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Trans. Proc. Palaeont. Soc. Japan, N. S., No. 101, pp. 247-263, pIs. 26-28, April 30, 1976

657.

ONTOGENIES OF THREE SPECIES OF SILICIFIED MIDDLEORDOVICIAN TRILOBITES FROM VIRGINIA *CHUNG-HUNG HU
Department of Earth Sciences, Cheng Kung University, Taiwan

if 7 - : / =- 71ii.ili[;;tlv r t:: 7-*Ct:j:IMftft=~£R 3 fj0)11BIf*3M:.: *1Jf~lt if 7 - : / =- 711f
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4-@llt, Dimeropyge virginiensis WHITTINGTON and EVITT, Mesotaphraspis acris, n.
sp. :to.tLf Illaenus valvulus RAYMOND 0) 3fjt:'''?\''-C~~Lt.:o ~IO)fjt:.~-r-011Blf*
3e1:.lt1'7'r:~t:. LiJ4Jj I? t.(iJ' '? t.:iJ~, ~ 2 ~t:. "?\, '-Clt~:H:f7'r:~t:.m§ij tt.tLt.:o '£ t.:, ~ 2 ~O)~fj~fiIll*Jt:'lt, .:t.tL-F.tL 2 ,,?O)MmlH\t:. -r- 0 ?' Iv- :tiJ~~5JJJ tt.tL, tI1Ui~~m~t:..t Goto)cmtt.tLoo
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dimorphism. In the species M. acris the"female pygidium possesses no axial tubercle, two complete pygidial segments, anda distinct marginal border, whereas themale pygidial axis is decorated by tubercles, three segments are present, and themargin is without a distinct border. The
female form of I. valvulus has a roundedcranidium, forwardly located palpebral
lobe, the pygidium is less convex, andsemicircular in outline, and that of malecranidium is subquadrate, posteriorly
located palpebral lobe, the pygidium istransverse trapezoidal and highly convex.
Acknowledgements-The writer wishes
to thank to Dr. K.E. CASTER, Universityof Cincinnati, Ohio, for his supervisionand kind reading over the present
manuscript. Thanks are also due to Dr.
F. RASETTI, Universita Degli Studi, Roma,for permission to study his excellent collections. The figured specimens are alldeposited in the Geology Museum, University of Cincinnati, Ohio (U.C.G.M).

Introduction
The present report represents a partof studies of ontogenetic development ofMiddle Ordovician trilobites from the
Edinburg Formation, Virginia (Hu, 1971,
1974a, 1974b, 1975a, 1975b). Three species
are described. They are Dimeropyge
virginiensis WHITTINGTON and EVITT,
Mesotaphraspis acris, n. sp., and Illaenus
valvulus RAYMOND. The earliest development of D. virginiensis is incompletely
known, and those of M. acris and I.
valvulus are well. The ontogenetic development of trilobite is divided into
anaprotaspid, metaprotaspid, para protaspid, early meraspid, and late meraspid
stages as proposed earlier by the author(Hu, 1964, 1971, 1974).
The studied specimens of M. acris andI. valvulus are represented by two different morphologic groups within each ofthese species populations. These bimodal
phenomena are postulated as sexual* Received Sept. 16, 1975; read Jan. 31, 1976
at Narugo.
247

Chung-Hung Hu

248
Systematic description

Family Dimeropygidae WHITTINGTON
and EVITT, 1953
Genus Dimeropyge OPIK, 1937
Dimeropyge virginiensis WHITTINGTON
and EVITT, 1953
PI. 26, Figs. 1-33; Text-fig. 1

Dimeropyge virl?iniensis WHITTINGTON and
EVITT, 1953, p. 37, pI. 2 and 3, figs. 1-30;
text-fig. 5-8.

Remarks-The present species is acommon member within the studied
WHITTINGTON and EVITT
materials.
(1953) gave a very detailed descriptionof the species. However, the ontogenetic
development was incompletely known by
them. An associated hypostoma in thepresent material, which is characterized
by its abundant granulation and thickness, seems to correlated with the previously known cranidium, pygidium, andlibrigena of this species.
Figured specimens-Cranidia, U.C.G.M.
40422k-n; librigenae, U.C.G.M. 40422w-z;
pygidia, U. C. G. M. 40422o-t, a'-d', f';hypostomata, U. C. G. M. 40422u, v.
Dimeropyge virginiensis WHITTINGTON
and EVITT, ontogeny
Early protaspid stage (PI. 26, Fig. 1 andText-fig. 1A)-Only a single skeleton ofthis stage has been recovered. It is pearshaped, gently convex, with a granulated
surface, and is about 0.35 mm in sagittal
length; the posterior half of the skeleton
is slightly broader than the anterior; theaxial and the pleural lobes, cranidium
and pygidium are all indistinctly separated; the ventral side of the skeleton

is smooth, with the anterior lateral margin curving slightly inward; the posterior
margin is rounded, and surrounded by anarrow doublure.
The present specimen shows no any
distinct structure which could assign toa certain specific growth stage. For thetime being it is considered to belong toa protaspis.
Paraprotaspid stage (PI. 26, Figs. 2-5,
and Text-fig. lB, C)-The skeleton is ovalin outline, gently convex, about 0.4-0.7
mm in length (sag.); the axial and thepleural lobes are well differentiated bydorsal furrows; a small protopygidium
appears behind of the large cranidial
shield; the glabella is conical, taperingslightly forward, and has the anterior
margin arching slightly forward; noglabellar furrows are seen; the narrow,convex occipital ring is well set off by
the occipital furrow and the posteriorcranidial suture; the lateral lobe of the
fixigena is slightly narrower than theglabella, gently sloping downward fromthe dorsal furrow and with the anterolateral margin curved slightly inward;
this suggests the position of the facial
suture, and a portion of the librigena;
the anterior border is indistinctly separated from the narrow preglabellar field.
The protopygidium is semicircular in outline, convex and undifferentiated.
The surface of the skeleton is coveredby both of fine and large granules; there
are three pairs of large granules on theglabella, four pairs on the fixigenae, one
to three on the pygidial axis, and a few
pairs along the anterior border and theskeletal margins.
Early meraspid stage (PI. 26, Figs. 6-8,
16-19 and Text-fig. 1D, G, H)-The trapezoidal cranidium is convex and has theanterior border arching slightly forward
and with a deeply impressed frontal
furrow; it is about 0.7-0.8 mm in length

./

J

657.

Ontogenies of Mid-Ordovician Trilobites

A

B

c

E

F

G

249

D

H

Text-fig. 1.

J

K

L

N

o

p

Dimeropyge virginiensis WHITTINGTON and EVITT.

A, an early protaspis, x 43; B, C, two paraprotaspides, x 40, x 25; D, early meraspid cranidium, x 20; E, a late meraspid cranidium, x 15; F, ventral view of an adult cranidium,x 15; G, H, two early meraspid pygidia, x 25, x 15; I, an adulat cranidium, x 13; J, an
immature librigena, x 10; K, librigena, x 10; L, a late meraspid pygidium, x 15; N, M,
ventral and back views of a pygidium, x 12; 0, hypostoma, x 8; P, a pygidium, x 8. (Alldra wings were made from photographs.)

250

Chung-Hung Hu(sag.); the glabella is cylindrical, parallelsided, convex, slightly higher than fixigena along the axial lobe, and the anterior
margin is round; the glabellar furrow is
unknown; the occipital ring is crescentic,
convex, well differentiated by the occipital furrow, and a small median tubercle; the preglabellar field is gently convex, sloping downward from the anterior
glabella, and is about one-half the lengthof the glabella (sag.) ; the convex anteriorborder is narrower than the preglabellar
field, and well divided by the frontal
furrow. The fixigena is convex, about
the same width as the glabella between
the palpebral lobe and the dorsal furrow;the small elevated palpebral lobe is welldemarked by the palpebral furrow, andis situated in front of the mid-line of theglabella (sag.). The surface of the cranidium is covered by both fine and large
granules; the large granules are symmetrically disposed; three to four pairsof them are on the glabella, four pairson the fixigena and posterior fixigenal
borders. Both short and long spines areabundant or thickly on the anteriorborder from which they radiate; medianfurrow is poorly marked from the anterior
glabellar margin to the frontal furrow.
The early meraspid pygidium is semicircular in outline, convex, and the marginal border is nearly vertical; the conical axial lobe is tapering posteriorly andcomposed of three axial rings, one ofwhich bears a slender medium-sized
median spine; the pleural bands are welldifferentiated, but the intrapleural grooves are indistinct; each pygidial segment
bears a pair of short spines. The surface
is covered by fine granules; large paired
pustules are present on both axial rings
and the pygidial margin. The medianpygidial spine has moved forward in correlation with the increase of pygidial
segments from the proximal end.

Late meraspid stage (PI. 26, Figs. 9-11,
20-22, 24 and Text-fig. lL, J.)- The cranidium is trapezoidal in outline, elongate,
highly convex, about 1.0-1.5mm in length(sag.); the dorsal furrow is deeply impressed; the glabella is expanded slightly
forward, and without any recognizableglabellar furrow. The fixigena is convex,
slopes downward, and is about one-third
the width of the glabella; the posterior
fixigenal border is well delimited by a
deep furrow, convex, and of the same
width as the occipital ring (tr.) ; the small
and well defined palpebral lobe is locatedin front of the mid-line of the glabella;
it is convex both vertically and laterally;
the preglabellar field is convex, slopes
downward from the anterior glabella; it
is about one-third the length of theglabella, and well delimited by a broad
frontal furrow; the convex anteriorborder arches strongly forward.
The librigena is narrowly elongate,convex, and with the ocular ring convex
above the ocular platform; no distinct
lateral border or border furrow is
known; the anterolateral border is acuminate and narrower than the doublure;
the posterior ocular platform is broad,gently convex at the genal angle, andhas a short, broadly based genal spine_
The ventral aspect of the librigenal doublure is narrow, but its posterior end
extends broadly with a deeply marked
notch at the genal angle. The hypostoma
is generally hexagonal in outline, convex,
well delimited by macular and marginal
furrows; the narrow posterior border
notches inward slightly.
The late meraspid pygidium is subsemicircular in outline, convex, anddivided into two segments and a terminal
portion; the marginal border slopes
nearly vertically from the marginal spine,
and is distinctly delimited.
The skeletal surface is densely gran-657. Ontogenies of Mid-01'dovician Trilobites
ular; there are short, radial spines areon the anterior border; the posterior halfof the hypostoma is covered by finegranules and larger ones are scatteredanteriorly.
The present stage differs from theearly meraspid by its expanded glabella
and the slightly flattened and transversal
pygidium; it is differentiated from holaspis by its expanded glabella, distinctly
marked librigenal border, hexagonal
hypostoma, and the transversal pygidium; whereas the holaspis is oval, with
distinctly divided librigenal border having
a lateral embayment, the hypostoma has
broader marginal border and a deep
median notch, and the pygidium is subtriangular.
Figured specimens- Early protaspis,
U.C.G.M. 40422; paraprotaspides, U.C.G.M.
40422a-e; early meraspides, U.C.G.M.
40422d-g; late meraspides, U.C.G.M.
40422h, e ' , y.
Genus Mesotaphraspis WHITTINGTON
and EVITT, 1953
l'vJesotaphraspis acris, n. sp.
PI. 27, Figs. 1-36; Text-fig. 2

Diagnosis - Cranidium trapezoidal,
moderately convex; glabella conical, subtriangular, tapering rapidly forward, withthe last glabellar furrows distinct; occipital ring crescentic, with the axis curving slightly anteriorly; preglabellar field
more than one-half length of the glabella;anterior border convex, less narrower
than the preglabellar field; fixigena
gently convex, slightly narrower than
the glabella. Librigena regular shaped,
having a medium-sized genal spine.
Hypostoma subquadrate, convex, with adistinctly depressed marginal furrow,three pairs of marginal spines and a251

terminal portion; with or without inner
marginal furrow or border; surface faintly granulated. Certain one thoracic segment occupied by a median spine, andtubercles along the pygidial axis.
Description-Cranidium is sub quadrate
to trapezoidal in outline, moderately convex, and with the dorsal furrow distinctly
marked; the posterior pair of glabellar
furrows is distinctly impressed and directed posteriorly from the mid-lengthof the glabella (tr.) to the occipital furrow; the anterior glabellar furrows arerather faint; the occipital ring is crescentic, convex, with the mid-line (sag.)curving slightly forward, and possessing
a minute tubercle; the occipital furrowis well-developed, it arches forward to
the mid-line, and deepens laterally toform a pair of elongate pits; the anteriorbrim is slightly narrower than the glabella (sag.), and well-delimited by afrontal furrow; the anterior border isnarrow crescentic, convex, slightly narrower than the preglabellar field. Fixigena is gently convex, less than one-halfthe width of the glabella; the palpebral
lobe is broad, without distinct palpebral
furrow or occular ridge, its maximum
width is located behind of the mid-lineof the glabella, and close to the posterior
fixigena; the posterior fixigena is very
narrow, possesses a broad, convex marginal border, and is slightly narrower
than the occipital ring (tr.).
Librigeno-rostrum is regular tongueshaped, convex, with the convex lateralborder delimited by a lateral furrow andbroad ocular platform; the lateral andthe posterior genal furrows are connected
at the genal angle, and thence extend
into the genal spine for a short distance;
the ocular ring is semicircular, locatedat the mid-line of the inner free margin
at the facial suture. The hypostoma is
generally sub quadrate in outline, convex;

252

Chung-Hung Hu

the median body is roundly triangular,
convex, surrounded by deeply impressed
marginal furrows; the posterior medianarea is U-shaped and convex; the lateralborder is convex, less narrow than theposterior margin, and bearing two pairsof short spines at the mid-line of thehypostoma (tr.); the antero-lateral wings
are short spines, tilted downward anddirected antero-laterally from the front
corners; the posterior border is convex,
and has a pair of short broad lateralspines.
The subtrianguhr pygidium is convex;
has the short broad axial lobe divided
into two unequal sized rings and a small
terminal portion by furrows; the pleurallobe is convex below the axis, and slopes
downward around the lateral margin, andis divided into a pair of distinct intrapleural furrows and a pair of faint interpleural grooves; the narrow marginalborder is convex and well delimited byan inner marginal furrow.
The exoskeletal surface is covered by
faint granules, certain one thoracic segment possesses a long median spine. andthe medium-sized tubercles-bearing along
the pygidial axis.
Remarks- The present species is represented by two different pygidial types;
in the first, the pygidial axis possesses
no median tubercle, there are two complete segments, and a distinct marginalborder; whereas in the other, the axial
rings are decorated by tubercles, threesegments are present, and the margin iswithout a distinct border. These differences are presumably sexual within
the same species.
The present species is differentiatedfrom Mesotaphraspis parva WHITTINGTON
and EVITT, and M. inornata WHITTINGTON and EVITT (1953) by its slenderly
conical glabella, broader preglabellar field,
broader facial suture line (tr.), and thesligh tly posteriorly directed fixigenal
border. The pygidium is triangular, has
three axial rings, with or without a marginal border, whereas in the other two
species the pygidium is semicircular,
without median axial tubercles.
Figured specimens- Holotype, cranidium, U. C. G. M. 4042lr;
paratype3,
cranidia, U. C. G. M. 40421m, q, n; hypostoma, U. C. G. M. 40421p;
pygidia,
U. C. G. M. 404210, 40421y (" female "),40421d', c' (" male "); thoracic segment,
U. C. G. M. 40421z.

Mesotaphraspis acris, n. sp.,

ontogeny
Problematica (PI. 27, Fig. 1, and Textfig. 2A)-There is a spherical specimen
in the collection about 0.30 mm in diameter, with broken surface, which showsan irregular hole; the inside of the holecontains certain unknown trilobitic (?)
skeletal fragments; the outer surface ofthe specimen is smooth. It is postulated
that this specimen is possibly an eggcase, possibly of a trilobite larval integument, or perchance a single·chambered
pro taste.
Anaprotaspid stage (PI. 27, Fig. 2, and
Text-fig. 2)-The shield is round or
slightly broader anteriorly, gently convex,
about 0.33 mm in length (sag.) ; the dorsal
surface shows few distinct characters
except for a pair of elongate pits broadly
marked on the anterior lateral margin;
no axial furrow or marginal spine is
known. The underside of the shieldshows a rather narrow doublure aroundthe posterior margin. The surface isgranulated.
Metaprotaspid stage (PI. 27, Figs. 3-5,
and Text-fig. 2C)-The shield is roundto subrounded, convex along the axis,
but without distinct dorsal or axial fur-

657. Ontogenies of Mid-Ordovician Trilobites

253

A

B

c

o

H

G

F

£

J
K

o

N

Text-fig. 2.

Lp

Mesotaphraspis acris, n. sp.

A, problematica, x 50; B, an anaprotaspis, x 50; C, a metaprotaspis, x40; D, a paraprotaspis, x 32; E, an early meraspid cranidium, x 23; F, H, two late meraspid cranidia, x 23,
x 16; G, a meraspid hypostoma, x 20; I, an holaspid crandium, x 12; J, K, an early and alate meraspid pygidium, x 20, x 30; L, librigena, x 5; M, N, dorsal and back views of a"female" pygidium, x15; O,P, baks and dorsal views of a "male" pygidium, xl0. (Alldrawings were made from photographs.)

rows; it is about 0.35-0.52 mm in length(sag.); the anterior margin arches slightly
forward but is nearly straight, and somespecimens show a frontal furrow whereas

the other does not. The elongate frontal
pits are deeply impressed at the anterolateral margin; the narrow marginalborder is nearly horizontal, faintly de-254

Chung-Hung Hu

pressed by the marginal furrow. The
exoskeleton is granulated.
The present stage differs from theprevious one in having the convex axis,
closely located frontal pits, and the presence of the anterior border.
Paraprotaspid stage (PI. 27, Fig. 10 and
Text-fig. 2D)-The shield is subround,convex, about 0.6 mm long (sag.), composed of a large cranidium and a small
protopygidium; the axial lobe is only
visible near the occipital segment, otherwise, it is incomplete; the anterior border is convex and delimited by a broad
conical frontal furrow, which is narrowcrescentic, arching forward; the facial
suture appears along the anterior lateral
margin, that is short, narrow, convex forwardly from the anterior border to the
mid-line of the shield (tr.). The proto-

pygidium is rather small, lenticular, andwithout any distinct segmental furrow;the axis is gently elevated but has no
defined dorsal furrow. The exoskeletal
surface is marked by both faint andmedium-sized granules.
Early meraspid stage (PI. 27, Figs. 8, 9,
11, 12, 21, 23, 24, 26, 31 and Text-fig. 2E,
F, J-K)-The cranidium is subquadrate
or trapezoidal, narrow and long, convex,
and about 0.6-0.8 mm in length (sag.);the dorsal furrow is faintly delimited; theglabella is cylindrical or slightly tapering forward, without distinct glabellar
furrow, except for three to four pairs ofrounded glabellar tubercles; the occipitalring is crescentic, convex, and well separated by the occipital ring and bears aminute median tubercle; the preglabellar
field is about the same width as the

Explanation of Plate 26
Figs. 1-33. Dimeropyge virginiensis WHITTINGTON and EVITT
1. Dorsal view of an early protaspid shield. x43, U.C.G.M. 40422.
2-5. Dorsal views of four paraprotaspid shields; notice the cylindrical glabella. 2, x 40,
U.C.G.M.40422a;3, x25, U.C.G.M.40422b;4, x20, U.C.H.M.40422c;5, xIS, U.C.G.M.
40422e.
6-S. Dorsal view of three early meraspid cranidia, showing the cylindrical glabella. 6,
x 20, U. C. G. M. 40422d; 7, x 20, U. C. G. M. 40422f; 8, x 20, U. C. G. M. 40422g.
9-11. Dorsal views of three late meraspid cranidia; notice the forwardly expanded glabella. 9, x 15, U. C. G. M. 40422h; 10, x 15, U. C. G. M. 40422e'; 11, x 15, U. C. G. M. 40422j.
12-15. Ventral and dorsal views of four rpmplete crandia; notice the elongate-oval glabella. 12, x 15, U. C. G. M. 40422k; 13, x 16, U. C. G. M. 404221; 14, x 14, U. C. G. M. 40-122m;
15, x 13, U. C. G. M. 40422n.
16-21. Dorsal views of a growth series of pygidia; notice that the spinous segment progresses forward during the different growth stages. 16, x25, U.C.G.M. 404220; 17,
x 14, U. C. G. M. 40422p; IS, x 15, U. C. G. M. 40422q; 19, x 14, U. C. G. M. 40422r; 20, x 10,
U. C. G. M. 40422s; 21, x 15, U. C. G. M. 40422t.
22-23. A small and a medium sized hypostoma, showing the increasing abundance ofgranules. x 10, U. C. G. M. 40422u; x 8, U. C. G. M. 40422v.
24-28. A growth series of librigenae, showing the increase in width of the ocular platform, and the lateral border. 24, x15, U.C.G.M. 40422w; 25, x10, U.C.G.M. 40422x;
26, x 10, U. C. G. M. 40422y; 27, x 15, U. C. G. M. 40422z; 2S, specimen missing.
29-33. Dorsal, ventral, and posterior views of five pygidia; notice the marginal spines
and the vertically directed pygidial border. 29, x 15, U. C. G. M. 40422a'; 30, x 7,
U. C. G. M. 40422b'; 31, x 10, U. C. G. M. 40422c'; 32, x 10, 40422d'; 33, x 8, U. C. G. M.
40422f' .

Hu:Ontogenies of Mid-Ordovician trilobites

Plate 26

657.

Ontogenies of Mid-Ordovician Trilobites

anterior border or slightly wider, convex,
downwardly sloping from the anterior
glabellar margin, without any separation;
the frontal furrow is broad and concave.
Fixigena is about the same width as orslightly narrower than the glabella, convex, and slopes downward from thedorsal furrow; the narrow crescentic
palpebral lobe is located on the mid-lineof the cranidium, well demarked by palpebral furrow, and convex; the posterior
fixigena is triangular, has a well developed border furrow; the posterior fix igenal border is elevated from the borderfurrow, convex, and about the same
width as the occipital ring. The earlymeraspid pygidium is often associatedwith two to three thoracic segments, along median spine, convex, and themargin is spinose; the terminal portionof the axis is narrow and slopes downward.
The skeletal surface is covered by bothfine and coarse granules; the pygidial
axis is either with or without an axial
node; a pair of coarse granules is present
on the pleural region of each pygidial
segment.
The distinct characteristics of thepresent stage are that the dorsal furrows
are well demarked, glabella cylindrical,
the palpebral lobe is located on the midline of the glabella, the pygidium is often
as:::ociated by a few thoracic segments,
and there is a median axial spine.
Late meraspid stage (PI. 27, Figs. 6, 7,
13,17,22,25,32,33 and Text-fig. 2G, 1)The cranidium is subquadrate to trapezoidal in outline, convex, with well developed dorsal furrows, and about 0.7-1.0
mm in length (sag.); the glabella isslenderly conical, marked by three pairsof well-defined glabellar furrows; thelast pair or the near occipital pair isdeeper than the anterior ones, and acute;the occipital ring is crescent, convex, and255

bears a minute median node; the preglabellar field is slightly narrower than
one-half the length of the glabella (sag.),slopes gently downward, and has a longitudinal median notch; the anterior borderis wider than the preglabellar field, convex above the broad frontal furrow, andarches forward. The fixigena is narrower than the glabella, convex below
the glabella, and well delimited by thepalpebral furrow; the palpebral lobe issickle-shaped, elongate and its widest
portion is located behind the mid-line of
the cranidium; the posterior fixigena israther narrow, and well set off by theborder furrow; the posterior fixigenal
border is rather narrow, and well delimited by the border furrow; the posterior fixigenal border is narrower thanthe occipital ring. The anterior facial
suture is divergent-convex, and theposterior one is laterally devergent andstraight.
The hypostoma is subquadrate, slightly expanded posteriorly and convex; themedian body is convex, triangular, andwell surrounded by furrows; the broad
posterior lobe is V-shaped, convex, anddeeply defined by a marginal furrow; themarginal border is narrow and convex,
and bears five pairs of marginal spines,of which the anterior and the third are
subequal in size and larger than the rest.
The pygidium is semicircular or triangular in outline, convex, and composedof 2-4 pygidial segments and a terminal
portion; the axial lobe is narrower thanthe pleuron, convex above the laterallobe, and well divided into axial rings by
furrows; the marginal border is narrow,with or without a distinct marginal furrow.
The surface of the skeleton is coveredby both of fine and medium-sized granules; a few rounded pits are present
along the median body furrow and the256

Chung-Hung Hu

marginal furrows; the pygidial axis may
or may not have axial nodes.
The present stage differs from theearly one in having a conical glabella,well differentiated posterior glabellarlobe, narrow posterior fixigena, and thelarge palpebral lobe situated behind of
the mid-line of the cranidium. The
pygidial axis is without an axial spine.
Remarks- The ontogenetic development of the present species resembles tothat of Dimel'opyge virginiensis WHITTINGTON and EVITT (1953), Otarion
trilobus Hu (1975), and Phaseolops canusHu (1971). The meraspides especiallyare almost indistinguishable. The protaspides of the present species is on theother hand, well differentiated by its
roundness, convexity, and the ornamentation of the shield. This may indicatethat they are derived from different ancestral stocks as suggested only in theyoung stage, but become similar latter
due to convergent evolution and ecology,
but ultimately emerging into characteristic and different adaptive forms reflected in the dissimilar ephebic morphologies.
Figured spec imens - Problematica,
U.C.G.M. 40421; anaprotaspis, U.C.G.M.
metaprotaspides,
U. C. G. M.
40421a;40421b-d; paraprotaspides, U. C. G. M.
40421i; early meraspides, U. C. G. M.
40421g, h, k, s, u, v, a'; late meraspides,
U. C. G. M. 40421e, f, 1, t, w, b', c'.

