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MUS. COMP. ZOOL.
LIBRARY
JUL 23 1970
HARVARD
UNIVERSITY!
POSTILLA
PEABODY MUSEUM
YALE UNIVERSITY
NUMBER 145. 25 MAY 1970
GENERIC STATUS OF THE
INOCERAMUS? TEGULATUS
SPECIES GROUP (BIVALVIA) OF
THE LATEST CRETACEOUS OF
NORTH AMERICA AND EUROPE
IAN G. SPEDEN
POSTILLA
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MUS. COMP. ZOOL.
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GENERIC STATUS OF THE INOCERAMUS?|TE@3 1970
ULATUS SPECIES GROUP (BIVALVIA) OF THE
LATEST CRETACEOUS OF NORTH AMERIGAARD
AND EUROPE UNIVERSITY:
IAN G. SPEDEN
New Zealand Geological Survey, Lower Hutt, New Zealand
(Received February 3, 1969)
ABSTRACT
Five named species of the latest Cretaceous Inoceramus? tegulatus
species group are, on present information, considered valid: two
from North America, fibrosus (Meek and Hayden) and argenteus
Conrad; three from Europe, tegulatus Hagenow, caucasicus Dobrov
and dobrovi Jeletzky. The morphology of the ligament area and the
pattern of muscle scars differentiate the species from Inoceramus,
and Tenuipteria Stephenson is the valid generic name for the broad
taxon encompassing the five species.
The five species can be divided into two lineages: a lineage of
equivalved species (tegulatus, fibrosus, caucasicus) and a lineage of
inequivalved species (argenteus, dobrovi). The equivalved species
occur in the uppermost Late Campanian, Early Maestrichtian and
lowermost Late Maestrichtian, and the inequivalved species appear
to be restricted to the Late Maestrichtian.
Tenuipteria fibrosa and argentea are redescribed and illustrated,
a neotype for argentea is designated, and a lectotype for T. tegulata
is designated.
POSTILLA 145: 45 p. 25 MAY 1970.
2 POSTILLA
INTRODUCTION
Externally similar species of Inoceramus?, characterized by relatively
strong concentric and radial plicae, occur in the latest Campanian
and Maestrichtian of Europe and North America. These species are
included by authors in a single species group, that of Inoceramus?
tegulatus Hagenow (Jeletzky and Clemens, 1965). The stratigraphic
range in regions of Europe and North America of the five species
here accepted as valid is given in Figures 1 and 2.
Species included in this group are frequently referred to in bio-
stratigraphic studies and in discussions of inter-regional correlations
among North America, Western Europe and Russia (Dobrov, 1951;
Seitz, 1959; Jeletzky, 1962). However, because of a lack of knowl-
edge of internal morphology, the generic position of I.? fibrosus
(Meek and Hayden) and the other species has been uncertain
(Jeletzky, 1962, p. 1014; Jeletzky and Clemens, 1965).
Well-preserved specimens of /.? fibrosus from the Mobridge Mem-
ber of the Pierre Shale and the overlying Fox Hills Formation in the
type area of the latter in north-central South Dakota, Western In-
terior of the United States (Waage, 1961, 1968), provide for the first
time full details of the hinge morphology and musculation of the
species. These data, together with similar data for two other mem-
bers of the species group, /.? tegulatus Hagenow from Europe and
Tenuipteria argentea (Conrad; Stephenson, 1955) from the Owl
Creek Formation, Gulf Coast, North America, permit a reevaluation
of the generic status of these species.
Abbreviations used in the text and plate captions are:
MMH — Mineralogisk-Geologiske Institut, Copenhagen, type
specimen number
NZGS—-WM — New Zealand Geological Survey, World Mollusca
Collection
UMMP — University of Michigan Museum of Paleontology
USGS — United States Geological Survey
USNM — United States National Museum
YPM — Peabody Museum of Natural History, Yale Univer-
sity, type specimen number
YPM-A_ —- — Peabody Museum of Natural History, Yale Univer-
sity, collection number
INOCERAMUS? TEGULATUS SPECIES GROUP 3
ACKNOWLEDGEMENTS
Comparison of the species of the Inoceramus? tegulatus species
group was facilitated through the loan of specimens, provision of in-
formation and discussions by the following persons whose assistance
is appreciated and gratefully acknowledged: Dr. Erle G. Kauffman,
United States National Museum; Prof. K. M. Waage, Peabody
Museum of Natural History, Yale University; Dr. J. A. Jeletzky,
Geological Survey of Canada; Dr. L. B. Kellum, Museum of Paleon-
tology, University of Michigan; Dr. Tové Birkelund, Mineralogisk
Museum, Universitetets Mineralogisk-Geologiske Institut, Copen-
hagen; and Prof. Dr. O. Seitz and Dr. F. Schmid, Niedersachsisches
Landesamt fur Bodenforschung, Hannover. S. N. Beatus took most
of the photographs for the plates. Drs. A. Wodzicki and G. A. Challis,
New Zealand Geological Survey, kindly translated parts of Polish
and Russian papers.
