豊橋市自然史博物館研報 Sci. Rep . Toyohashi Mus. Na t. Hist. , No. 16，ト14， 2006

Miocene Mollusks from the N agashino Formation of the Shitara Group in Shinshiro City, Aichi Prefecture, central J apan

Hiroshi Shibata * and Takashi Ichihara **

愛知県新城市の設楽層群長篠層産中新世貝類化石

柴田博*市原俊**

(Abstract)

The present pap巴r d巴scribes and illustrat巴s a molluscan fauna coll巴ct巴d from the N aga shino Fo rmation of th e Shita ra Group at Arumi,

Shinshiro City, Aichi Prefecture. The collect ion loc ality of mollu sks is identical with or very clos巴 to th e localit y from which Haya shi

and Koshimizu (1992) reported mollusks ide ntifi ed by them w ith middle Eoce ne speci巴s. The molluscan faun a cons ists 01' nine spec ie s;

Modiolus sp. , Crassostrea gravit esta (Yokoyama), Laeνicardium sp. , Phaco soma kωνagensis (Araki), M ere tr ix aru gai Otuka, H iat ula

minoensis (Yokoyama), Solen sp. , Na ticidae ge n. et sp. inde t. and C hicoreus sp. The Nagashino Forrnation is referr巴d to ea rl y Mioc巴n巴 age

on th巴 basis of their geo lo gic ranges

for the Nagas hin o Format ion of the Hok usetsu Subgroup

Introduction from associated mollusks. After the publi shm ent of

Hayashi and Koshimizu (1992) , Ma tsuoka (1996) report ed

Miura (1890) was the first to mak e r巴ferenc巴 to the ag巴 Miocene mollu sks from th巴 Hokusetsu Subgroup, and

of the Shitara Group in th巴 Shitara ar巴a， Aichi Pr巴fecture， Aoyama (1996) assigned th e Shitara Group to Miocene

ass igning it to Miocene ag巴 on the basis of th巴 molluscan age on the stratigraphica l basis. More recently Hoshi and

fauna . Ther eafter many workers referred it to early or others (2000) suggested the 巴arly Miocene as the age for

ear ly to middle Mioc巴ne age on th巴 paleontological or the Hokus巴tsu Subgroup from correlatio n of radiolarians

stratigra phic basis for abou t a hundred yea rs. Th巴y includ巴 from its middle to upper par t. Thus it is h巴lpful to 巴xamme

Is hikawa (1900; 1901), Notomi (1 929), Tsuboya (1 936), the molluscan fauna from th e Naga shin o Formation for

Hayashi (1973) , Yoshida (1953) , K ato (1 962) , Shibata carrying forward th巴 age assignment of this formation

and oth巴rs (1977), Shibata (1 978), Collaborative Resear ch and the Shit ara Group . Conc巴rning th巴 molluscan fauna

Group for th巴 Shidara Basin (1979) and Shib ata and Ina from th e Na gashino Formation seve ral works hav巳 been

(1983). pl巴viously pub lis hed besides Ha yashi and Koshimizu

Hayashi and Koshimizu (1 992), how巴ver， gave fission (1992) . They are occurre nc e records of Miocen巴 species by

track dates of Paleogen巴 ag巴 for the Hokus巴tsu Subgroup Hayash i (1973) , Shibata and others (1977) and Yokoyama

of the Shitara Group , and suggested middle Eocene ag巴(1987) ， description of M iocene sp巴cies by Shibata and In a

*豊橋市自然史博物館. Toyoha shi Mus eum of Natura l History ， ト238 Oana, Oiwa-cho, To yohashi 441-3147, Japa n.

**名古屋大学大学院環境学研究科. Gr adu ate School of Environm ent al Studies, Nago ya University, Furo-cho, Chikusa-ku, Nago ya 464-8601 , Jap an

Manuscript rec eived Dec. 13, 2005 原稿受付 2005年 12 月 13 日.

Manuscript ac cepted Jan. 18, 2006 原稿受理 2006年 l 月 1 8 日

Key words : Mol lusks，巴arly Miocene, N aga shino Formation, Shi tar a Group, Shin shiro City, Aichi Prefectur巴キーワード:貝類, 前期中新世, 長篠層, 設楽層郡.新城市, 愛知県.

Hiroshi Shibata and Takashi Ichihara 2

(1983) and a taxonomic revision of th巴 previously r巴ported

mollusks (Hayashi , 1973) by Hayashi (1988) .

W巴巴xamm巴d a larg巴 molluscan collection by Y oshiaki

Y okoyama and an additional on巴 by K巴iji Matsuoka both

1'rom the Nagashino Formation at Arumi , Shinshiro City

for this study . Collecting of them was mad巴 separately

at the same n巴w exposure mad巴 by roadworks in 1987

Their collections consist 01' nine species including thre巴

sp巴cies previously not reported from th巴 Nagashino

Formation. The purpos巴 of this paper is to describ巴 and

illustrate them and to discuss th巳 age 01' that 1'ormation . We

1'ollow Hayashi and Koshimizu (1992) 1'or the stratigraphic

classi 1'ication of the Shitara Group .