Family Illaenidae HA WLE
and CORDA, 1847
Genus fllaenus DALMAN, 1827

fllaenus valvulus RAYMOND, 1925
PI. 28, Figs. 1-40; Text-fig. 15
lliaenus valvulus RAYMOND, 1925, p. 106, pI.
4, figs. 13, 14.

Diagnosis-Cranidium sub trapezoidal,
with rounded anterior margin, convex,
and without distinct dorsal furrows;
palpebral lobe small; palpebral furrow
indistinct; glabeUar furrow absent; palpebral lobe located extremely posteriorly;
posterior fixigena very narrow, convex,
underneath the palpebral lobe. Librigena
subtriangular in outline, convex, without
marginal furrow, lateral border, or genal
spine; o::ular ring located behind thegenal angle. Rostrum transverse, pentagonal, convex, and the anterior marginswollen upward and pointed medially.
Thoracic segment convex; axial lobe
same width as pleuron; no half-ringfurrow or interpleural furrow. Pygidium
semicircular or trapezoidal in outline,
convex, without axial or pleural furrows.
Remarlls-The present species is very
common in the studied materials; abouta few hundred of both immature andmature forms have been selected fromamong isolated trilobite fragments. Allshow well its ontogenetic growth stages.
The adult specimens fall into two morphologic groups, the first of which hasstrongly convex cranidium, posteriorly
located palpebral lobes, and trapezoidal
pygidium; and in the second, the cranidium is less convex, with forwardly
located palpebral lobes, and semicircular
These bimodal traits are
pygidium.
possibly the expression of the sexual
dimorphism within the same genus andspecies population. The first group is
more numerous and is postulated as male,the other as female.
Two rather well preserved specimens
comprising a cranidium and a pygidium
were reported from Holston, Catawaba
Valley, north of Salem, Virginia by RAYMOND (1925). The cranidium is transverse trapezoidal; the pygidium is semioval in outline, and associated with athoracic segment. The measurement of657.

Ontogenies of Mid-Ordovician Trilobites

the cranidium is 5 mm in length (sag.).
and the pygidium 6 mm (sag.). They are
similar both in morphology and occurence
to the present studied material.

Illaenus valvulus RAYMOND. "male"PI. 28, Figs. 35, 36, 39, 40;
Text·fig. 3K, L, S.

DescrijJtion-Cranidium is subtrape·
zoidal in outline, very convex, smooth,
without distinct dorsal and glabellar
furrows except near the occipital ringwhich is slightly depressed laterally; no
preglabellar field or anterior border are
known; the anterior margin arches gently
forward and is surrounded by a narrow,elevated ridge; the posterior fixigena isnarrower than the occipital ring, being
convex, and slopes downward from theglabella; the palpebral lobe is small,indistinctly separated by the palpebral
lobe; it is convex laterally. and locatedfar behind of the mid-line of the crani·
dium; the posterior fixigena is very narrow, convex, and directed laterally; itlies underneath the palpebral lobe. The
subtriangular librigena is convex, withouta lateral border or furrow; the anterior
ocular platform is very broad; the ocularring is located far posteriorly, and theposterior facial suture is underneath theocular platform; the under side of thelibrigena is occupied by a broad doublure
along the lateral margin; It IS convex
anteriorly, but depressed or concave
posteriorly (PI. 28, Fig. 10). The rostrum
is transverse pentagonal, convex, and has
the anterior margin swollen upward withthe median margin slightly pointed for·ward; the lateral, or the connecting
suture and the hypostomal suture areconcave (horizontal). The thoracic segment is convex, without distinct ringfurrow or intrapleural furrow; the pleural257

lobe is convex below the axis, and ex·
tended laterally from the dorsal' furrow
for a short distance and then directed
posteriorly, and ends with a rounded
pleural tip.
The pygidium is transverse trapezoidal
in outline, highly convex, with indistinct
dorsal and pleural furrows; the axis isconvex above the pleural lobe; no axial
ring is known; the posterior margin
slopes downward from the mid-pleuralregion, and is without a marginal border
or inner marginal furrow; ventrally the
pygidium is surrounded by a broad dou·
blure along the posterior margin. and its
mid-terminal portion is pointed inward.
The skeletal surface is covered by
faint pits.

Illaenus valvuLus RAYMOND, "female"PI. 27, Figs. 25-27, 30, 32-34, 37;
Text.fig. 3M, R, Q.

Comparison- The supposed female
form of the present species has a roundedcranidium; the palpebra! lobes are narrower, smaller, and elongate, and locatedslightly forward; the pygidium is lessconvex and semicircular in outline; theskeletal surface is faintly granulated. It
is less common than the "male". The
sexual ratio is about 112.
Figured specimens-" Female" form:
Cranidia, U.C.G.M. 40418v-x; librigenae,
U.C.G.M. 404180, p, s, u ; pygidia, U.C.G.M.
40418a', d', c', e', h'; rostrum, U.C.G.M.
40418t. "Male" form: Cranidia, U.C.G.M.
40418j', k'; pygidia, U.C.G.M. 40418f', g'.
Illaenus valvulus RAYMOND, ontogeny
Anaprotaspid stage (PI. 28, Fig. 1 andText-fig. 3A)-The shield is gently convex, about 0.35 mm in length (sag.), no
axial and pleural lobes are separable, andChung-Hung Hu

258

the dorsal furrows are indistinct; theaxial region is slightly convex, andmarked by a faint longitudinal furrow;neither marginal spine nor marginal border is observed. The surface is faintly
granulated; the anterior margin is demarked by a pair of distinct pits.
Only a single incomplete specimen is
known of the present stage; it shows nodistinct characteristics, except for a pairof frontal pits on the dorsal surface.
This essentially growth form has been
observed previously in several growthstudies; e. g., Norwoodella halli RESSER(Hu, 1963), Coosella convexa TASCH (Hu,
1968), Flexicalymene granulosa (FoERSTE) and Missisquoia cyclochila (Hu,1971), etc.
Metaprotaspid stage (PI. 28, Figs. 2-7,
and Text-fig. 3B-D)-The shield is roundor rounded oval in outline, convex, about
0.5-0.7 mm in length (sag.), with the axial
and pleural lobes well defined by dorsal
furrows; the axis is narrow fusiform,
tapering both anteriorly and posteriorly
from the mid-line (sag.); the frontal pits
are distinctly demarked, and are locatedbehind of the anterolateral eye-ridges;
the posterior end of the axis is indistinctly delimited by the dorsal furrows,
roundly convex, and does not extend thefull length of the shield; the pleural lobe
is about the same width as the axis,
convex, and sloping downward from thedorsal furrow; it has a rounded margin;
the border furrow is absent. The protaspid librigeno-ro3trum and the hYPoJtoma

Text-fig. 3.

are fused as a single plate; the hypostomal portion is oblong and bears a few
pairs of marginal spines; the medianbody is acute-triangular, conical, tapering
backward, and well delimited by innerfurrows; the posterior lobe is V-shaped,
convex, and without a distinct marginalborder; the librigenal portions are narrow, perrostraloid, and curving posterior
laterally from the anterior hypostomal
wings or rostrum.
The surface of the shield is faintly
granulated, and the ventral side of theshield has three pairs of marginal spines,of which the first pair extends from theanterolateral margin, the second is at the
mid-line of the shield, and the third pairis on the marginal doublure, behind theaxial lobe.
The present stage differs from theearly one in having the axial and thepleural lobes well differentiated by thedorsal furrows.
Paraprotaspid stage (PI. 28, Figs. 8, 9,
11, and Text-fig. 3E, I)-The shield iscomposed of a large cranidium and asmall protopygidium, oval, convex, 0.71.0 mm in length (sag.); the glabella iscylindrical and the fixigenal lobes arewell defined by a dorsal furrow; theglabella is expanded slightly forward,
convex, and without distinct glabeUar
furrows; the occipital ring is convex andwell demarked by a furrow; the anteriorborder is narrow, elevated, and makes
contact with the anterior margin of theglabella; no preglabellar field is known;

Illaenus valvulus RAYMOND.

A, anaprotaspis, Y. 45; E, C, D, dorsal and ventral views of two metaprotaspides, x 30, x 27 ;E, I, two paraprotaspides, x 17; F, N, two early meraspid pygidia, x 12; G, a rostrum, x 2 ;H, J, two early meraspid cranidia, x 18, x 15; K, a "male" pygidium, x 7; L, a late meraspid cranidium, x 14; M, Q, ventral and dorsal views of two" female" pygidia, x 4, x 5;0, a "female" cranidium, x 5; P, a small sized librigena, x5; R, a "female" cranidium,x5; S, a "male" cranidium, x4. (All drawings were made from photographs.)

657.

A

c

13

I

J

K

L

N

o

p

F

H

R

D

G

E

fv(

259

Ontogenies of Mid-Ordovician Trilobites

Q

5

260

Chung-Hung Hu

the frontal pits are shallow and indistinct; the fixigena is convex at the samelevel as the glabella, and wider than theglabella; the narrow elongate palpebral
lobes are well defined by furrow, crescentic, and its wides portion is situatedon the mid-line of the glabella (tr.); theposterior fixigena is broad, convex, andslopes downwardly to the lateral margin;
the narrow posterolateral border is convex, more than twice as wide as theoccipital ring, and faintly delimited by afurrow. The anterior facial suture isconvergent, nearly straight, and the posterior one is slightly divergent-convex.
The protopygidium consists of two to
three segments, convex; the axis is conical tapering posteriorly and divided into
two axial and a terminal portions by distinct ring furrows; the pleural segment
is extended laterally, horizontally, anddeeply separated by intersegmental grooves; the three pairs of marginal spines
are continuously directed posteriorly

Explanation of Plate 27
Figs. 1-36. Mesotaphraspis acris, n. sp.
1. A problematium, showing the spherical ball and rounded internal hollow. x 50, U.C.G.M.
40421.
2. An anaprotaspid shield, showing the elongate and deeply impressed anterior pits. x 50,
U. C. G. M. 40421a.
3-5. Three possible metaprotaspid shields. 3, x 50, U. C. G. M. !!0421b; 4, x 50, U. C. G. M.
40421c; 5, x40, U.C.G.M. 40421d.
10. A paraprotaspid shield, showing the presence of the facial suture and the small
protopygidium. x 32, U. C. G. M. 40421i.
8,9,11,12,26. Four early meraspid cranidia; notice the cylindrical glabella and the palpebral lobes, situated on the mid-line of the cranidium. 8, x 23, U. C. G. M. 40421g; 9,x 23, U. C. G. M. 40421h; 11, x 23, U. C. G. M. 40421j; 12, x 23, U. C. G. M. 40421k; 26,
ventral view of figure 12, showing the hypostoma and librigena in place.
6,7,13. Three late meraspid cranidia, showing the conical glabella and the narrower
posterior fixigena. 6, x 23, U. C. G. M. 40421e; 7, x 16, U. C. G. M. 1042lf; 13, x 15,
U. C. G. M. 404211.
14,19,20. Dorsal view of three holaspid cranidia. 14, paratype, x 16, U. C. G. M. 40421m;
19, paratype, x 15, U. C. G. M. 40421q; 20, holotype, x 12, U. C. G. M. 40421r.
15. Dorsal view of a complete crandium; x 11, U. C. G. M. 40421n.
16. Posterior oblique view of a small pygidium. x 9, U. C. G. M. 404210.
17,18. Two problematic hypostomata, showing the well-preserved marginal spines. 18,
x20, U.C.G.M. 40421p.
21,23,24,31. Dorsal views of four early meraspid pygidia, each associated with two or
three thoracic segments in front of the spiny one. 21, x 20, U. C. G. M. 40421s; 23,x30, U.C.G.M. 40421u; 24, x15, U.C.G.M. 40421v; 31, x10, U.C.G.M. 40421a'.
22,25,32,33. Dorsal views of four late meraspid pygidia; notice one or two rows of granules along the axial lobe. 22, x 10, U. C. G. M. 4042lt; 25, x 10, U. C. G. M. 40421 w; 32,
x 21, U. C. G. M. 40421b'; 33, x 15, U. C. G. M. 40421c'.
27-29. Back and dorsal views of three female pygidia (paratype); notice the depression
at the terminal portion. 27, 28, x 15, U. C. G. M. 40421y; 29, x 15 (specimen missing).
30. A spiny thoracic segment; x 10, U. C. G. M. 40421z.
34-36. Dorsal and posterior views of there male pygidia, a row of granules along theaxis. 34, x 10, U. C. G. M. 40'121d'; 35, 36, para type, x 10, U. C. G. M. 40421e'.

Hu:

Ontogenies of Mid -Ot'dovician tt'ilobites

Plate 27

657.

Ontogenies of Mid-Ordovician Trilobitesfrom the pleural segments; there are
fiat, and shallowly depressed part aroundthe inner margin; the skeletal surface iscovered by faint granules.
Early meraspid stage (PI. 28, Figs. 10,
12, 13, 23, 31 and Text-fig. 3F, H, j, N)The cranidium is trapezoidal in outline,
convex, about 0.8-1.0 mm long (sag.); theforwardly expanded glabella is deeply
delimited by dorsal furrows; it is convex,
and indistinctly demarked by glabellar
fUrrows; the occipital ring is convex,
and separated by a deep occipital furrow;the narrow anterior border is elevated,
up-turned from the frontal furrow; it ishorizontal and straight. The fixigena isstrongly convex, elevated to about thesame level as the glabella; encompassedby the palpebral and the posterior fixigenal furrow; the palpebral lobe is narrow, elongate, and elevated from thepalpebral furrow; its anterior end iscontinuous with the ocular ridge, andends at the posterolateral margin of theanterior glabella; the posterior fixigena
is about twice as wide as the occipitalring, with the posterior border well delimited by a broad border furrow; theanterior fixigenal area is concave, andturned upward along the lateral freemargin and the anterior border. The
pygidium is semicircular in outline, convex, and consists of more than sevensegments; the axis is conical, tapering
posteriorly, and slender; the terminal
portion slopes downward; the pleurallobe is more than twice as wide as theaxis, convex below the axis, and slopes
downward along the margin; each of thepleural segments ends in a pair of flat
pleural spines, which are de ric ted posterolaterally or posteriorly, surrounding
the terminal portion. The surface of theskeleton is covered by fine and coarse
granules; the latter are fairly marked on
the glabella and the fixigenae.

261

The present stage is characterized by
the narrow palpebral lobes situatedbehind of the mid-line of the cranidium(tr.), the narrower fixigena, and thecoarser granules. The pygidium increases in the number of the segments.
Late meraspid stage (PI. 28, Figs. 17, 18,
24-26, 30, 32, 33, 35, 38 and Text-fig. 3L,0, P)- The cranidium is nearly of a regular trapezoidal outline, convex, about
1.2-1.5 mm in length (sag.); the glabella
is strongly expanded forward, convex,
delimided by an indistinct dorsal furrow,except these adjacent to the occipital;
glabellar furrows are unknown; the narrow occipital ring is faintly delimited bya ring furrow; it is convex and arches
posteriorly; the anterior margin makes afaint, elevated and horizontal ridge; thefixigena is broad at the palpebral lobes,
convex, and faintly delimited by thepalpebral furrow; the posterior fixigena
constitutes the fixigenal border, which
is vertical to its lateral end locatedunderneath the palpebral lobe; the anterior fixigena is broad and concave.
The librigena is trapezoidal, convex,
and without lateral border or the borderfurrow; the ocular platform is broad,with the ocular ring situated at the posterior margin; the genal spine is shortand stout, and extends posterolaterally
from the lateral margin.
The pygidium is semicircular in outline,
convex, without a distinct dorsal furrow;the anterior margin of the pygidium isassociated with one or few segments.
The specimens of the present stage
might be segregated into two morphologic groups: The first group (PI. 28,
Figs. 25, 26, 30, 32, 33) having less convex
cranidium, forwardly situated palpebral
lobes, well defined fixigenal border,
arched anterior margin, and a semicircular pygidium; the second (PI. 28,
Figs. 31, 35, 39, 40) has a highly convex

262

Chung-Hung Hu

cranidium, posteriorly located palpebral
lobes, incompletely developed posterior
fixigenal border, and a sub trapezoidal
pygidium. These differences within thesame species population are interpreted
as sexual differences as indicated above.
Figured specimens - Anaprotaspis,
U.C.G.M. 40418; metaprotaspides, U.C.G.M.
40418a-d; paraprotaspides, U. C. G. M.
40418e-h; early meraspides, U. C. G. M.

40418i-m,y,z,b'; late meraspides, U.C.G.M.
40418n, i'.
References
BEECHER, C. E. (1895): The larval stages oftrilobites. Am. Ceol., vol. 16, p. 166-197,
pI. 8-10.
COOPER, B. N. (1953): Trilobites from theLower Champlainian formation of the

Explanation of Plate 28
Figs. 1-40. Illaenus valvulus RAYMOND
1. Dorsal view of a broken anaprotaspid shield; notice the undifferentiated axial andpleural lobes. x 45, U. C. G. M. 40418.
2-7. Dorsal and ventral views of a few metaprotaspid shields; notice the three pairs ofmarginal spines and librigenorostrum. 2, x 30, U. C. G. M. 40418a; 3, x 30, U. C. G. M.
40418b; 4,5, x 27, U. C. G. M. 40418c; 6,7, x 27, U. C. G. M. 40418d.
8,9,11. Dorsal views of three paraprotaspid shields; notice the appearence of the protopygidium. 8, x20, U.C.G.M. 40418e; 9, x17, U.C.G.M. 40418f; 11, x17, U.C.G.M.
40418h.
10,12,13-16. Dorsal views of six nearly complete early meraspid cranidia, showing thedeep dorsal furrow and the anterior glabellar expanding. 10, x 18, U. C. G. M. 40418g;
12, x18, U.C.G.M. 40 '1l8i; 13, x18, U.C.G.M. 40418j; 14, x17, U.C.G.M. 40418k; 15,x17, U.C.G.M. 404181; 16, x15, U.C.G.M. 40418m.
17,38. Dorsal views of two male forms of the late meraspid cranidia; notice the shallow
dorsal furrow and the broad anterior glabella. x 14, U. C. G. M. 40418n; x 14, U. C. G. M.
40418i'.
18,19. Ventral views of immature and mature librigenae; notice the doublure and theabsence of the librigenal spine. x 5, U. C. G. M. 404180; x 5, U. C. G. M. 40418p.
20,21. Oblique and dorsal views of two thoracic segments. x 4, U. C. G. M. 40418q; x 7,
U. C. G. M. 40418r.
23. A rostrum. x 3, U. C. G. M. 40418t.
22,24. Dorsal view of mature and immature librigenae; notice the absence of the librignal spine. x 5, U. C. G. M. 40418s; x 14, U. C. G. M. 40418u.
25,26. Dorsal view of two female forms of the late meraspid cranidia. x 14, U. C. G. M.
40418v; x 14, U. C. G. M. 40418w.
27. Dorsal view of a nearly complete female crandium. x 5, U. C. G. M. 40418x.
28,29,31. Three early meraspid pygidia. 28, x 12, U. C. G. M. 40418y; 29, x 20, U. C. G. M.
40418z; 31, x12, U.C.G.M. 40418b'.
30,33. Two female forms of the late meraspid pygidia. x 10, U. C. G. M. 40418'a; x 10,
U. C. G. M. 40418d'.
32,34,37. Dorsal and ventral views of three female pygidia. 32, x 7, U. C. G. M. 40418c';
34, x 4, U. C. G. M. 40418e'; 37, x 5.5, U. C. G. M. 40418h'.
35,36. Dorsal views of a small and a large sized pygidia. x 10, U. C. G. M. 40418f'; x 7,
U.C.G.M.40418g'.
39,40. Dorsal view of two male cranidia; notice the punctuated surface. x 10, U. C. G. M.
40418j'; x4, U.C.G.M. 40418k'.

Hu.'

Ontogenies of Mid-01"dovician t1"ilobites

Plate 28

657. Ontogenies of Mid-Ordovician Trilobites
Appalachian VaHey. Ceol. Soc. America,
Mem. 55, 66p., pis. 1-19, 2 text-figs., 1
table.
Hu, C. H. (1963): The dimorphism and ontogeny of Norwoodella halli RESSER. Trans.
Proc. Palaeont. Soc. japan, .. N. S., no. 52,
p. 129-132, pI. 19.
- - (1964): The ontogeny and dimorphismof Welleraspis lata HOWELL (Trilobita).
jour. Paleont., vol. 38, no. 1, p. 95-97,
pI. 24.
- - (1968): Notes on the ontogeny anddimorphism of Upper Cambrian trilobitesof the Welleraspis faunule from Pennsylvania. jour. Nanyang Univ., vol. 2, p. 321357,. 4 pis., 8 text-figs.
- - (1971): Ontogenies and sexual dimorphism of Lower Paleozoic Trilobita.
Palaeontogr. Americana, vol. 7, no. 44,
p. 31-125, pis. 8-26, 58 text-figs.
- - (1974a): O.ntogenies of . two Middle
Ordovician trilobites from the Edinburg
formation, Virginia. Trans. Proc. Palaeont. Soc. japan, N. S., no. 95, p. 353-363,
pis. 48, 49.
- - (l974b): Ontogenies of a few Middle

263

Ordovician trilobites from the Edinburg
formation of Virginia, U. S. A. Bull. Ceol.
Surv. Taiwan, no. 24, p. 51-67, 4 pis., 6
text-figs.
- - (1975a): Ontogenies of two species ofsilicified trilobites from Middle Ordovician, Virginia. Trans. Proc. Palaeont_Soc. japan, N. S., no. 96, p. 32-47, pis. 24, 3 text-figs.
- - (1975b): Ontogenies of four species ofsilicified Middle Ordovician trilobitesfrom Virginia. Proc. Ceol. Soc. China,
no. 18, p. 115-127, 2 pis., 4 text-figs.
MOORE, R. et al. ed. (1951): Treatise on
Invertebrate Paleontology, Part 0, Arthropoda 1. Ceol. Soc. America & Univ. Kansas, 541p., 415 text-figs.
RAYMOND, P.E. (1925): Some trilobites of
the Lower Middle Ordovician of eastern
North America. Mus. Compo Zool. Bull.,vol. LXVII, no. 1, 180p., pis. 1-10.
WHITTINGTON, H. B. and EVITT, W. P. (1953) :Silicified Middle Ordovician trilobites.
Ceol. Soc. America, Mem. 59, 135p., 27
text-figs., 2 tables.