Drs. Kauffman, Waage, Birkelund, and G. R. Stevens and C. A.
Fleming, New Zealand Geological Survey, read the manuscript and
made valuable suggestions.
Specimens of Inoceramus? fibrosa were collected and described as
part of a dissertation for the degree of Doctor of Philosophy at Yale
University while the author was on leave from the New Zealand
Geological Survey under a New Zealand Department of Scientific
and Industrial Research National Research Fellowship.
THE INOCERAMUS? TEGULATUS HAGENOW SPECIES GROUP
NORTH AMERICAN SPECIES
Two groups of thin-shelled Inoceramus? with weak to moderately
strong radial and concentric ornament have been recognized in
latest Cretaceous sequences of the United States: (a) Equivalved or
possibly subequivalved species with moderately inflated and weakly
projecting, anteriorly situated umbones. (b) Inequivalved species
with a strongly inflated left valve possessing a projecting, swollen
umbone and a flattish right valve with a very slightly projecting
umbone.
Three names have been given to species classified in the equivalved
group. All are known only from the Western Interior.
1. Inoceramus fibrosus (Meek and Hayden, 1856a). Lectotype,
4 POSTILLA
by subsequent designation of Meek (1876, Pl. 17, fig. 17a), USNM
460, a steinkern of a right valve, oblique length 34.7 mm. Type
locality: Forks of the Cheyenne River, South Dakota. Stratigraphic
position: Pierre Shale, Early Maestrichtian.
2. Inoceramus whitii Toepelman (1922, p. 63). Location of type
material unknown (see Cobban, in Jeletzky and Clemens, 1965,
p. 958). Type locality: White River Badlands, South Dakota. Strati-
graphic position: from the “transitional beds between the Pierre and
Fox Hills” (Toepelman, 1922, p. 63), Early Maestrichtian.
Jeletzky (Jeletzky and Clemens, 1965) thought that this interval
might be equivalent to part of the Mobridge Member, at the top of
the Pierre Shale, in the Missouri Valley succession, but it could in
part be equivalent to even older Pierre Shale units (Waage, 1961,
1968).
3. Inoceramus cobbani Kellum (1964, p. 1006; = radiatus Kel-
lum, 1962, non Heine, 1929). Holotype, the original (and only)
specimen of Kellum (1962, PI. 3, fig. 17), UMMP 37433, a left valve,
length 22.9 mm. Type locality: 1924/K—6, Old Woman Creek,
Niobrara County, Wyoming. Stratigraphic position: Fox Hills Sand-
stone, Maestrichtian.
In addition to these three named “species” Cobban (1964, p.
A136) has recognized a stratigraphic succession of four forms, each
with a different pattern of ornament: :
. an early form with weak radial and concentric folds, a
later form (typical form) in which radial folds dominate over
the concentric ones, and a still later form in which radial and
concentric sculpture is of about equal strength, and a final form
in which the concentric sculpture dominates.
The typical form of J.? fibrosus is rhomboidal in shape, has strong
radial plicae and corresponds to the second group of Cobban (1964).
Inoceramus cobbani Kellum is characterized by extremely weak
radial ornament and stronger concentric plicae, and could be classed
in Cobban’s group four.
Jeletzky, in one of his important studies of the North American
species of the /.? tegulatus species group (Jeletzky and Clemens,
1965, p. 958), noted that “representatives of J. whitii always occur
in association and appear to intergrade with the more typical repre-
sentatives of Inoceramus? tegulatus” (= fibrosus, according to
Jeletzky). He considered whitii to be an extreme morphological vari-
INOCERAMUS? TEGULATUS SPECIES GROUP 5
ant of the one “‘polytypic species”. Jeletzky also placed cobbani
(= radiatus) in synonymy with whitii.
Populations of /.? fibrosus from all biostratigraphic zones of the
Fox Hills Formation in its type area are extremely variable in shape
and ornament. Individual specimens from populations of fibrosus
match exactly the specimen of cobbani figured by Kellum (1962,
Pl. 3, fig. 17). The same applies to whitii which, on the basis of
Toepelman’s description, is indistinguishable from the Fox Hills
species. Specimens with strong radial ornament (fibrosus sensu
stricto) occur in populations from all stratigraphic zones in the Fox
Hills Formation but are more common in the underlying Mobridge
Member of the Pierre Shale.