All specim巴ns d巴 scribed her 巴 in are deposited in

Toyohashi Mus巴um 01' Natural History.

Fig. 1. Map showing th巴 collection locality in Shinshiro City, Aichi Pr巴fecture.

We are ind巴bted to M r. Yoshiaki Yokoyama of (Yokoyama) , Phacosoma kawagensis (Araki) , Meretrix

Horaijisan Natural History Museum and Dr. Keiji Matsuoka arugai Otuka, Solen sp . and Hiatula minoensis (Yokoyama)

of Toyohashi Museum 01' Natural History 1'or allowing us to have b巳en known to occur outside the Shitara ar巴a .

examm巴 th巴ir molluscan collections from Arumi . Phacosoma kawagensis (Araki) and Solen sp. hav巴 been

known from the 巴arly Mioc巴n巴， and Meretrix αrugai Otuka

Locality and Hiatula minoensis (Yokoyama) have been r巴corded

from the early to middle Mioc巴ne . Crassostrea gravitesta

The two molluscan collections 巴xamined were obtain巴d (Yokoyama) has a g巴ologic range 01' the early Miocene to

S巴parately by Yoshiaki Yokoyama and by Keiji Matsuoka th巴 Pliocen巴 The geologic ranges of thes巴 species indicat巴

1'rom the same exposure of the Nagashino Formation the 巴arly Mioc巴ne is most probable as the age for the

at Arumi (Fig. 1) in 1987. Enclosing sedim巴nts 01' Nagashino Formation.

mollusks consist of coarse-grained sandstone and granule Shibata and others (1977) r巳port巴d a total 01' nin巴 species

conglomerate. That exposure was made by roadworks in of mollusks from the Nagashino Formation at their localiti巴8

1987 , and is now los t. A detail巴d description 01' its location 1 and 2, which are n巴ar to the present coll巴cting locality.

and the stratigraphy at it can b巴 found in Yokoyama Among them are Trapezium modiolaeforme Oyama and

(1987) . Hayashi and Koshimizu (1992) gav巴 no detailed Saka and Cyclina japonica Kamada. These species hav巴

description 1'or the 10cality at which they collected mollusks a geologic range 01' the early Miocen巴 and that of the 巴arly

regarded by th巴m as middl巴 Eoc巴ne ones , only showing it to middle Mioc巳n巴， resp巴ctively. There is , how巴ver， no

on th巴ir geologic map. The present collection locality is speci巴 s of which geologic range 巴xtends to th巴 Paleog巴ne

considered to b巴 id巴ntical with or very close to that locality in th巴 nm巴 species . These facts support the ag巴 asslgnment

by referenc巳 to its location on their geologic map . mentioned abov巴. All thos巴 S巴ven species are found in th巴

molluscan 1'auna (Itoigawa and others, 1974, Itoigawa and

Age oth巴rs ， 1981) 1'rom the Mizunami Group in Gifu Pre1'，巴cture ，

and their occurrence in the group is r巴strict巳d to th巴 lower

Th巴 molluscan collections 1'rom Arumi consist 01' nin巴 part 01' th巳巴arly Mioc巴ne Akeyo Formation. Thus the

sp巴cies ， which ar巴 Modiolus sp., Crassostrea gravitesta Nagashino Formation is correlated with it.

(Yokoyama) , Laevicardium sp. , Phαcosoma kawagensis

(Araki) , Meretrix arugai Otuka , Hiatula minoensis

(Yokoyama) , Solen sp. , Naticidae g巳n. et sp. inde t. and

Chicoreus sp . Fiv 巳 of them , Crassostreα grα v z testα

Descriptions

Phylum Mollusca

Miocene Mollusks from the Nagashino Formation

Class Bivalvia

Subclass Pteriomorphia

Order Mytiloida

Superfamily Mytilacea

Family Mytilidae

Subfamily Modiolinae

Genus Modiolus Lamarck, J 799

Modiolus sp.

(Fig. 2-1)

Modiolus sp. Hayashi , 1973, pl. 2, fig. 3

Mytilus sp. Hayashi, 1988, pl. 2, fig. 3

Material -. One specimen.

Crassostrea gravitesta (Y okoyama, J 926)

(Fig. 2-4 )

3

1926 Ostrea gravitesta Yokoyama, Jour. Fac. Sci. , Imp. Uni v

Tokyo, Sec . 2, vo l. 1, pt. 9, p. 388, pl. 45, figs. 1, 2

Ostrea gravite sta Yokoyama. Nomura, 1938, p. 248, pl. 33, fig

15 ; Makiyama, 1958, pl. 57, figs . la-c, 2a-c ; Ogasawara,

1973, pl. 13, fig. 28 ; Hayashi, 1973, pl. 2, fig. 5.

Ostrea (Crassostreα) gravitesta Yokoyama. Kaseno, 1956, p. 7, pl

1, figs. 5a-c

Crassostrea gra vitest a (Yokoyama). Itoi gaw a and oth巴rs ， 1974,

p. 72, pl. 17, fig. 1; Yoon, 1976, p. 9, pl. 1, figs. 24, 25 , pl.