Trans. Proc. Palaeont. Soc. Japan, N. S., No. 101, pp. 264-270, pI. 29, April 30, 1976

658. DISTRIBUTION AND BIOSTRATIGRAPHIC SIGNIFICANCE
OFDICTYOCHA SUBARCTIOS (SILICOFLAGELLATE)
IN THE NORTH PACIFIC*
HSIN YI LING
Department of Oceanography, University of Washington,
Seattle, Washington 98195

Dictyocha subarctios (l!~Ul=€ID ll)~t:;t3jZi$wJ101U.¥!.J.:pt:'lJHt 7.>1t!!WB9~t:.:11!!.f;{B".J~*t:..t IJ .:pflB~t:;t3jZi$Il).:p~Jl!:m!tfijJ1i;Ji.¥!.J.J: IJ ~tl:l ~.nt.: Dictyocha subarctios(l!f;{.=€I!) t:.¥t-c1jlf~~kiI&H"td6!l:, Jitll)fiIIlt-,,- !J :/ !l'~, S*tfij~~tr.:p, iliIi~Jl!:1t!!~1l):3t~t:;t3jZi$tfijJ1i;t:'Il)~JA O!tl:l~.n, m~1l) Distephanus octangulatus 1l)~;fpt:.ft!.-c~,7.>.iJ~~JjfjJn... t.:o -t L -C*fiIIll)1t!!f;{B".Jtl:lmlt~~-:lI'!~titll)~W, llPt> Matuyama ~r~liM.:pIl) Olduvai !ll!JtIl-e Eucyrtidium matuyamai (:Q!(IIX;g) c 9ft cTiij~-e~ 7.>0 ~ L -C -t1l)~iJiJG
It Brunhes lEJatli:Jtllc Matuyama ~Jat~JtIlIl)~W.J: IJ It*<, 0.6-0.65 m. y. cll:iE~.n
7.>0 JitQ)*5!l:, fl!t~t:;t3jZi$1t!!~?Jla:. S*Il):lI'!~tit!f.JtIlgll;1t-t.nt:.%t.lt~.n7.>1t!!}j.:p, * L < It
1977~t:'7:iE~.n7.>~~m!tfijWlf!jm@j (IPOD).:p, :;t;J<- ')I ?tfij.J: IJ Kuril Arc t:'iJ'H"-CQ)~;fp:

mi!tfijIIfJi.¥!.J.:pt:'*filliJ'~tl:l~.n7.>': b'];Tll!tl~.n7.>o

**

-ta-

Project (DSDP). Since then the biostratigraphic utility of this once neglectedgroup for both deep-sea sediments andland based sections has received ample
demonstration from various parts of theworld, paticularly in the middle to highlatitude region of both hemispheres.
A silicoflagellate species, Dietyaeha subaretias, was proposed by the present
author because of its ubiquitous limited{)ccurrences in both time and space in
the Central North Pacific sediments.
In this paper the author further discusses its distribution based on the observations from deep-sea sediments of theentire North Pacific together with resultsof magnetic measurements and radiolarian and diatom analyses undertaken
for some of the cores.

Introdutory note
The unexpected discovery of abundant
Late Cenozoic silicoflagellate and ebridianskeletons from middle latitude deep-sea(piston) core sediments in the Central
North Pacific (LING, 1970) led the present
author to continuously investigate biostratigraphic occurrence of the group ofsiliceous microfossils mainly from themarine deposits. Two years later (LING,
1972) initial documentation of the geological distribution of these microfossils
since Late Cretaceous time, based on
samples mainly from deep-sea sediments,
was completed. Material studied included
the experimental Mohole drilling and thefirst three Legs of the Deep Sea Drilling* Received Dec. 25, 1975; read Jan. 30,
1976 at Narugo.

264658. Distribution and Biostratigraphy of Dictyocha subarctios
Material sources

Besides the previously reported North
Pacific cores collected by the R/V THOMAS G. THOMPSON cruises 28 and 49(abbreviated as TT 28, 49), the occurrence of the present species was alreadyreported from deep-sea sediments recovered during the Legs XIX (Sites 183193) and XXI (Sites 299-302) of the DSDP
(Ling, 1973, 1975). In addition, the following core sediments also contained thespecies:Core

Latitude(North)Longitude

Water depth(in m)

TT 3-847°07.1'
39°57.71'
56°57.38'
36°26.0'132°12.2'W125°27. 12'W
147°07. 86'W
178°38.2'E

3,U6
2,927
4,218
3,902

DSDP Site 173
DSDP Site 178
ARIES 49 G

Data

Geographic distribution-Sedimentcores in which Dictyocha subarctios wasobserved are shown in Text-fig. 1. It isreadily apparent that its geographic distribution covers the entire North Pacific
Ocean and its marginal seas including theBering and Japan, but is limited to the
middle to higher latitude region only. Its
southern limit can be drawn approximately at the so-called "subarctic boundary"of the area (DODIMEAD et ai., 1936). A
similar distributional pattern has been
observed from surface sediments for amodern species, Distephanus octangulatus
in the area (Text-fig. 2), inferring that
this extinct species thrived under a similar physicochemical environment as its
modern counterpart of the area. Because
the occurrence of modern Distephanus
octangulatus extends to the Sea of Okhotsk (LING, 1974), it will not be a surprisethat Dictyocha subarctios may be encountered in the sediments of the Okhotsk Sea when the D/V GLOMAR CHALLENGER drills the area in 1977 during
the International Phase of Ocean Drilling(IPOD) of the Deep Sea Drilling Project.
Geologic ranges-Among the previously
studied piston cores from the Central

265

North Pacific, the initial appearance ofDictyocha subarctios was observed onlyin the TT 28-24 and TT 49-4 sediments.
The magnetic reversal history of the corerecognized by KINOSHITA, HENSHAW and
MERRILL extends downward to below thesecond normal event within the reversed
epoch. Radiolarians recognized for thecore sediments (PI. 29, Text-fig. 3) agreewith the above interpretation in that evolutional appearance of Eucyrtidium matuyamai was observed. From the sediments
collected during the two DSDP legs, theinitial appearance of the species wasalways at or slightly after the Plio-Pleistocene boundary drawn by diatom analysis (KorZUMI, 1973, 1975).
The upward extinction of Dctyocha
subarctios has been observed, on thecontrary, in numerous cored sediments(see LING, 1970, text-fig. 4). The paleomagnetic analysis of the TT-cores indicates that this extinction level falls
slightly above the Brunhes Normal andMatuyama Reversed epoch boundary. If
the figure of .69 m. y. for this polarity
boundary is accepted (Cox, 1969), theage of the extinction of Dictyocha subarctios falls within .60-.65 m. y. (Text-fig.
4). In constructing this figure, the assumption has been made that the sed i-Hsin Yi LING

266
1500 E

180 0

150 0 W

1200

90 0

6N~'-------~~~~7T~---'r-----~~7n~~~-----'---~7.~:----~'---'

/)

\~
450

USA

o
o

o
OO~~L---------~------------~~--~~~~~--~~~

1500 E1800__---L-------------L--~O°

150 0 W

90·

1200

Text-fig. 1. Occurrence of Dictyocha subarctios (filled symbols) from deep sea sedimentsof the North Pacific Ocean and its marginal seas (data from LING, 1970, 1973, 1975, unpublished data). Symbols for core location; D, /:::,., LI:--', R/V THOMAS G. THOMPSON cruise,
3, 28, 49 respectively; 0, ARIES expedition (Scripps) ; 0, Deep Sea Drilling Project. Double
symbol indicates cores in which the first appearance of the species was also observed. Occurrences of Mesocena cf. elliptica recognized in the sediment cores are shown by diagonal lines
over the core location (data from JousE and MUKHINA, 1973, LING, unpublished data).
150·E

180 0

150 0 W120·

90·

6o·r-------~~~~~rr~----r------=~~~~_q~------r_--~----_r_r--_,60

fr

N

450

USA

N

J/

"

45·

o
o

o
o

00

o

OO ..~L---------~------------~------------~--~~~-----L------------_L__~O°1500 E

180 0

150·W

1200

90·

Text-fig. 2. Distribution of Distephanus octangulatus (filled symbols) from deep sea
sediments of the North Pacific Ocean and its marginal seas (data from LING, 1970, 1973,
1974, 1975, unpublished data). For symbols for core locations, see Text-fig. 1.

658. Distribution and Biostratigraphy of Dictyocha subarctios
TT 28-24a:

267

TT49-4

200

200

250

250

m
300

300

<I

::<

350
...J
...J
<I-

400

::<
::<<l

a:

..,

<l<l

>-

450

:::>

500

:::>

::<~

:::>

0

...J

400

f-

<l
::<

f-

<l_

350

<I

>-

0

450
~
>
:::>

500

...J

550

0

550

0

600

600

0

650

en
en

:::>
<l

700

'"
Text.fig. 3. Distribution of silicoflagellates and radiolarians in the TT 28-24
and TT 49-4 sediment cores. Taxonomy of microfossils are according to HAYS
(1970) and LING (1970).

mentation rate has been constant withineach core sediment at least for the last
.70m.y.
To test the above, the extinction levelof a radiolarian species, Stylatractus universus HAYS, is plotted in the figure. It
falls approximately at .40-.43 m. y., thus
is in good agreement with the observation from the North Pacific by HAYS
(1970). At the same time, the extinctionlevel of a diatom species, Nitzchia reinholdii KANA Y A, could be defined more
precisely should more samples from thesesediment cores be examined closely for
their diatom microflora.
The significance of this Dictyocha subarctios extinction level is further enhanced when it· is recognized that thisis the same level where another silicoflagellate species, Mesocena d. elliptica
becomes extinct in some cores.
As already discussed in detail, theQuaternary occurrence of Mesocena d.
elliptica has been restricted in the middle
to low latitude areas (JOUSE and MUKHINA, 1973; LING, 1970, unpublished data)Hsin Yi LING

268
500

C
B

400

~

~

A

t

E 300
u

:r:
I0...

w 200
0

100

00

0.7

Text-fig. 4. Time versus depth plots within Eruhnes Normal Epoch for sediment cores from the North Pacific. The heavy black bar represents the limits,within the extinction level of A, Stylatractus universus (radiolarian); E, Nitzchia
reinholdii (diatom) (KOIZUMI, unpublished data) ; and C, Dictyocha subarctios (silico. iflagellate) falls.

(see Text-fig. 1), therefore its extinction
with Dictyocha· subarctios in the middle
latitude region serves as the bridge between the low and high latitudes of theNorth Pacific during the Pleistocene interval.
The above conclusion regarding thegeologic range of Dictyocha subarctios
would then lead to the following discussion. In hoping to establish nannoplankton stratigraphy of Japan, UCHlO (1974)
examined a series of outcrop samples
from the Sado Island in Niigata Prefecture of Honshu, Japan for silicoflagellate
and coccolith assemblages, and reported
the occurrence of specimens similar, if
not identical, to the present species as
Dictyocha fibula var. subarctios (LING)
from the Pliocene Kawachi Formation,
the lower part of the Sawane Formation(his samples nos. 48 and 56). To date
this constitutes the only record for the

species from the land outcrops throughout the Circum-North Pacific region.
It is important to note here that inthese two samples, UCHlO also recognizedother silicoflagellate species includingDistephanus crux, Corbisema triacantha
whose last geologic appearances havebeen limited to the Miocene age. Therefore, re-examination of samples from the
Sado Island for silicoflagellates together
with similar studies for other groups ofco-occurring microfossils will be necessary in order to ascertain the occurrenceof this species from the Sado Island.
Conclusion
1. Dictyocha subarctios is a silicoflagellate species, distributed widely in the
middle to high latitude regions of theentire North Pacific and its marginal seas.
Comparison of its distribution with that

658.

Distribution and Biostratigraphy of Dictyocha subarctiosof the modern silicoflagellate species,
Distephanus octanguiatus, suggests that
it will be encountered in the s'edimentsof the Sea of Okhotks during IPOD drilling in 1977.
2. The geologic range of Dictyocha
subarctios has been discussed. Its initial
appearance generally corresponds withthat of a radiolarian Eucyrtidium matuyamai approximately at Plio-Pleistocene
boundary or Olduvai event of the Matuyama Reversal Epoch, while its extinction
occurs at about .60-.65 m. y., which falls
slightly above Brunhes Normal and Matuyama Reversal epoch boundary.
3. Finally, the present species has notbeen found inland of the Circum-North
Pacific Ocean, except for the Sado Island,but its reported occurrence there deserves further clarification. Judging fromaccompanying microfossils, particularly
radiolarians and diatoms, it is highly
probable that it can be found in the
Pleistocene deposits of Japan.

Acknowledgements

The author is indebted to Hajimu KINOSHITA of Tokyo University, Paul C. HENSHAW, and Ronald T. MERRILL of the University of Washington for their magnetic
measurements of sediment cores, and to
Itaru KOIZUMI of Osaka University forproviding his unpublished data of diatom
analysis. Samples taken by the R/V
THOMAS G. THOMPSON were collected
through the cooperation of the crews andscientists of the U ni versity of Washington
under the financial support of the Officeof Naval Research. Participation on thetwo cruises aboard the D/V GLOMAR
CHALLENGER were made possible by
the Deep Sea Drilling Project under thefinancial support of the National Science
Foundation. The present author's re-

2B9search has been supported by grants fromthe National Science Foundation, and themanuscript is completed under grant
DES 73-00489 AI (formerly GA 40 142 X).
Thii"'is contribution No. 897 of the
Department of Oceanography, Universityof Washington.
References
Cox, A. (1969):
Geomagnetic reversals.
Science, vol. 163, no. 3854, p. 237-245.
DODIMEAD, A. J., FAVORITE, F. and HIRANO,
T. (1963): Review of oceanography ofthe subarctic Pacific Region. Internal.
North Pacific Fish. Comm. Bull., no. 13,
195 pp.
HA YS, ]. D. (1970): Stratigraphy and evolutionary trends of Radiolaria in North
Pacific deep-sea sediments. In: HAYS,]. D. (ed.) "Geological investigations of
the North Pacific ", Ceol. Soc. Amer.,
AIem. 126, p. 185-218.
JousE, A. P. and MUKHINA, V. V. (1973): The
AI ecocena elliptica EHR. Zone in the Pleistocene sediments of the Pacific. Okeanologia, vol. 13, no. 3, p. 467-475.
KOIZU:'vII, 1. (1973): The Late Cenozoic diatoms of Sites 183-193, Leg 19 Deep Sea
Drilling Project. In: CREAGER, J.S.,SCHOLL, D. W. et al., Initial reports of
the Deep Sea Drilling Project, vol. 19,
Washington (U. S. Government Printing
Office), p. 805-855.
- - (1975): Neogene diatoms from the western margin of the Pacific Ocean, Leg 31,
Deep Sea Drilling Project. In: KARIG,
D. E., INGLE, J. C. Jr. et. al., Ibid., vol.
31, p. 779-819.
LING, H. Y. (1970): Silicoflagellates from
central North Pacific core sediments.
BUll. Amer. Paleont., vol. 58, no. 259, p.
85-129.
- - (1972): Upper Cretaceous and Cenozoic
silicoflagellates and ebridians. Ibid., vol.
61, no. 273, p. 135-229.
- - (1973): Silicoflagellates and ebridiansfrom Leg 19. In: CREAGER, ].S., SCHOLL,
D. W. et al., Initial reports of the Deep

270

Hsin Yi LING

Sea Drilling Project, vol. 19, Washington(U.S. Government Printing Office), p.
751-775.
- - (1974): Polycystine Radiolaria andsilicoflagellates from surface sedimentsof the Sea of Okhotsk. Geol. Surv. Taiwan, Bull., no. 24, p. 1-11.
- - (1975): Silicoflagellates and ebridiansfrom Leg 31. In: KARIG, D. E., INGLE,
J. C. Jr., et al., Initial reports of the

Deep Sea Drilling Project, vol. 31, Washington (U.S. Government Printing Office),
p. 763-777.
UeHIo, T. (1974): Tertiary nannoplankton
stratigraphy of Sado Island, Niigata Prefecture, and a proposal of the Braarudosphaera bigelowi - Coccolithus pelagicus
Zone for the Pliocene of Japanese oilfields of Japan Sea side. Geol. Surv.
Japan, Report, No. 250-1, p. 235-254.

Explanation of Plate 29
Fig. 1. Dictyocha fibula EHRENBERG TT 49-3 PC, 80-38 cm, R-2 (C46/0), x 500.
Fig. 2. Dictyocha fibula var. aculeata EHRENBERG TT 49-4 PC, 340-343 cm, L-2 (U49/2), x 500.
Figs. 3, 4. Dictyocha subarctios LING TT 49-4 PC, 340-343 cm, L-2 (Y32/4), x 500. Different
focus level.
Fig. 5. Distephanus speculum EHRENBERG TT 49-22 AC, 0-3 cm, L-2 (T23/0), x 500.
Figs. 6, 7. Distephanus octangulatus WAILES TT 49-21 PC, 30-33 cm, L-2 (N13/3), x 500.
Different focus level.
Fig. 8. Mesocena ct. elliptica EHRENBERG TT 49-2 PC, 50-53 cm, L-2 (Z13/2), x 500.
Fig. 9. Mesocena ct. elliptica EHRENBERG TT 49-3 PC, 130-133 cm, L-2 (X12/1), x 500.
Figs. 10, 11. Druppatractus acquilonius HAYS TT 3-8 GC, 224-227 cm, R-1 (X34/4), x 200.
Figs. 12, 13. Stylatractus universus HAYS TT 49-4 PC, 340-343 cm, R-2 (S31/2), x 200.
Figs. 14, 15. Eucyrtidium matuyamai HAYS TT 49-4 PC, 482-485 cm, R-1 (H16/3), x 200.

L I NG :Distribution of Dictyocha subarctios

Plat e 29

3

2
I

4

9

8
7
14

10

12

15

II

13

Trans. Proc. Palaeont. Soc. Japan, N. S., No. 101, pp. 271-290, April 30, 1976

659.

THORIUM AND PROT ACTINIUM ISOTOPES IN SOMEPRESENT-DAY HERMATYPIC CORALS AND
THEIR IMPLICATIONS TO DATING'
AKIO OMURA

Department of Earth Sciences, Faculty of Science, Kanazawa Universitym~~.~~~~~~~Y~A~~~~P~7'~=~A~&~~kh0~.~~~~~~~;[11l1E~pillljlt.l> 0 New Britain ~icl.J,vt-e ~:;tft$fJ.§~'il!Iiqa? 9 :l1!!.J!i!(~~Jtt~.~~~ :,..~,

U ·Th ~ ~~ Pa ~&~mst~ U ~7t;{fl~:i:iC"'?\',-e~WU.:o k~f:I'i:!~!':' li~!v
Pa ~&~I.J~~I±l~ht,.:o it,.:, i¥ifJ.§im~iliHt:.:fi~M~
Ica, ~:l1!!.J!i!(~m~~M ~~:§l~~ 232Th 1.J~1Hh -e\',~ ~ ~I.J' 0, '.Jrts:. <~ t i¥ifJ.§im~i£:{t:.
:fi~ ~ ::{I.J' 0 230Th ~ Hf 231Pa :ti:lcM.%~*1>b ~~irlcft, fJJ~(l'~ts:. 230Th ~ 231Pa :I:~
Ji!,1'.I!t1), fmIE.%~*I>b~~,~I.J~~~o ~0iC, 71 "'c/3~' ~7",'i*'"(·Wl.~~ht,.: U~;'F:M:J-7t;{fllt, 238U :I:~'il!I7ti¥Jt,dH~J\i* 30% ic;iiL, 238U J\i§7'il!1~J\i:Y''il!IF,,''"(·Ji!,I.J'vt~
230Th· 231 Pa .%~ tic, H~~£tJl:~£~~f~JJjUZSlicts:. ~ liJfi§~ t~~o Ji!,1.J'vt~ 230Th.%flli!:~fmmt, m~flIl~ 230Thj232Th :ti:l(jftfi§.ltt.J~ 1.4-3.0 ~~! 0htdlilJIIliCA ~ ~ ~I.J' 0,{t:.:fi~M~~ 232Th :l:1.J~* i hli, i!IiCJi¥JicltliJfi§'"('~ ~o ~ ~ 01.J~, 4'@l~ 0hUI'I&flIl~
230Thj232Th .lt1.J~, ~.IJ!,J!i!(~$7.K~~.It~ I), Ji!,1.J'vt l:\,' 7tii1ii\"~j:1Kl±§ Lts:.vthlits:.0ts:.
c'~~M-C-il!U~liJfi§:I:~ Th ~ ~~<\"0~~~ ~vt, ~~M~7ttJT~ht,.:'il!I&I.J~~.-~-t-.tJJiiJic~st~ht,.:'il!I7t-C-~~t,.:l>b,~:lSfl*~llifi'"('vC@:t1Z~mt~flIl-C-~~ 234U 1.J'0st*Lt,.: 230Th I.J~, 1'f:m7tt£,~~~ 230Th/
232Th .It~, Ji!,1.J'vt l:l1!*~-ltt,.:t,.:1>b ~IDtI!J3 ~h~o *6JjiJ, {t:.:fi~ ~ ::{~Ji!,I.J'vt~ 230Th.%~flfiIEvcffl\"~fJJM 230Thj232Th .It~ L-e, ~Mi£:I±l:l1!!.fji!I~$7.K~ 230Thj232Th .It~ffl\"~$I.J~, t-:> ~ t:ii!li-j;1Jts:.:1Ji*~\"*-~o ;ij>:'1'imu'"(U, i¥ifJ.§im~{t:.:fi~~ :iK, ~ilffff~~~~1!@
Z~~i"dJ¥:7.K~ 230Thj232Th .It~f:M:JJm (1.4) ~fJJM 230Thj232Th .It ~ L -em\", fftiIE 230Th.%~*I>bf,.:C~0, 5.fJ§~ts:.\"{lli!:~~~~~I.J~I±l*t,.:o
H I!J3 U$*

KONISHI et al., 1970, 1974). Yet there is
still a room to reexamine rigorously thereliability of 230Th and 231Pa dates ofhermatypic corals, which are accepted as
the most favorable sample lacking thepostmortem enrichment of secondary
uranium like in molluscan shells.
There appears to be two ways thatfossil corals give uncertain 230Th and231Pa dates. The one is presence of the"initial 23°Th and 23lPa ", which were uptaken into the hard tissues together withuranium during fossils' lifetime. The
premise to produce 230Th and 231Pa coralages is the sample in which these daugh-

Introduction
Both the deficient 23°Th and 231Pa
methods allow to extend the radiometric
Pleistocene time scale back to about
250,000 years, and have greatly contributed to solve the Quaternary problems
such as fluctuation of sea-level and tectonic movement (e. g. BROECKER et al.,
1968; MESOLELLA et al., 1969; JAMES etai., 1971; STEINEN et al., 1973; VEEH and
CHAPPELL, 1970; CHAPPELL, 1974a, 1974b;* Received Feb. 2, 1976; read Jan. 17, 1973
at Sendai.

271

Akio OMURA

272

ters are initially free. From fossil sample
with the initial daughters. therefore, theprecise death time of the coral cannot
be estimated without a reasonable correction. Any uncorrected dates are regarded as the maximum ages.
Secondly, if the initial thorium andprotactinium are distributed in no relation with uranium like at the two structural layers of molluscan shells (OMURA
et al., 1973), the heterogeneities in uranium distribution can complicate the picture to secure the reliable dating.
The purpose of this study is to makea close investigation on the amount ofthorium and protactinium isotopes andthe uranium distribution in presen~-dayhermatypic corals as a basis to understand the extent of potential uncertaintyof the observed 230Th and 231Pa dates
from fossil corals. The analytical resultof the present-day samples can be adirect estimate the undecayed amount of
the initial daughters in fossil counterparts grown at the same geographic location, and also can provide the method
to correct the apparent 230Th and 231Pa
coral dates. If the uranium concentration
in a corallum systematically changes,
furthermore, the intraskeletal varia tionof the apparent age obtained may be
critically evaluated.