Future detailed statistically based studies on adequate samples
from various horizons may prove the existence of successive sub-
species. Until this type of study is undertaken the information avail-
able suggests that only one morphologically variable species, for
which the name fibrosus has priority, should be recognized in the
uppermost Cretaceous of the Western Interior of the United States
and Canada. This procedure is accepted for the purpose of this
paper.
Two species of inequivalved, radially plicate Inoceramus? have
been described from the Maestrichtian of the Gulf Coast of the
United States (Fig. 2).
1. Inoceramus argenteus Conrad (1858, p. 329). Type specimen
lost (Stephenson, 1955, p. 111; Richards, 1968). Type locality: Owl
Creek, Tippah County, Mississippi. Stratigraphic position: Owl
Creek Formation, Maestrichtian.
2. Inoceramus costellatus Conrad (1858, p. 329). Other data as
for I. argenteus.
Stephenson (1955, p. 111) synonymized costellatus under argen-
teus but did not discuss the reasons for this step. As Conrad de-
scribed argenteus first on page 329, Stephenson probably used the
argument of page priority. Conrad’s (1858) illustrations do not
permit positive conspecific identity of the two specimens. The figure
of argenteus is poor and shows an incomplete left valve apparently
marked only by fine concentric plicae. His figure of costellatus (1858,
Pl. 34, fig. 12) is good and shows an inequivalved specimen with
strong radial and concentric plicae on the right valve. Conrad re-
corded the presence of an inoceramid hinge on the specimen. Con-
6 POSTILLA
sequently it would have been better to select costellatus as the valid
name of the species.
Stephenson (1955) separated argenteus from Inoceramus, largely
on the basis of its possession of a narrow ligament area bearing only
a few (5 to 6) shallow ligament pits of irregular width, spacing and
impression, and made it the type species of a new genus Tenuipteria.
The status of this taxon is discussed in a later section.
EUROPEAN SPECIES
Three species and eight varieties of small, thin-shelled Inoceramus
closely resembling /.? tegulatus Hagenow and fibrosus (Meek and
Hayden) have been named from latest Cretaceous sequences of an
area extending from Western Europe to the Caucasus.
1. Inoceramus tegulatus Hagenow (1842, p. 559). Lectotype,
here designated, the original of Wolansky (1932, Pl. 5, fig. 6), an
almost complete left valve in the original collection studied by von
Hagenow, in the Geological-Paleontological Institute, University of
Griefswald, East Germany. Type locality: Riigen Island, East Ger-
many. Stratigraphic position: Mukronatenkreide, Lower Mae-
strichtian (Wolansky, 1932; Nestler, 1965).
2. Inoceramus caucasicus Dobrov (1951, p. 167). Holotype, by
original designation, specimen no. 12 of Dobrov (1951, Pl. 2, fig. 2),
bivalved, height 35 mm, length of ligament area 17 mm. Type lo-
cality: Dobrun Zolka River, Northern Caucasus. Stratigraphic posi-
tion: Maestrichtian (Mst. s,). (Specimen in the Geological Cabinet
of Moscow State University.)
3. Inoceramus dobrovi Jeletzky (Jeletzky and Clemens, 1965,
p. 956). Holotype, by original designation of Jeletzky (Jeletzky and
Clemens, 1965, p. 956), the original of Dobrov (1951, Pl. 2, figs.
la-c), a complete bivalved specimen, length 37 mm, height 30 mm.
Type locality: Darya River, Northern Caucasus. Stratigraphic posi-
tion: Maestrichtian (Mst. s.). (Specimen in the Geological Cabinet
of Moscow State University.)
Dobroy (1951) also proposed eight new varieties, three under his
concept of regulatus Hagenow and five under his concept of cauca-
sicus Dobrov, namely:
I. tegulatus Hagenow var. gibbera Dobrov
!. tegulatus Hagenow var. undulato-sulcata Dobrov
I. tegulatus Hagenow var. curta Dobrov
INOCERAMUS? TEGULATUS SPECIES GROUP 7
. caucasicus Dobrov var. monilifera Dobrov
. caucasicus Dobrov var. cabardinica Dobrov
. caucasicus Dobrovy var. fluctuosa Dobrov
. caucasicus Dobrov var. fistulata Dobrov
I. caucasicus Dobrov var. ravni Dobrov
Hagenow (1842, p. 559) did not illustrate any of his specimens of
tegulatus. A translation of his brief description follows:
La a
6) I. tegulatus n. The present very damaged 10 examples allow
only a general comparison to the former similar species [refers
to I. mytiloides Mantell, a species described directly before],
and both valves appear to be symmetrical and moderately
strongly inflated. Just as in the case of J. mytiloides growth
ridges are crossed by 14 to 18 radiating furrows which have
a sharper base, among which 3—4 are always more prominently
impressed. The generally equally broad and flat raised intervals
resemble a row of overhanging flat roof-tiles with a somewhat
convex front margin.
