameter of at least 6_5 km. The
initial coral reef settled directly onto the Pliocene basement (Somachi Fonnation; Nakagawa,1969) might be a fairly extensive table reef.
(4) The limestone deposited approximately
100,000 years ago is traced up to a height of
170 m. Assuming that the displacement is
continuous, the amount and the rate of verticaldisplacement since the past 100,000 years are
estimated to be 184 - 194 m and 1.84 - 1.94
mmjy, respectively. Moreover, it is very strong
possibility that the most elevated point of 224
m on this island has been submerged at thetime of the last interglacial, 120,000 - 130,000
years ago.
(5) The date correlative to the age of the
Araki Limestone (Konishi et al., 1974) was
obtained for a coral which was sampled at theother spot than the type locality of it. This
fact supports the conclusion of Tsuji (1979)
that the Araki Limestone is sporadically distributed in the southwestern part of the island.
(6) Some corals in the Araki Limestone may
be detrital in origin, even though they are ap-

Akio OMURA et al.

204

parently in their original position of growth.
Acknowledgments
We thank Professors K. Konishi, Kanazawa
University and Y. Ota, Yokohama National
University, for their continuous encouragement
throughout this study. This research was supported in part by the Grant-in-Aid for Scientific
Research (nos. 59540500 and 59380024) from
the Ministry of Education, Science and Culture.
References
Bloom, A. L., Broecker, W. S., Chappell, J. M. A.,
Matthews, R. K. and Mesolella, K. J. (1974):
Quaternary sea level fluctionations on atectonic coast: new 230Th/234U dates fromthe Huon Peninsula, New Guinea. Quaternary Res., vol. 4, p. 185-205.
Broecker, W. S., Thurber, D. L., Goddard, J., Ku,
Teh-Lung and Matthews, K. J. (1968):
Milankovitch hypothesis supported by precise dating of coral reefs and deep-sea
sediments. Science, vol. 159, p. 297-300.
Davies, T. T. and Hooper, P. R. (1963): The
determination of the calcite: aragonite
ratio in mollusc shells by X-ray diffraction.
Mineral. Mag., vol. 33, p. 608-612.
Embry, A. F. and Klovan, J. E. (1971): Devonian
reef tract on northeastern Banks Island,
N. W. T. Bull. Can. Petrol. Geol., vol. 19,
p.730-781.
Emiliani, C. and Shackleton, N. J. (1974): The
Brunhes epoch: isotopic paleotemperaturesand geochronology. Science, vol. 183, p.
511-514.
Hanzawa, S. (1935): Topography and geologyof the Riukiu Islands. Tohoku Imp. Uniu.,
Sci. Rep., 2nd Ser. (Geol.), vol. 17, p.1-31.
Ikeya, M. and Ohmura, K. (1983): Comparisonof ESR ages of corals from marine terraces
with 14C and 230Thf2 34 U ages. Earth Planet.
Sci. Letters, vol. 65, p. 34-38.
Komura, K. and Sakanoue, M. (1967) Studies on
the dating methods from Quaternary samples by natural alpha-radioactive nuclides.
Sci. Rep. Kanazawa Uniu., vol. 12, p. 2166.
Konishi, K. (1967): Rates of vertical displace-ment and dating of reefy limestones in themarginal facies of the Pacific Ocean Application by natural alpha-radioactive
nuclides in biogenic carbonate rocks up to
150,000 years old -. Quaternary Res.
(Tokyo), vol. 6, p. 207-223 (in Japanesewith English abstract).
- - , Schlanger, S. O. and Omura, A. (1970):
Neotectonic rates in the central Ryukyu
Islands derived from 230Th coral ages. Marine
Geol., vol. 9, p. 225-240.
- - , Omura, A. and Nakamichi, O. (1974):
Radiometric coral ages and sea level records
from the Late Quaternary reef complexesof the Ryukyu Islands. Proc. 2nd Int. Coral
Reef Symp., vol. 2, p. 595-613.
- - (1980): Diverse plate convergence as deduced from raised coral reefs since theLast Interglacial. Quaternary Res. (Tokyo),vol. 18, p. 241-250 (in Japanese withEnglish abstract).
Ku, Teh-Lung, Knause, K. G. and Mathieu,
G. G. (1977): Uranium in open ocean:concentration and isotopic composition.
Deep-Sea Res., vol. 24, p. 1005-1017.
Mesolella, K. J., Matthews, R. K., Broecker, W. S.
and Thurber, D. L. (1969): The astronomical theory of climatic change: Barbados
data. Jour. Geol., vol. 77, p. 250-274.
Nakagawa, H. (1967): Geology of Tokunoshima,
Okierabujima, Yoronto, and Kikai-jima,
Amani Gunto: Part 1. Tohoku Uniu., Inst.
Geol. Pal. Contr., no. 63, p. 1-39 (inJapanese with English abstract).
--(1969): Geology of Tokunoshima, Okierabujima, Yoronto, and Kikaijima, Amami
Gunto: Part 2. Ibid., no. 68, p. 1-17 (inJapanese with English abstract).
Omura, A. (1976): Thorium and protactinium
isotopes in some present-day hermatypiccorals and their implications to dating.
Trans. Proc. Palaeont. Soc. Japan, N. S.,
no. 101, p. 271-290.
- - (1982): Uranium-series age of the "Kametsu Formation", Riukiu Limestone on the
Tokuno-shima, Ryukyu Islands. Ibid., no.
126, p. 327-333.
- - (1983): Uranium-series ages of some solitarycorals from the Riukiu Limestone on the
Kikai-jima, Ryukyu Islands. Ibid., no. 130,
p.117-122.

801. Uranium-8eries Dates of Corals(1984): Uranium-series ages of the Riukiu
Limestone on Hateruma Island, Southwestern Ryukyus. Ibid., no. 135, p. 415426.
Ota, Y., Hori, N. and Omura, A. (1982): Age anddeformation of marine terrace of Hateruma
Island, Southwest Japan. Abstract of XI
INQUA Congress, Moscow, vol. 2, p. 232.
Schlanger, S. O. and Konishi, K. (1966): Contrasting bryozoa content of Plio-Pleistocene
to Present-day carbonates from Guam,
Mariana Islands, and Kikai-jima, Ryukyu-

205

Islands, and its regional implications. A bstract of Papers. Proc. of the 11 th Pacific
Science Congress, Tokyo. vol. 4, p. 35.
Tsuji, Y. (1979): Quaternary history of thewestern part of Kikai-jima, Ryukyu Islands.
M. Sc. Thesis. Fac. Sci.. Kanazawa Univ .•172 p. (Unpublished manuscript).
Veeh, H. H. and Burnett, W. C. (1982): Carbonate and phosphate sediments. In Ivanovish,
M. and Harmon, R. S. (eds.) Uranium Series
disequilibrium: Applications to environmental problems, p. 459-480, Clarendon
Press, Oxford .