Materials studied
All samples listed in Table 1 are hermatypic corals accompanied by symbiotic
zooxanthellae, and most of them werecollected alive in order to eliminate any
possible postmortem alteration. They
were collected from nine locations which
extended from Shikoku (Southwest Japan)
to New Britain Island along the westernpart of the Pacific Ocean. These samples are designated CAM-I, CYM-l,
CTM-l, CNM-l and so on, where" C ",indicates "coral"; "A ", "Amami-oshima"; "Y", "Yoron-jima"; "T" "Taiwan (Formosa)"; "N ", "New Britain
Island"; and "M ", "modern (presentday) ", respectively.
The sea-water samples are coastal
water collected from the locations without any distinct influx of land drainage.
These samples, however, may not necessarily represent the life-long environment
in which the sampled corals grew, because of the possible seasonal variation
in local mixing. WY -1 and WY -2 werecollected at Chichibina-banare (128°24.2'E,
27°02.8'N) and south of Akazaki (128°27.3'E, 27"01.1'N), Yo ron- jima, respectively; WTk-l, ~t Hedono (128°53.5'E,
27" 48.4'N), T okuno-shima.

Experiments

Sample preparation Due to low concentration in sea-water, the analysis ofuranium and thorium isotopes requires alarge amount of sample water; 201 ofsample water was used for the analysis
of uranium and 3601 for thorium, respectively. After filtered through a cotton gauze in field, suspensions coarser
than 0.54 f.l in diameter were excluded
with a millipore filter.
Carbonate samples for isotopic analysis
by a-spectrometry were prepared by thesame manner as OMURA et al. (1973).
The sample for the fission track analysis was prepared separately depending
upon the growth form of the corallumcolony, whether branching or massive.
The massive colonial sample (CEM-l)
was first embedded in an epoxy resin
under vacuum. After solidifying of resin,
the sample was trimmed to specific orientation and smoothened the surface bycarborundum and chromium oxide powder on polished wheel. And then, it wasgiven similar treatment as tridacnid

659.

Thorium and Protactinium Isotopes in Corals
Table 1.

List of the present-day coral samples.

SampleGenus

CSM-l*
CSM-2*

Leptoria
Favia

CCM-l··
CCM-2**

Favia
Acropora

Kominato, Chichi-jima, Ogasawara Islands
Drift on beach, Okumura, Chichi-jimajul., 1969
jul., 1969

CHM-l**

Pocillopora

Oki-ko, Haha-jima, Ogasawara Islands

jul., 1969

CAM-I··

Goniastrea

Dead sample, Saneku, Amami-o-shima,
Ryukyu Islands

Aug., 1968

CEM-l
CEM-2
CEM-3
CEM-4
CEM-5
CEM-6
CEM-7
CEM-8
CEM-9

Favia
] Kunigami-misaki, Okierabu-jima,
Ryukyu Islands
PoritesWanjo-hama, Okierabu-jima
Favites
Okidomari, Okierabu-jima
Acropora
Wadomari, Okierabu-jima
Goniastrea
Psammocora
Acropora] Shim.h,m" Okimb,·jim,
Acropora
Stylophora

CYM-l
CYM-2
CYM-3
CYM-4
CYM-5
CYM-6
CYM-7
CYM-8

Acropora
Acropora
Goniastrea
Acropora
Montipora
Porites
Goniastrea
Acropora

COM-l*

Hydnophora

CTM-l*·* Turbinaria
CNM-l·
CNM-2*
CNM-3*

Acropora
Acropora
Pocill opora

Location] Drift on beach, Muroto-misaki, Shikoku

]N

273

of Chabana, Yoron- jima, Ryukyu Islands

1

Cpllection date
May 29, 1969

Mar. 28, 1968
Mar. 27, 1968
Mar. 24, 1968
Aug. 23, 1967

Aug. 24, 1967

Mar. 31, 1968

E. of Ak,."ki, Yowo·jim,

Apr. 1, 1969

SW. coast of Kudaka-jima, Ryukyu Islands

Sept. 4, 1960

Suoa, Taiwan (Formosa)

Date unknown] R,b,ul. N,w a,imio [,loudFeb. 26, 1971

* collected by Dr. Kenji KONISHI, Depart. Earth Sci., Fac. Sci., Kanazawa Univ.
** collected by Dr. Yasehide hYASAKI, Geological Institute, University of Tokyo.
*** collected by Dr. T. Y. H. MA of National Taiwan University.

sample (OMURA et aI., 1973).
The branching colony as CYM-8 sample was ground carefully with a file, after
cleaning throughly. The powdered sample prepared was homogenized for grainsize, with sieving between 200 to 250
mesh (74 to 62 f-l) screens. The sample
was uniformly poured on the muscovite
detector placed at the bottom of thepolyethylene tube. Both the sample pow-

Akio OMURA

274

I SAMe:} 6N-HNO,+O.lN-HF

Tracer (DIU, 254Th. Z»Pa)(heating)I(boiling)~ Fe··· carrierr---NH. gas
ecentrifugation)

~

r-

x

xx
HNO. + HClo.

(evop. up)~ ~eN-HCI(evop. up)t-conc. H,so.

(evap. up)-I--eN-Hcl
rNH3 gas( centrifugation)~(washing)+-Q5M-HzC.o.
(onion exchange)t-3N-HCI(cation exchange)

IDowex ~xe. H-fonn I

I(washing)

f--3N-HCIr-x**(evap. up)(evop. up)i=-F

eN-HCI
QI.e.K.}

8N -HCI
0. I.B.K. }(shaking)[.~'/;'+ [ "aq.

(washing)~( elution)

0.5M -H.C.o.

I}-HNO.+HClo.

~eN-HCI(stripping)

iHNO.+HCI04

,3)
org.

T.l.OA},31~T(washing)( evap. up)~eN-HCI+O.5M-H,C.o.
( eleefrodep. )dul(stripping)(evop. up)

O.IN-HCI-t-0.5N-HCI
I eleetrodep.)

rkJJ(evop. up )+2M-HCI04(electrodep. )chText-fig. 1.

Analytical scheme of the carbonate samples.

der and muscovite detector were fixedwith absorbent cotton and a lid of the
tube_ The reference powder sample withknown concentration of uranium wasused as the monitor to examine various
factors when a uranium concentration
was calculated from track density.
a-spectrometry analysis a-spectrometry method was used the isotopic analysis
of uranium, thorium and protactinium
in carbonate samples and uranium andthorium in sea-water samples. In thepresent work, it was essentially important to separate each nuclide because ofsimilarity in the energies of the alphaparticles emitted by 230Th (4.62 MeV, 4_68
MeV) and by 234U (4.72 MeV, 4.77 MeV).
The anion exchange technique established by SAKANOUE et al. (KOMURA andSAKANOUE, 1967; SAKANOUE et al.,1967)

and partly modified by the author was
successful for the separation of eachnuclide. The electrode position technique
was used to prepare the thin sources,
which was also important to get a goodpeak resolution. The separation andpurification procedures of each nuclide
are schematically summarized in Textfigs. 1 and 2, in the case of carbonate
and sea-water samples, respectively. For
details of the actual procedures thepapers by SAKANOUE et al. should bereferred to.
Fission track analysis Only the procedures used in this study are briefly outlined below, as the principles of fission
track analysis had been detailed already(e. g. LAHOUD et al., 1966; SCHROEDER659.

Thorium and Protactinium Isotopes in Corals

275

Fe-+++ carrier
NH40H

*2
-t-3N-HCI( cation exchange)( leave for a day )I Dowex saxs. H-form I

I( centrifugation)

up.
~
ppt.

T.I.O.A. }SN-HCI
HN03+HCI04( evap. up )i:=SN-HCI(shaking)I
I(elution)(washing)( shaking)x31~~O.5M-H2C204(e~dep.)( washing)

DIS K }

f---SN-HCI·51(stripping)~N-HCI(evap. up)I~~( electrodep.)

dJ*
Text-fig. 2.

Analytical scheme of the sea-water samples.

et al., 1970).
Neutron irradiations were carried out
in Pn-3 tube of the KUR reactor of
Research Reactor Institute, Kyoto University, whose thermal neutron flux
density was 2.34x10 13 n/cm 2 osec. The
total neutron flux was determined by theuranium concentration in each sample,
which resulted in track density in theorder of 10 1 to 10 6 tracks/cm 2 •After etching by 46% hydrofluoric acidsolution for 30 minutes at room temperature, fission tracks in muscovite were
ob3erved under micro3cope and photographed. The dimension of the photographed area was' calculated from thephotograph of the objective micrometerscale with minimum division of 10 fl. The
counting areas were placed at random
for the powdered sample, but for thesolid sample they were located successively along a traverse to map the ura-nium distribution. The fission tracks ona microphotograph were counted byhand-counting which proved to be fairly
rapid and reliable; for example 1,000
tracks in a photograph could be counted
in approximately ten minutes.
Results and discussions
The results on isotopic analysis ofpresent-day corals are summarized inTable 2. The standard errors attachedto these and other results are derived
from counting statistics and does notinclude any systematic errors.
238U concentration ranges from 2 to 3.5
ppm within the limits of the error. These
data agree with those reported previously
by many workers (e.g. TATSUMOTO andGOLDBERG, 1959; BROECKER and THURBER, 1965; VEEH, 1966; OSMOND et al.,
1967; Ku, 1968).

Akio OMURA

276

Table 2.

Analytical results of

Isotope content
Sample238U (ppm)

232Th (ppm)

230Th (dmg)231Pa (dmg)C SM-1
C SM-22.45±0.1O
2.6S±0.OS

0.120±0.005
0.110±0.00S

O. 0609±0. 0020
O. OS21 ± 0.0017<0.001O. OOSOl ± 0.00019

C CM-1CCM-2

2. 7S±0. 06
3.44±0.07

0.0511 ± 0.0024
0.0632 ± 0.0056

0.0214 ± 0.0009
O. 0249±0. 0016

0.00409 ± 0.00017
O. 00198±0. OCO}8CHM-1

2.46±0.05

o. 0609±0. 0040

O. 0242±0. 0013

O. 0140±0. OOOS

CAM-1

2. 22±0. 05

0.0275 ± 0.0009

O. 0229±0. OOOS

O. 00908±0. 00040

C EM-1
C EM-2
CEM-3
CEM-4
CEM-S
CEM-6
CEM-7
CEM-8
CEM-9

2. 70±0. 07
2. 70±0. 07
2.63±0.05
3.43±0.08
1. 90±0. 08
2.61±0.13
2.86±0.132.75±0.03
229±0.06

0.116±0.005
0.183±0.008
O. 0903±0. 0049
0.0321 ± 0.0018
0.OS17±0.0024
O. 0323±0. 0022
o. 0675±0. 0054
o. 0386±0. 0025
O. 0149±0. 0013

o. 0788±0. 0022

O. 0168± 0.0008
O. 00858±0. 00038
O. 00S94 ± 0.00026
0.0113 ± O. OOOS
O. 00809±0. 000117
O. 0143± 0.0005
O. 00700±0. 00029
0.00287 ± 0.00026
O. 00460±0. 00017

CYM-1
C YM-2aCYM-2b
CYM-3
CYM-4
CYM-5
CYM-6
C YM-7a
CYM-7b
CYM-7c
CYM-7dCYM-7eC YM-7f

2.7S±0.06
2.82±0.14
3.61±0.1O
3. Sl±O. 07
2.99±0.1O
3. 02±0. 06
2.9S±0.07
2.1O±0.04
2.10±0.03
2.07±0.04
2.18±0.03
2.10±0.02
1.98±0.03

O. 0678±0. 0033
O. 0372±0. 0021
O. 0768±0. 0040
O. 0442±0. 0027
0.177±0.009
0.0337 ± 0.0021
O. 0608±0. 0029
O. 0143±0. 0012
O. 0119±0. 0009
O. 00960±0. 00068
0.0101 ± 0.0006
O. 0102±0. 0006
o. 00882±0. 00055

O. 0288±0. 0012
O. 0196±0. 0009
O. 0723±0. 0031
o. 016S±0. 0007
0.0224±0.0010
o. 00700±0. 00043
0.00550 ± 0.00036
O. 004S1 ±O. 00025
O. 00384±0. 00017
O. 00486 ± O. 00023
O. 00412±0. 00018

O. 00402±0. 00017
O. 00343±0. 00015
0.00421 ± 0.00024<0.001
O. 00142±0. 00009
O. 00230±0. 00013
0.00141 ±O. 00009
O. 0108± O. OOOS
0.0111 ± O. OOOS
0.00850 ± 0.00028
O. 00810±0. 00031
O. 00820±0. 00030
O. 00730±0. 00030

COM-1

2.67±0.OS

0.371 ±O. 019

O. 121 ± 0.005

O. 0238±0. 0015

CTM-1

2.57±0.05

O. 0432±0. 0041

O. 023S±0. 0016

<0.001

CNM-1
CNM-2
CNM-3

2. 72±0. 08
3.17±0.14
3. 32±0. 08

0.109±0.006
O. 0387±0. 0013
O. 0624±0. 0037

O. 0360±0. 0016
O. 012S±0. 0004
o. 021S±0. 0013

<0.001<0.001<0.001O. 0716±0. 0033
0.0517 ±O. 0019
0.0187±0.0008
0.0187±0.0007
O. 021S ± 0.0009
O. 0270±0. 0018
0.0131 ± 0.0007
O. 0149±0. 0008
O. 0300±0. 0014
O. 0156±0. 0007

659.

Thorium and Protactinium Isotopes in Corals

277

the present-day coral samples.
Activity ratio

Apparent age

234Uj238U

23OThj232Th

23OThj234U

231Pa/ 235 U

230Th Age

231Pa Age1.l4±0.06
1. 07±0. 03

2.13±0.11
1. 98±0.11

O. 0296±0. 0015
0.0251 ± 0.0010-O. 0560±0. 0023

3,200±200
2, 800± 100

2, 700± 100

1. 13±0. 04
1.13±0.03

1. 76±0.11
1.66±0.18

O. 00938± 0.00040
O. 00873±0. 00060

O. 0440±0. 0021
0.0170±0.0007

1,000±50
1,000±70

2, 100± 100
810 ± 30

1. 19±0. 03

1.67±0.14

O. 0113±0. 0007

0.142±0.006

1,200±70

7,200±300

1.13±0.03

3.51±0.14

O. 0124±0. 0004

0.121 ±O. 006

1,400±40

6,100±300

1.15±0.03
1.15±0.03
1. 18±0. 03
1.09±0.03
1. 18±0. 07
1.16±0.07
1. 15±0.07
1.16±0.03
1. 04±0. 03

2.86±0.14
1.65±0.10
2.40±0.16
2.45±0.17
1. 52±0. 09
2. 80±0. 23
1.68±0.17
1.42±0.12
5.34±0.57

O. 0346±0. 0012
O. 0313±0. 0013
0.0227 ± 0.0009
O. 00680±0. 00032
O. 0113±0. 0006
O. 0112±0. 0007
O. 0128±0. 0010
O. 00556±0. 00030
O. 00850 ± O. 00054

0.184±0.009
0.0941 ±O. 0045
O. 0669±0. 0031
O. 0973±0. 0046
0.126±0.010
0.162±0.009
O. 0723±0. 0043
0.175±0.016
O. 0593±0. 0026

3,800±100
3,400±100
2, 300± 100
760±401,200±60
1,200 ±80
1,400±100
650±40870±509,500±500
4,700±200
3,300±200
4,800±200
6,300±500
8,300±500
3,500±200
8,500±800
2,900±100

1. 16±0. 03
1. 18±0. 08
1.1O±0.05
1. 09±0. 03
1. 07±0. 05
1. 11±0. 03
1.08±0.03
1.10±0.03
1. 10±0. 02
1. 04±0. 03
1.05±0.02
1.06±0.02
1.10±0.02

1. 86±0.14
1. 75±0.12
1. 58±0.11
1.86±0.14
1. 72±0.12
2.06±0.16
1. 55±0.1O
2. 06±0. 21
1. 94±0. 20
1. 97±0.18
1. 60±0.12
2.00±0.15
1. 96±0.15

O. 0128±0. 0006
0.00754 ±O. 00048
O. 00988 ± O. 00050
O. 0070±0. 0004
0.0307±0.0017
O. 00673±0. 00032
0.00961 ± 0.00045
O. 00412±0. 00026
0.00324 ±O. 00021
0.00286 ± 0.00017
O. 00229±0. 00011
O. 00298±0. 00014
0.00257 ±O. 00012

O. 0433±0. 0020
O. 0359±0. 0024
O. 0345±0. 0022
0.0141 ± 0.0010
O. 0225±0. 0014
0.0141 ±O. 0010
0.153±0.007
0.156±0.008
O. 121 ± 0.005
0.1l0±0.005
0.1l6±0.005
0.109±0.005

1,400±70
870±601,100±60760±403,400±200
740±301, 100± 100
450±30360±20320±20250± 10320±20280±102, 100± 100
1,700±100
1,700 ± 100--700±50
1,100±100
700±507,800±400
8,000±400
6,100±300
5,500±200
5,800±200
5,400±200

1.10±0.03

1. 37±0.09

0.0563 ± 0.0027

0.264±0.017

5,700±300

14,400±900

1. 16±0. 03

2. 29±0. 27

0.0107 ± 0.0007-

1,200±80-

1. 07±0. 04
1. 12±0. 07
1. 13±0.04

1. 39±0.10
1. 36±0. 06
1.45±0.13

0.0167±0.0009
O. 00480±0. 00026
O. 00779±0. 00050-

1, 800± 100
520±30860±60

-

-

-

-

-----

Akio OMURA

278

23·V /238 V activity ratio in all samples
ranges from several to less than twenty
percent, which is close enough to thereported value of 1.15 from the presentday corals and oolites by THURBER (1962)
and VEEH (1966). This anomaly in theuranium ratio prompted the possibilityof an independent dating method, named
either " uranium ratio method" or "23'V
method ", which is based on the disintegration of the initial excess 23·V in thesample. This method could be useful tocross-check the deficient 230Th and 231Pa
dates, but any a6s by this method appears to be less ~eliable. The measurement of 23·V / 238 U ratio is necessarily
accompanied by the relatively large error
as suggested from the gentle slope ofthe 23·V decay curve, and the initial ratio(23'V /238 V activity ratio in the present-day
samples) varies considerably among theindividuals even in the same genera at
the same habitat. Furthermore, even
23·V /238 V ratio of three sea-water samples
in the nearby region is not necessarily
constant, though the 23'V /238 V ratio is
not unity and show that the activity of
23·V is ten or more higher than that of
238V (Table 3).
It might be argumental if the concentrations of thorium and protactinium isotopes in the present-day samples are "toolow to be determined accurately becauseof the analytical method used here, butthey can hardly be attributed to theanalytical contamination as confirmed by"repeated blank tests, and can be accepted
reliable (Table 2).
In addition to uranium isotopes, measurable amounts of 23°Th and 231Pa weredetected together with 232Th in the most
samples examined. It is clear that corals
studied here have initially uptaken thorium and protactinium isotopes into their
hard tissues from sea-water. In otherwords, most of the samples which mustshow zero year actually produce theinitial 230Th and 231Pa ages due to thepresence of the initial thorium and protactinium isotopes. These observations
probably reflect that the concentrationsof thorium and protactinium isotopes are
relatively high in sea-water at the sites
where the present-day corals examined"were collected. The analytical results ofsea-water samples support at least theappreciably high concentration of thorium isotopes (Table 3).
Among the samples, the 232Th concentration ranges from 1.7 to 6.0 X 10- 9 g/ I,
and the 230Th from 1.3 to 4.0 X 10- 14 gil.
Comparing these data with those reported by the previous workers (e. g. MOORE
and SACKETT, 1964), the observed concentrations of both 232Th and 230Th aretaken as relatively higher level within
the reasonable limit.
These important observation, coupledwith that of the concentration of 238V (2to 3.5 ppm) and thorium and protactini"umisotopes (measurable amounts of both
230Th and 231Pa) in the present-day sam:

Table 3. Summary of a-spectrometry analysis of the sea-water samples.
Isotope content
SampleActivity ratio-

238U (l0-6 g /l)

232Th (l0-9 gil)

230Th (10- 14 gil)23'U/238U

23OTbj232Th

WTk-1

3.76±0.17

5. 75±0. 27

3.7S±0.16

1. 15 ±O. 07

1. 33±0. 09

WY-1

3. 54±0. 21

5.47±0.25

3.41 ±0.141.ll±0.09

1. 26±0. 08

WY-2

4.31 ±O. 16

1. 67 ±O. 15

1.29±0.O9

1.16±O.O6

1.57±0.1S

659.

279

Thorium and Protactinium Isotopes in Corals

pected to increase with time. Text·fig. 3
shows the change of the ratio between
the initial and total 23°Th and 231Pa withtime. The values, 10% and 20% equil.
are assigned not only as a matter of convenience, but 10% equii. for 230Th and
20% equii. for 231Pa may be regarded as
the maximum values observed in thepresent-day corals of the Ryukyu Islands.
If the initial amount of 23°Th and 231Pa
were 20% equii., these nuclides would
reach more than one-third of the total
amounts after 10,000 years, but decreasesignificantly to approximately several
percents beyond 100,000 years. In practice, however, only a few samples exceed
10% equii. in the total amounts of both
230Th and 231Pa. In terms of percent
equilibrium with respect to the parent
nuclide, 231Pa seems to be contained moreabundantly than 23°Th in the present-day
samples. Thus, the initial 231Pa appears
to be more effective to deviate the ap-

pies examined, are suggestive of complicated conditions that render both the
23°Th and 231Pa dating methods to apply
to the fossil corals in the same region.
The uncertainty associated with the.. apparent ages" due to the initial 23°Th
and 231Pa, however, is so small that it
can be masked with the statistical error
and become negligible, in the case offossils several tens of thousand years
old. Within the order of several thousands years, on the contrary, any observed apparent ages may become amatter of serious consideration as dis·cussed below.
Text-fig. 3 was prepared to visualized
the effect of the initial 230Th and 231Pa
upon the reliability of the apparent ages.
Both the initial 230Th and 231Pa decrease
with time, while the decay of uranium
isotopes is to result in the accumulationof the radiogenic 230Th and 231Pa, in turn.
As a whole, both 23°Th and 231Pa are ex-

1.0

r--.--..
0.9~,"~.,
"-

,,

,

~

",,

"'~

,

O.8~

1'--."~~"". ~o",...
'«-c
" :'"

"

""

I

Q)

0 .7 I

~

.".0"
.

~?

" i".'"' ~~<:-"".

i'"

-§-'

0

.~

,.""

, <"'o",'~-E-', .

~0-, ' ..... , PG-J",,".'.",. ',.....

.....

.....

,

'-

......
.1.5'" f"\..

-'",'- ..... ,- 1'.......""".,--..... ..............

--....

--:::::.::: r---:.~ :~..
10

TIME
Text.fig. 3. Changes of the initial to total 230Th and 231Pa ratios with time.
(The dashed and dotted curves represent the changes of theinitial to total 230Th and 231Pa ratio, respectively.)Table 4. Isotopic composition, apparent and corrected 230Th ages
and conventional 14C age of some fossil coral samples.
230Th age

Activity ratio

Isotope content

I:'-'

00
.0

I'C age*
(yr.)

Riken
radiocarbon
code*

3,000
±300

2,190
±120

N 546

5,500
±200

3,400
±300

2,340
±115

N 548

0.0463±0.0022

5,200
±200

3,600
±300

3,950
±125

N 549

8.11
±0.50

0.0454±0.0015

4,900
±200

4,200
±200

3,410
±125

N 551

1.11
±0.06

9.76
±0.98

0.0493±0.0034

5,300
±400

5,000
±400

2,880
±120

N 407

0.127
±0.010

1.11
±0.03

8.59
±0.14

0.0639±0.0053

7,400
±500

6,000
±700

4,040
±120

N 399

0.0064±0.0005

0.145±0.004

1. 12
±0.06

94.8
±7.5

0.0694±0.0033

7,400
±300

7,300
±400

7,050
±145

N 402

2.65
±0.06

0.0275±0.0030

0.0935±0.0056

1. 12
±0.06

19.4
±2.1

0.0590±0.0030

6,600
±300

6,100
±400

5,260
±140

N 405

2.89
±0.05

0.0488±0.00200.0713±0.0047

1. 16
±0.03

6.15
±0.48

0.0290±0.0020

3,200
± 150

2,200
±200

1,780
±115

N 447

Sample

238U
(ppm)

232Th
(ppm)

230Th
(dmg)

23'Uj238U

23OThj232Th

CA-1

2.43
±0.14

0.0856±0.00450.0807±0.0022

1.10
±0.08

CA-3

2.61
±0.07

0.130
±0.0070.107±0.003

CK-16

3.28
±0.11

0.118
±0.008

CE-6

2.08
±0.04

CT-1

23OThj234U

Apparent
age

Corrected
age

3.97
±0.23

0.0434±0.0024

4,200
±200

1.11
±0.04

3.44
±0.21

0.0502±0.00200.124±0.004

1.11
±0.05

4.42
±0.34

0.0416±0.00250.0802±0.0019

1. 16
±0.03

2.48
±0.09

0.0935±0.00560.0402±0.0040

CT-2

2.45
±0.04

0.0625±0.0088

CT-5

2.57
±0.09

CT-8

CT-10

~

-

* Radiocarbon dates measured by Dr. and Mrs. T. HAMADA at Riken; they are "conventional !.IC ages"
based on half-life of 5,568 years.