The last part of the first sentence of Hagenow’s description makes it
almost certain that he was studying an equivalved species. This
interpretation is supported by Wolansky’s (1932, p. 28—29) revision
of the original collection of von Hagenow. Her statement (p. 29)
“Der Angabe 6dums, dass die rechte Klappe kleiner sei als die linke
und keinen vorspringenden Wirbel besitze, kann ich nicht folgen, da
mir auch solche Schalen mit kraftig ausgepragtem Wirbel vorliegen”
indicates a similar degree of projection of the umbones of both
valves. Although Wolansky says the right valve has a strongly pro-
jecting umbone, her illustrations (PI. 4, fig. 4; Pl. 5. figs. 5, 6), while
not good, especially for the left valve, clearly show, as noted by
Jeletzky (Jeletzky and Clemens, 1965, p. 956), that Hagenow’s
species is equivalved and has similar moderately inflated and slightly
projecting umbones on each valve. Wolansky (p. 34) synonymized in
tegulatus the specimens classified as mytiloides by von Hagenow.
Prior to Wolansky’s (1932) restudy of Hagenow’s original collec-
tion, @dum (1922, p. 10) examined specimens from the “White
Chalk of Denmark” and defined /. tegulatus Hagenow:
The main characteristics of Inoceramus tegulatus are as fol-
lows: the long anterodorsal angle, the considerable difference in
convexity of the right and left valves, the radial ribs and the
small ear formed by the long anterodorsal angle. To these
8 POSTILLA
features may be added the absence of small pits in the ligament
area. (Translation by New Zealand Department of Internal
Affairs.)
In his detailed description @dum stressed the inequivalveness and
the presence of a strongly inflated and projecting umbone on the left
valve and a small very weakly projecting umbone on the right valve.
The few specimens and illustrations available to the writer suggest
that the umbone of the right valve is less prominent than that on
Hagenow’s specimens (see also Jeletzky, in Jeletzky and Clemens,
1965, p. 956).
Seitz (1959, p. 123-124) was the first to point out the existence of
two concepts for J. tegulatus: an equivalved “Avicula-like” J. tegula-
tus Hagenow (see PI. 2, figs. 1-3) and an inequivalved ““Pholadomya-
like” I. tegulatus Hagenow of @dum (see PI. 2, figs. 4-6). Jeletzky
(Jeletzky and Clemens, 1965) later fully documented the differences
between the two species and renamed @dum’s species concept as
I. dobrovi Jeletzky, but he selected the holotype for his new species
from a suite of Caucasian specimens described and illustrated by
Dobrov (1951).
Seitz also considered there to be a possible difference in ornament
between fegulatus Hagenow and dobrovi Jeletzky. Specimens of the
two species sent to the writer by Dr. Tové Birkelund tend to confirm
Seitz’ observation. J. dobrovi appears to have consistently finer and
more regular concentric plicae and more regular radial plicae that
are restricted to the anterior half of the valve, whereas the broad
posterior wing has regular concentric growth lamellae only. As
stressed by Seitz (1959, p. 124), additional well-preserved and
accurately identified specimens are required to clarify the apparent
differences in ornament and to document more adequately other pos-
sible morphological differences, especially of the form of the anterior
ear of the left valve and of the ligament area of I. dobrovi.
Differences in the prominence of the umbone and the form of the
anterior ear of valves figured by @dum (1922) and my knowledge of
these features on the North American J.? fibrosus led me to suspect
that Odum may have studied specimens of both tegulatus Hagenow
and dobrovi Jeletzky. My suspicion was confirmed independently by
the observations of Birkelund, who commented (letter of January
15, 1966):
In @dum’s paper both /.? tegulatus v. Hag. (fig. 4, 5, 6) from the
Lower Maastrichtian and /.? dobrovi Jeletzky (fig. 1, 2, 3, 7)
INOCERAMUS? TEGULATUS SPECIES GROUP 9
from the Upper Maastrichtian are figured. @dum (1922) did not
mention any differences between the specimens he examined
from the Lower and Upper Maastrichtian of Denmark and
Jeletzky (in his 1965 paper) did not realize that Odum figured
both the so-called /.? dobrovi and the real J.? tegulatus v. Hag.
The nonrecognition by Jeletzky of the mixture of species studied by
@dum does not affect in any way Jeletzky’s conclusions of the
validity of the two species.
The third European species, J. caucasicus Dobrov, was named
by Dobrov during his study of the J. tegulatus species group in the
uppermost Cretaceous of the Caucasus. Dobrov recognized two
species: J. caucasicus in the upper Lower and lower Upper Mae-
strichtian (Mst. s,; upper marl) and J. tegulatus Hagenow in the
upper Upper Maestrichtian (Mst. s.; limestone). Dobrov’s text and
illustrations prove conclusively that he followed @dum’s concept of
I. tegulatus, and I agree with Jeletzky (in Jeletzky and Clemens,
1965) in accepting the J. tegulatus Hagenow of Dobrov as con-
specific with J. dobrovi Jeletzky.