3, fig s. 17, 18; ltoi gawa and Nishikawa, 1976 , pl. 33, fig

11 ; Ogasawara and Noda, 1978 , p. 32, pl. 3, fig. 23 ; Taguchi

and others, 1979, pl. 1, fig. 15 ; Yoon, 1979 , p. 10, pl. 3,

fig. 1; Amano, 1980, p. 106, pl. 13, figs. 29a, b; Takayasu,

Description -. Shell small , ovate , expanded posteriorly, 1981 , p. 99, pl. 2, fig. 15; Itoiga wa and others, 1981 , 1982,

bulged along an oblique medial line running from beak p. 53, pl. 10, fig. 3; Shibata and lna, 1983 , p. 43 , pl. 4, fig. 9;

to postenor 巴nd. Beak low, situated close to anterior end. Naka ga wa and Takeyama, 1985, pl. 2 1 ，行gs. la, b; Okumu ra

Anterior and post巴rior ends rounded. Post巴ro-dorsal margin and others , 1985 , pl. 49, fig s. 2a, b; Itoigawa and Shibata,

slightly arched, passing into posterior margin with a blunt 1986, pl. 16, fig . 11; Hayashi, 1988, pl. 2, fig. 5; Kanno and

angle . Postero-ventral corn巴r produced post巴ro-ventrally. others, 1988 , pl. 2, fig . 12; Okamoto and others, 1989, pl. 5,

Surface smooth. Dimensions; length 19.5 mm , height 17 .0 fig s. 14a, b; Muramatsu, 1992, pl. 49, fig . 14

mm. Crassost rea gravitesta eoli ensis Kim, Noda and Yoon , 1974, p.

274, pl. 38, fig . 15, pl. 39, fig s. la -c; Lee, 1992, p. 79, fig s.

Discussion - The sp巴clm巴n at hand is a d巴form巴d 28-10a, b.

inner cas t. It bears a similarity in shape and siz巴 to

Modiolus nakamurai Itoigawa an d Shibata from the ear ly Material -. Two right vaJves .

Miocen巴 Akeyo Formation of the Mizunami Group in

Gifu Prefecture, but it is impossibl巴 to mak巴 a detailed 0巴scription - Right valve large , v巴ry thick , ovate,

comparison of the specim巴n with that speci巴s owing to flatt巴n巴d. 8eak pointed , with a triangular ligamenta l

the ill stat巴 of its preservation . The specimen res巴mbles groove b巴low it. Surface with rudel y co rrugated growth

Modiolus yasuhiroi Kamada describ ed from the middle lin巴s

Mioc ene Taga Group in the Joban Coal-Fi巴ld and Modiolus

arakaw ensis (Kanno) from the middle Miocen e Nagura

Formation of th巴 Chichibu-machi Group in Saitama

Pre1'ecture, but the shell is smaller

Ord er Pt巴rioida

Subord er Ostr巴ma

Sup巴rfamily Ostl巴acea

Family Ostreidae

Subfamily Ostr巴mae

G巴nus Crassostrea Sacco, 1897

Dim ensions (in mm) 一

Length

82.3

Height

188. 7

88.5 125 .3

Discus sion -. The lar ge and thick shell is a di ag nos tic

charact巴r 0 1' C ra ssostrea graν ites ta (Yokoyama).

Crassostrea graνltestα(Yokoyama) clos巴ly resemble s

Crassostr ea gigas (Thunberg), a li ving species of Japan, but

th巴 shell is thi cker.

4 Hiroshi Shibata and Takashi Ichihara

G巴ologic rang巴ー. Early Miocene to Pliocene

Subclass Heterodonta

Order Veneroida

Superfamily Cardiacea

Family Cardiidae

Subfamily Laevicardiina巴

Genus Laevicardium Swainson, 1840

Laevicardium sp.

(Figs. 2-2, 3a, b)

Phacosoma kawagensis (Araki, 1960)

(Figs. 2-5a-c, 6; Fig . 3-1)

1960 Dosinia japonica kωνagensis Araki , Bul l. Lib. Arts Dept.,

Mie Univ. , Spec. Vo l., (1), p. 95 , pl. 7, fig. 3

Dosinia (Phacosoma) kawagensis Araki. Masuda, 1963, p. 22 ,

pl. 4, figs. 1-8; Yoon , 1979 , p. 15 , pl. 2, figs. 7, 9, 10;

Matsubara , 1995 , p. 330, figs. 4-9-11 ; Honda and others ,

1998, p. 20, fig. 5-16

Dosinia anguloides Nomura (non Nomura). Hata, 1967, pl. 4, figs.