• ~A~~~~~~~.~~~.~Y~~~'Y*~.~~~~~~.M:R.~A.~(Hanzawa. 1935. ~ Riukiu Limestone) iI'G. tTL < 230Th/
23·U 1'*1::' J: '? '"CttM.f\;>a-*&?t.: o ;:;: '"C'¥li1!f~ ~.~{j~Jt. ~lc Iv EiI;, ;:;h i '"C'!tM.~
i1;%IG.n '"C~,tJ:\":I1!!.,~'"C'!*. Lt.: 7 ~ (Favia, Goniastrea. Porites. Montipora. Favites.
Galaxea. Montastrea) • .g.~i21 OO~ ~i1.~ Y :l'11:~i1' G~t.: t ~'"C';6 ~o .:t~ki5* c L '"C •• W.A~~~tiIt~-ffiHt, ~~I!!:.pJl)jI::.:}.;!1" ~ 2 @]~ifijifa**JUH::.*jJil1:~;ht.:;: c i1~~ GiI'l::'tJ: '? t.:o -'?It. :}.;:}.; J: .:t20n.litr~ EmiIiani and Shackleton (1974) ~ oxygen isotopic
stage 7 1::,;6t.:/). ft!!~-,?"t, 25n.J;l.1::litr~ stage 9 (;6~~'ft. J: IJJ;l.litr~~fIU.IJ) t::.
:m~~ ~o 1&~~ipfl;:;flRlt. A~*ffl'"C'~iHl€ L t.:~MiI' G~G;ht.:i1~. .:t.n G:!*.:I1!!.,~~a.i1·
IJ c .:t;hG~Y :l'fl:~~~tr~~~~~;f§tJ: c'i1'G. ~fIif. ~i1.~ Y :l'~~Wil~RJ~tdii:lt$.%1::'1t~~~"!f~tiIt~)J}(~~~i1'.-'?~~ffil'jdJ:< c t6.5km ;6~Qii!JmI::.a.i1''?-C~,t.:c,\!!,b;h~o ~tJ:bb. ~§(1::'iiIl.~~tiIt.!f!.IIIJ~; .pJfl. 1969) 1::1::'. ItC&?-CMJil1:~;ht':~Y:l'l!!lt. tJ,tJ:IJ~a.tJ·lJ~t '? t.:.lji.Iiii\'"C';6 '? t.:RJfftl1 t;6 IJ. ~fIif~~~MJil1: L -C~ ,t.:~)J}(~It. ffl-tE. Konishi et ai,(1974) fltJ'~mt:I!J(~I!}(~"2l· <j:r:}.; J: V:~WJ'iiIlfl~~~'iiIlH:.lJil1: L -C~,~ c~;:t G;h~o
4-@I~t.:I::'~G.nt.: 230Th/ 234 U ~ Y :l·.~tJ, G. ):)'litr Konishi et at. (1970) I::' J: '?-C

fiSi~~ ~ I::' L -C;ill""G;ht.:*A~:I1!!~~. j&l~137J1f-r..'~f:fll1tlt~*B9I::.f!r~~~'~lttJ:~' t~~. -'iiIl~lELtJ:!1";hlftJ:GtJ:~';: c~m~~~o*M~~·fr .~·*M-~·m*~~Trans. Proc. Palaeont. Soc. Japan, N.S., No. 139, pp. 206-217, pIs. 28-30, September 30, 1985

802. ADDITIONAL SILURIAN TRILOBITES TO THE YOKOKURA-YAMA
FAUNA FROM SHIKOKU, JAPANTEIICHI KOBAYASHIThe Japan Academy, Ueno Park, Tokyo

and

TAKASHI HAMADA
Department of Earth Science and Astronomy, College of Arts and Sciences, University of Tokyo

Abstract.
A new trilobite collection by Sak6 contains 12 species including
11 new species three of which were already described in the advance report andthe remainder is included in this paper. Pseudocheirurus and Staurocephalus are
two new genera for the Silurian fauna of Yokokura-yama. The former indicatesthe faunal connection from Japan to Bohemia through the Mongolian geosyncline.
Some species of Encrinurus on the other hand are related to the Australian ones.

In 1974 the authors described a copious
fauna of Mt. Yokokura com prizing 26 species
in 14 genera and seven families of trilobites.
Recently a new collection made therefrom by
Sako was placed by Katto at the authors' disposal for study. Most trilobites in this collection
were obtained at the Gomi quarry and its vicinity
and some others found at loc. D among drifts
which are presumably derived from the same
quarry.
As shown in fossil list, the collection con·tains 12 species beside a few exactly indeterminable forms, among which three species ofBumastus (agmakros, kattoi, sakoi) have been
already described in the advance report (Koba·
yashi and Hamada, 1984). The remainder isdealt with in this article. As genera, Pseudo-cheirurus and Staurocephalus are new to thefauna, although Staurocephalus (?) sp. wasalready found. Staurocephalus as a genus ap·
peared in the Middle Ordovician in Norway,
spread widely from Europe to North America
on one side and to Australia through Central
Asia on the other, being especially extensive in
the Wenlockian rocks. Among the Silurian
species Staurocephalus trichochin looks similar
to S. struszi from the Wenlockian of Australia.
A pygidium is identifiable with Proetus
sugiharensis. This find confirms that the Encrinurus tosensis horizon at Sugihara shrine isnear the fossil beds of Gomi quarry, as considered before. Among 8 new species Dindymene(?) megacranidia belongs probably to an unnamed genus. Japonoscutellum and Apolichas
are two endemic genera.
As noted already (Kobayashi and Hamada,1974), Pseudocheirurus beyrichi (Barrande)occurs in the lower Ludlovian Kopanina Forma-

Received October 29,1984.
*Studies on Japanese Trilobites and AssociatedFossils XXXVI.
206

802. Silurian Trilobites from Shikoku

tion (Horny and Bast!, 1970). It is the typespecies of Pseudocheirurus to which Pseudocheirurus gomiensis appears most similar. Among
the Asiatic cheirurids this species is very similar
to Nan's Cheirurus strabo from the Upper
Silurian of Inner Mongolia (1960), instead ofLower Devonian Cheirurus strabo Weber, 1932
of Ferghana. These two species suggest that the
Yokokura fauna was connected with the Bohemian one through the Mongolian geosyncline
in the early Ludlovian age.
Encrinurus subtrigonalis is an aberrant speciesof the genus resembling Encrinuroides uncatus
in certain aspects of the cheek. A pygidiumreferred to this species is similar to Encrinurusnodai. Encrinurus similis is represented byanother pygidium distinct from that of E. subtrigonalis, but they agree with each other soclose that the differences may reveal sexual
dimorphism. Encrinurus stenorhachis is closely
related to E. tosensis. Combined with E. yoko-

Trilobites~207

kurensis, E. mamelon, E. ishii and E. fimbriatus
these two species i.e. similis and subtrigonalis
show an intimate relationship with E. mitchelli
and its allies in Australia through Encrinurus
konghsaensis in Burma, as pointed out already(Kobayashi and Hamada, 1974).
In adding new elements it can be concluded
with more certainty that the Silurian fauna of
Mt. Yokokura indicates the faunal connection
to Australia through Burma on one side and to
Bohemia or Europe on the other through the
Mongolian geosyncline.
All of the type specimens of new species
were donated by the collector to the Kochi
University where they are kept. Before entering
into description of trilobites, the authors wish
to record their sincere thanks to Professor
Emeritus Jiro Katto of the Kochi University
and Mr. Yukio Sako, ardent fossil collector, forthe privilege of describing these interesting
trilobites.

Localities

A

Japonoscutel/um geniculatum, sp. nov.

x

Bumastus agmakros Kobayashi and Hamadax

Bumastus kattoi Kobayashi and Hamadax

Bumastus sakoi Kobayashi and HamadaxIllaenoid (?) gen. et sp. indet.

x

B

C

Proetus (Gerastos) sugiharensis Kobayashi and HamadaxPseudocheirurus gomiensis, sp. nov.

x

Encrinurus subtrigonalis, sp. nov.

x

Encrinurus similis, sp. nov.

x

Encrinurus stenorhachis, sp. nov.
Dindymene (?) megacranidia, sp. nov.

x
x

Staurocephalus trichochin, sp. nov.
Phacopid (?) gen. et sp. indet.

xx

Apolichas perconuexus, sp. nov.
Lichid (?) hypostoma, gen. et sp. indet.

Dxx

Fossil list of additional Silurian trilobites to the Yokokura-yama Fauna
A. Gomi quarry
B. Boulder found near Gomi quarry
C. About 1 km east of Gomi quarry
D. Boulders found between Gomi and Ichiyama villages

208

Teiichi KOBA YASHl and Takashi HAMADA
Description of trilobites

Family Scutelluidae R. and E. Richter, 1955
Genus Japonoscutellum Pfibyl and Vanek, 1971

Japonoscutellum geniculatum
Kobayashi and Hamada, sp. nov.
PI. 28, Figs. 2a--c.