The varieties of J. tegulatus and dobrovi proposed by Dobrov
(1951), some of which apparently occur together, are here believed
to be extreme morphological variants of their respective species.
Inoceramus caucasicus Dobrov includes specimens with strong con-
centrics but with very weak radials (holotype of caucasicus) to
those with very strong radial plicae (caucasicus var. fistulosa). The
latter closely resemble the holotype of /.? fibrosus. Specimens of
I. dobrovi Jeletzky (= the tegulatus of Dobrov) show a comparable
range of ornament, i.e., weak radials (tegulatus var. gibbera of
Dobrov) to strong radials (tegulatus var. undulato-sulcata of Dob-
rov).
To summarize: As in North America, two species occur in the
latest Cretaceous: an equivalved species with moderately inflated
and projecting umbones, distinct anterior ears, and similar ornament
on each valve (/.? tegulatus Hagenow), and an inequivalved species
with a strongly inflated and projecting umbone on the left valve and
an almost flat right valve on which the umbone barely projects above
the dorsal margin (J.? dobrovi Jeletzky).
The problems of whether /.? caucasicus and 1I.? tegulatus are
synonymous or distinct subspecies and the status of the varieties of
Dobrov require a statistical study of stratigraphically located samples
of adequate numbers of specimens, as suggested above for the North
American /.? fibrosus. The holotype of caucasicus has strong con-
10 POSTILLA
centrics and weak radials, whereas the lectotype of tegulatus has
strong radial and concentric plicae. Evidence of successive popula-
tions dominated by different ornament types would favor the possi-
bility of different subspecies or species.
Because of past confusion in the concept of the species, specimens
recorded in the literature as J. tegulatus should be reexamined to de-
termine whether they are tegulatus (sensu stricto) or dobrovi.
GENERIC POSITION OF THE SPECIES OF THE INOCERAMUS?
TEGULATUS SPECIES GROUP
The generic position of the species of the J.? tegulatus species group
has been uncertain from the date they were proposed, in part be-
cause of the pteriid-like shape and presence of a distinct anterior
ear, largely because of our lack of knowledge of the internal mor-
phology of the species. Jnoceramus? fibrosus has been classified in
Avicula Lamarck, Pholadomya G. B. Sowerby, Pinna Linnaeus,
Pteria Scopoli, Pseudoptera Meek, Inoceramus J. Sowerby, Actino-
ceramus Meek, and Tardinacara Elias (nomen nudum) — Inocera-
mus being the most frequently used (see Jeletzky, 1962). Inocera-
mus? tegulatus Hagenow has been placed under Inoceramus and
Spyridoceramus Heinz (1932).
Inoceramus? fibrosus (Meek and Hayden) from the type area of
the Fox Hills Formation has a ligament area that is longitudinally
striated, with a few irregular depressions crossing the area under
the umbone, but lacking the regular incised ligament pits character-
istic of Inoceramus (PI. 1, figs. 1, 3). The specimens also bear a dis-
tinctive pattern of muscle scars. The true tegulatus Hagenow of
Odum (1922, figs. 4-6; Pl. 2, fig. 2) has a similar ligament area, but
some specimens (Odum, fig. 6) have small, faint, irregular pits along
part of the ligament area similar to but less distinct and regular than
those on the ligament area of species of the I. barabini group from
the Pierre Shale (see p. 31). Dr. Birkelund (letter of February 7,
1966) has informed me that @dum’s specimen with the ligament
pits is “stratigraphically older than the specimens from Alborg”
which have no pits. Consequently, the degree of impression and
regularity of the pits probably degenerated during the late Cam-
panian-early Maestrichtian.
Although the musculation of tegulatus Hagenow is unknown,
and although some doubt may exist as to the degree to which weak
INOCERAMUS? TEGULATUS SPECIES GROUP 11
ligament pits are present on the ligament area, the similarity of the
ligament areas and of external morphology make it reasonably
certain that fibrosus and tegulatus are congeneric. The ligament area
and musculation of caucasicus were not observed by Dobrov. How-
ever, because of its close external similarity and approximate time
equivalence with regulatus, I tentatively accept caucasicus as con-
generic with fibrosus and tegulatus.
The musculation of the inequivalved species argenteus Stephen-
son and dobrovi are unknown. The ligament area of argenteus has
two to six shallow irregular pits as described by Stephenson (1955);
that of dobrovi is unknown. Except for the inequivalveness, and the
presence of irregular weak pits crossing the ligament area, argenteus
is closely similar to tegulatus and fibrosus and is here considered
congeneric with them under the broad generic diagnosis given below.