2, 3

Dosinia kawagensis Araki. Hayashi and Miura, 1973 , pl. 2, fig. 12;

Glycymeris cisshuensis Makiyama (non Makiyama). Hayashi , Hayashi , 1973, pl. 1, figs. 2, 3; Ishida and others , 1980, pl. 3,

1973 , pl. 1, fig. 6. fig.12

Glycymeris cf. altoumbonata Nagao. Hayashi , 1988, pl. 1, fig. 6. Dosinia nomurai Otuka (non Otuka). Hayashi , 1973 , pl. 1, fig. 1

Dosinorbis kawagensis (Araki). Itoigawa and others , 1974, p. 87 ,

Mat巴rial -. Two specimens. pl. 23 , fig s. 1-6.

Phacosoma kawagensis (Araki). Itoigawa and others , 1981 ,

Description -. Shell small , thin , ovate in outlin巴， slightly 1982, p. 80, pl. 14, figs. 6a, b; Shibata and Ina, 1983 , p. 48 ,

longer than high , moderately intlated . Beaks small , situated pl. 5, fig. 12; ltoigawa and Shibata, 1986, pl. 16 , fig. 13;

at a little ant巴rior of the middle of th巴 shelll巴ngth. Ant巴rior Muramatsu, 1992, pl. 49 , fig. 10

end rounded , v巴ntral margin arched , postero-ventral corn巴r Dosinia (Phacosoma) chikuzenensis nomurai Otuka (non Otuka)

roundlyangulate . Surface with many radiating rib s. Hayashi , 1988 , p. 5, pl. 1, fig s. 2, 3

Dimensions (in mm)

Length H巴ight Thickn巴ss

32.6

26.1

30.0

2l.8

13.0

Dosinia (Phacosoma) chikuzenens is Nagao (non Nagao)ー Hayashi ，

1988 , pl. 1, fig. 1

Material -. More than 160 specimens in th巴 Yokoyama's

collection and 22 sp巴cimens in the Matsuoka's collection .

About 2/5 of them are with their both valves conjoined,

Discussion -. Laevicardium sp. r巴sembles Laevicardium and the others are with their both valves disarticulated. All

undatopictum (Pilsbry) living in the West Pacific in shap巴 specimens are more or less lat巴rally compressed.

but the sh巴11 is larg巴r ， and radial ribs in the posterior part

of th巴 shell are less prominen t. Laevicardium sp. is also 0巴scription -. Shell of medium size, suborbicular, longer

analogous to Laevicardium yoshidense Kanno from the than high , slightly intlated. Beaks pointed , turned forward ,

early Miocene Nenokami Sandstone of the Ogano-machi a little ant巴riorly situated. Ant巴ro-dorsal margin short,

Group in Saitama Pr巴fecture ， but it has a larger number n巴arly straigh t. Post巴ro-dorsal margin gently arcuate ,

of radial ribs. It somewhat res巴mbles Nemocardium sp. pa ssing into anterior margin with an obtuse angle . Ventral

reported by Shibata (1970) from th巴巴arly Miocen巴Ichishi margin round巴d. Pallial sin us deep , angulat巴 Surface

Group in Mie Prefecture , but the shell is mor巴巴longate. with regular concentric lines. Lunul巴 W巴11 mark巴d ， small ,

cordate, depressed. Escutcheon long, naηow.

Superfamily Veneracea

Family Veneridae

Subfamily Dosiniinae

Genus Phacosoma Jukes-Brown , 1912

Dim巴nsions (in mm) ー.

Length

47.2

42.6

Height Thickness

4l.4 18.5

39.2 12.5

Miocene Mollusks from the Nagashino Formation

41.8

40.5

46.2

36 .2

36.7

43 .1

16.1

11.7

5

Mactra squalida (Yokoyama) (non Yokoyama). Hayashi, 1988, pl.

2, fig. 2

Eomeretrix sp. Hayashi and Koshimizu, 1992, figs. 3-4, 5

Discussion -. Phacosoma kawagensis (Araki) res巴mbles Mat巴rial -. Twenty-s巴ven specimens in the collection by

Phacosoma japonicum (Reeve) living in th巴 adjacent Yokoyama and 2 specim巴ns in the co Jlection by Matsuoka .

seas of Japan , but th巴 shell is smaller, and the proportion Most of th巴m are well preserved , and 7 sp巴cimens in th巴

of th巴 shell I巴ngth to the sh巴llh巴ight is small巴r. 1t also former are with their both valv巴s articulated.

r巴sembles Phacosoma nomurai (Otuka) described from

the early Mioc巴ne Lower Kadonosawa Formation in Iwate

Pref，巴cture ， but the shell is slight ly depr巴ssed in th巴 antenor

and posterior parts , and the post巴ro-dorsal margin less

slopes ventrally .

This species is the most ab undant speci 巴 s at the

collection locality . Specimens occur in a clust巴r ， mostly

with the convex sides of their valves parallel to the bedding

planes of th巴Ir 巴nclosing sedimen t.

Geologic range -. Early Mioc巴n巴.