Description:-Pygidium semiparabolic in outline about three-fourths as long as wide, flatin i~ner part, but slanting to depressed margin
in outer part. Axial lobe small, elevated above
pleural lobes, subtrigonal, tripartite, half as
long as wide and a quarter as wide as straightanterior margin which indicates maximum
breadth of pygidium; median lobe of axis alittle higher than its lateral lobes, crossed by
five or six transverse lirae with regular intervals,
articulating half-ring stout, isolated from axial
lobe by a profound furrow. First pleural rib
straight anteriorly, regularly thickening laterally,
more prominent than others and isolated fromthem by a strong pleural furrow well broadened
laterally; succeeding furrows narrower than
the above rib, anterior ones of which extend as
far as lateral margin, but posterior ones die out
shortly inside of the margin; median rib muchbroader than these lateral ribs, most distinctly
geniculated, more or less depressed mesiallybehind the geniculation, but the depression isby no means so distinct as pleural furrows;
geniculation becomes insignificant laterally; many
weak sub concentric lirae recognizable on all ofthese ribs, but they become obscure proximallyfrom margin. Test smooth except for such finelirae.
Comparison:-This species is represented bya single, but almost complete, well preserved
pygidium. Its dorsal carapace is exfoliated in
the l~ft anterior part where it is seen that the
doublure extends at least to the geniculation.
It agrees nicely with the pygidium of Japonoscutellum japonicum (Kobayashi and Hamada,1965), in the outline, texture and some otheraspects. It is, however, specifically distinct
from that species in regard of the distinct geniculation most emphasized a little behind the

mid-length of the broad median rib, shallow
mesial depression in its posterior part and thedistinct tripartition of the axial lobe withseveral transverse lirae on its median lobe.
Such geniculation is seen in some genera,
Pia tyscu tellum,
Bojoscutellumand Plan iscutellum, for example. In the first and second
genera, both Lower Devonian in age, the pygidium is respectively pentagonal and elliptical in
outline. In Silurian Kosovopeltis the median rib
is typically simple.
Family Proetidae Salter, 1864
Subfamily Proetinae Salter, 1864
Genus Proetus Steininger, 1831
Subgenus Gerastos Goldfuss, 1843

Proetus (Gerastos) sugiharensis
Kobayashi and Hamada, 1974
PI. 29, Figs. 1a--c.

1974. Proetus (Geratos) sugiharensis Kobayashi
and Hamada, p. 116, pI. 12, figs. 5-----u,text-fig. 8e.
Beside an incomplete pygidium this species
was founded on the complete pygidium (holotype). The third specimen before hand is alsoa well preserved pygidium which coincides withthe holotype in detail. In this specimen anterior
seven ribs, instead of five, are clearly defined.
Eight ribs are countable on the right pleurallobe among which the second to fifth ribs are
distinctly divided into two bands by insertionof an interpleural rib from their lateral margin.
Family Cheiruridae Salter, 1864
Subfamily Cheirurinae Salter, 1864

GenusPseudocheirurus Prant! and Pribyl, 1947
Pseudocheirurus gomienesis
Kobayashi and Hamada, sp. nov.
PI. 28, Figs. 1a--c.

1984. Pseudocheirurus sp. Kobayashi
Hamada, p. 253, pI. 5, figs. 5a-b.

andDescription:-Cheirurid cranidium with two

802. Silurian Trilobites from Shikoku

anterior lateral furrows gently curving backward and extending laterally as far as one-thirdof glabella; preoccipital furrow diagonal andconfluent with occipital furrow which is in turnbent forward in its median part. Frontal lobe ofglabella nearly as long as two anterior laterallobes; preoccipital lobe trigonal. Neck ring
expanded in median part twice as thick as its
lateral terminus. Axial furrows profound andslightly divergent forward. Fixed cheek narrow
and ornamented with irregular anastomozing
lirae; eye small, located far anteriorly and close
to axial furrow. Glabella and marginal borders
smooth.
Observation and comparison:-In the frontal
view of the cranidium it is seen in the basal
part of the frontal lobe of the glabella that
there are a pair of linear furrows which aredisconnected in the median part.
The principal distinction of the subgenus
Pseudocheirurus from Cheirurus s. str. lies inthe seven lobate pygidium of the former. In
the cephalon it is noteworthy that the preoccipital furrow is subrectangular and the preoccipital lobe is subquadrate in typical Cheirurus.
In the diagonal preoccipital furrow and its
confluence with the forwardly bent occipital
furrow, this subgenus agrees better withCheirurus (Crotalocephalus) , but in the latterthe two pairs of anterior lateral furrows areunited into two transversal furrows. By this
distinction Crotalocephalus is separated now
from Cheirurus generically.
The chief distinction of this species from
Cerauroides orientalis and Cerauroides elongatus
in the Yokokura fauna lies in the confluenceof its preoccipital furrow with the forwardly
bent occipital furrow. The glabella is more
expanded anteriorly in C. orientalis. The expansion is particularly emphasized at the frontal
lobe in C. elongatus. Additional differences
are the median tubercle on the occipital ringand the relatively broad cheek in Cerauroides
orientalis.
Didrepanon Lane, 1971 and Hadromeros
Lane, 1971 have similar glabellae, but theircheeks are broader and their eyes placed more209

posteriorly.
Nan's Cheirurus strabo from the Upper
Silurian of Inner Mongolia (Nan, 1976) looks
very similar to this species. Cheirurus strabo
Weber, 1932, is however, a Lower Devonian
trilobite of Ferghana, Turkestan.
Family Encrinuridae Angelin, 1854
Subfamily Encrinurinae Angelin, 1854
Evitt and Tripp (1977) included in thissubfamily the following twelve genera.
Encrinurus Emmrich, 1844
Cromus Barrande, 1852
Frammia Holtedahl, 1914
Coronocephalus Grabau, 1924
Encrinuroides Reed, 1931
Fragiscutum Whittington and Campbell, 1967
Encrinuraspis Webby, Moors and McLean,
1970
Erratencrinurus Kruger, 1971
Senticuculus Xia in Chang, 1974
Kailia Chang, 1974
Celtencrinurus Evitt and Tripp, 1977
Physemataspis Evitt and Tripp, 1977
Then Wu Hong-ji (1979) splitted Coronocephalus and Kailia each into two subgenera
as follows:Coronocephalus (Coronocephalus) Grabau,
1924
Coronocephalus (Coronocephalina) Wu, 1979
Kailia (Kailia) Chang, 1974
Kailia (Parakailia) Wu, 1979
Strusz (1980) synonymized Encrinuraspis
with Cromus on one hand and on the other headded Paraencrinurus Antelo, 1973 andBatocara,gen. nov. whose type species is Encrinurusbowningi Foerste, 1888. An additional genus is
Balizoma Holloway, which is founded on
Calymene variolaris Brongniart, 1822.
Genus Encrinurus Emmrich, 1844
According to Strusz (1980), Cryptonymus
Eichwald, 1840, Michellaspis Henningsmoen in
Moore, 1959, Mitchellia Vogdes, 1917, non deKoninck, 1877 and Calcachia, Paracalcachia,

210

Teiichi KOBA YASHI and Takashi HAMADA

Aristobeggia, Letichia and Trippia Lamont,1978 are all synonymous with Encrinurus.
He recognized in this genus three species plexi
as follows:
1. Encrinurus variolaris plexus
2. Encrinurus punctatus plexus
3. Encrinurus mitchelli plexus
Holloway (1980) on the contrary proposed
Balizoma for members of the variolaris species
group listed by Tripp, Temple and Gass (1977)
except E. diabolus and E. anticostiensis whichwere both considered to belong to Fragiscutum,
but it includes E. nereus Hall, 1867, E. indianensis Kindle and Bregger, 1904, E. tuberculifrons
Weller, 1907 and E. hyperborea Thomas inThomas and Narbonne, 1979. Strusz on theother hand referred the following species to his
Encrinurus variolaris plexus.
Cromus transiens Barrande, 1852
Encrinurus poloeckensis von Gaertner, 1930
Encrinurus kiltsiensis Rosenstein, 1941
Encrinurus pilisyverensis Rosenstein, 1941
Encrinurus rumbatensis Rosenstein, 1941
Encrinurus brevispinosus Haas, 1968
Encrinurus schmidti Mannel, 1968
in addition to E. diabolus, E. anticostiensis, E.
indianensis, E. rosensteinae and some others.
The Encrinurus mitchelli plexus most flourished in eastern Australia where occur Encrinurusmitchelli Foerste, 1888.
Encrinurus etheridgei Mitchell in Etheridge
and Mitchell, 1916
Encrinurus rothwellae Etheridge and Mitchell,
1916
Encrinurus silverdalensis Etheridge and
Mitchell, 1916
Encrinurus borenorensis Fletcher, 1950
Encrinurus civica Strusz, 1980
Strusz (1980, p. 53) is of opinion that theexistence of intennediate species precludes therecognition of the three plexi as distinct genera
or even subgenera.
As to the Japanese species of Encrinurus, E.
yokokurensis, E. mamelon, E. tosensis, E. ishii,
E. fimbriatus and Encrinurus stenorhachis, sp.
nov. are comparable with Encrinurus borenorensis, E. mitchelli, E. rothwellae (Le. E. incertus)