Because of its close external similarity to, and approximate strati-
graphic equivalence with argenteus, dobrovi is here tentatively con-
sidered congeneric with argenteus.
The lack of incised regular ligament pits crossing the full width
of the ligament area and the presence of a distinctive pattern of
muscle scars clearly separate the regulatus species group from Ino-
ceramus J. Sowerby, as defined by the type species J. cuvierii J.
Sowerby (1814) (Cox, 1955).
Three names are available for the generic taxon to include tegu-
latus Hagenow, fibrosus (Meek and Hayden), argenteus Conrad,
and probably the other two species also: Tardinacara Elias (1931,
opp. p. 58, p. 122, 130), Spyridoceramus Heinz (1932, p. 19) and
Tenuipteria Stephenson (1955).
Tardinacara was proposed by Elias (1931, p. 130) in the form
“|. Inoceramus fibrosus Meek & Hayden (Tardinacara [Pseudop-
tera] fibrosa of the writer)...” and was not accompanied by a diag-
nosis or use of the words new genus or type. As stated by Jeletsky (in
Jeletzky and Clemens, 1965, p. 955) it is a nomen nudum.
Spyridoceramus Heinz was proposed as follows:
“Spyridoceramus Nov. gen.
Genotyp: Inoceramus tegulatus HAG.
Die systematische Stellung dieser Gattung ist noch ungewiss.”
There was no diagnosis, discussion or illustration, and it is not certain
which concept of I. tegulatus Hagenow, the equivalved or inequi-
valved, was meant by Heinz. As @dum’s (1922) description was
12 POSTILLA
relatively recent and superior to earlier descriptions, Heinz may have
accepted the concept of an inequivalved J. tegulatus Hagenow (= I.?
dobrovi).
Heinz’ name Spyridoceramus is invalid (Article 12, International
Code of Zoological Nomenclature, adopted by the 15th International
Zoological Congress with later minor amendments (Stoll et al.,
1964)), as has been recognized by Vokes (1967, p. 171), even though
Heinz selected a type species and obeyed the rules operative prior to
1931. Other workers have accepted (Aliev, 1958) or validated (Seitz,
1961) names proposed by Heinz (1932). However, as recommended
by the International Commission of Zoological Nomenclature
(1950, Bull. Zool. Nomenclature, v. 14, p. 563, paragraph 48),
the validation of nomina nuda or invalid names may cause confusion
and should be avoided.
Tenuipteria Stephenson 1955 is a valid name and is here applied
to the five species discussed above. A diagnosis and discussion of
my concept of the genus is given in the systematic section of this
paper.
ADDENDUM. In the recently published Part N, Mollusca 6, Bivalvia,
of the Treatise on Invertebrate Paleontology (R. C. Moore, ed., Geo-
logical Society of America and University of Kansas Press, 1969), a
copy of which was received while this paper was in galley proof,
the generic taxon Spyridoceramus Cox, new genus, was validated
(p. N320) by the late Dr. L. R. Cox, who noted that “Jnoceramus
argenteus Conrad is the North American representative of this genus”
and placed the genus in the Inoceramidae. On page N310 Cox ac-
cepted the genus Tenuipteria Stephenson, 1955, with Inoceramus
argenteus as type species, and classed it in the Bakevelliidae.
If argenteus and tegulatus are considered conspecific, as clearly
held by Dr. Cox and by myself in this paper, Tenuipteria has priority
and is the valid name for the generic taxon. Future studies may per-
mit the application of the name Spyridoceramus to an equivalved
generic or subgeneric taxon.
BIOSTRATIGRAPHY AND CORRELATION
EUROPE
In Europe the species of Tenuipteria are recorded from the latest
Campanian and Maestrichtian of the Russian Platform, northern
INOCERAMUS? TEGULATUS SPECIES GROUP 13
Poland, northern East and West Germany, Sweden and Denmark.
The species are restricted to the Boreal Province (Jeletzky, 1948,
1951; Naidin, 1954; Kongiel, 1962).
Biostratigraphic subdivision of the latest Campanian and Mae-
strichtian of Europe has been based on many phyla and classes of
organisms. Up to seven zones have been recognized in the Mae-
strichtian (Troelsen, 1937; see Birkelund, 1957, table 4). Belemnoids
are of primary importance for zonation, and two (Naidin, 1952;
Maslakova, 1959; Moskvin, 1962), three (Kongiel, 1962), four
(Birkelund, 1957; Jeletzky, 1951) or five (Jeletzky, 1958, 1962;
Naidin, 1960) zones are accepted.