Subfamily Meretricinae

G巴nus Meretrix Lamarck, 1799

Meretrix arugai Otuka, 1938

(Figs. 3-2-5a, b)

1938 Meretrix arugai Otuka, Jour. Fac . Sci. , Imp. Univ. Tokyo ,

Description -. Shell medium in size , thick , subtrigonal ,

longer than high , inflated. Beaks swollen , high , turned

inward , locat巴d at a little front of the cent巴r of the sh巴 11

Antero-dorsal margin straight , post巴ro-dorsal margin

sligh tly arcuate , ventral margin broadly rounded. Anterior

end round巴d ， post巴rior end more narrowly rounded. Lunule

and escutcheon absen t. Three cardinal t巴eth on cardinal

plate . Pallial sinus moderat巴Iy deep , angulat巴. Surfac巴

smooth with fine growth lines .

Dimensions (in mm) ー.

Length Height Thickness

71.0 59.0 30.2

59.4 51.2 34 .4

79 .5 65.2

79 .3 65.1

79.1 61.8

S巴c . 2, p. 30, pl. 2, figs. 11 , 12. Discussion -. Meretrix arugai Otuka is charact巴rized by

Meretrix arugai Otuka. Hatai , 1940, p. 129; Araki , 1960, p. 93 , pl. the well swollen beak. It resembles Meretrix lusoria

7, fig. 5; Itoigawa and others , 1974, p. 86 , pl. 22 , figs. 5-8; (Rりding) and Meretrix lamarcki (Deshayes) , both living

Itoigawa and Nishikawa, 1976, pl. 34, fig. 8; Taguchi and species of Japan , but the beak is more swollen

others , 1979, pl. 3, fig. 8; Ishida and others , 1980, pl. 3, fig.

5; Itoigawa and others , 198 1, 1982, p. 89 , pl. 17, figs. 4a, b,

5a, b; Takahashi , 1984, pl. 1, fig. 2; Itoigawa and Shibata,

1986, pl. 17 , fig. 5; Sasaki and Ogasawara, 1986, pl. 5, figs.

7a, b; Nakagawa, 1989, pl. 1, fig . 8; Noda and oth巴rs ， 1989,

pl. 25 , figs. 5a, b; Okamoto and others , 1989 , pl. 6, fig. 12;

Okamoto and others , 1990, pl. 9, fig. 6; Noda and others ,

1994, figs . 6-10 , 14a, b, 18; Matsubara, 1995 , p. 333 , figs.

5-8.9. 11

Meretrix cf. arugai Otuka. Hayashi , 1973 , pl. 2, figs. 1, 2

?Meretrix arugai Otuka. Oga sawara and Noda, 1978, p. 35 , pl. 3,

figs. 17, 20, 22a, b

Pitar? sp. Shibata and Ina, 1983 , p. 48 , pl. 5, fig . 15.

Callista cf. han zawa i (Nagao) . Hayashi , 1988, pl. 2, fig . 1

Geologic range -. Early to middle Miocene .

Superfamily Tellinac巴a

Family Psammobiidae

Subfamily Sanguinolariinae

Genus Hiatula Modeer, 1793

Hiatula minoensis (Yokoyama, 1926)

(Figs. 4-1 a , b, 2a, b)

1926 Soletellina minoensis Yokoyama, Jour. Fac. Sci. , Imp. Univ

Tokyo, Sec . 2, vo l. 1, pt. 7, p. 221 , pl. 28 , figs. 13 -16

Soletellina minoensis Yokoyama. Masuda , 1955 , pl. 19, fig. 9;

Hiroshi Shibata and Takashi lchihara 6

Fig. 2. Mollusks from th e Na gashino Formation at Arumi , Shinshiro City (1). 1. Modiolus sp. ( X 2). 2, 3a, b. Laevicardium sp. 3b, apical vi巴w. ( X 1.5). 4. Crassostrea gravite sta (Yokoyama ). ( X

0.8 ). 5a-c, 6. Pha cosoma kawagensis (Araki) . 5c, ap ica l view . ( X 1.5) .

.. ・・・

Miocen巴 Mollusks from the Nagashino Formation

Fig. 3. Mollusk s from th e N ag ashino Fo rm ation at Arumi , Shin shiro City (2).

6

7

1. Ph acos oma kawagensis (Ar aki ). (X 1.5 ). 2-5a, b. M eret rix ar uga i O tuk a. 5b, sho w in g th巴 cardinal te eth. ( X 1). 6, 7

Solen sp. ( X 1).

7

Hiroshi Shibata and Takashi Ichihara 8

Fig. 4. Mollusks from the Nagash ino Formation at Arumi , Shinsh iro City (3) .

la, b, 2a, b. Hiatula minoensis (Yokoyama) (X 1). 3a-c, 4a-c . Naticidae gen 巴t sp . ind巴t. ( X 2). 5. Chicoreus sp . Dorsa l view. (X 2).

Miocene Mollu sks from the Nagashino Formation 9

Araki, 1960, p. 100, pl. 8, fig. 1; Kamada, 1962, p. 126, p1. the middle of the shelllength. Antero- and post巴ro-dorsal

14, fig. 7; Mizuno, 1964, pl. 4 , figs. 3, 4; Mizuno, 1965, margins gently sloping; ant巴rior margin round ; post巴rior

p. 34, p1. 1, fig. 3; Uozumi and Fujie, 1966, pl. 12, fig. 12; margin subtruncate; ventral margin arcuate. A blunt ridge

Hayashi , 1973, pl. 1, figs. 9, 10 ; Hayashi and Miura, 1973 , running from beak to the postero-ventral corne r. Surface

p1. 1, figs. 19, 20; Kim and others, 1974, p. 278, p1. 38, fig. 4; smooth.