or/and E. silverdalensis in one or other characteristic. They are, as a whole, considered by Strusz
to belong probably to the mitchelli plexus. As
pointed out by the authors Encrinurus yokokurensis may be nearest to Encrinurus konghsaensis
Reed, 1906 from Bunna which is in tum referredalso to the mitchelli plexus. Therefore the
Encrinurus mitchelli plexus must be a characteristic trilobite group for the western Pacific faunain the Silurian period.
Encrinurus nodai is probably better placedin the variolaris plexus or Encrinurus (Balisoma)
rather than the punctatus plexus or Encrinurus(Encrinurus). Encrinurus sub trigona lis, sp. nov.
which resembles Encrinuroides uncatus Evittand Tripp, 1977 is quite distinct from most
species of Encrinurus, although it is not an
Encrinuroides.
Among six species of Encrinuroides describedby Chang (1974) from the Silurian of Southwest China E. meitanensis Chang and E. meijiangensis Chang were referred to Encrinurus or theE. variolaris plexus by Strusz (1980). The fonnerhas long genal spines. Both of them have nonmucronate triangular pygidia with mediantubercles on the axes like Encrinurus fimbriatus,
but the median smooth band is apparently absent
or undeveloped in them.
Encrinurus subtrigonalis
Kobayashi and Hamada, sp. nov.

PI. 28, Figs. 4a-e; PI. 29, Figs. 2a-d.
1984. Encrinurus sp., Kobayashi and Hamada,p. 254, pI. 5, figs. 5a-b.

DescflPtion:-Cephalon subtriangular withbroadly rounded genal angles and strongly
inflated, highest in frontal part of glabella anddensely covered by granules of different sizes.
Glabella very large, strongly convex, expanding
forward, shortly projected beyond frontal
border and drooping; granules of various sizes
distributed densely on surface; three pairs oflarge nodose lobes clearly defined by deep
but short lateral furrows in posterior part ofglabella; three granules or nodes of medium

802. Silurian Trilobites from Shikoku

size aligned on antero-Iateral margins and twelve
granules on anterior margin; median interspacea little broader than other intergranular space,but not depressed in form of a furrow; small
and large granules scattered on glabella irregularly besides medium sized ones in smaller
number; most granules pitted at center. Occipital
furrow very deep; a pair of narrow preoccipitallateral ridges present; neck ring a little broader
than glabellar base, but bent up mesially withstraight posterior and gently arcuate anterior
margins; axial furrow as strong as occipital one
continuing to shallow marginal furrow on one
side and deep lateral marginal furrow on theother side at the most expanded point of glabella.
Fixed and free cheeks well united and globular,
but truncated by axial furrow, densely granulated and pitted at each interspace; three large
granules disposed alternately with nodose laterallobes of glabella on two sides of axial furrow;eyes located a little behind cheek center andprominent. Frontal marginal rim indicated bya row of granulation, 12 to 14 in number.
Lateral border embracing cheek, very wide,
ornamented with two rows of granules, coarser
on the inner side than the other and arranged
more or less alternately; these granules pitted
at center; outer margin of lateral border edged
and provided with numerous minute granules.
Posterior cheek border, occipital ring and all
furrows non-granulate.
Pygidium subtrigonal, a little wider than longand strongly convex; anterior margin arcuate,
longer than lateral margin, and distinctly bent
postero-Iaterally from middle part of first pleuralrib. Axial lobe highly elevated above pleurallobes, composed of about 14 tuberculate axial
rings and a terminal piece whose segmentation
is obscure; first axial ring particularly large andprominent, separated from smooth articulatinghalf-ring by profound furrow; anterior two ring
furrows transversal, but succeeding ones areinterrupted by flat median band with whichring furrows are confluent; anterior two axial
rings with five tubercles, median one of which
is somewhat larger than others; large tubercles
present in median band, particularly large at

211

third and sixth rings; succeeding tubercles may
be aggregates of two or three small tubercles.
Pleural lobe rising up gently from axial furrow,then strongly arching down to lateral margin;pleural ribs nine in number, separated by deep
furrows, truncated at their termini and carrying
tubercles, countable five on second rib and three
on seventh rib; such tubercles aligned subparallelto axial furrow or lateral margin, forming fiverows among which third and fourth rows are
persistent through all ribs.
Observation:-The granules on the glabella
vary in size, and their distribution is so disordered to find no definite pattern. The minutepits are seen on many granules. As stated above,the median anterior space is a little broader
than lateral ones along the frontal marginal
furrow, but it is by no means a distinct medianfurrow.
The position of the eye can be ascertainedby its scar or eye-socle which is a little elevatedabove the general cheek surface. It is probablethat the eye in question is shortly stalked. Theintergranular pits are distributed regularly on
the cheek. The facial suture runs from the eyeto the lateral expansion of the marginal border.
Its anterior branch is obscure. The granulesaligned on the outer edge of the lateral border
are numerous, small and close-set. The posterior
cheek border and occipital ring are not granulate,but they are rectangularly cut with some interspaces. This aspect, however, looks secondary
rather than primary. The granulate and pitted
texture of the cheek, the very broad lateralcheek border, its two rows of granules and its
prominent peripheral edge are important characteristics of this species.
The collection contains two pygidia of similar
outline between which the one having tuberculate pleural ribs are provisionally selected forthis species. In the antero-ventral view the twolateral borders of the cephal on form an angleof about 80 degrees in front of the glabella
which fits in the subtrigonal pygidium in rolling.
The long and short rows of the tubercles throughthe ribs are very distinctive of this pygidium.
These characteristics of the cephalon as well

212

Teiichi KOBA YASHI and Takashi HAMADA

as the pygidium easily distinguish this species
from other species of Encrinurus. Like Encrinurus nodai this pygidium is paucisegmented
and its axis is broad and provided with mediantubercles, but it has one more pleural rib thanE. nodai and the median band is well developedin this species.
In the tuberculation and punctuation of thecheek and its very thick lateral border thisspecies closely resembles Encrinuroides uncatus
Evitt and Tripp, 1977 (pI. 6, figs. 7a-b). In thiscephalon, however, the genal angle is wellrounded without spines. Furthermore, theantero-median glabellar furrow is absent andthe preoccipital ridge present. The narrowpreglabellar area as seen in Encrinuroides sexcostatus (Salter) (in Whittington, 1950) andother species is also absent in this cephalon.
The pygidum is subtriangular in this species.
Encrinurus similis Kobayashi and
Hamada, sp. nov.

PI. 29, Figs. 4a-<l.
This pygidium is very similar to the preceding in the outline and convexity of the carapace,
proportional size between the axial and pleurallobes, number of their segmentation and thepossession of the median band and tubercles
on the axial lobe, but the tuberculation is lessdeveloped in this pygidium. The postero-Iateralbent of the anterior margin on its two sides
is more distinct and the arching down of thepleural lobe in its abaxial part is more emphasized in this pygidium. The pleural ribs number
nine or ten in that pygidium, but seven oreight in this pygidium.
In this axial lobe the anterior three axial
rings, instead of two in that pygidium, aredefined by two transverse ring furrows. Accordingly the smooth median band extends backward from the fourth ring. The large tubercles
on the band are at the fifth, eighth (scar), twelfth
and sixteenth rings, while they are at the third,
sixth, eighth, ninth and eleventh rings in thepreceding pygidium, although such a distribution may vary within a species to some extent.
Small tubercles occur on the lateral part near
the median band at a few rings. The most important distinction from the preceding pygidiumlies in the absence of large tubercles on thepleural ribs in this pygidium. In the exfoliate
part it is clearly seen that the post-axial ridge isembraced by the last pair of pleural ribs.
This pygidium is so similar to the precedingthat they may reveal sexual dimorphism.
Among the other species of Encrinurus in
Japan it is very similar to E. tosensis and E.
ishii, but less segmented in this species.
Encrinurus stenorhachis
Kobayashi and Hamada, sp. nov.