?;-'
.".

o

a

ts::

c:::

::tI

::..

659.

Thorium and Protactinium Isotopes in Corals

7

281

CT-5
~

6
~

>.

I==-==l2

J------I

3

,., 5
0

CT-S

x

.......;.....~---t=+.l:r--:!t---t'+,-+'--:It-~~T_2

W 4

CK-16

(9

«

I! If I! ICE-6

I Ii

0 3
v
I.

2

2

!±-"
t-'I<-I I

3

4

230Th AGE

ICT_I

I I 'cA-3

I
CA-I

5
( X 10

6
3

7

8

yr.)

Text.fig. 4. Comparison of the conventional 14C with the apparent andcorrected 230Th ages of some fossil corals.
(1, conventional HC age; 2, apparent 230Th age; 3, corrected 230Th age.)parent age from the true age than theinitial 230Th. But such a deviation in theapparent age will be relatively smaller inthe 231Pa age than in the 230Th age forthe same fossil sample, because of theshorter half-life of 231Pa.
It is always desirable, if not necessary,evaluate the reliability of a given radiometric date in comparison with that ofan independent different radioactive
series. Both apparent 230Th and 231Pa
ages younger than 35,000 years B. P. canbe cross-checked with the He ages.
Although it is open to question whether

the conventional He ages represent true
ages or not, the discrepancy between the
He ages and the apparent 23°Th ages, asseen in Text-fig. 4, may come at least
partly from the presence of the initialthorium isotopes. If the apparent 230Th
ages are to be regarded as the ambiguous
ones, the next question will be how toreconcile the discordant ages with reasonable accuracy for the samples in which
the initial 23°Th is contained.
The apparent ages in the deficient
23°Th and 231Pa datings are the values
calculated on the assumption that all of282

Akio OMURA

230Th and 231Pa are originated from radioactive disintegration of each parent. If
the remaining amounts of the initial 230Th
and 231Pa in a fossil can be estimated,
we can evaluate the amounts of the radiogenic 230Th and 231 Pa grown from theirparents. Though difficult for 231Pa, it
seems to be possible for 230Th to estimate
the residual amounts of those initiallyincorporated.
The 23°Thj232Th ratios in Ryukyuanpresent~day corals are characterized byvery limited ranges from 1.4 to 3.0 witha few marked exceptions (slightly higher
than 2.0, on an average; Text-fig. 5). On
the other hand, the decay of 232Th is soslow that the decrease in amount of theinitial 232Th can be ignored for the time
range of the deficient 230Th dating. If

the assumption can be made that theinitial 230Thj232Th ratios in fossil remains
had been the same degree of constancy
as those in their present-day counterparts, the residual initial 230Th could be
estimated by the equation from the 232Th
concentration, as follows;
23°Thinitial=R· 232Th· e-·l!· ..... (1)where A is the decay constant of 230Th,
and R is the initial 230Thj232Th ratio anddefined by the following equation;
230( Th
R= 232Th) t=o
230Th _ 234 U. (l-e-.l m t)
232Th.e .l232 t••••• ·(2)where A234 and Am are decay constantof 234U and 232Th, respectively. Then theradiogenic 230Th (23°Thrad.) can be calcu---- 1.0 I-

E'

0...

U

>>

f--

f--

~0.5-

-

...c
f--

o

:I

+:2
+:3

(\J

r0
(\J

I

I

1.0

1.5

230Th ACTIVITY ( cpm)

Text-fig. 5. 230Th/ 232Th activity ratios in sea-water and present-day coral samples.
(1, sea· water samples; 2, massive colonial corals; 3, branching colonial corals.)

2.0

659.

Thorium and Protactinium Isotopes in Corals

lated by the foIlowing equation;
230Thrad. =23°Thtotal- R· 232Th· e-lt . •..

238 V =2.7 ppm
234V/238V=1.15 A. R.
232Th=0.05 ppm.

(3)

If the uncertainty of an apparent 23°Th
age depends only on the amount of theinitial 23°Th, it can be satisfactorily solvedby the proper estimation of the R value.
The R values have been previously
estimated from either the analytical dataof sea-water or comparison between HC
and 23°Th dates of fossil moIluscs andcorals (KAUFMAN and BROECKER, 1973;
THURBER et al., 1965; VALLENTINE andVEEH, 1969; VEEH and CHAPPELL, 1970;
KAUFMAN et at., 1971). In this study,
this value was determined directly byanalyses of present-day corals and seawater where corals were sampled.
The average 230Thj232Th ratio in theexamined sea-water samples of the Ryukyu Islands is 1.4 (Table 4), whereas thepresent-day coral samples have a little
higher ratio as described above. In thecase of the present-day massive corals
such as Favia and Goniastrea, the analyses were carried out at the inner portionof the coraIlum away from the surface
where polyps were attached, in order toavoid the contamination of nuclides fromsoft tissue. If the sample was taken
about 5 em inside from the surface of a
massive colony, Favia, it would represent an growth increment approximately
about 10 years old, if a growth rate isaccepted to be 0.5 em/year (OMURA et at.,1972). In this case, all 23°Th in the portion analyzed may not be incorporated
through secretion process of the skeleton,
but might have grown in part from radioactive disintegration of 23·'V during thelast ten years.
Then, the apparent increase of 230Th/
232Th ratio in "present-day coral" samples can be explained by assuming theinitial isotopic composition as foIlows:

283

These values are not absurd assumption
but fair average among the present-day
corals of the Ryukyu Islands. The
results of the calculation are shown in
Table 5 which lists data for growth ages
versus apparent changes of the R value.
After all, it seems acceptable to adopt
the 2:lOThj2 32 Th ratio of the sea-water in
habitat regardless of taxa of the organisms, as the R value.
Table 5. Apparent changes of R
values (the initial 230Thj232Th ratios)with growth ages.
Age(years old)

R

0

10

20
30 40 50
- -- -- - - 1.0 1.2 1.4 1.6 1.8 1.9- -- -- -- - - 1.5 1.5 1.9 2.1 2.3 2.4
r - - - -- -- -- - - 2.0 2.2 2.4 2.6 2.8 2.923lPa also is probably incorporated initiaIly along with thorium isotopes. With
our present knowledge, however, it is notpossible to estimate the residual amountsof the initial 231Pa in fossil remains by
any logical steps.
Thus, the corrected apparent 23°Th
ages, substituting 1.4 as the R value forequation (3), were compared again withthe conventional HC ages (Text-fig. 4).
The discrepancies between the corrected
230Th and l4C ages undoubtedly become
somewhat smaIler, although they are notin entire agreement. These discrepancies
between two dates may be attributable
to the uncertainty inherent to the Rvalue. However, there exists uncertainty
for the conventional HC ages.
The I'C age is conventionaIly computed,
in principle, assuming that all the samples

Akio OMURA

284

initially contained the same 14ct2c ratio.
If this assumption was not accepted, theConventional HC age may not be relied
upon. SUESS (1965, 1967, 1969) and KIGOSHI and HASEGAWA (1966) inferredfrom the discrepancy between dendrochronometric ages of wood sam pIes andtheir HC ages that HCt 2C ratio, or 14C
content in atmosphere has changed dur.ing the past 6,000 years. Additionallythey proposed the correction curves forthe conventional I'C ages.
Text-fig. 6 compares the corrected
23uTh age with the 14C age converted
graphically with the correction curve of
SUESS (1969). From the text-figure, it
seems as if the discrepancies between
two corrected dates reduce further
smaller. If the correction of 23°Th ages
proposed here can be substantiated with
future works, a similar correction curveof the conventional I'C ages may be ob-

w

(!)

<l:

o
:!:

_

cr.z F==I==9

--

0(·16

4000

;
o

CN

CT-'

8 20002000

4000

CORRECTED

Text-fig. 6.

Z30Th

EOJO

6000

AGE (yr. )Comparison between corrected
230Th and 14C dates.

tained beyond the dendrochronometricage, based on the 23°Th ages of hermatypic corals.
The results of the fission track analysisN§b 2 .0

""~

x

~

+/""+

+'

£
'" 1.5Qx>-I-U)I.O~-------------------------------------------------ZWo

0 0 .5
«0::

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!

2

3cm

I--

10

15

20

25

30

DISTANCE FROIV1 FIDUCIAL POINT
Text-fig. 7. Fission track counts measured along an axial line
on a longitudinal section of CEM-l specimen.

35 (rnm)659.

Thorium and Protactinium Isotopes ~n Corals

285

'€u
0'b
)(

"'rJl

.::£

U

C
~

'0
)(

>-

51(f)

Z

W
0
~

~
100 (mm)

90

80

70

60

0

DISTANCE FROM FIDUCIAL POINT
Text-fig. 8.

Variation of track density in the axial growth directionof a branching coral (Acropora sp., CYM-8).

to examine the uranium distribution incoral skeletons are given in Text-figs. 7
and 8 where uranium distribution is expressed as the relative changes of track
density.
Text-fig. 7 is the results obtained bycounting the fission tracks along an axial
line on a first-cycle septum in which no
growth increments are recognized morphologically. Text-fig. 8 shows the uranium distribution in axial growth direction of a branching corallum (Acroporasp.). From these illustrations, it is clearthat uranium distributes not necessarily
in uniform but heterogeneously. The
variation of the uranium concentration
is estimated to be 30% at the maximum,
although the much profound differences
like those between two structural layersof tridacnid shells are not confirmed(OMURA et ai., 1973).

Assumed that both 230Th and 231Pa are
distributed homogeneously, in contrast to
the heterogeneities of uranium, the difference in isotopic composition can becalculated by combining a-spectrometry
and fission track analyses for the threerespective parts in which uranium isotopes are maximum, average and minimum in concentration. As to the analytical results of CEM-1 (Table 6), thefollowing possibilities may be pointed out.
If this sample had been well preserved
as a closed system during its diagenetic
history, 231Pa should grow from its parent
235U as shown in Text-fig. 9. The growth
curve of 230Th might have the same pattern as that of 231Pa. The theoretical
growth curve (Gt) estimated from thesample in which the initial 231Pa is free,also is shown together in text-figure. We
notice readily by assuming the arbitary286

Akio OMURA
Table 6. Difference in isotopic composition among the various portions in apresent.day coral sample (U x , the maximum portion in uranium concentration; Ua,
the average portion in uranium concentration; Um , the minimum portion in uranium
concentration).
Activity (dmg)
238U

234U

Ux

2.28

2.62

Ua

1. 98

2.28

Um

1.72

1. 98

230Th

O. 788

Activity ratio
231Pa

0.0168

Apparent age (yr.)

23OThj2"'U

231Paj235U

230Th age

231Pa age

0.0301

0.160

3,300

8,200

0.0346

0.184

3,800

9,500

0.0398

0.212

4,400

11,000(% equiU
100

90
80
70
60
50
40
30

Gm
20

Gx

10

.CI~-------------.~5L---~~~--L---------f-----~'-------------·5~00( xl0 4 yr.)
Text·fig. 9.

Growth curve of 231Pa estimated in CEM-l sample.

(C t , theoretical growth curve; C m , growth curve estimated in the minimum partin uranium concentration; C x , growth curve estimated in the maximum part inuranium concentration.)time (t) that the 231Pa/235U ratio of CEM-l
is rm or r x higher than that of the ideal
sample. Moreover, there should be thedifference (r) in 231Pa/235U ratio, be·tween the maximum and minimum partsof uranium isotopes in concentration.
This r is responsible for the partial dif·ference in apparent 231Pa age, which isrepresented as Am-x in Text·fig. 9. The
decrease of r with time must be notedat this point. The relation between r
and time can be seen also in Table 7
which shows the magnitude of Am-x in
various stages. Namely, the older the
sample, the smaller the uncertainty due
to heterogeneities in uranium distribution

659.

Thorium and Protactinium Isotopes in Corals

Table 7. Changes of Am_x values invarious stages (see text for detailed discussion on Am-x value).
Time (yr.)

Am-x

(yr.)

230Th age

23lPa age

0

1,100

2,800

1,000

1,100

2,800

5,000

1,000

2, 70010,000

1,000

2,400

50,000700

900

100,000

500

300

appears to be the general rule. After
more than several tens of thousand years,
this uncertainty in apparent ages of
CEM-1 sample may become too small tobe distinguished from the statistical errorof counting. However, it is undoubtedly
one of the unfavorable factors for reliable
dating, if a sample is younger than 10,000
years old.
The above discussion may not fit in
the reality, because we possess but very
incomplete information on thorium andprotactinium isotopes distribution invarious pre3ent-day organisms. If 232Th
microanalysis using fission tracks (HAIR
et ai., 1971) be developed, we may beable to obtain the distribution patternsof 232Th in skeletal carbonates.
Conclusion
The a-spectrometry combined withfission track analysis was performed to
get informations as to the concentrations
and the activity rati03 of uranium, thorium and protactinium isotopes in somepresent-day and fossil hermatypic corals,
and to examine critically the effectiveness of the deficient 230Th and 231Pa dating
methods.

287

The analysis of the sea-water samples
from the Ryukyu Islands revealed thaturanium was contained to the same extent as the sea-water in the other regions,while the concentrations of thorium isotopes were a little higher than those in
the mid-oceanic region. These results
vindicate that marine organisms are
generally grown under the same environment with respect to uranium, but notnecessarily so for thorium isotopes (andprobably protactinium isotopes as well).
The 230Th and 231Pa concentrations
were not low enough to be neglected in
the observed present-day corals. Becauseof such high 230Th/23·U and 231Pa/235U
ratios, the present-day coral samples examined had the initial 23°Th and 231Pa
ages. From tne presence of the equivalent amounts of 232Th, it may be inferred with certainty that the Ryukyuan
fossil corals initially withheld similar
230Th/23·U ratio.
If it is a safe assumption that thefossils initially had the constant 23°Th/
232Th ratio similar to the present-day
counterparts in the same region, the residual amounts of the initial 232Th canbe estimated by the following equationfrom the 232Th concentration:

where A is the decay constant of 230Th,
and R is the initial 23°Thj"32Th ratio.
The uncertainty of an apparent 230Th
age, due to the presence of the initial
23°Th, can be satisfactorily solved by theproper estimation of the R value.
The present-day corals apparently had
higher 230Thj"32Th ratio than Cle seawater in their habitat. Accordingly, it
could be questioned to adopt the 230Th/
232Th ratio of the present-day coral samples as the R value. The higher 230Th/
232Th in the present-day samples is accounted for by the growth rate of herma-288

Akio OMURA

typic corals and the concentration of 234U
enough to let the initial 230Thj232Th ratio
grow for several decades. After all, for
the Ryukyuan fossil corals, it seems reasonable to use 1.4, an average 23°Thj232Th
ratio of the coastal water in habitat, as
R value.
In the Ryukyuan fossil corals in which
the initial 230Th and 231Pa are contained,
the difference in distribution pattern between uranium isotopes and their daughter nuclides also become a troublesome
problem. Although an extreme casecomparable to the two structural layersof molluscan shell had not been confirmed, the differences in uranium concentration to attain 30% at the maximum
were observed in axial growth directionof two scleractinian corallites. If theinitial thorium and protactinium isotopes
were distributed in no relation with uranium isotopes, the apparent 230Th and231Pa ages may be partially different, andthe different growth curves of 23°Th and231Pa must be used for dating.
The age ambiguity due to the initialdaughters and the heterogeneities inuranium distribution must always be
evaluated critically, but these factors
may not cause any practical effect on
dating the samples older than tens of
thousand years.
Acknowledgments I wish to express
my sincere thanks to Prof. Kenji KONISHI
of the Department of Earth Sciences,
Faculty of Science, Kanazawa University,
without whose constant guidance and encouragement this project would havebeen impossible. My deep appreciation
also extends to Prof. Masanobu SAKANODE and Dr. Takashi NAKANISHI of the
Department of Chemistry, Faculty of
Science, Kanazawa University for theirhelpful advice on the radiochemical treatment of the samples. Dr. and Mrs. Tatsuji HAMADA of the Institute of Physicaland Chemical Research (Riken) kindly
provided all the radiocarbon dates citedin this paper. Dr. Tetsuo HASHIMOTO
of the Research Reactor Institute, Kyoto
University was major assistance in thecourse of the experiments which was
performed there as a visiting researcher.
I wish, fUrther, to express my hearty
thanks to Dr. Yasuhide IWASAKI of theGeological Institute, University of Tokyo
for kind supply of the coral samples
from the Ogasawara (Bonin) Islands.
Finally, I thank to Professors Noriyuki
NASU and Yoshibumi TOMODA of Ocean
Research Institute, University of Tokyo,
for providing the occasion to Dr. K. KoNISHI during KH -71-1 Cruise to collectsome of the coral specimens used for thepresent study.

References
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- - , THURBER, D. L., GODDARD, J., Ku,
Teh-Lung and MATTHEWS, K. J. (1968):
Milankovitch hypothesis supported by
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CHAPPELL, ]. (1974a) : Upper mantle rheology
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- - (1974b): Geology of coral terraces,
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HAIR, M. W., KAUFHOLD, J., MAURETTE, M.
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JAMES, N. P., MOUNTJOY, E. W. and OMURA,
A. (1971): An Early Wisconsin reef
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Thorium and Protactinium Isotopes in Corals

its climatic implications. Ceol.Soc.Amer.
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KAUFMAN, A. and BROECKER, W. S. (1965):
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--,BROECKER, W. S., Ku, Ten.Lung and
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KIGOSHI, K. and HASEGAWA, H. (1966):
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KOMURA, K. and SAKANOUE, M. (1967):
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KONISHI, K., SCLANGER, S. O. and OMURA, A.
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- - , OMURA, A. and NAKAMICHI, O. (1974):
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289

OMURA, A., KONISHI, K. and NAKANISIII, T.
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H. L. (1965): Th 230 /U234 age of the Pleistocene corals and oolites of Florida.
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290

Akio OMURA

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Trans. Proc. Palaeont. Soc. Japan, N. S., No. 101, pp. 291-312, pis. 30-32, April 30, 1976

660. Dictyozamites AND SOME OTHER CYCADOPHYTES FROMTHE EARLY LOWER CRETACEOUS OGUCHI FORMATION,
THE ITOSHIRO GROUP, CENTRAL HONSHU, JAPAN~
TATSUAKI KIMURA and SHINJI SEKIDOTokyo Gakugei University, Koganei, Tokyo 184
and Science Education Centre, Ishikawa Prefecture

Tffll~.i!E7Wrffll;P11&~~llf~ IJ ]i,'ij0) Dictyozamites :to J: Lf-tO)iillO) 'J T :/ ~m:;PJI\iJi!,
1961)
iJ' I?~ I?nt-::M:!ffrJfl::.;P 0) ') t:" -"q:. 7- T ;;<, 13 0) Dictyozamites 6.fi] (') t:, 4 flllmfl) , m;f!
1 n1!~~tr Otozamites 2fi, 'J T :/ 13 0) Ctenis 3 fl (') t:, 1 f.JH1m.fiJD, Nilssonia 1 fi,:to J: Lfflr -/ 3J""13 0) Ctenozamites sp. ~§c.tx: L t-::o tJJ::O) ') t:" Nilssonia lobatidentata
11~JtvC,\lIj~ts.:mt:ifr~O)£I,ilt:ifr0);b G fill-c", -: 0) J: ') ts.:£lilt:ifrO);b G Nilssonia ~I1, -/""' Y 7M:!ffrJ.ttI!J'!!!JKM:!ffrJ:!lfvcilfiffilEfj-c-;bGo i t-::, Ctenis burejensis 11, Fillftti4m.ttl!:£!IKO)fJJ:JtIl~.9E*cM:!ffrJf.fvcilfiffilft'')ts.:;fi-c-, -: n 1?I1 ~ ~ vc§c.JfiX:¥!i15 Lt-:: Neozamites ~4-f&§c.JfiX:-t 7.> -/ 3J"I3:to J: Lf);J(*l3vc~-t7.>;f!O)-ffllC: C: tvc , ~1JM:4m:!lfc:Fill'*ff\:;O)-/,,", Y 7:JlH4m:l1Q:£!IKM:4mllfc:O)F,,'0);tI<jj~~-c';b Go~ IJ M:!ffrJfri'l1 i t-::, ~i'!: C: t vC1~U:'ffits.: Dictyozamites vC J:"'") ""(tfIf:/lt-::5vt I?n Go 4-1iN: 6;fi~§c.l!iIi:-t7.> C: C: tv;::, fit
ti!JTr'."*}IM'I?§c.JfiX:~nt-::;fiC:0)l:ti\l'1~ili\;z,..t-::o~ IJ M:4m:!lf0) 'J T :/~m (cycadophytes) O)mRltI1, fj:l:fFill'*ff\:; C: ~x.l?nG WealdentWO)~Ji;PM:4m~O)-tn C: 11fljj l?iJ,v;::!J,ts.: I), jjf.j~O)F,,'f;::I1;t1<jjfjfH1~:Z00l?nts.:~
nv;:: 1rJt-::
WIf,*1l -/ 3J'"13 ~);J(* 13 0) mRlt t;:: "'?c'""( t ~:Z00l?n 7.>
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7h'ff0)~.!rfiM:4mllT-~, Fill t: < Wealden tW 0) Wii'fji'fij}I"\ O)fJJ:JtIl~!lli*~1la4mf.l' J: IJ 11, gg~~B<.JvCJjj:
c', 7,b.-lvrOJ, vTjilJ, ::z I) "'rilJlifEJ1PiICffil?n ""(c'G -/""' Y 7:JlH4fr.JJt.I2Jm.lKfJJ:JtIl~.9E*cM:4mf.l'v;::j[[~-c·;b7.>o
H ~ fljj. I*l p 1B ?X;PJI\W~m~M:to J: Lf ~ IJ Mvc7j-;frJ-t GTffll~.9E*TffllO) ;P11&BJi;']llf~ IJ ~ (jilJ if .iI17E,

*,

'0

-:

0

*

(1963), and differ from the corresponding
floras of Wealden-type in the ," Outer
Zone Palaeofloristic Province" of Japan
in floristic character.
The rich Oguchi Flora derived from the
Kuwashima (=Kuwajima) sandstone andshale alternation member and its equivalents, the Oguchi Formation (KAWAI,
1961), the Itoshiro Group, the Tetori
Supergroup is the representative of" T etori Flora" and has been studied by
GEYLER (1877), YOKOYAMA (1889), Y ABE(1905, 1922, 1927), OISHI (1933, 1940, 1941),
MATSUO and OMURA (1968), KIMURA

General remarks

KIMURA (1975) subdivided the" Tetori
Flora" into the Late Jurassic Kuzuryu,
Early Neocomian Oguchi, Late Neocomian
Akaiwa and Aptian Tamodani Floras
based on the stratigraphical standpoint
and their floristic characters. They are inthe" Inner Zone Palaeofloristic Province"of Japan formerly proposed by KIMURA(1961, 1975) and KIMURA and SEKIDO* Received Feb. 23, 1976; read Nov. 29,
1969 & Jan. 25, 1975 at Kagoshima and Tokyo.
291

292

Tatsuaki KIMURA and Shinji SEKIDO(1961, 1967) and KIMURA and SEKIDO(1963, 1965-1975).
The Oguchi Flora closely resembles thecoeval Siberian floras in the "Siberian
Palaeofloristic Area" proposed by VAKHRAMEEV (1964, 1966, 1970, 1971). Detailsof Oguchi Flora have been given by KIMURA (1975) and KIMURA and HIRATA(1975).
In this paper we describe six Dietyozamites species among which four are
new to science, two Otozamites speciesof which one is new, two Ctenis species,
one Nilssonia species and one Ctenozamites species, based on new specimensfrom the Oguchi Formation.
The discovery of Ctenis burejensis andNilssonia lobatidentata with markedly
dentate distal margin is noteworthy, because they are known to be of Siberian
habitants.
The pteridosperms and cycadophytes
from the Oguchi Formation now include
ten genera and thirty species listed below
but some of them are not yet described.
Species with asterisk are described in thepresent paper.
Pteridosperms and Catoniales*Ctenozamites sp.
*Sagenopteris sp. (MS)Bennettitales*Otozamites endoi KIMURA, 1961
?D. klipsteinii (DUNKER) SEWARD, 1895
*0. pseudoanglica KIMURA and SEKIDO,
sp. nay.
• Dictyozamites auriculatus KIMURA and
SEKIDO, sp. nov.
D. falcatus (MORRIS) OLDHAM, 1863
D. grossinervis YOKOYAMA, 1889
* D. ishikawaensis KIMURA and SEKIDO,
sp. nov.
D. kawasakii TATEIWA, 1929
D. imamurae OISHI, 1936
D. cfr. imamurae OISHI, 1936
• D. reniformis OISHI, 1936
- D. tetoriensis KIMURA and SEKIDO,
sp. nov.