The controversy over the identification and nomenclature of
belemnoid species important for the zonation of the European
Maestrichtian (Kongiel, 1962, p. 23; Birkelund, 1965, p. 153), the
diversity of proposed zonations, and the overlapping range zones of
many belemnoid species (Kongiel, 1962, tables 6, 7; Birkelund,
1957, table 4) raise doubt as to the validity of the standard zonation
and proposed correlations between sections (see also Wood, 1967),
and are perhaps responsible for the difficulties encountered in decid-
ing the position of the Campanian-Maestrichtian boundary (Birke-
lund, 1957) and of boundaries within the Maestrichtian (Ebens-
berger, 1962, p. 9). As most workers have employed a fourfold sub-
division of the Maestrichtian, it is here accepted as a framework to
which can be related the ranges of the European species of the
Tenuipteria tegulata species group.
The stratigraphic range of the species of Tenuipteria in important
areas is given in Figure 1. For four reasons this table should be
interpreted with caution:
Firstly, caucasica Dobrov is treated as distinct from fegulata
Hagenow, although future systematic work may show them to be
conspecific.
Secondly, in the absence of illustrations the specific status of spec-
imens listed as tegulata by many authors is uncertain. These records
are treated as tegulata (sensu lato) but may include equivalved
tegulata or caucasica and/or the inequivalved dobrovi.
Thirdly, the belemnoid zones of Northwest Europe and Russia are
taken as approximately time equivalent. This is probably only partly
true, for in Russia Jeletzky (1958; 1962, p. 1013) considers the
zone of Belemnella kasimirovensis to include some of the “latest
lower Maestrichtian” and the zone of Belemnella lanceolata to ex-
tend down into the uppermost Campanian.
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INOCERAMUS? TEGULATUS SPECIES GROUP 15
Fourthly, in relating the threefold belemnoid zonation of the
Lower Maestrichtian to the twofold zonation, the zone of B. lanceo-
lata is taken to be equivalent to the Lower Lower Maestrichtian
and the other two zones to the Upper Lower Maestrichtian. This
does not correspond to the proportions shown by Jeletzky in tables
accompanying his papers of 1958, 1960 and 1962.
Figure | suggests three patterns:
1. In both Northwest Europe and Russia older equivalved species
(tegulata-caucasica; upper Campanian to lowermost Upper Mae-
trichtian) are followed by a younger inequivalved species (dobrovi;
Upper Maestrichtian).
2. The equivalved species appears earlier in Russia (caucasica),
in the zone of Bostrychoceras polyplocum (Maslakova, 1959), than
in Europe (tegulata; Seitz, 1959), whereas the inequivalved species
appears to have similar stratigraphic ranges in both regions.
3. The equivalved tegulata may extend into younger rocks in
Northwest Europe than the equivalent caucasica in Russia, where
caucasica probably did not continue to the top of the Lower Mae-
strichtian (Jeletzky, 1960, p. 1013; Dobrov and Pavlova, 1959).
However, it should be noted that Dobrov (1951) originally recorded
caucasica in the uppermost Lower Maestrichtian (Mst. i.) and lower-
most Upper Maestrichtian (Mst. s,).
Dr. Friedrich Schmid (letter of September 27, 1966) has recently
collected a poorly preserved specimen identified as /. tegulatus from
the beds outcropping at Hemmoor at some 50 to 60 meters above
the “Tonband” (Schmid, 1955, fig. 1). If the specimen is an equi-
valved tegulata Hagenow, this discovery represents a significant
increase in the upward stratigraphic range of the species and places
it well within the lower Upper Maestrichtian zone of Belemnitella
junior.
If further systematic and biostratigraphic studies support these
patterns, then the equivalved species (as caucasica) may have evolved
on the Russian Platform, spreading later to Northwest Europe, and
possibly becoming morphologically distinct (as tegulata) in the pro-
cess. In this case the inequivalved dobrovi possibly also evolved on
the Russian Platform but spread more rapidly to Northwest Europe.
FIG. 1. Stratigraphic distribution of the species of the Tenuipteria tegulata
species group in the Upper Cretaceous of Europe. Note: T. tegulata (sensu
lato) may include equivalved (tegulata, caucasica) and/or the inequivalved
(dobrovi) species.
16 POSTILLA
NORTH AMERICA
In North America species of Tenuipteria are recorded from the
Maestrichtian of the Gulf Coast and the Western Interior of the
United States and Canada. Until recently the epicontinental upper-
most Cretaceous sea of the Western Interior was considered to open
to the south (and doubtfully to the north) (Reeside, 1957; Hattin,
1967). Gill and Cobban (1966) and Birkelund (1965, fig. 125) have
shown that the sea also opened to the north into the boreal ocean.