PI. 29, Figs. 3a--c.
1974. Encrinurus A-2 type pygidium, Kobayashi and Hamada, p. 98, pI. 10, figs.

Explanation of Plate 28
Pseudocheirurus gomiensis, sp. nov . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 208
Figs.1a--c. Dorsal, left-lateral and frontal views of the holotype cranidium. x2.0
KGS 3625.
Japonoscutellum geniculatum, sp. nov. . . . . . . . . . . . . ' . . . . . . . . . . . . . . . . . . . . Page 208
Figs. 2a--c. Dorsal, right-lateral and posterior views of the holotype pygidium.
x2.2
KGS 3624.
Dindymene (?) megacranidia, sp. nov. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 213
Figs. 3a--c. Dorsal, frontal and left-lateral views of the holotype cranidium. x2.5
KGS 3624.
Encrinurus subtrigonalis, sp. nov. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 210
Figs. 4a--e. Dorsal, frontal, left-lateral, antero-ventral and upper frontal views of
the holotype cephalon. x1.9 except e x1.2
KGS 3627.

KOBA YASHI and HAMADA : Silurian Trilobites from Shikoku

Plate 28

802. Silurian Trilobites from Shikoku
9a-c, text-fig. J.

This is a subtrigonal pygidium having anarrow axial lobe without median tubercles.
It is an internal cast whose outline and convexity are somewhat modified secondarily bylateral compression.
The axial lobe is narrow and tapers backrather abruptly in anterior, but gradually in the
middle and posterior parts and rounding off
at the terminus at a short distance from theposterior margin of the pygidium. It is divided
into about 22 axial rings by ring furrows which
are not exactly countable in the posterior part.
The post-axial area is ill-preserved. The lobe is
one-fifth or less as wide as the pygidium in its
middle part, strongly arching down near theposterior end. It is a little elevated above thepleural lobes and flattopped. The median smoothband is not well developed.
Separated from the axis by strong axial
furrows, the pleural lobes are divided into
about nine ribs by pleural furrows which arebroader than the ribs on the cast. In the lateralhalf the lobe is distinctly sloping down to themargin.
Compared to another pygidium of the A-2
type subgroup the axial lobe looks somewhat
broader in this by deformation. There are also
some differences on the posterior terminal
part which is not well preserved in these pygidia.
Nevertheless, these two pygidia agree with eachother in most other characteristics. Encrinurustosensis is similar to this species in the outlineof the pygidium and its ribbing, but the axial
lobe is broader and penetrated by a mediansmooth band in that species.
Subfamily Dindymeninae Kielan, 1959
Genus Dindymene Hawle and Corda, 1847
Dindymene (?) megacranidia
Kobayashi and Hamada, sp. nov.

PI. 28, Figs. 3a-c.
Description:-Cephalon strongly vaulted toward its center, globular but truncated byposterior margin, widest through mid-length213

of cheeks, and trisected by nearly straightaxial furrows into very large glabella and relatively small cheeks. Glabella with a pair oflinear longitudinal furrows of moderate length
incised into anterior part of glabella near its
lateral ends, but no distinct lateral furrows
are present. Marginal rim narrower than marginal
furrow. Test densely granulate.
Observation:-The occipital ring is unpreserved and the posterior outline of the cephalon
unknown. The glabella exclusive of the ring as
long as 0.7 of the cephalic breadth and as wide
as 0.6 of the breadth in posterior, but expanded
to 0.7 in anterior. The cheek occupies only
0.17 of the cephalic breadth.
One or two rudimentary lateral furrows
may be present on the left side of this glabella,
but they are so obscure that their being furrows
cannot be convinced. On the left cheek an
elliptical more or less smooth area is seen on
its antero-Iateral side, but it is not clearly outlined and a few granules are found also in thisarea. Therefore it is probably not an eye-scarand this is most probably blind.
Comparison:~ompared to Dindymene thecephal on is quite narrow and the cheek verysmall, if compared to the glabella. This cephalon
lacks the distinct preoccipital lobe typical of
Sphaerexochus.
Family Staurocephalidae
Prantl and Pnbyl, 1948
Besides Staurocephalus this family included
Oedicybele Whittington, 1938 in Moore's
Treatise, 1959. Evitt and Tripp (1977) added
Liberella Hu, 1971 to them and suggested
that Rongxiella Chang, 1974 may be still anothergenus of the family.
Genus Staurocephalus Barrande, 1846
Staurocephalus appeared in the Middle
Ordovician age in Norway, spread widely inEurope from Britain to Poland and further to
Kazakhstan and widest in the Silurian period,
particularly in Wenlockian, occurring not onlyin Eurasia but also in Australia and North

Teiichi K OBA YASHI and Takashi HAMADA

214

America (Kielan, 1957).
In describing Staurocephalus susanae, sp.
nov. from the Wenlockian of Dudley, England,Thomas (1981) enumerated nine other speciesof the genus as follows:
Staurocephalus murchisoni Barrande, 1846,
Wenlock, Ludlow; Bohemia
S. obsoletus Weller, 1907, Niagaran; lllinois
S. elegantus Freyburg, 1923, Llandeilian;
Germany
S. struszi Chatterton and Campbell, 1980,
Wenlockian, Canberra
S. mitchelli Chatterton and Campbell, 1980,
Ludlow; New South Wales
S. pilafrons Owen and Bruton, 1980, CaradocAshgill, OsloS. lagena Holloway, 1980, Wenlockian,
Arkansas
S. otarion Holloway, 1980, ditto.
The eleventh species is Staurocephalus trichochin here described.
Staurocephalus sp. and Staurocephalus (?) sp.
were reported from Upper Ordovician andStaurocephalus murchisoni from Silurian all in
Turkestan by Weber (1948, 1951). The second
is represented by a glabella and the two others
by cranidia whose frontal lobes of glabellae
are protruded far from their cheeks which are
relatively large and not so convex as in S. trichochin.

Staurocephalus trichochin

Kobayashi and Hamada, sp. nov.
PI. 30, Figs. 2a"'""1!.
1984. Staurocephalus sp., Kobayashi and Hamada, p. 254, pI. 5, figs. 6a-b.

Description :-Cephalon a little longer thanbroad and strongly inflated. Glabella composedof a very large frontal lobe and a comparatively
small posterior lobe; frontal lobe three-fourths
as long as cephalon, sphaerical, elevated highly
toward its center; posterior lobe exclusive ofneck ring nearly half as long as frontal lobe,
truncato-conical in outline; lateral furrows
indistinct; occipital and axial furrows deep.
Cheek suboval, more or less elongate, highly
swelling up, but its top is slightly lower thanposterior glabellar lobe, much smaller thanfrontal lobe of glabella; eyes small, located at
top near cheek-center. Marginal border notindented, describing semicircle and running
below frontal glabellar lobe behind its midlength; lateral marginal border flat and depressed,lacking furrow on its inner side. Small tubercles
widely distributed on whole surface except for
furrows.
Observation:-Neither distinct furrow nor
pit is seen on the lateral side of the glabella.
The position of the eye is indicated on thespecimen by its scar. The genal angle is obtuse;genal spine apparently absent.

Explanation of Plate 29
Proetus (Gerastos) sugiharensis Kobayashi and Hamada . . . . . . . . . . . . . . . . . . . . . . Page 208
Figs. 1a-c.

Dorsal, posterior and right-lateral views of a pygidium. x7. 7.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 210
Figs. 2a-d. Dorsal, right-lateral, left-lateral and posterior views of the paratypepygidium. x1.9
KGS 3628.
Encrinu.rus stenorhachis, sp. nov. . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . Page 212
Flgs.3a-c. Dorsal, left-lateral and posterior views of the holotype pygidium.
x2.9
KGS 3630.
Encrinurus similis, sp. nov. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 212
Figs. 4a-d. Dorsal, right-lateral, left-lateral and posterior views of the holotype
pygidium. x5.5
KGS 3629.
Illaenoid (?) gen. et sp. indet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 207
Figs. 5a, b. Dorsal and left-lateral views of a cranidium. x2.5.