-D. yamazakii KIMURA and SEKIDO,
sp. nov.

D. spp. OISHI, 1936
?Pterophyllum lyellianum DUNKER,
1846
P. spp. (MS)Neozamites elongatus KIMURA and
SEKIDO, 1970
Cycadales*Ctenis burejensis PRYNADA, 1934
*C. cfr. formosa V ACHRAMEEY, 1961
C. kaneharai YOKOYAMA, 1906
C. nipponica KIMURA and SEKIDO, 1972
Nilssoniocladus nipponensis(YOKOYAMA) KIMURA and SEKIDO,

1975 (leaf = Nilssonia nipponensis
YOKOYAMA, 1889)

Nilssonia kotoi (YOKOYAMA) OISHI,
1940- N. lobatidentata V ASSILEYSKAJA, 1972
N. orientalis HEER, 1878
N. ozoana YOKOYA~IA, 1889
Tetoria endoi Kn'luRA and SEKIDO,
1974

In addition to the above, MATSUO andOMURA (1968) described Taeniopteris
vittata BRONGNIART from Togadani now
named Nilssoniopteris vittata (BRONGNIART) FLORIN.
In the coeval flora of the Ryoseki Formation in Kochi Prefecture, in the Outer
Zone Palaeofloristic Province, the known
cycadophytes are listed below (KIMURA
and HIRATA 1975).
Bennettitales

Otozamites klipsteinii (DUNKER)SEWARD, 1895

Pterophyllum spp.
Ptilophyllum ex gr. pecten (PHILLIPS)MORRIS, 1841

Zamiophyllum buchianum(ETTINGSHAUSEN) NATHORST, 1890

Zamites tosanus o ISI-II, 1940
CycadolePis oblongiformis OISHI, 1940
Cycadales

Nilssonia orientalis HEER var. minor
FONTAINE, 1889

660.

Dictyozamites and some other cycadophytes

N. schaumburgensis (DUNKER)
NATI-IORST, 1890
N. schaumburgensis (DUNKER) var.
parvula YABE, 1913

In its cycadophytes, as well as in ferns,
the Oguchi Flora is quite different fromthe coeval Ryoseki Flora (s. str.) and also
from the floras of Upper Neocomian
Lower Monobegawa and Aptian-Albian
Upper Monobegawa Formations in Kochi
Prefecture.
One of the characteristics of the Oguchi
Flora is the rich representation of Dictyozamites with nine species and three orfour other forms that may be distinct.
Not one of these has so far been recorded in the floras of Outer Zone Palaeofloristic Provine of Japan.
Unfortunately we could not study cuticles in the present work because thespecimens available were all inpressions
without organic material.
Later a monograph of the Oguchi Florawill be contributed by us, based on theabundant materials accumulated for fifteen years.

Acknowledgement

Here we record our cordial thanks toProfessor Emeritus Thomas M. HARRISof the University of Reading for his
critical reading this manuscript and forcontinuously receiving his valuable suggestions. We would also like to express
our appreciation to Dr. V. A. VAKHRAMEEV of Geological Institute of the
Academy of Sciences of the USSR, whokindly gave us many valuable papers regarding palaeobotany.
Acknowledgement is extended to Miss
Tamiko OHANA, a student of the Tokyo
Gakugei University for her kind help of
drawing the figures in the present work.
The present paper would have been much293

difficult to write without their generous
contributions.
The present study was supported inpart by the Grant in Aid for Scientificresearches from the Ministry of Education of Japan and also by the Sectionof Cultural Properties Protection, Boardof Education, Ishikawa Prefecture.
Systematic description

Pteridospermales
Genus Ctenozamites NATHORST, 1886: 122
Ctenozamites sp.
PI. 31, Fig. 1; Text-fig.

Description: Two leaf-fragments on asmall slab were obtained. PI. 31, Fig. 1(KU-Y0016) shows a part of a leaf fragment which is long and narrow, morethan 6.5 cm long, nearly parallel-sided,
1 cm wide. Segments rhomboidal or triangular in outline, typically 0.5 cm longand 0.17 cm wide, set closely or slightly
spaced, upper margin straight, lower
margin convex with the broad curve tomeet cuspidate or aristate apex, attached
at a wide angle by their whole base to
the upper surface of comparatively thickrachis, 3 mm across measured on impression. The bases of segments not contracted but somewhat decurrent. Nerves
5-7 in number at base, parallel each other,
mostly simple, but sometimes forking;upper ones converging to the apex andlower ones ending in the apical basiscopic
margin as shown in Text-fig. 1.
Remarks: The fragments of this species do not show whether the leaf isbipinnate as in Ctenozamites or simply
pinnate as in the older Ptilozamites, nor
whether the main rachis forks. Accordingly we merely name it as Ctenozamites
sp. provisionally. Had the acroscopic

294

Tatsuaki KIMURA and Shin}i SEKIDO
1966. Otozamites endoi KIMURA em. KIMURA
and SEKIDO: p. 2, pI. 1, figs_ 1, 2; pI.
2, fig. 2. (Oguchi Formation).

em
Text-figs_ 1-4.

1. Ctenozamites sp.; showing outline ofsegments or pinnae and venation (KUY0016). (x2)
2. Otozamites endoi KIMURA em. KIMURA
and SEKIDO; showing outline of pinna
and venation (KM-71006).
3. Otozamites pseudoanglica KIMURA and
SEKIDO, sp. nov.; showing outline of
pinnae and venation (KM-71003 Holotype) .
4. Otozamites pseudoanglica KIMURA and
SEKIDO, sp. nov.; (KM-71004).

segment margin been rounded, it would
have resemble a Ptilophyllum.
Occurrence: Rare.
Specimen: KU-Y0016 (collected by Y.
KANSHA from Kuwashima of the Oguchi
Formation).
Bennettitales
Genus Otozamites BRA UN. 1842
Otozamites endoi KIMURA em.

KIMURA and SEKIDO, 1966
PI. 31, Figs. 4, 5; Text-fig. 2
1961. Otozamites endoi KIMURA: p. 27, pI. 5,
fig. 4; text-fig. 6. (Oguchi Formation).

Description & remarks: PI. 31, Fig. 4(KM-71006) is a new specimen in which
pinna outline and venation are moreclearly shown than those previously described_ This specimen represents middle
to upper part of a leaf and agrees withthe emended diagnosis of KIMURA and
SEKIDO.
PI. 31, Fig. 5 enlarged shows an entire
pinna and Text-fig. 2 shows its venation.
The form of this species has been compared with some similar ones, e. g., Otozamites graphicus (LECKENBY) and O.
lancifolius OISHI by KIMURA (1961). Otozamites pterophylloides BRONGNIART (non
YOKOYAMA) is also similar but differs in
its pinnae which are straight, gradually
narrowing to the acuminate apex andwith a markedly auriculate acroscopic
pinna base.
Occurrence: Common.
Specimens: KM-63004, KM-63005, KM63006, KM-59001 (Holotype), KM-71006,
KM-75052 and many leaf-fragments.

Otozamites pseudoanglica KIMURA

and SEKlDO, sp_ nov.
PI. 30, Figs. 4, 5; Text-figs. 3, 4

Diagnosis: Leaf small, more than 4 cm
long and about 3.2 cm wide, shape ofwhole leaf unknown, with tapering base.
Pinnae remotely set, nearly perpendicular
to the slender rachis, 1 mm thick. Apical
pinna unusually set, being nearly parallelto the rachis and broader than the others.
Pinnae elongate-obovate or elongate-oblong in outline with obtusely pointed
apex, attached by the narrow area below
the middle of pinna base; both auricles
weakly developed. Nerves radiating from

660.

Dictyozamites and some other cycadophytes

the narrow area, branching at all levels,
fairly crowded.
Description: Four leaf-fragments wereobtained. Pi. 30, Fig. 4 (KM-71003) shows
two leaves represented by under surface.
They appear to converge towards a supposed common support point below. If
so, the length of each leaf except theapical pinna might be estimated to be
7.5 cm right and 4.5 cm left respectively.
Text-fig. 3 (KM-71003) shows the outlineof pinnae and venation. Pi. 30, Fig. 5(KM-71004) shows a similar leaf indicatedby the under surface, of which pinnae
are rather elongate-oblong in outline asshown in Text-fig. 4, 1.8 cm long and0.6 cm wide, attached to the rachis in asimilar way to the above.
Comparison & remarks: Though thespecimens available are few and imperfect. they are distinguished specificallyby their small size and narrow region of
attachment just below the middle.
Had the attachment been in the middle
they would have fitted the definition of
Zamites. The upper auricle is developed
feebly and the lower basal margin iseven less expanded.
Otozamites anglica (SEWARD) HARRIS(1949, p. 275, text-figs. 1, 2; 1969, p. 39,
pi. 1, fig. 5; text-fig. 17) looks rather
similar but its pinnae are attached by
the lower half of their bases. Its veins
are much less crowded.
The present species named after theYorkshire species.
Occurrence: Rare.
Specimens: KM-71003 (Holotype), KM71004.

295

Genus Dictyozamites OLDHAM
and MORRIS, 1863: 37
This genus was at first known from theJurassic of India, then from Japan, Bornholm, Yorkshire, Nagdong, Ussuri and
Primorye, Patagonia, Iran, Malaysia andrecently from the Lena Basin. The geological distribution of this genus has
interested many palaeobotanists (Textfig. 33).
From Japan, five species, D. falcatus,
D. grossinervis, D. imamurae, D. kawasakii and D. reniformis and one unnamed
form, D. cfr. imamurae described fromthe Upper Jurassic Kiyosue Formation,
Yamaguchi Prefe<;:ture and the Kuzuryu
Group and mainly from the Oguchi Formation, Central Honshu.
We now add four new species, D. auriculatus, D. ishikawaensis, D. tetoriensis
and D. yamazakii, and one unnamed form,
D. sp. from the Oguchi Formation at theupper course of the Mekkodani, a branchof Tetori River.
In addition there are D. sp. A and D.
sp. B described by OISHI (1936) which
may be distinct but are imperfectly
known from poorly preserved specimens.
So far as we know, Dictyozamites has
now 25 species of which the oldest record
is D. crusinensis KON'NO (1972) from theUpper Triassic of East Malaysia.
We offer a key to these 25 species on
p. 296. It relates primarily to the Japanese species but with these we groupsimilar looking leaves of other lands.

Tatsuaki KIMURA and Shinji SEKIDO

296

Key on macroscopic form of typical specimens of leaves
1 I-P~nna length up to t.wice i~s ,,:idth ................................................... 2-PInna length exceedIng tWice Its width .............................................. 5
2"I-Pinna sessile (or stalk under 1 mm) ................................................ 3.lI -Pinna stalk distinct, exceeding 1 mm .............................................. 4-Pinna large, exceeding 4 cm long
D. kawasakii TATEIWA (Text.fig. 5)
3
D. cordatus (KRYSHTOFOVICH) PRYNADA (Text.fig. 6)
D. crassinervis MENENDEZ (Text·fig. 13)-Pinna small, less than 3 cm long
D. yamazakii KIMURA and SEKIDO, sp. nov. (Text.fig. 7)
D. indicus FEISTMANTEL (Text.fig. 10)
D. crusinensis KON'NO (Text.fig. 8)
D. minusculus MENENDEZ (Text.fig. 9)-Pinna circular, reaching 3.5 cm in diameter
4
D. reniform is OISHI (Text.fig. 11)-Pinna oblong, less than 6 cm long
D. grossinervis YOKOYAMA (Text.fig. 12)
5 I-P~nna length up to t.wice it.s w!dth ............................................... 6-PInna length exceedIng thnce Its width ........................................ 7-Pinna elongate.oblong or broadly lanceolate, less than 4 cm long
D. ishikawaensis KIMURA and SEKIDO, sp. nov. (Text.fig. 20)
6
D. tateiwae OISHI (Text·fig. 14)
D. tetoriensis KIMURA and SEKIDO, sp. nov. (Text.fig. 16)-Pinna rectangular, less than 6 cm long
D. imamurae OISHI (Text.fig. 18)
D. latifolius MENENDEZ (Text·fig. 19)
7 I-P~nna length up to ~our times. its ,,:idth ...................................... 8-PInna length exceedmg four times Its length .................................. 9-Pinna base markedly auriculated
8
D. johnstrupi NATHORST (Text.fig. 27)-Pinna base rounded or slightly auriculated
D. falcatus (MORRIS) OLDHAM (Text·figs. 23, 24, 25, 26?)
D. areolatus ARCHANGELSKY and BALDONI (Text.fig. 17)
D. hawelli SEWARD (Text.fig. 29)
D. obliquus SAMYLINA (Text.fig. 15)
D. ussuriensis KRYSHTOFOVICH (Text·fig. 30)-Pinna base markedly auricula ted
D. auriculatus KIMURA and SEKIDO, sp. nov. (Text.fig. 31)
D. asseretoi BARNARD (Text.fig. 32)
9 -Pinna width less than 2 mm
D. bagjoriensis JACOB (Text.fig. 22)
D. hallei SAHNI and RAO (Text.fig. 21)-Pinna width exceeding 5 mm
D. cazaubonii ARCHANGELSKY and BALDONI (Text.fig. 28)

II

660. Dictyozamites and some other cycadophytes

297

10

(3

Text-figs. 5-13.

5. Dictyozamites kawasakii TATEIWA; after KIMURA, 1961, pI. 4, fig. 2 (KM-57001).
6. D. cordatus (KRYSHTOFOVICH) PRYNADA; after KRASSILOV, 1967, pI. 43, fig. 1.
7. D. yamazakii KIMURA and SEKIDO sp. nov.; drawn from PI. 31, Fig. 3 of thepresent work (KM-61469).

8. D. crusinensis KON'NO; after KON'NO, 1972, text-fig. 4D.
9. D. minusculus MENENDEZ; after MENENDEZ, 1966, text-fig. 14.
10. D. indicus FEISTMANTEL; after FEISTMANTEL, 1879, pl. 3, fig. 3a.
11. D. reniformis OISHI; drawn from PI. 32, Fig. 4 of the present work (KM-433-1).
12. D. grossinervis YOKOYAMA; after YOKOYAMA, 1889, pl. 7, fig. 10.
13. D. crassinervis MENENDEZ; after MENENDEZ, 1966, text-fig. 18.

Dictyozamites auriculatus KIMURA
and SEKIDO, sp. nov.
PI. 30, Figs. 1, 2; Text-fig. 31

Diagnosis: Leaf unknown in size. Pinnae set closely, alternate, long and narrow gradually tapering upwards (butapex unknown), attached to the uppersurface of a rachis up to 4 mm thick by
the lower half of pinna base, acroscopic
base free, markedly auriculate; auricle
concealing the rachis and overlapping
the lower pinna base on opposite side.
Nerves consisting of 5-6 nearly longitudinal strong ones running from attach-

298

Tatsua lc i KIMURA and Shinji SEJ(IDO

Text-figs . 14-20.

14. Dictyozamites tateiwae OI SHI ; afte r 01 5 1-11, 1936, pI. 9, fig. 3 a nd text -fig . 3.
15. D. obliquus SAMYLl NA ; after SAMY Ll NA, 1964, plate, figs. 10, II.
16 . D. tetoriensis KIM URA a nd S EKIDO sp . no v . ; draw n from P I. 31, Fig. 2 of theprese nt work (KM- 61468) .
17. D. areolatus ARCH ANG ELSKY a nd BALDO NI ; afrer AR CHANGE LSKY and BALD ON I,
1972, pI. 1, fig. 4 .
18. D. imamurae OISH I ; af te r KI MU I~ A , 1961, pI. 5, fi g . 1 (KM - 59811 ) .
19. D. lali/olius M ENENDE Z ; after ME NENDEZ, 1966, text-fi g. 2l.
20 . D. ishilwwaensis KI MU RA and SEK IDO, sp. no v.; draw n fr om PI. 32, Fi g . 3 ofthe present wor k (KM- 63010) .

ment to apical part along the medianax is, and weaker ones curving out tomargins, both forming reticular meshes;
longitudinal meshes longer and narrower,
typically 0.8 cm X 0.5 mm, marginal ones
shorter and broader, ty pically 0.5 cm X

0.75mm.

Description: Several frag ments arecollected, one of which is shown in PI.
30, Fig. 1 (Holoty pe) (KM- 61418). PI. 30,
Fig. 2 shows basal part of pinnae andTex t-fi g. 31 shows detailed venation.

660.

Dictyozamites and some other cycadophytes

Comparison & remarks: This species
is characterized by the strongly auriculate acroscopic base, though the specimens at present available are only
several number and not one shows thewhole leaf or even the apex of a pinna.
Two species have similar large auricle.
Dictyozamits johnstrupi from the Jurassicof Bornholm (MOLLER, 1903, pI. 5, figs. 1,1a) is distinguished by its shorter andfalcate pinnae. D. asseretoi described by
BARNARD (1965, pI. 99, figs. 3, 4; textfigs. 7 A-C) from the Liassic of Northern
Iran has different shaped auricles asshown in Text-fig. 32.
Occurrence: Not frequent.
Specimens: KM-61418 (Holotype), KM71007, KM-61410, KM-75003, KM-75004.

Dictyozamites ishikawaensis KIMURA
and SEKIDO, sp. nov.
PI. 32, Figs. 1-3; Text-fig. 20

1966. Dictyozamites dr. imamurae OISIII:KIMURA and SEKIDO, p. 4, pI. 2, fig. 2;
text-fig. 3 (Mekkodani, Oguchi Formation).

Diagnosis: Leaf length unknown, morethan 17 cm long, 6 cm wide at the widest
portion. Rachis up to 4mm thick. Pinnae
evenly pinnate, sessile, set closely, alternately attached at an angle of 70-90°.
Pinnae nearly parallel-sided but increasing their width gradually towards theapical portion, then narrowing abruptly
to meet at an angle of about 70° insteadof gradually tapering; pinna base mostly
contracted; both basal margins rounded,
not prominently auriculated; typical pinnae, 3-3.5 cm long and 1.2-1.4 cm wide.
Nerves dense, 18-20 per cm at the middle
portion of pinna, divergent, ending atouter margin, anastomosing to form polygonal meshes; meshes in the median cen-299

tral region being typically 4 mm long and
1 mm wide, becoming shorter and narrower towards the margin.
Description: Many new specimens
were collected. PI. 32, Fig. 1 (Holotype)(KM-6301O) reinserted here from our previous paper (1966, pI. 2, fig. 2) representing the middle or upper part of a leaf,
proves typical.
PI. 32, Fig. 3 shows the outline of atypical pinna and Text-fig. 20 shows thedetailed venation. PI. 32, Fig. 2 (KM690014) is a similar specimen to the holotype, clearly demonstrating the characteristic pinna form of this species.
Comparison & remarks: Dictyozamites
ishikawaensis is mainly characterized byits pinna form as typically shown in PI.
32. Fig. 3 and Text-fig. 20. It is close in
pinna form to D. tateiwae originally described by OISHI (1936, p. 28, pI. 9, fig. 3;
text-fig. 3; 1940, p. 327) based on the
Nagdong material, together with two
specimens formerly regarded by Y ABE(1905. p. 11, pI. 2, figs. 6, 7; non figs. 2-5)
as D. fa/catus from the Nagdong Group.
Dictyozamites ishikawaensis differsfrom D. tateiwae which has elongatetriangular pinnae with a straight acroscopic margin and convex basiscopic
margin then abruptly curving upwards
at the distal portion.
Some specimens from Ozo in the Oguchi Formation described by YOKOYAMA
as D. indicus var. distans and later by
OISHI (1936, p. 26; 1940, p. 325) as D.
fa/catus resemble both D. tateiwae or D.
ishikawaensis but in our view do notagree fully with either D. fa/catus or D.

indicus.
Occurrence: Common.
Specimens: KM-63010 (Holotype), KM690014, KM-434-1 and many leaf fragments.

Tatsuaki KIMUR A and Shinji SEKIDO

300

29

tIIJIIIII'o
Text-fi gs . 21-32.
21. Dictyozamites hallei S AHNI a nd RAo; after S AI-INI a nd R AO , 1931, pI. 14, fi g. 25 .
22. D . bagjoriensis J ACO B; after SITH OLEY, 1963, pI. 6, fig . 42 .
23. D . falcalus (M ORRI S) ; after O LDH AM a nd M ORRI S, 1863, pI. 24, fig . la ( r .=gard e d by
OLDH AM an d M ORR IS as Dictyopteris falcata).
211. D. falcatus (M OR RI S) ; ibid., fig. 2a ( rega rd ed by OL DHAM a nd MORRIS as Dictyopteris
falcata va r. obtusifolia) .
25 . D. falcatus ( M ORR IS) ; after Y ABE , 1905, pI. 2, fig. 2.
26. D. falcatus ( M ORR IS) ? ; after YOKOYAMA, 1889, pI. 10, fi g . 8 ( r ega rded by YOKOYAMA
as D. indicus va r. di stans a nd late r by OI SH I as D . falcatus; this speci m e n is s imilarin pinna form a nd venat ion t o so m e of t ho se reg arded as D. tateiwae or D. ishilwwa ensis , tog ether w ith YOKOY AMA'S fig. 8a).
27. D. johnstrupi N ATHOR ST; after M OL LER, 1903, pI. 5, fig. 2.
28. D . cazaubonii ARCH ANGELSKY a nd BALDONI; after H ALLE, 1913, pI. 5, fi gs . 29-33 ( re garded by H ALLE as D. cfr. falcatus) ; recon st rcuted by K IMUR A and SEKIDO.
29. D . hawelli SEW AR D; after SEWARD, 1917, fig. 609.
30. D. ussuriensis KRYSI-ITOrovlcH ; after KRYSHTOrOvI CH, 1957, fig. 303- 4.
31. D. auriculatus K IMUR A and SEKIDO, sp . no v.; drawn from PI. 30, Fig. 1 of the present
work (KM- 61418).
32 . D . asseretoi BARNARD; after BARNA RD, 1965, text-fig. 74.

660.

Dictyozamites and some other cycadophytes301o ----- Neocomian.. ----- Late Jurassic/:::,. ----- Middle Jurassic• ----- Early Jurassic
Late Triassico -----

Text-fig. 33.

Localities and occurrence of Dietyozamites
species with works quoted.