Okamoto and T巴rachi ， 1974, p1. 47, fig. 9; Yoon, 1979, p. 14,

pl. 2, fig. 12 ; O'Hara and Nemoto, 1984, pl. 1, fig. 17; Kanno

and others, 1988, p1. 1, fig. 10.

Sanguinolaria (Soletellina) minoensis (Yokoyama). Otuka, 1934,

p. 619 , p1. 49, figs. 65a, b; Otuka, 1938, p. 34, p1. 2, fig s.

14, 18; Oyama and Saka, 1944, p. 141 , pl. 15, figs. 17, 18

(misspell巴d as Sanguinoraria)

Soletellina cf. minoensis Yokoyama. Kaseno, 1956, p. 8, p1. 3,

figs.14a-c. Discussion -. Hiatula minoensis (Yokoyama) resembles

Sanguinolaria minoensis (Yokoyama). Makiyama, 1958, pl. 39, Hiatula diphos (Linnaeus) living in th巴 West Pacific, but

figs. 13-16 . the beak is more post巴riorly located. It has some similarity

Mya cuneiformis (Bりhm) (non B�m). Hayashi, 1973, p1. 1, fig . 4. to Hiatula kobiyamae (Kanno) described from the

Latemula sp. Hayashi , 1973, p1. 1, fig. 8. Oligocene Asagai Formation in Fukushima Prefecture, but

Hiatula minoensis (Yokoyama). ltoigawa and others, 1974, p. 96, the shell is more elongat巴

pl. 28, figs. 10, 11a, b; Itoigawa and Nishikawa, 1976, p1. 34,

fig. 10 ; Ogasawara and Noda, 1978, p. 36, p1. 4, figs. 10-12,

15 , 17-19, 21, 22; Taguchi and others, 1979, pl. 3, fig. 4;

Ish ida and others, 1980, pl. 4, fig. 7; Taguchi, 1981 , p1. 2, fig

12; Itoigawa and others , 1981 , 1982, p. 102, pl. 20, figs.1 a,

b; Shibata and Ina, 1983 , p. 51 , pl. 7, fig. 4; Okamoto and

others, 1983 , p1. 23 , figs. 31 , 32; Nakagawa and Tak巴yama，

1985, pl. 17, fig. 11; Ozawa and oth巴rs ， 1986, p1. 14, fig . 4;

Shibata and Kato, 1988, pl. 3, fig. 14; Nakagawa, 1989, pl.

2, figs. 3a, b; Okamoto and others, 1989, p1. 6, figs. 17, 18,

pl. 7, fig. 30; Iwamura Res巴arch Group, 1989, p1. 21 , fig. Solen (Solenarius) sp. Itoigawa and others, 1974, p. 100, pl. 31 ,

Dimensions (in mm) ー.

Length Height Thickness

71.5 40.0 21.5

69.6 40 .4 16.4

49.7 32 .5 10.8

55 .1 32.3

Geologic range -. Early to middle Mioc巴ne.

e

'

I

ML巴ー

片

山白川

d

n

a

?'en

-

-

-

r

o

u

hdSL

m

hdMJ

i

--'U

J

I

町O

白釦SP

F

s

u

u

s

n

巴G

Solen sp.

(Figs. 3-6, 7)

4; Okamoto and others, 1990, pl. 9, fig. 29; Amano, 1992, figs. 2, 3a, b.

pl. 57, fig. 14; Lee, 1992, p. 86, fig s. 31-4, 5, 14; Noda and Solen (s. s.) sp. Itoigawa and others, 1981 , 1982, p. 103, pl. 20,

others, 1994, figs. 6-8, 11 , 16; Ogasawara and Nagasawa, figs. 2a, b.

1992, p. 1241, figs. 8-1a, b, 2a, b, 5, 6a, b, 9-27 ; Matsubara, Solen sp. Shibata and Ina, 1983, p. 52, pl. 7, fig. 1

1995, p. 327, fi gs. 1-20, 21; Taguchi, 2002, pl. 5, fi g. 2.

Mya? sp. Hayashi , 1988, pl. 1, fig. 4

Hiatula sp. Hayashi, 1988, pl. 1, fig. 9.

Gobraeus つ sp. Hayashi, 1988, p1. 1, fig. 10

Material -. Three cast sp巴clmens

Description - Shell large , transversely elongate ,

compressed, ga ping at posterior 巴nd. Beaks very low ,

Mat巴rial -. Eight巴en specimens . About 1/3 of them are situated at anterior 巴nd . Anterior margin truncated ,

with their both valv巴s conjoined, and the rest are with th巴ir posterior margin round. Dor sa l and ventral margins

both valv巴s disarticulated. straight, paralle 1.