Encrinurus subtrigonalis, sp. nov.

KOBA YASHI and HAMADA: Silurian Trilobites from Shikoku

Plate 29

802. Silurian Trilobites from Shikoku
Comparison:-The extraordinarily large andstrongly convex frontal lobe of the glabella,
its long forward protrusion far beyond thefrontal border, obsolete lateral furrows on theglabella, the comparatively small cheeks andnon-indented marginal border are very distinctive from other species of this genus. Compared to Staurocephalus murchisoni (Hornyand Bastl, 1970, pI. 15, fig. 7) the frontal lobeof the glabella is larger, but less projected forward and the posterior lobe is very small, if
compared with the cheeks as well as the frontal
lobe.
Among several forms described by Kielan(1957, 1959) this species closely resembles
Staurocephalus sp. b (pI. 3, figs. a-c, 1957)
and also Staurocephalus clavifrons (pI. 26,
fig. 9, 1959) from the Upper Ordovician of
Sweden and Poland respectively. In this species,
however, the frontal lobe of the glabella ismuch larger in comparison with cephalon andcheeks. This species is similar to Staurocephalus
struszi in the glabellar aspect, but it has a very
thick margianl border. In this species the borderis narrow and short margianl spines and long
genal spines are apparently absent.
Staurocephalus (?) sp. indet. described by
the authors (1974) from the Yokokura-yamalimestone at Gomi is quite distinct from thisspecies in the frontal glabellar lobe not so longand provided with a narrow granulate belt
along its posterior margin.

Family Lichidae Hawle and Corda, 1874
Subfamily Homolichinae Phleger, 1936

215

pressed.
This cephalon differs from Apolichas truncatus in the much longer outline and greater
convexity of the cephalon and the shape of themain glabellar lobe limited by straight longitUdinal forrows.
The cheeks are not preserved in the specimen.
Lichid (?) hypostoma, gen. and sp. indet.
PI. 30, Fig. 4.
The main body of this hypostoma is subquadrate, much broader than long, broadly
arcuate anteriorly and narrowing backward;
posterior margin straight; at about one-third
the length of the body; a pair of profoundfurrows cutting into the body from lateral sides
for about a quarter of the breadth and pitted
at the termini. Lateral and posterior furrows
strong; lateral border more or less crescentic
and depressed; a pair of large flat spines extending postero-Iaterally from main body.
This hypostoma is similar to that referred to
Apolichas truncatus in the subquadrate main
body provided with the flat and depressed
lateral and posterior borders. It is, however,quite different from that hypostoma in thepossession of the crescentic lateral border andthe large and flat posterior spines.
The posterior part of the hypostoma iscommonly produced backward from its lateralsides in the Lichinae, Homolichinae and Tetralichinae (Tripp, 1957, text-fig. 4), but theposterior projections are not so far prolonged
into such posterior spines.

Genus Apolichas Kobayashi and Hamada, 1974
Apolichas perconvexus
Kobayashi and Hamada, sp. nov.

PI. 30, Figs. 3a-d.
Cephalon semi-elliptical, as long as strongly
vaulted; its height corresponding to threefourths of its length; median lobe separated
from tricomposite lateral lobes by nearly straightlongitudinal furrows; lateral lobe half as wide as
median lobe; marginal border narrow and de-References
Chang, W. T. (1974): Silurian trilobites. Handbook of stratigraphy and palaeontology ofSouthwest China, 454 pp., 202 pIs. Compiled by Nanjing Institute of Geology andPalaeontology, Academia Sinica.
Evitt, W. and Tripp, R. (1977): Silicified Middle
Ordovician trilobites from the family Encrinuridae and Staurocephalidae. Palaeontogr. Abt. A, Bd. 157, S. 109-174 (24pIs.).

216

Teiichi KOBA YASHI and Takashi HAMADA

Harrington, H. J. et al. (1959): Arthropoda 1.
In Moore's Treatise on Invertebrate Palaeontology, Part 0, 560 pp.
Holloway, D. J. (1980): Middle Silurian trilobites from Arkansas and Oklahoma, U.S.A.
Part 1. Palaeontogr., Bd. 170, S. 1-85 (10pIs.).
Horny, R. J. and Bastl, F. (1970): Type specimens of fossils in the National Museum
Prag. vol. 1, Trilobita, 354 pp., 20 pIs.,
4 tables.
Hu Chung-Hung (1971): Ontogeny and sexual
dimorphism of lower Paleozoic trilobita.
Palaeontogr. Americana, v. 7, no. 44, p.
31-155, pIs. 7-25.
Katto, J. (1984): New observations of Silurian
rocks in Shiroishi-ohsawa, Mt. Yokokura,
Kochi Prefecture, Shikoku. Res. Rep. Kochi
Univ., v. 32, Nat. Sci. p. 235-239, 2 pIs.
Kielan, Z. (1957): On the trilobite Staurocephalidae. Palaeont. Polonica, no. 2, p.
155-180.
--(1959): Upper Ordovician trilobites from
Poland and some related forms from Bohemia and Scandinavia. Ibid., no. 11, 198pp., 36 pIs.
Kobayashi, T. and Hamada, T. (1974): Silurian
trilobites of Japan in comparison with
Asian, Pacific and other faunas. Palaeont.
Soc. Japan, Sp. Pap. no. 18, 155 pp., 12 pIs.
--and - - (1984): Advance report on a new
trilobite collection of the Silurian Yoko-kura-yama fauna, Shikoku Island, Japan.
Res. Rep. Kochi Univ., v. 32, Nat. Sci.
p. 253-258, pI. 5.
Kuo, Hong-tsun (1962): Some Silurian trilobitesfrom the Er-tao-gou group of Jilin. Acta
Pal. Sinica, vol. 10, no. 3, p. 377-381, 2 pIs.
Lamont, A. (1978): Pentlandian miscellany:
Mollusca, Trilobita, etc. Scott. Jour. Sci.
v. 1, pt. 5, p. 245-302.
Lane, P. D. (1971): British Cheiruridae (Trilobita), 95 pp., 16 pIs., Palaeont. Soc.
Nan, Junsan (1976): Trilobites, p. 333-352,
pIs. 190-201. Fossil Atlas of Northeast
China. Inner Mongolia, (1) Palaeozoic
Part 502, 232 pIs.
Reed, F. R. C. (1906): The Lower Palaeozoic
fossils of the Northern Shan States, Burma.
Palaeont. Indica (Mem. Geol. Surv. India),n.s. 2, 154 pp.
Strusz, D. L. (1980): The Encrinuridae andrelated trilobite families, with a descriptionof Silurian species from southeastern Australia. Palaeontogr. Bd. 168, S. 1-68, 6 pIs.
Thomas, A. T. (1981): British Wenlock trilobites,
Part 2, Palaeontogr. Soc. p. 57-99, pIs.
15-25.
Tripp, R. T. (1962): The Silurian trilobite
Encrinurus punctatus (Wahlenberg) andallied species. Palaeontology, v. 5, p. 460477.
- , Temple, T. and Gass, K. C. (1977): The
Silurian trilobite Encrinurus variolaris andExplanation of Plate 30
Bumastus sakoi Kobayashi and Hamada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 207
Figs.1a-e. Dorsal, posterior, frontal, left-lateral and right-lateral views of theholotype cranidium. x3.3 KGS 3529.
Staurocephalus trichochin, sp. nov. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 214
Figs.2a-e. Dorsal, anterior, posterior, right-lateral and left-lateral views of theholotype cephalon. x3.4
KGS 3631.
Apolichas perconvexus, sp. nov. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 215
Figs. 3a-d. Dorsal, frontal, left-lateral and right-lateral views of the holotype
cephalon. x2.1
KGS 3632.
Page 215
Hypostoma of Lichid (?), gen. et sp. indet. . . . . . . . . . . . . . . . . . . .
A ventral view. x3.6.
Fig. 4.
Bumastus kattoi Kobayashi and Hamada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 207
Figs.5a-c. Dorsal, frontal and right-lateral views of the holotype cranidium.
x3.7
KGS 3590.
Bumastus agmakros Kobayashi and Hamada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 207
Fig. 6.
A dorsal view of the holotype pygidium. x2
KGS 3588.