1. Tierra del Fuego: D. eazaubonii (HALLE, 1912, 1913; ARCHANGELSKY and BALDONI,
1972). 2. Tico and Baquero: D. areolatus (ARCIIANGELSKY and BALDONI, 1972), D. erassinervis (ME:-.IENDEZ, 1966), D. lati/olius (MENENDEZ, 1966; ARCHANGELSKY and BALDONI,
1972) and D. minuseulus (MENENDEZ, 1966; ARCIIANGELSKY and BALDONI, 1972). 3_ Chubut:
D. eazaubonii (CAZAUI30N, 1947; ARCHA"GELSKY and BALDO"I, 1972). 4. Yorkshire: D.
hawelli (SEWARD, 1903,1917; THOMAS and BANCROFT, 1913; HARRIS, 1969). 5. Bornholrn:
D. johnstrupi (NATHORST, 1889,1907; MOLLER, 1903; FLORI:", 1933). 6. Dolud: D. asseretoi(BARl"ARD, 1965). 7. Madras coast, MURRERO and GORAPILLI: D. /aleatus (FEIST:O-IANTEL,
1877,1879) and D. indieus (FEISTMANTEL, 1877, 1879). 8. Rajrnahal Hills: D. bagjoriensis(JACOI3, 1951), D. /aleatus (SEWARD, 1903; BANCROFT, 1913; SAl-IN! and RAO, 1931) and D.
hallei (non CAZAUI30N) (SAHNI and RAO, 1931). 9. East Malaysia: D. erusinensis (KON'NO,
1972). 10. Lena Basin: D. eordatus (V AKHRAMEEV, 1970). 11. Central Sikhota-Alin: D.
obliquus (SAMYLINA, 1964). 12. Southern Primorye: D. eordatus (KRYSHTOFOVICH, 1929:KRYSIITOFOVICH and PRYNADA, 1932; PRYl"ADA, 1963; KRASSILOV, 1967), D. /alcatus (KRASSILOV, 1967), D. grossinervis (KRASSILOV, 1967), D. kawasakii (KRASSILOV, 1967) and D.
ussuri2nsis (KRYSIITOFOVICH, 1957; KRYSHTOFOVICH and PRYNADA, 1932). 13. Nagdong:
D. /alcatus (Y ABE, 1905 pars; OISHI, 1936, 1940), D. kawasakii (T ATEIWA, 1929; OISHI, 1940)and D. teteiwae (YAI3E 1905 pars; OISHI, 1936,1940). 14. Kiyosue: D. /alcatus (OISHI, 1936,1940), D. kawasalzii (TAKAHASHI and NAITO, 1930) and D. reni/ormis (TAKAHASlII and
NAITO, 1950). 15. Mochiana and Kizaki: D. /alcatus (KIMURA, 1958, 1959). 16. Oguchi:
D. auriculatus (present work), D. /alcatus (YOKOYA:VIA, 1889; OISHI, 1936, 1940), D. grossinervis (YOKOYAMA, 1889), D. imamurae (OISIII, 1936, 1940; KIMURA, 1961; KIMURA and
SEKIDO, 1966), D. ishikawaensis (KIMURA, 1961; KIMURA and SEKIDO, 1966; present work),
D. kawasakii OISlII, 1940; KIMURA, 1961; KIMURA and SEKIDO, 1966, 1967), D. reni/ormis(OISHI, 1933, 1936, 1940; KIMURA, 1961; present work), D. tetoriensis (present work) andD. yamazakii (present work).

302

Tatsuaki KIMURA and Shinji SEKIDO

Dictyozamites reniformis OISHI, 1936
PI. 32, Fig. 4; Text-fig. 11

1933. Chiropteris? sp. OISHI: p. 628 (nameonly, Yambara of the Oguchi Formation) .
1936. Dictyozamites reniform is OISHI: p. 29,
pI. 9, figs. 1, la (Yambara of the Oguchi Formation).
1940. Dictyozamites reniformis OISHI p. 327(general remarks).
1950. Dictyozamites kawasakii TATEIWA:
TAKAHASHI and NAITO, p. 188; textfig. 2 (Kiyosue Formation).
1961. Dictyozamites reniformis OISHI: KrrvlURA, p. 25, text-figs. 3,4 (Mekkodani of
the Oguchi Formation).

Description: Several good new specimens were collected. PI. 32, Fig. 4 (KM433-1) is possibly the lower part of a leaf.
Rachis stout, 5-6 mm thick. Pinnae withstalks about 1 cm long and 2 mm thickattached at 60-70° to upper part of rachis,
distant but laminae of adjacent pinnae
overlapping. Laminae reniform in outline, 2.8-3.2 cm in diameter, their uppersurface convex, attached to the stalk
below the middle of their bases, accordingly lamina is asymmetrical. Some oflaminae as shown in PI. 32, Fig. 4 appear
to be circular in outline, because theirbasal angles are refiexed, especially so in
acroscopic angle shown in Text-fig. 11.
The nerves radiate from the top of
the stalk and anastomose to form finemeshes, filling over the lamina in almost
equal at about 20 per cm in density.
Text-fig. 11 drawn from PI. 32, Fig. 4
shows the pinna form and the detailed
venation.
Remarlzs: The present specimens
agree with the original specimen of thisspecies described by OISHI from Yambaraof the Itsuki (or Ittsuki) Bed, the equivalent of the Oguchi Formation, exceptthat their basal margins are less reniform.

TAKAHASHI and NAITO (1950, p. 188)
combined Dictyozamites kawasakii and
D. reniformis based on their material
from the Kiyosue Formation, Yamaguchi
Prefecture. The result of our observationof many specimens obtained from the
Oguchi Formation, however, made us
believe that D. kawasakii was distinct
and text-fig. 2 (TAKAHASHI and NAITO)
agreed well with the present specimens.
OISHI (1936) stated that "An isolated
pinna may remind one strongly of Chiropteris. But, as the pinnate habit of thegenus Chiropteris is not yet known, it isappropriate to use the generic name Dietyozamites for the present specimens."
We agree.
Occurrence: Common.
Specimens: KM-433-1, KM-57003, KM59010, KM-75001 and many pinna fragments.
Dictyozamites tetoriensis KIMURA

and SEKIDO, sp. nov.
PI. 31, Fig. 2; Text-fig. 16

Diagnosis: Leaf probably elongate,
length unknown, more than 7 cm longand 5.5 cm wide at 5 em below the apex.
Rachis slender, bearing pinnae on its
upper surface. Pinnae set closely, often
overlapping, occasionally just separate,arising nearly perpendicularly, and still
at a wide angle in the apical portion.
Pinnae lanceolate, up to 3 em long, 1.1 em
wide at the widest portion, narrowing
gradually to an obtuse apex, attached bya small area on middle basal margin;
basal margin ret use, neither basal angles
expanded. Nerves distant, 5-7 in number
at base, diverging and anastomosed toform polygonal meshes; meshes 0.5-0.8
em long and 1-2 mm wide.
Comparison & remark s : One, in PI.
31, Fig. 2 gives the main basis of the660.

Dictyozamites and some other cycadophytes

diagnosis. Dictyozamites tetoriensis isdistinguished . from all species by the
distant nerves arising from the small
area at the pinna base. Dictyozamites
tateiwae OISHI (1936, p. 28, pI. 9, fig. 3;
text-fig. 3) is similar but has far more
densely crowded nerves at about 20 per
cm in density. Dictyozamites tetoriensis
is named after the Tetori River.
Occurrence: Rare.
SPecimens: KM-61468 (Holotype), KM71008.

303

PI. 31, Fig. 3; Text-fig. 741, figs. 1-5; text-fig. 19a) from the Lower
Cretaceous of Southern Primorye also
has distant nerves, but differs in its
larger and shortly stalked pinnae.
Dictyozamites crusinensis KON'NO (1972,
p. 155, pI. 32, figs. 3, 4a; text-fig. 4D)
from the Upper Triassic Bed of Sarawak,
East Malaysia, is similar in pinna outline
and size, but differs in its more crowded
nerves.
Dictyozamites yamazakii is named inhonour of Mr. K. YAMAZAKI, an instructor of the Komatsu City Girl's HighSchool, who has cooperated with us incollecting fossil plants for fifteen years.
Occurrence: Rare.
SPecimens: KM-65010 (Holotype) andseveral leaf-fragments.

1967. Dictyozamites sp. (sp. nov. ?) KIMURA
and SEKIDO: p. 417, pI. 3, fig. 1 (Mekkodani of the Oguchi Formation).

Dictyozamites sp.

Dictyozamites yamazakii KIMURA

and SEKIDO, sp. nov.

Diagnosis: Leaf small, approximate
dimensions 3 cm long and 2 cm wide, withvery slender rachis, up to 1.5 mm wide.
Pinnae delicate, alternate, set closely,
oval with rounded apex, attached by the
middle point of pinna base to the uppersurface of the rachis, sessile. Nervesdelicate, distant, about 10 per cm indensity, radiating from the attachment,
anastomosing to form polygonal meshes;meshes 0.3-0.5cm long and 1-1.5mm wide.
Comparison & remarks: Several fragments of the delicate leaf were obtained,
one of which is enlarged and shown in
PI. 31, Fig. 3 (reinserted from pI. 3, fig. 1of our previous paper) on which theabove diagnosis is based. This species
is distinguished from all others by its
oval pinnae with distant nerves.
Dictyozamites grossinervis YOKOYAMA(1889, p. 56, pI. 7, fig. 10) from Kuwashima (formerly Shimamura) of the Oguchi Formation and recently by KRASSILOV (1967, p. 153, pi. 40, figs. 2-4; pI.

1961. Otozamites dr. beani(LIKDLEYandHUTTON) BRONGl\IART: KIl\WRA, p. 27,

text-fig. 5 (Mekkodani of the Oguchi
Formation).
1966. Otozamites? sp. KIMURA and SEKIDO:
p. 3, pI. 2, fig. 3 (Mekkodani).

Remarks: The two specimens cited
above and some newly collected fragments all show nerve anastomosis andmust be placed in Dictyozamites. But
although we consider that their characters-a long leaf with round, overlapping and obliquely set pinnae distinguishthem from any other Japanese species.
We consider them insufficiently known
for specific description. The most similar
specimen is one illustrated by KRASSILOV(1967, pl. 42, fig. 1) from the Lower Cretaceous of Southern Primorye, under thename of Dictyozamites cordatus (KRYSHTOFOVICH) PRYNADA.
Occurrence: Occasional.
SPecimens: KM-59005, KM-63007.

304

Tatsuaki KIMURA and Shinji SEKIDO

Cycadales
Genus Ctenis LINDLEY and HUTTON,

1834
In 1972, we described Ctenis keneharai
YOKOYAMA, C. nipponica, sp. nov. andC. sp. from the Oguchi Formation. We

now suspect that Ctenis nipponica may
be the same as C. kaneharai, but better
material is needed before we regard it
as a synonym. Better material of C. sp.
enables us to identify it as C. burejensis
PRYNADA of the Lower Cretaceous of
East Siberia. We also add Ctenis cfr.
formosa VACHRMAEEV.

Text·figs. 34-37.

34. Ctenis burejensis PRYNADA; typical pinna reproduced from VAKHRAMEEV and
DOLUDENKO, 1961, text-fig. 26.
35. Ctensis burejensis PRYNADA; typical pinna from the Oguchi Formation; present
work (KM-71002).
36. Ctenis nipponica KIMURA and SEKIDO; reproduced from KM-57101 (KIMURA,
1961, pI. 6, fig. 2; KIMURA and SEKIDO, 1972, pI. 45, fig. 2).
37. Ctenis nipponica KIMURA and SEKIDO; reproduced from KM-61328 (KIMURA and
SEKIDO, 1972, pI. 45, fig. 1).

660.

Dictyozamites and some other cycadophytes

305

Key to the Oguchi species of Ctenis
1 I-P~nna length about twice it.s W.idth ...................................... C. burejensis-Pmna length more than tWice Its length ............................................ 2
2 I-P~nna length up to f.our times. its \~idth .' ............................. C. nipponica-Pmna length exceedmg four times Its width .......................... C. kaneharai
C. cfr. formosa is too little known (in Japanese specimen) to be placed in a key.

Ctenis burejensis PRYNADA, 1934
Text-figs. 35, 38, 39
1934. Ctenis burejensis PRYNADA: in KRYSHTOFOVICH and PRYXADA (1934), p. 70,
fig. 25-2 (Lower Cretaceous of Ussuri).
1935. Ctenis sp. TOYAMA and OISHI: p. 66,
pI. 4, fig. 1 (Jurasso-Cretaceous ofNortheastern China).
1957. Ctenis burejensis PRYNADA: KRYSIITOFOVICII, p. 287, fig. 268-1 (Lower
Cretaceous of U ssuri).
1961. Ctenis burejensis PRYNADA: VAKIIRA:VIEEV and DOLCDENKO, p.89, pI. 39,
figs. 1, 2; pI. 40; text-fig. 26 (JurassoCretaceous of Bureja Basin).
1963. Ctenis burejensis PRYNADA f. typica
PRYNADA: SAMYLINA, p. 82, pI. 10,
figs. 3-6; pI. 11; pI. 12, figs. 1-5 (Lower
Cretaceous of Aldan).
1972. Ctenis sp. (n. sp. ?) KI~lu\u. and SEKIDO: p. 365, pI. 4£1, fig. 3; pI. 45, fig. 3;
text-fig. 2E (Mekkodani of the Oguchi
Formation) .
1974. Ctenis sp. cfr. C. burejensis PRYNADA:KIMURA and SEKIDO, pI. 1 (in association with Tetoria endoi, a cycad withbipinnate frond) (Mekkodani of the
Oguchi Formation).

Description:
Many new specimens
were collected. Leaf in Japanese material
probably large. Text-fig. 38 (KM-71002)
shows a leaf fragment, more than 13 cm
long and 11.5 cm wide. Rachis fairly
slender, 4 mm thick measured at thebroken proximal end, then narrowing
gradually, 1.5 mm at the upper part,
longitudinaly striated, bearing pinnae
laterally. Pinnae variable in shape, tri-

angular, elongate-oval or ovate, 7 cm X
2.6 cm, 4.4 cm X 2.5 cm to 3.5 cm X 2.5 cm,
arising nearly perpendicularly in contact.
Acroscopic margin strongly curving,
mostly directed backwards at apex, andbasiscopic margin nearly straight, meeting at obtuse or blunt apex. Margins,constricted near the base, particularly
the acroscopic one usually constrictedbasally, expansion follows inevitably.
Nerves prominent, parallel at base thendichotomously forking and anastomosing
to form elongate meshes, ending at themargin, often decurrent at base, about 8
per cm in density.
Judging from general appearance of
pinnae and coarse nerves. Text-fig. 39(0-17) is probably near a leaf apex. It
was broken during collection.
The specimen (KM-61452) figured by
KIMURA and SEKIDO (1974, pI. 1) andregarded as Ctenis sp. cfr. C. burejensis,
associating with a large impression of bipinnate cycad, Tetoria endoi, is although
its pinnae are remotely set, referable ingeneral feature to this species.
The specimen (KM-61450) regarded as
Ctenis sp. (n. sp.?) and figured by us(1972, p. 365, pI. 44, fig. 3; pI. 45, fig. 3;
text-fig.2E) is now also referable to thisspecies, because its pinna outline is likethat of the specimen shown in Textfig. 38.
Comparison & remarks: It is difficult
to distinguish externally the present
specimens from the Siberian species
Ctenis burejensis and its varieties (f.
tYPica and f. rarinervis) of which pinna

306

Tatsuaki KIMURA and Shin}i SEKlDO
3840------o

1
I

2
I

em

Text-figs. 38-41.
38. Ctenis burejensis PRYNADA; middle part of a leaf (KM-71002).
39. Ctenis burejensis PRYNADA; apical part of a leaf (D-17).
40. Ctenis cfr. formosa V AClIRAMEEV; showing a leaf apex in which the apicalnotch is reconstructed from the specimen shown in PI. 30, Fig. 3 of the present
work. ( x 1/2)
41. Nilssonia lobatidentata VASSILEVSKAJA; KM-75-309-1.

outline and coarse nerves are quite characteristic, though the present specimens
have rather denser nerves than those of
the Siberian ones.
As was stated before (KIMURA and
SEKIDO, 1972, p. 365, text-fig. 2), Ctenis
auriculata FONTAINE? and Ctenis uwatokoi TOYAMA and OISHI resemble thepresent species. Ctenis auriculata? described by FONTAINE (in WARD, 1905, p.
117, pI. 29, fig. 1) from the Jurasso-Cretaceous of Oregon resembles the present
species in its coarse nerves but differs
in pinna outline. Ctenis uwatokoi originally described by TOYAMA and OISHI(1935, p. 65, pI. 3, figs. 2, 3) from theJurassic of Chalai-nor, North Hsingan,

Northeastern China and later described
by SZE and XU (or HsU) (1954, p.56, pI.
49, figs. 2, 3) from the same locality, resembles C. burejensis in pinna outline,
but C. uwatolwi showing small-sizedlanceolate leaf-outline, 10.5 cm long and
4.5 cm wide at the middle widest portion,is different from C. burejensis having
fairly large leaf as shown in Text-fig. 38.
Ctenis sp. described by TOYAMA andOISHI (1935, p. 66, pI. 4, fig. 1) is probably
identical with the present species.
Occurrence: Common.
Specimens: KM-71002, KM-61452, KM61450, D-17 (collected by Dr. A. ISHII,Tokyo Gakugei University) and manyleaf-fragments.

660. Dictyozamites and some other cycadophytes
Ctenis cfr. formosa V ACHRAMEEV, 1961
PI. 30, Fig. 3; Text.fig. 40

Compare:1961. Ctenis formosa V ACHRAMEEV: V AKI-I·
RAMEEV and DOLUDENKO, p. 91, pI. 41,
figs. 1, 2; text.fig. 27 (Jurasso.Creta.
ceous of Bureja Basin).

Remarks: The only specimen is thefragment of a leaf apex and all its visible
characters are displayed in our figures.
This specimen resembles closely that
illustrated and described by VAKHRA·
MEEV and DOLUDENKO from the Jurasso·
Cretaceous of Bureja Basin, under the
new name of Ctenis formosa, though theSiberian specimen is more smaller in size
than the present one.
We have nothing more to say about
this specimen because leaf apices arevery inconstant within a species of pin.
nate leaves.
In the drawing of Ctenis yabei from theUpper Triassic of Nariwa (OISHI, 1950,
pi. 27, fig. 2), the leaf apex was wrongly
reconstructed by OISHI as rounded with·out notch.
We here regard provisionally the pre·sent specimen as Ctenis cfr. formosa.
Occurrence: Rare.
Specimen: KM-71005.

Genus Nilssonia BRONGNIART, 1825
Isolated Nilssonia leaves are abundantin the Kuwashima sandstone and shale
alternation member, Oguchi Formationfrom which Nilssonia kotoi, N. nippon.
ensis, N. orientalis and N. ozoana havebeen known.
The leaf Nilssonia nipponensis has beenfound attached to a slender stem withspirally arranged dwarf shoots and thestem and leaves together have been
named Nilssoniocladus nipponensis (KI.

307

MURA and SEKIDO, 1975, p. 113; in thispaper we stated erroneously the specificsuffix as nipponense). Bnt the isolate
leaf is correctly named Nilssonia nippon.
ensis.
Recently we found in our collection
three Nilssonia leaf·fragments with amarkedly dentate distal margin from the
Oguchi Formation and also from theUpper Neocomian Akaiwa Formation
respectively. The specimens from the
Akaiwa Formation will be shown in detailin our later paper.
Nilssonia lobatidentata

VASSILEVSKAlA, 1972
Text·fig. 41

1972. Nilssonia lobatidentata V ASSILEVSKAJA :p. 322, pI. 74, figs. 1, 2 (Lower Creta·
ceous of the Lena Basin).
1963. Nilssonia lobatidentata V ASSILEVSKAJA :V ASSILEVSKAJA and PAVLOV, pI. 6,
figs. 1-3 (Lower Cretaceous of the
Lena Basin).
1970. Nilssonia lobatidentata V ASSILEVSKAJA :ABRAMOVA, p. 45, pI. 4, figs. 2-5 (Lower
Cretaceous of the Lena Basin).

Description: Text·fig. 41 (KM-75-3091) shows three Nilssonia leaf fragments
preserved on one slab. The leaf is pos·sibly oblanceolate in outline, tapering
gradually below. The lamina is devided
into segments of very uneven width.
They are commonly equal to length in
the lower part as shown in Text·fig. 41,
but longer than broad in the middle andupper part of leaf. The shape of thesegments is very varied and the distal
margin mostly irregularly dentate, often
forked.
Remarks: The present specimens gen·erally agree with those described as
Nilssonia lobatidentata by V ASSILEVS·
KAlA and ABRAMOVA from the Lower

308

Tatsuaki KIMURA and Shinji SEKIDO

Cretaceous of the Lena Basin.
Nilssonia orskica originally describedby GENKINA (1963, p. 64, pI. 32, figs. 8,9;
pI. 33, figs. 1, 2) from the Middle Jurassicof Eastern Ural, is also with dentate
distal margin, but N. orskica differs fromthe present species in that it has rectangular segments.
Nilssonia prinadae originally describedby V AKHRAMEEV (V AKHRAMEEV and
DOLUDENKo, 1961, p. 95, pI. 42, fig. 3;
pI. 43, fig. 1) from the Jurasso-Cretaceousof the Bureja Basin, is rather similar to
N. lobatidentata, but its distal margin isless strongly dentate.
Nilssonia serrulata originally describedby OISHI (1940, p. 317, pI. 26, figs. 8, 8a)from the Lower Cretaceous NagdongGroup, Korea differs in lacking a dentate
distal margin.
Nilssonia magnifolia SAMYLINA (1964,
p. 73, pI. 13, figs. 1-3; pI. 15, figs. 1, 2;
pI. 16, figs 6, 7; pI. 17, fig. 1) from theLower Cretaceous of the Kolyma Basin,
is a much longer leaf, but the segments
are often dentate or serrate.
Besides the above, Nilssonia leaves
with more or less dentate margin are
known as Nilssonia denticulata THOMAS(1911, p. 88, pI. 7, figs. 3-5) from theJurassic of Kamenka and as Nilssonia
compta (PHILLIPS) BRONN (see HARRIS,
1969). Unfortunately we could not com-pare here Nilssonia serrata PRYNADA
with the present one, because we havenot acquainted its paper.
At any rate, these Nilssonia leaves withdentate distal margin are mostly of Siberian habitants. The new occurrenceof this species and its allied form (to be
described later on) with markedly dentate
distal margin from the Oguchi Formation
might be worth mentioning.
Occurrence.- Rare (but fairly abundantin the Akaiwa Formation).
Specimen.- KM-75-309-1.

Localities and material
Specimens with letters KM- in registered number were from the equivalentof the Kuwashima sandstone and shale
alternation member, the Oguchi Formation, exposed at the upper course of
Mekkodani, a branch of the Tetori River,Ozo, Oguchi-mura, Ishikawa-gun, Ishikawa Prefecture, and are deposited in
the Komatsu City Museum, Komatsu,
Ishikawa Prefecture.
A specimen with letter D- in registerednumber was collected by Dr. A. ISHII fromthe same locality as the above, and isdeposited in Department of Astronomy
and Earth Science, Tokyo Gakugei University.

Explanation of Plate 30
Figs. 1,2. Dictyozamites auriculatus K1MURA and SEKlDO, sp. nov.
1. Showing markedly auriculated acroscopic basal angle (Holotj·pe, KM-6141S). Loc. Mekkodani. nat. size.
2. Showing pinna base enlarged from the Holotype. x 2.
Fig. 3. Ctenis dr. formosa VACHRAMEEV; Showing two apical pinnae and two lateral ones
incompletely preserved (KN' -71005). Loc. Makkodani. x O. S.
Figs. 4,5. Otozamites pseudoanglica K1MURA and SEKlDO, sp. nov.
4. Showing two leaf-fragments which appear to converge towards a supposed common
support below (Holotype, KM-71003). Loc. Mekkodai. nat. size.
5. Showing a similar leaf-fragment to the above (KM-71004). Loc. Mekkodani. nat. size.

KIMU RA and SEKIDO:

Dictyozamites and some othe1' cycadophytes

Plate 30

660.