Description -. Shell medium , thin , ovat巴， compr巴ssed.

Beaks low, turned inward, situat ed at a littl e ant巴rior of

l

Hiroshi Shibata and Takashi Ichihara

Dim巴nsions (in mm) 一.

L巴ngth H巴ight Thickness

90.0

9.9

l ト4

16.2

7.0

Discussion -. Solen sp. resembles Solen strictus Gould

living in Japan , China and Kor巴a and Solen saitamensis

Kanno from the Oligocene Us hikubitoge Fo rmation in

Saitama Prefecture, but it differs from these species in

having a round posterior end. 1t has close affinity in shape

and size with Solen (Solenarius) sp. described by 1toigawa

and oth巴rs (1974) from the 巴arly Mioc巴neAk巴yo Formation

of the Mizunami Group in Gifu Prefecture，創1d it seems to

be conspecific with th巴 latter.

Geologic range -. Early Miocene

Class Gastropoda

Subclass Prosobranchia

OrderM巴sogastropoda

Family Naticidae

t

nl

ノ

p

a

t

'

e

c

l

a

g

4

.0FA

-

E

(

4EL

9u

N

Material -. Thre巴 d巴form巴d cast specimens

(Fig.4-5)

Material -. One cast of which dorsal part is covered wi th

sandstone. The apical part of the she ll is crus hed in the

sp巴CImen.

Description -. Shell of medium siz巴， fusiform , w ith

conical spire . Whorls more than thre巴， separated by deep

suture, shouldered at a little above their middl巴. The last

whorl large, with contract巴d ba se. Th巴 penultimate whorl

and th巴 last whorl ornamented with two and thre巴 spiral

cords, respectively. Both whorls bearing promin ent varice s

besides spiral cords . Dimension s; height 46.2 mm, width

28.6 mm

Discussion The specim巴n is similar in shape and

surface sc ulp ture to Chicoreus (R hi zophorimu rex)

tigan ouranus (Nomura) described from the early Miocene

Chiganoura Formation in Miyagi Prefecture, but the state

of preservation of it is not good enough for a positive

identification of it with that species.

References

Amano, K. , 1980. Miocene molluscan fossi ls from the Yudoro

Formation in the east of Rumoi , Hokkaido. Prof S. Kaηno

Mem. Vol., 99­120

Description -. Shell small, globula r. Whorls more than 3, Amano , K. , 1992 . Cypra ea ohi ro i and its associated mollu scan

separated by distinct sutur巴. Spire small, conica l. The last species from the Miocene Kadonosawa Formation, Northea st

whorllarge, swollen . Japan. Bu ll . Mi zun ami Fossil 凡1us . ， (19): 405-4 11. (in

Japan巴s巴 with English abstrac t.)

Aoyama, M. , 1996 . Rocks and mineral s. Jn Geography of Horaiｭ

cho, -Nature- , 130-224. Horai-cho , Aichi Prefectur e. (in

Japan巴se . )

Araki , Y., 1960. Geology , pa1巴ontology and s巴dim巴ntary struct ure s

(including prob lema tica ) of the Tertiary formations

Discussion -. A lI spec imen s at hand are too poor in the developed in the environs ofT su City, Mi巴 Prefecture， Japan

state of pr巴servation to d巴termine their generic and specific Bull. Lib. Art s Dep. , Mi e Uniν" Spec., 1: 1-1 18.

names . Collaborative Research Group for the Shidara Basin, 19 79. The

Dimensions (in mm) ー.

Height

82 .4

Width

13.8

14.8 12. 7

Order Neogastropoda

Family Muricidae

Genus C hi coreus Montfort, 1810

Chicoreus sp

N eogene D istr ibu ted in th巴 South District of Mt . Horaiji,

Aichi Prefecture, C巴ntral Japan. Mem. G eol. Soc. Japan ,

(16): 63- 75. (in Japan巴se with En gli sh abstrac t.)

Hata , Y. , 196 7. Cenozoic sequenc es in the Komono area, Mi巴

Pr efect ure. Rep. Resour ce s Exploitationallnst., 4: 77 -107

(in Japan巴se.)

Miocene Mo Jlusks from th巴 Nagashino Formation 11

Hatai , K. , 1940. On some fossils from th e Ninohe district, Mutu Japan, Spec. Pap. , (29): 149-159

Province, North巴ast Honshu , Japan (No.1). Bull. Bio geogr. Itoigawa, J. , Shibata, H. and Nishimoto , H. , 1974. Molluscan

50c. Japan, 10: 119-137. fo ss il s from the Mizunami Group. Bull. Mi zunami Fossi l

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Horaijisan, -Natur巴 and Culture-. 10-17. Horaijisan Natural Itoigawa, J. , Shibata, H. , Nishimoto, H . and Okumura, Y. , 19 81.

Science Museum. (in Japanese.) Miocene fo ss ils of the Mizunami Group, central Japan. 2.

Hayashi , T. , 1988 . A review of fossils from the environs of Molluscs. Monogr . Mizunami Fo ssil Mus. , (3 -A): 1-53. (in

Horaijisan (Hayashi , 1973). Bull . Horaijisan Nat. 5ci. Mus. , Japanese.)