KOBA Y A SHI and HA MA DA: Silurian Trilobites from Shikoku

Plate 30

802. Silurian Trilobites from Shikoku
allied species, with notes on Frammia.
Ibid. v. 20, no. 4, p. 847-867.
Weber, V. N. (1932): Trilobites of Turkestan,Wsejusnoje geol.-vasw. ob., NK'TP, S.SSR:
I-IV. 167 pp., 4 pIs. Moskou and Leningrad.
--(1948): Trilobites of the Silurian rocks No.
1. Lower Silurian trilobites, Monogr. Palaeonto USSR, VSEGEI, V. 69, 113 pp., 11 pIs.

217--(1951): Upper Silurian trilobites, USSR.
72 pp. (6 pIs.) Trud. VSEGEI, Ministry of
Geology.
Whittington, H. B. (1950): Sixteen Ordovician
genotype trilobites. Jour. Palaeont. V. 24,
no. 5, p. 68-75.
Wu, Hong-ji (1979): Silurian Encirnuroids(Trilobita) from Southwestern China. Acta
Pal. Sinica, V. 18, no. 2, p. 125-149, 2 pIs.

f;T!3[!!J 17)~~ili 7 :t -7 :::.)J1ltln-t ~ ·;/J\.-'\.-*C':::::~.9=l. : Ej3~~:a~~I7)Rr~-e·tr:f<iJ:z v? '/ a :/>:r1Vf~ L{tQ~H::.7f--'Ji IJ 17)!ii5Ef.5*I::'~ Lt.:o 1IlH!lfiI7)7H:'11~fiEiJ;~ ').:t17) 3 :m!r1l'il)!i
i?i1.ll*~I7)~C~:::.~tit L t.:o ?l#<17) 8 ~fi.p Pseudocheirurus C Stau1"ocephalus C Itji C

L -r t :: 17) 7 :t -7 !::.~ L ~,{, 17)-C~ ~o Pseudocheirurus gomiensis 11 Ludlow fltrjl)jr::.:: 17)
fr!l/j-cEncrinurus 17)~lfffil'1 ~- ,\.-" :z.jm c. -r7i" -.7, r '7 ~ nlUf!l17) 7 :t -:t" C 17)1llU,f-j;~ ~o'Hlq!t- • ~8J~1:±
7:t -7iJ'~i1Jmf<iJ6\'f:z.~-r:f.""' ~ 717){,l7)c~-?-r~,t.::: C:z.7f--'oTrans. Proc. Palaeont. Soc. Japan, N.S., No. 139, pp. 218-221, September 30, 1985

803. DISCOVERY OF A MIDDLE JURASSIC AMMONITE KEPPLERITESFROM THE MINO BELT, CENTRAL JAPAN*
TADASHI SATO
Institute of Geoscience, University of Tsukuba, Ibaraki 305
YOSHIO KASAHARA
Gifu Prefectural Museum, Seki, Gifu 501-32
and
KOJIWAKITA
Geological Survey of Japan, Yatabe, Ibaraki 305

Abstract. A Middle Jurassic Keppleritis (Seymourites) was discovered fromthe olistostrome bed exposed on the Nagaragawa River bed, NW of Gujo-Hachiman.
Because this genus is known to occur in the boreal realm in Upper Bathonian to
Lower Callovian, the occurrence of this genus from the Mino Belt bears particularly
important meaning in the paleogeographical reconstruction of Jurassic Japan.

A Middle Jurassic ammonite, Kepplerites,
was discovered from fine-grained sandstone
exposed on the river bed of the Nagaragawa
River near Tokunaga in Yamato-mura of Gifu
Prefecture. The location is about 10 km NW
of Gujo-Hachiman, between two junctions of
the Nagaragawa River with its tributaries
Oomamigawa and Kurisugawa Rivers (35 0 48'
15"N and 136°54'10"E) (Text-fig. 1).
Mr. K. Kijima, inhabitant at Tokunaga, whilefishing at the site, noticed the occurrence of thisammonite, and communicated to Mr. H. Tanaka,
member of the Editorial Committee of theVillage History. Mr. Tanaka collected the specimen in collaboration with Kasahara. A resin

mould was taken in situ, and sent to Sato for
identification. Wakita studied the geology ofthe fossil locality.
The ammonite was preserved in sandy siltstone exposed on the river bed of the middle
reaches of the Nagaragawa River. This is a partof the sequence of slump facies A of Wakita
and Okamura (1982), composed mostly of
massive sandstone and alternation of mudstone-sandstone with allochthonous blocks andslabs of chert and greenstone, zonally distributed
in NW-SE direction along the main stream of
the Nagaragawa River. This has been hithertoclassified in Upper Paleozoic, but the Jurassic
age is recently proved by the discoveries ofradiolarians (Wakita and Okamura, op. cit.).

Received November 1, 1984.
218

Discovery of Jurassic Keppleritest::]Andesitic rock
~Siliceous shale_Chert (CH)~ Turbidite facies[;-=1 Slump faciesr:;1 Greenstone (GS)® Fossil locality
Text-fig. 1. Location of the occurrence ofBase map adopted from Wakita
and Okamura, 1982.

Kepplerites.

Description of species
Kepplerites (Seymourites) sp.

Text-fig. 2.
cf.

Kepplerites(Seymourites)

acuticostum

Kobayashi,1947, p. 28, pI. 7, fig. 2.
Material:-An outer cast impressed on the
sandy siltstone. Very fragmentary, only a part219

around the umbilicus is preserved. Observablemaximum size is 7 cm.
Description:-The whorl in the inner stage
is very involute but later suddenly becoming
evolute, giving rise to an eccentric volution.
The section of the whorl is unknown but in thepreserved part, the umbilical wall is rounded
and the flank is slightly convex. The ventral
region is not observed.
The ribs are sharp and closely spaced. Strong
and clearly concave primary ribs, numbering
about 34 per one volution, are bi- or tri-furcatedat the inner 1/3 height of the flank. Secondary
ribs are distinctly finer, and somewhat sinuous
in general. Free intercalatory ribs are frequent
beside the bi- or tri-furcated secondary ribs.
A small but well definable tubercles are superimposed on the points of bifurcation.
No suture line is visible.
Remarks:-The specific determination IS Impossible because the specimen is very fragmentary. However, the strongly eccentric coilingwith sudden widenning of the umbilicus andthe sharp, closely spaced and bi- or tri-furcatedribbing are all indicative of Kepplerites (Seymourites).
Among already known species of this genus,
the Japanese specimen of K. (S.) acuticostum
described from the Kuzuryu area resembles
considerably the pres~nt specimen, in view of
its closely spaced, and sharp ribbing. Unfortunately, lack of other characteristics in the present
specimen does not allow the identification withthat species.
Age:-Even if the species is undeterminable,
the present ammonite shows undoubtedly late
Middle Jurassic age.
The genus Kepplerites has been generally
thought to be a Lower Callovian indicator, andis chosen as a representative of the Kepplerites
zone in NE Pacific. This was also adopted in theJurassic biochronology proposed in the Kuzuryu
area. However, its time range is now considered
to extend into Upper Bathonian, as indicatedin British Columbia by the coexistence with
Iniskinites where an independent zone wasestablished in Upper Bathonian (Frebold, 1978).

Tadashi SA TO et al.

220

Text-fig. 2. Side view of Kepplerites (Seymourites) sp . Natural size.
Photograph was taken from the resine mould. Original is an impression .