Dictyozamites and some other cycadophytes

A specimen with letters KU-Y in reg·istered number was collected by Y. KANSHA from Kuwashima (a classical localityof the Oguchi Flora), Shiramine-mura,
Ishikawa-gun, Ishikawa Prefecture, andis deposited in Department of Astronomy
and Earth Sciences, Tokyo Gakugei U niversity.
References
ABRAMOVA, L. N. (1970): Early Cretaceous
flora from Zygansk and the adjacent areaof the Lena Basin. Palaeont. Biostr., B.
29, p. 36-57, pIs. 1-10 (in Russian).
ARCHANGELSKY, S. and A. BALDONI (1972):
Dictyozamites cazaubonii nuevo nombre
para Dictyozamites hallei CAZAUBON non
SAl-IN[ et RAO. Ameghiniana, t. 9, no. 1,
p. 91.
- - and - - (1972): Revision de las Bennettitales de la formacion Baquero (Cretacico Inferior), Provincia de Santa Cruz.
I. Hojas. Rev. Mus. La Plata (N. S.),
Palaeont., t. 7, p. 195-265, pIs. 1-16.
BARNARD, P. D. W. (1965): Flora of theShemshak Formation. Pt. 1. Liassic
plants from Dorud. Riv. Ital. Paleont.,
v. 71, n. 4, p. 1123-1168, pIs. 95-99.
FONTAINE, W. N. (1905, in WARD, L. F.) :Status of the Mesozoic floras of theUnited States. U. S. Ceol. Surv. Mon., 48,
p. 1-616, pIs. 1-45.
GENKINA, R. Z. (1963): Fossil flora of the
Mesozoic coal-bearing deposits of theEast Ural-field of Orsk Coal-Basin. Acad.
Nauk, Moscow, 1-115, pIs. 1-51 (in Rus·sian) .
GEYLER, H. T. (1877): Ueber fossile Pflan·
zen aus der Juraformation Japans. Palaeontgr., Bd. 24, p. 221-232, pIs. 30-34.
HALLE, T. G. (1912): On the occurrence ofDictyozamites in South America. Palaeob.
Zeitschr., Bd. 1, H. 1, p. 40-42.
--- (1913): Some Mesozoic plant-bearing
deposits in Patagonia and Tierra delFuego and their floras. K. sve. Vet. Acad.
Handl., Uppsala and Stockholm, Bd. 51,
no. 3, p. 1-58, pIs. 1-5.

309

HARRIS, T. M. (1949): Notes on the Jurassic
flora of Yorkshire, 40-42. 40. Otozamites
anglica (SEWARD) n. comb.; 41. The
narrow leaved Otozamites species; 42.
Ptilophyllum hirsutum THOMAS and BANCROFT and its differentiation from P.
pecten (PHILLIPS). Ann. Mag. Nat. Hist.,
London, ser. 12, vol. 2, p. 275-299.
- - (1964): The Yorkshire Jurassic flora,
II. Caytoniales, Cycadales and Pterido·
sperms. Brist. Mus. (Nat. Hist.) , p. 1185, pIs. 1-7.
- - (1969): The Yorkshire Jurassic flora,
III. Bennettitales. Ibid., p. 6+ 1-186, pIs.
1-7.
KAWAI, M. (1961): Late Mesozoic crustal
movements in the Hida Plateau, Central
Honshu, Japan. Mem. Fac. Sci., Kyushu
Univ., ser. D, Geol., vol. 11, no. 3, p.
347-380.
KIMURA, T. (1958): Mesozoic plants fromthe Kizaki District, Nagano Prefecture,
Japan. Jubl. Publ. Comm. Prof. H. FUJIMOTO, p. 135-138.
- - (1958) : On the Tetori flora, Pt. 1,
Mesozoic plants from the Kuzuryu Subgroup, Tetori Group, Japan. Bull. Sen.
High Sch., Tokyo Univ. Educ., no. 2-2,
p. 1-47, pIs. 1-4.
- - (1959): On the Tetori flora, Pt. 2, Addition to the Mesozoic plants from theKuzuryu Subgroup, Tetori Group, Japan.
Ibid., no. 3, p. 104-117, pIs. 1-2.
- - (1961): Mesozoic plants from the Ito·shiro Subgroup, the Tetori Group, Central
Honshu, Japan. Pt. 2. Trans. Proc. Palaeonto Soc. Japan, N. S., no. 41, p. 21-32,
pIs. 4-6.
- - (1967): On the Middle-Upper Jurassic
and Lower Cretaceous floras. Fossils, nos.
19-20, p. 11-24 (in Japanese).
- - (1975): Middle-late early Cretaceous
plants newly found from the upper courseof the Kuzuryu River area, Fukui Prefecture, Japan. Trans. Proc. Palaeont.
Soc. Japan, N. S., no. 98, p. 55-93, pIs.
5-8.
- - and HIRATA, M. (1975) : Early Cretaceous
plants from Kochi Prefecture, Southwest
Japan. Mem. Nation. Sci. Mus., no. 8, p.

310

Tatsuaki KIMURA and Shin}i SEKIDO

67 -90, pIs. 10-13.
- - and SEKJDO, S. (1963): On the Tetori
flora-A summary notes on the Itoshiro
flora, with special reference to the Mesozoic floral provinces of the Japanese Islands. Fossils, no. 6, p. 35-46 (in Japanese) .
- - (1966): Mesozoic plants from the Itoshiro Subgroup, the Tetori Group, Central
Honshu, Japan. Pt. 3. Mem. Mejiro Cakuen Woman's Jr. Coll., vol. 3, p. 1-7, pIs.
1-4.
- - (1967): Some Mesozoic plants from the
Itoshiro Subgroup, the Tetori Group,
Central Honshu, Japan. Prof. SHIBATA
Mem. Vol., p. 416-419, pIs. 1-3.
- - and - - (1972): Ctenis species fromthe Itoshiro Subgroup (Lower Cretaceous), the Tetori Group, Central Honshu, Japan. Trans. Proc. Palaeont. Soc.
Japan, N. S., no. 86, p.360-368, pIs.
44-45.
- - and - - (1974): Bipinnate cycadean
fronds newly found from the Lower Cretaceous Itoshiro Subgroup, the Tetori
Group, Central Honshu, Japan. "Symposium on Morphological and Stratigraphical
Palaeobotany", Spec. Publ., no. 2, BIRBALSAHNI Inst. Palaeobot., p. 23-27, pIs. 1-3.
- - and --- (1975): Nilssoniocladus, n. gen.
(Nilssoniaceae n. fam.), newly foundfrom the early Lower Cretaceous of Japan. Palaeontogr., B, Bd. 153, p. 111-118,
pIs. 31-32.
KON'NO, E. (1~72): Some late Triassic plantsfrom the southwestern border of Sara-

wak, East Malaysia. Ceol. Palaeont. SEAsia, Tokyo Univ. Press, vol. 10, p. 125278, pIs. 24-32.
KRASSILAV, .V. A. (1967): Early Cretaceous
flora from Southern Primorye and its
significance for stratigraphy. Moscow, p1-248, pIs. 1-93 (in Russian).
KRYSHTOFOVICH, A. N. (1929): Discovery of
the oldest dicotyledons of Asia in theequivalent of the Potomac Group in Sut-schan, Ussuriland, _ Siberia. Bull. Com_
Ceol. Leningrad, vol. 48, no. 9, p. 13571390 (in Russian).
- - (1957):
Palaeobotany(Text-book).
Leningrad, p. 1-650 (in Russian).
- - and PRYNADA, V. D. (1932): Contribution to the Mesozoic flora of theUssuriland. Bull. Ceol. Prosp. Servo
U.S.S.R., vol. 51, p. 363-373, pIs. 1-2.
MATSUO, H. and OMURA, K. (1968): On the
Taeniopteris from the Togadani flora(Tedorian), at Togadani, Ishikawa Prefecture, Central Japan. Trans. Proc.
Palaeont. Soc. Japan, N. S., no. 71, p_
285-295, pI. 29.
MENENDEZ, C. A. (1966): Fossil Bennettitales
from the Tico flora, Santa Cruz Province,
Argentina. Brit. Mus. (Nat. Hist.), Ceol.,
vol. 12, no. 1, p. 1-42, pIs. 1-19.
MOLLER, H. (1903): Bidrag till Bornholm
fossila flora (Rhiit och Lias), Gymnospermer. K. sve. Vet. Acad. Hendl., Stockholm, Bd. 36, no. 6, p. 1-56, pIs. 1-7.
NATIIORST, A. G. (1878, 1879, 1886): Om
floran i Skanes Koeforande Bildningar,
1. Floran vid Bjuf. Sverig. geol. Unders.

Explanation of Plate 31
Ctenozamites sp. ; Showing outline of segments and comparatively thick rachis in lower
surface view, both ends of the present leaf omitted here (KU-Y0016, collected by Y.
KANsr-IA). Loc. Kuwashima. x 3.
Fig. 2. DictyiJzamites tetoriensis KIMURA and SEKJDO, sp. nov.; (Holotype, KM-61468). Loc_
Mokkodani. xl. 5.Fig. 3. Dictyozamites yamazakii KIMURA and SEKJDO, sp. nov.; Reinserted from KIMURA andSEKJDO, 1967, pI. 3, fig. 1 enlarged (Holotype, KM-65010). Loc. Mekkodani. x 2.
Figs. 4,5. Otozamites endoi KIMURA, em. KIMURA and SEKJDO.
4. (KM-71006). Loc. Mekkodani.-- nat. size.
5. Showing pinna outline and venation enlarged from the above. - x 2.
Fig. 1.

KIMURA and SEKIDO:

Dictyozamites and some other cycadophytes

Plate 31

660. 'j)i,ctyoz:amites and some other cycadophytes
A/h., Stockhollf!"n(C), nos. 27, 33, 85, p.
1-131, pis. 1-26",- - (1889): Sur la presence du ,genre Dictyozamites OLDHAM dans;le couches jurassiquescle Bornlwlm .. Bull.. de l' Acad,
Royale Danoise Des Sciences et des Lettres
pour Lannee, p. 96-104, pI. 5.
OISHI, S. (1933): On the Tetori Series, withspecial reference to its fossil zones, Pt.
1. Jour. Ceol. Soc. Tokyo, voL"40, no.
481, p. 61.7-644; Pt. 2, Ibid;, no. 482, p.
669-699.
- - (1936) : On the Japanese species of Dictyozamites. Japan. Jour. Ceol. Ceogr., vol.
13, nos. 1-2, p. 25-30, pI. 9.
- - (1940): The Mesozoic floras· of Japan.
Journ. Fac. Sci., Hokkaido<Imp. Univ.,
Sapporo, ser. 4, vol. 5, p. 123-480, pis.
1-48.
SAMYLINA, V. A. (1963): Mesozoic flora of
the lower course of the Aldan River.
Trudy bot. Inst. Akad. Nauk, SSSR, ser.
8, palaeobot., vol. 4, p. 59-138, pis. 1-37
(in Russian).
- - (1964): Lower Cretaceous flora fromthe Central Sikhota-Alin. Bot. Jour., vol.
49, p. 1286-1287 (in Russian).
- - (1964): Mesozoic flora of the area to'the west of the Kolyma River (Zyrianka.
Coal-Basin). Pt. 1. Trudy bot. Inst. Akad.
Nauk, SSSR, ser. 8, palaeobot., vol. 5, p ..
41-78, pis. 1-18 (in Russian).
SWARD, A. C. (1900): The Jurassic flora, 1.
The Yorkshire coast. Catalogue of the
Mesozoic plants in the Department of
Geology, British Museum (Natural History). Brit. Mus. (Nat. Hist.), p. 12+1341, pis. 1-21.
- - (1903): On the occurrence of Dictyozamites in England, with remarks on theEuropean and Eastern Mesozoic floras.
Quart. Jour. Ceol. Soc. London, vol. 59,
p. 217-233, pl. 15.
- - (1917): Fossil plants. A text-book forstudents of botany and geology, vol. 3.
Cambridge, p. 18+1-656.
SZE, H. C. and XU, R. (1954): Index fossils ofChina-plants. Di-zhi Chu-ban-she, ,Peking,p. 1-99, pis. 1-69 (in Chinese).
TAKAHASHI, E. and NAITO' G., (1950): Dic-

311

tyozamites from the Jurassic Toyonishi
Series of Pro,v. Nagato. Jour. Ceo!. Soc.
Japan, voI..56', no. 655, ,po 188. 'THO'MAS, H. H. (1911) ~ The Jurassic flora ofKamenka in the District of Isiu~. Mem.
Com. geol. St.-Petersb. (N. S.), vol. 71, p.
1-95, pis. 1-8.
TO'YAMA, S. and OISHI, S. (1935): Notes onsome Jurassic plants from Chalai-nor
Provo North Hsingan, Manchoukuo. Jour.
Fac. Sci., Hokkaido Imp. Univ·., vol. 4,
no. 3, p. 61-77, pis. 3-5.
VAKHRAMEEV, V.A. (1964): . Jurassic andearly Cretaceous floras of Eurasia and thepalaeo floristic provinces of this period.
USSR Acad. Sci. Trans., 102, p. 1-261(in Russian).
- - (1966): Jurassic floras of the USSR.
Palaeobotanist, voL 14. nos. 1-3, p. 118123.
- - (1970): The first discovery of Bennettitalean Dictyozamites from the Mesozoic
of Siberia. Palaeont. Jour. no. 4, p. 120123 (in Russian).
- - (1971): Development of the early Cretaceous flora in Siberia. Ceophyt., 1 (1),p. 75-83.
- - and DOLUDENKO, M. P. (1961): Upper
Jurassic and Lower Cretaceous flora of
the Bureja Basin and its signiflcance forstratigraphy. USSR Acad. Sci. geol. Inst_
Trans., vol. 54, p. 1-135, pis. 1 -40 (ill!
Russian).
VASSILEVSKAJA, N. D., IMINOV, Y. Kh., LoSEVA, N.M. and MOGUTCHEVA, N.K.
(1972) : New Mesozoic gymnosperm~
from Central Asia and Siberia in "Newtypes of ancient plants and invertebratesof USSR". Acad. Nauk USSR, Moscow"
p. 319-324, pis. 73-74 (in RUSSian).
- - and PAVLOV, V. V. (1963): Stratigraphy
and flora from Cretaceous beds of LenaOlenek region of Lena Coal-Basin-II.
Problems of oil and gas content beds in
Arctica . .Trudy nauchno--issled. Inst. ,ceol.
Arkt., t. 128, p. 1-96, pis. 1-49 (in Russian).
_YABE, H. (1905): - ,Mesozoic plants from
,Korea. Jour. Call. Sci., Imp. Univ. Tokyo, vol. 22, no. 8, p. 1-59, pis. 1-4.

312

Tatsuaki KIMURA and Shinji SEKIDO- - (1922): Notes on some Mesozoic plantsfrom Japan, Korea and Chiqa, in the collection of the Institute of Geology andPalaeontology of the Tohoku Imperial
University. Sci. Rep. Tohoku Imp. Univ.,
Sendai, sec. ser. (Geol.), vol. 7, no. 1, p.
1-28, pis. 1-4.
......
Akaiwa7ffi'Ei
Chalai-nor
J'L ~ Mdfi
Hsingan
JI!!
Itoshiro;0 f(jI( ~Kiyosue
KizakiiIF.f
Komatsu'j't'~
Kuwashima (Kuwajima) ~~Kuzuryu:fL jiJ( """
It!.

m

*

*
*

- - (1927): Cretaceous stratigraphy of theJapanese Islands. Ibid., vol. 11, ·no. 1, p.
27-100, pis. 3-9.
YOKOYAMA, M. (1889): Jurassic plants from
Kaga, Hida and Echizen. Journ. CoIl. Sci.,
Imp. Univ. Tokyo, vol. 3, no. 1, p. 1-66,
pis. 1-14.

Mekkodani
Mochiana
Nagdong (Naktong)
NariwaOguchiRyoseki
TetoriTogadani
Ushimaru

§

it

~

:M'

/I:

rti.

3fl

m

~

~

J:J

M

;0

~

1&

m ?" ~
11.
.tt-

Explanation of Plate 32
Figs. 1-3. Dictyozamites ishikawaensis KIMURA and SEKIDO, sp. nov.
1. Reinserted from KIMURA and SEKIDO, 1966, pI. 2, fig. 2 (Holotype, KM-63010).
Mekkodani. nat. size.
2. Showing a middle portion of a leaf (KM-690014). Loc. Mekkodani. nat. size.
3. Showing a typical pinna enlarged from the Holotype. x 2.
Fig. 4. Dictyozamites reni/ormis OISHI; (KM-433-1). Loc. Mekkodani. nat. size.

Loc.

K I MURA and SEKIDO:

Dictyozamites and some other cycadophytes

Plate 32

313

PROCEEDINGS OF THE PALAEONTOLOGICAL SOCIETY
OF JAPAN

B *tl iE ~~~ 1976 ~1t~~ . ~~Ii, 1976 ~1 Jj 30 (~) . 31 (±) fo!IT B i.::.*~I::*~JIIlll!J"1'81 ~ ~:T-~/'?i'-I'::'~\"L~Hl!~.hk: (~~~ 511;).
;m9~~~1±1 Itfllili

IGCP Project: Mid-Cretaceous Events, 1stConference *~t~*~~~UNESCO-lUGS I.::. J: Q*m7 ~7:1t!!.~'W~tt:*i..................

~~~~*~......................

~EB~~~

fl::E-If" /'01" 7Jl..rY -If" /' O1·'!iI!n.::. ~-r Q ~ 2 @] @l~://,;f-~':7A*~.................... ~EB~~~ 1 @]lfl:iE 1fiL!R@l~~~ (7J:T ?i'-) *~..... .

.................................. Et3~f!f:m
IPOD Panel Meeting on Ocean Paleoenvironment ('7 -'E' /' r) *~jl1Ij;WUr'Fn.............. ..
..
..................................

*m7 ~7:1t!!.~~im(~~ (1 /' F';f. :/7) *~.................................. if!llr=~~~12@]7J@lifii~~~~ ( 1/ =- /' 7" '7 -F) *~l:Itr"j-~

00 A.

~

~

Fusulinids and geological structure of the
Hakusan Limestone in Gifu Prefecture ..
............ T. CHISAKA & J. MATSUMURA
mg§~.J1l,1tl;~*.J1l,1;if~t;!iiii!RftE(7*) ....
.................................. Em ~.

Phylogenetic significance of the fusulinacean genus Montiparus, with several species of Japan ................... T. OZAWA
Restudy of the Miocene planktonic Foraminifera from Shimoshiraiwa, Izu Peninsula,
Japan .............. T. SAMATA & H. UJIIE
Distribution and biostratigraphic singnificance of Dictyocha subarctios (silicoflagellate) in the North Pacific (f\;im) .. H. Y. LIN
Planktonic foraminifera in the Lake Waco
Formation (Eagle Ford Group), in central
Texas, U. S. A. (f\;im) ...... K. KANAMORI
Triassic coral fauna from Mt. Daifugen,
Nara Prefecture, Southwest Japan ..... .
.............. H. OKUDA & N. YAMAGIWA
On the Permian bryozoa from the northernpart of Sainbeyli, Central Turkey ..... .
· ............................. S. SAKAGAMI
Colour patterns in some Cretaceous ammonites from Hokkaido ................... .
· ........... T. MATSUMOTO & H. HIRANO
Barremian cephalopods from the Arita Formation ............ 1. OBATA & Y. OGAWA
Quantitative analysis on the problem of
sexual dimorphism in Scaphites (Cretaceous ammonites) ............ K. TANABE
Sexual dimorphism and transient polymorphism of Gaudryceras denseplicatum,a late Cretaceous ammonite .... H. HIRANO
On the internal structure of Trigonioides(s. s.) paucisulcatus ........... . S.-Y. YANG
B *.@:S!lUc=txJ'l. Neithea 0)7HJi~Et3:pJ~W•••••••..••....••••....••••.••.... ))t7J'( ;f/\.
Preliminary report of the Upper Cretaceous
mollusks from the Menabe area, Madagascar .............. Y. KANIE & 1. OBATA"Crassostrea" konbo (J:$S1IE*.@:0)t.J' ~) "· .. .. .. .. .. .. .. .. .. .. .. •• •. .. .. ... ~g!jifljl1lj

Paleogene molluscan fauna from Plateau
Series, Sarawak, Borneo ............... .
. ..................... S. KANNO & D. TAN
mlpJII~llfiitiR~O) J'l.ftEI'::' -?\, 'L......... .
... .. .... .. .. ......... !6~~~' IHr jf!i

Introduction of Checklist and Bibliographyof the Cenozoic Fossil Mollusca of Japan,
1950-1974 ........ K. MASUDA & H. NODA
Miocene mollusca from Watari-machi, Miyagi Prefecture .. K. MASUDA & H. NODA*~~O) Turritella O)*WCI.::.-?\,'L ......... .

· ....... , .. .. .. .. ...

IJ'jl1Ij~:t::. IH~1JiU"IZY~~

1f!H'C.J1l,!JlU~!'\.J1l,'@: Venus (Ventricoloidea) foveo-

lata SOWERBY .................... t~llJltlJJl~

m&""-If" 01' (Umbonium costa tum) O)7tM~Et3:pJ~W........................... ,1J'iR:gpiE

Checklist of Japanese Ostracoda ......... .
. ............................. N. IKEYA,
T. HANAI, K. ISHlZAKI & Y. SEKIGUCHI
Taxonomic studies on some fossil and-.---~--

314
Recent Balanus in Japan .. T. YAMAGUCHI~.$.~.@: -/ Iv Iv~~=~!tt;F~':' -?~, -C......... .

.......... IN*ft:...:....· ~mlii±' TRG"!';://~':"'"

Devonian trilobites of Japan, 'in cO'mparison
with Asian, Pacific and other faunas ....
............ T. KOBAYASHI & T. HAMADA
Ontogenies of three species of silicified
Middle Ordovician trilobites of Virginia(~~) ... : ....... , ................ C.H. Hu
Mesozoic plants from the Daedong Group,

Korea (Part 2) .... T. KIMURA & B. K. KIM

lJ.1:. Spirodela polyrhizaSCHElD o)1:.1m ....
.: ..': ;'.: ,::' .. ! ... ,·:ij~. f, . . ':.,}.,.'. ,.•.. 1h1lt-t~zllD
Man'churiophycus--+Spirodela from Sakari--+
Recent Spirodela polyrhiza tV*ki1E1iIf~ ....

................................

1h1lt-t~zllD

Sinomegaceros yabei (SHIKAMA) tV*fIHl)jj{~.:.

-?~'-C ...... ~~JII'i!\'5fll . :k~mz . IJ'!l!f~7 ~ /~.A,;('of- !I ;i. 9 tV*m{l)jj{t.:.-?~'-C .... '..
.... ... '.....' ..... ~' ..... :~~JII'i!\'5fll . 'NjHiB1:.

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1975~m:~t;Iij~/fjjJ~mi.lJc*t-t.~8: B*~*1:.~~P~'tV~~.. ,.
B *t~~,;~ Q *1:.~llii~lt'@:J±ltJ~il:&"t:, .-f:-tV:k~WI!lti\ii:;k:fi=R~~':' .t '? -C~JIit*15' ~.n, *1!t~ 7 p 'ljIf~tV£~11/Jl~~.nt.:o.
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l~1~ jKt~IU!L: .Notes on the.· genus Trigonioides(Bivalvia) .. Trans. Proc. Palaeon!. Soc. Japan,
N, S. No. 95, pp •. 359,40S, 6 text.figs., pis. 54, 55,. 1974.
Trigonioides ~It. KOBA Y A'sill and SUZUKI i::. J: t), 1936if., ~jE!lI',';jl¥i;gjiIJ*ll1I~l¥iITli7.Kr~11Itl J: t) tIE
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Transactions and Proceedings of the PalaeontologicalSociety of Japan

April 30, 1976 'New Series No. 101

CONTENTS
TRANSACTIONS
657.

Hu, Chung-Hung:

Ontogenies of three species of silicified Middle Ordovician

trilobites from Virginia ............. . . . . . .. .. ........ . ... . . ..... ... .. 247
658.

Distribution and biostratigraphic si g nificance of Dictyocha
subarctios (silicoflagellate) in the North Pacific ... . . ........ ... . ... . . . . 264

LING, Hsin Yi:

659. OMURA, Akio: Thorium and protactinium isotopes in some present-day
hermatypic corals, and their implications to dating ... . ....... . . . ... . . . 271
660.

KIMURA, Tatsuaki and SEKIDO, Shinji: Dictyozamites and some other cycadophytes from the early Lower Cretaceous Oguchi Formation, the Itoshiro
Group, Central Honshu, Japan . ...... . . . ..... ... ... . . ... .... . .. . ... . . . 291

PROCEEDINGS .... . . .. .......... ........ ...... .. .. . .. . ... ... .. . . .. .. .. . .. .. ... 313