(18) ・ 3-14. (in Japanese.) Itoigawa, J. , Shibata, H. , Nishimoto, H. and Okumura, Y., 1982.

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Shitara Group in th巴 northeast巴rn part of Aichi Prefectur e Molluscs (Continu巴d). Monogr . Mi zunam i Fossil Mus. , (3-B ):

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southem part of Okazaki City, central Japan. Bull. Aichi Univ . Kamada, Y. , 1962. Tertiary marine Mollusca from the Joban Coa l-

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from the Kumano Group of the Ukui area, southeastern part associated molluscan fauna from th e Kunnui Formation in

of the Kii P巴ninsula， southwest巴rn Honshu, Japan. Palaeont. Oshamanbe, Southw巴st Hokkaido. Saito Ho-on Kai Spec .

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Hanawa Basin , North Honshu. Bu ll . Geol. Surv. Japan, 16 Goyasu Formation of th巴 Joban Coa lfield. Jour. Coll. Arts

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abstrac t.) Tateiwai a Speci巴s and Sub st rata -Study of th巴 Bihoku Group

Nakagawa, T. , 198 9. lntertidal mollu sc an assembla ges in the 2 -. Bull. Mi zunami Fo ss il Mus., ( 1 6) ・ 43 -53. (in Japanese

Miocene Kunimi Formation, Fukui Prefecture, Central Japan. with English abstrac t.)

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Associations and Paleo-envi ronment of the Uchiura Group, South west Japan - Stud y of the B ih oku Group 3 -. Bull

Fukui Pr巴fecture ， Centra1 Jap an. Bu ll . Mi zunami Fossil Mus. ， 凡1izunamiFossil Mus., (17): 35-49 . (in Japanese w ith Eng lish

(12): 27 -47. (in Japanese with English abstrac t.) abs tr ac t.)

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the Tanakura Tectonic Zone . Sci. Rep. /ns t. Geosci. , Univ . Mi zunami Fossil Mus. , (10): 85- 102. (in Japanese with

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Nomura, S. , 1938. Molluscan fossils from the Tatunokuti Shell from the M iocen e Bihoku Group, Shobara City, Hiroshima

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Shidara G roup (Miocene), centra 1 Japan . Monogr. Mizunami Yokoyama, Y. , 19 87 . On Fossils collect巴d from th巴 Nagashino

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Iwata, J. , Osawa, S. Owaki , M. , Kandori, H. , Shibata, K. , (in Japane se.)

Shibata, R., Taguchi , K. and Fuma, M. , 1977. Miocene Yoonヲ S. ， 19 76. Geology and Paleontology of the T erti ary

Molluscs and p1ants from the Shidara basin, Aichi Prefecture. Poh ang Basin, Pohang District, Kor巴a. Part 2, Pal eonto logy

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assemb lages from the Katsuta Group, Okayama Prefecture Japanese.)

wi th spec ial r巴ference to brackish faunal zonation in th巴

Miocene of Japan . BuLL. Mizunami Fo ssi l Mus. , (8) : 7-2 0.

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paleoenvironment of the Miocene Katsuta Group in Okayama

Prefectur巴， Sout hw est Japan. Bull. Mi zunami FossiL Mus. ,

(29) ・ 95-133 .

Taguchi, E. , Ono, N. and Okamoto, K. , 19 79. Fossil mollu sca n

assemblages from th巴 Miocene Bihoku Group in Niimi C it y

and Ohsa-cho, Okayama Prefecture, Japan. Bu /l. Mi zunami

Fossil Mus. , (6) : 1-15 . (in Japanese wit h English abstract.)

Takahぉhi ， H. , 1984. Mollu sca n assem blag es from th e M iocene

Nakayama Formation in the Kadono district, Joban Coal-

Field, Fuku sh im a Prefecture. Fo ssils (Palaeont. So c. Japan),

(36): 1-17. (inJapanes巴 with Engli sh abstrac t.)

Takayasu , K., 198 1. Fossi l Molluscs from the Miiocene Masuda

Group at Okuda, M asuda City - Molluscan foss il s from

14 Hiroshi Shibata and Takashi Ichihara

(要旨)

柴田博・市原俊:愛知県新城市の設楽

層群長篠層産中新世貝類化石.

愛知県新城市有海の設楽層群長篠層より産出

した貝類化石を記載し，それらの写真を示した .

これらの貝類化石の採集地は，林・輿水 (1992)

が中期始新世の種に同定した有海の長篠層貝

類化石の産地と同じかそれに極めて近い地点

である . 貝類化石は ， Modiolus sp. , Crassostrea

gravitesω(Yokoyama) ， Laevicardium sp., Phacosomα

kωvagensis (Araki) , Meretrix arugai Otuka, Hiatula

minoensis (Yokoyama) , Solen sp. , Naticidae g巴n. et

sp. indet.そして Chicoreus sp.の9種よりなる.貝

類化石の地質時代から長篠層の時代は前期中新

世と考えられる.