This is also true in the Western Interior of theUnited States, where this genus occurs with
Cobbanites, Parareineckeia or Cadoceras (Imlay,
1981).
In .lapan, in particular in the Kuzuryu area,
Kepplerites (S eymourites) forms an assemblage
zone in association with Grossouvreia and
Lilloettia which were assigned to Lower Callovian (Sato, 1962). There are coexisting genera
known from the Bathonian, such as Lilloettia,
but their identifications are not very reliable ,because the specimens are all fragmentary .
It is therefore concluded that the present specimen of Kepplerites (Seymourites) indicates arange from Upper Bathonian to Lower Callovian,but most probably Lowest Callovian.
Discussion
The occurrence of Kepplerites (Seymourites)in the Mino Belt bears an important meaning.
Firstly, it gives the firm basis for the correlation

with the Middle Jurassic, besides the radiolarians. Secondly , this is an ammonite indicativeof the "boreal" faunal province in Middle Jurassic(e.g. Enay, 1980) and the southern limit of the
distribution of this genus in the Circum-Pacificregion lies as south as Western Interior U.S .A.
and central Japan (e.g. Westermann , 1980).
It was further discussed that Japan was situatedat the locus of encounter of cold and warm
oceanic currents in Jurassic (Sato, 1960). In
fact, Kepplerites (Seymourites) is . known fromKuzuryu and southern Kitakami (Kobayashi,1947) in addition to the occurrences of Kepplerites (Gowericeras), though different subgenerically, from southern Kitakami (Takahashi , 1969).
The discovery of the "boreal" ammonite
genus from the Mino Belt tells as a matter ofconsequence that the belt was in the realm of
the "boreal" biogeographic province. Whether
the climate Of this province was actually cold
or not is of little importance, but it should

Discovery of Jurassic Kepplerites

be emphasized that the province encompassed
the northern part of the present Northern
Hemisphere. The restoration of the paleocontinent does not alter much the situation (Owen,
1983). The claim that the Mino Belt was locateddown south from the paleomagnetic requirement(e.g. Hattori, 1982) cannot be easily admitted,
from the paleobiogeographic point of view.
References
Enay, R. (1980): Paleobiogeographie et Ammonites jurassiques (Rhythmes fauniques)et variations du niveau marin; voies
d 'echanges, migrations et domaines biogeographiques. Liv. Jub. Soc. geol. France,
Mem. h.-s., no. 10, p. 261-281.
Frebold, H. (1978): Ammonites from the Late
Bathonian "Iniskinites Fauna" of central
British Columbia. Geol. Surv. Canada,
Bull., 307, p. 1-8, pIs. 1-9.
Hattori,1. (1982): The Mesozoic evolution of the
Mino terrane, central Japan: a geologic andpaleomagnetic synthesis. Tectonophysics,
85, p. 313-340.
Imlay, R. W. (1981): Jurassic (Bathonian andCallovian) ammonites in eastern Oregon
and western Idaho. U.S.G.S. Prof. Pap.,
1142, p. 1-24, pIs. 1-5.
Kobayashi, T. (1947): On the occurrence of

221

Seymourites in Nippon and its bearing on
the Jurassic paleogeography. Japan. Jour.
Geol. Geogr., vol. 20, p. 19-31, pIs. 7-8.
Owen, H. G. (1983): Atlas of continental displacement, 200 million years to the present.
p. 1-159. Cambridge Univ. Press.
Sato, T. (1960): A propos des courants oceaniques froids prouves par l'existence desAmmonites d'origine arctique dans Ie
Jurassique japonais. Rept. I.G.C., XXI
Session Norden, Pt XII, p. 165-169.
- - (1962): Etudes biostratigraphiques des Ammonites du Jurassique du Japon. Mem.
Soc. geol. France, N.S., Vol. 41, Mem. no.
94, p. 1-122, pIs. 1-10.
Takahashi, H. (1969): Stratigraphy and ammonite fauna of the Jurassic System of thesouthern Kitakami Massif, Northeast Honshu, Japan. Sci. Rept., Tohoku Univ., 2ndSer., vol. 41, p. 1-93, pIs. 1-19.
Wakita, K. and Okamura, Y. (1982): Mesozoic
sedimentary rocks containing allochthonous
blocks, Gujo-hachiman, Gifu Prefecture,
central Japan. Bull. Geol. Surv. Japan,
vol. 33, p. 161-185.
Westermann, G. E. G. (1980): Ammonite biochronology and biogeography of the CircumPacific Middle Jurassic. in House, M. R. and
Senior, J. R. eds., The Ammonoidea. Systematic Association Spec. Vol., no. 18,
p.459-498.

Gujo-Hachiman mU:i\~Kanji f!!t~Kanjigawa River fijli~J11
Komami 'N~'Ji!.
Kurisugawa River !¥!~JII
Nagaragawa River ~!i!:)11
Oomami *r~'Ji!.
Oomamigawa River::kllnJVII
Shima If/;
Tokunaga ~Ei7k
Yamato-mura ::k;fllH<prmEl*~ll*n'I?<pW]'; "" '7*c7 :/.:£:-7"1 r Kepplerites O)itl±lo mJ::i\~~tl1§:n¥-J
10 k~ O)~~JIIfnJ*O)II]iJ{n'I?, <pW]'; "" '7~.c0)7 :/.:£:-7"1 r Kepplerites (Seymourites)
sp. n'~Ji!.c';.ht.:o .:.h11, Bathonian ~W]n'l? Callovian fJJW]l.::.n'Irt"Z:1:.:ff:L-, .: O)IlijW]f'::'W1ll$;t.::.~ZIJ c'; .ho~t~lKt.::.~1it,l:7 :/.:£:-7"1 r -c-1> 00 n]iJ{~ - ~tJ::n"? ~ Iff] t:~O)ittHn';:ilI?.h "Z:\" 0 n', .: .h11~1lij0) EI *O)J!l:l1!!l!Ila-~.:t oJ::-c-J!~tJ:~*:f C tJ:0 ?
{t;:~ JE - ~Jll{m.ffi -l]&hlIlfn:::.
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222

PROCEEDINGS OF THE PALAEONTOLOGICALSOCIETY OF J AP AN...................... 'ia'!!lUJI:::: (:kIllR:~W:k)~-€tiit~iftr-4't~O)IDI!m

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Paleogene radiolarian biostratigraphy ....... .

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1iJ(ft$O)MJt.O)r~9J1liI::""?\"-C ............... .

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· ....... Goto, H., Ishii, K. and Ichikawa, K.
Coccolith us pelagicus (Wallich) Schiller O)i;~~~()9t.l: I? tJ.t::..Jlf:ii.~B9M.~t::.. "?\, '-C ... " .

· ................................... i!§EB5eR~
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Kitakami Massif, Northeast japan ....... .
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Some inoceramids (Bivalvia) from the Cenomanian (Cretaceous) of japan-I ........... .
· . . . . . . . . . . . .. Matsumoto, T. and Noda, M.
Dinosaur footprints and other indentation in
the Cretaceous Sebayashi Formation, Sebayashi, japan .... Matsukawa, M. and Obata, I.
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Palaeovegetation and palaeoclimate of the
Nyuzen Submerged Forest on the continental

223
shelf of Toyama Bay, Central Japan ..... .
............................ Fuji, N. (f(;mt)
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core 'samples from Lake Biwa, Central Japan............................ Fuji, N. (f(;mt)*E~.7X~*W~~.K~~~&~ • • ~R
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M. posthernsteini (Upper Triassic conodonts)................................ Nagano, N.
Pseudodoliolina pseudotepida
Pseudodotio-ctina ozawai ~/flilf*J1l(;~c1t~ ............. .

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Transactions and Proceedings of the PalaeontologicalSociety of Japan
New Series No. 139

September 30,1985

CONTENTS
TRANSACTIONS
799. MATSUI, Seiichiro: Recurrent molluscan associations of the Omma-Manganji faunain the Gojome-Oga area, Northeast Honshu, Part 1. General discussion of faunaand systematic notes on gastropod and scaphopod species . . . . . . . . . . . . . . 149
800. MATSUOKA, Keiji:

Pliocene freshwater gastropods from the Iga Formation of theKobiwako Group, Mie Prefecture, Central Japan . . . . . . . . . . . . . . . . . . . . . 180
801. OMURA, Akio, TSUJI, Yoshihiro, OHMURA, Kazuo and SAKURAMOTO, Yuji: Newdata on hermatypic corals from the Pleistocene limestone on Kikai, Ryukyu
Islands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
802. KOBAYASHI, Teiichi and HAMADA, Takashi: Additional Silurian trilobites to the
Yokokura-Yama fauna from Shikoku, Japan . . . . . . . . . . . . . . . . . . . . . . . 206
803. SATO, Tadashi, KASAHARA, Yoshio and WAKITA, Koji: Discovery of a Middle
Jurassic ammonite Kepplerites from the Mino Belt, Central Japan . . . . . . . . . 218
PROCEEDINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222