Two faunal provinces can be recognized. There is a Western In-
terior province, including central Canada, with faunas dominated
by baculitid and scaphitid ammonoids and bivalves; this province
has affinities with the Boreal Province (Birkelund, 1965). And there
is a Gulf Coast province with faunas characterized by different
families and species of bivalves, a more diverse gastropod fauna
(Sohl, 1964) and sparse cephalopods. Because of the incomplete
systematic coverage of phyla in one or both regions, documentation
of the definitive characteristics of the provinces is at present in-
adequate.
Biostratigraphic zonation of the upper Campanian and Maestricht-
ian of the Western Interior is based principally on baculitid and
scaphitid ammonoids (Cobban and Reeside, 1952; Jeletzky, 1962;
Gill and Cobban, 1966), although zonation of the upper part of the
section equivalent to the Fox Hills Formation is hampered by a
lack of systematic work on the scaphite ammonoids (Waage, 1968).
The Gulf Coast sequence is zoned at a grosser level by oysters (Sohl
and Kauffman, 1964), gastropods (Sohl, 1960, 1964), and other
molluscs (Stephenson et al., 1942). Cephalopods are uncommon
and of limited importance. Zonation of the Western Interior and
Gulf Coast sequences is complicated by the occurrence of nonmarine
beds at the top of the Cretaceous and by stratigraphic breaks, re-
spectively. Consequently, the range of species and zones based on
marine organisms is likely to be incomplete.
Correlation of North American sequences is given in Figure 2.
Correlation between the Western Interior and the Gulf Coast is com-
plicated by a paucity of common taxa (Waage, 1968) and depends
largely on the work of Jeletzky (1960), who argues that the Scaphites
(Discoscaphites) nebrascensis zone of Fox Hills Formation in its
type area is approximately isochronous with the S. (D.) conradi zone
of the Prairie Bluff Chalk. Because of the close similarity of their
INOCERAMUS? TEGULATUS SPECIES GROUP 17
faunas, correlation between the Western Interior and south-central
Canada is good.
Figure 2 also shows the stratigraphic range of the North American
species of Tenuipteria. The short range zone of T. fibrosa in south-
central Canada is undoubtedly due to the change from marine to
nonmarine deposition.
Tenuipteria argentea is known only from the Owl Creek and Prairie
Bluff formations of northern Mississippi and southeastern Missouri.
As these formations have unconformable lower and upper limits, the
stratigraphic range of the species may have been much longer, a view
supported by Sohl (1964, p. 155) who considers that a “moderate
part of the Maestrichtian is missing.” No radially ribbed, equivalved,
mytiloid-shaped Jnoceramus with relatively weak plicae which re-
sembles T. fibrosa has been reported from the older units of the
Navarro Group. A large subcircular right valve from the Nacatoch
Sand, recorded as “7. vanuxemi Meek & Hayden?” by Stephenson
(1941, Pl. 13, fig. 3), has strong, widely spaced, narrow concentric
plicae, and fine, weak radial plicae. As the left valve holotype (Meek,
1876, Pl. 14, figs. 2a,b) and right valves studied by Meek (1876,
p. 57) lack radial plicae, Stephenson’s specimen should be reeval-
uated.
In contrast to the situation in Europe, no succession of an equi-
valved species followed by an inequivalved species has been recog-
nized in any one region of North America. This may be largely due
to the incompleteness of sequences and the onset of nonmarine
deposition. If, as proposed by Jeletzky (1960), the Fox Hills Forma-
tion in its type area and the Prairie Bluff Chalk are correlatives,
then argentea and fibrosa could have overlapping ranges much as
tegulata and dobrovi overlap in the lower part of the Upper Mae-
strichtian Belemnitella junior zone of Northwest Europe (fig. 1).
CORRELATION BETWEEN THE LATEST CRETACEOUS OF EUROPE
AND NORTH AMERICA
Correlations between the latest Cretaceous sequences of Europe and
North America have been based on scaphitid and sphenodiscid am-
monoids, belemnoids, and the bivalve genus “Jnoceramus’” (Seitz,
1959; Jeletzky, 1960, 1962; Birkelund, 1965; Waage, 1968). Only
Cobban and Reeside (1952) and Jeletzky (1960, 1962) have pro-
posed correlations at the intrastage level.
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INOCERAMUS? TEGULATUS SPECIES GROUP 19
Cobban and Reeside (1952, p. 1026) did not document their
statement that “the Fox Hills fauna corresponds to the upper Mae-
strichtian fauna of the European sequence”. They seem to have
accepted the correlation given by Stephenson and Reeside (1938, fig.
3). Jeletzky argued that the S. (Discoscaphites) nebrascensis zone of
the type Fox Hills Formation and its equivalents in Texas and north-
ern Mexico are Upper Lower Maestrichtian (upper part of the
Belemnella cimbrica zone) (1960, fig. 2), and the Triceratops beds
are of late Maestrichtian age (equal to part or all of the Belemnitella
junior and Belemnella kasimirovensis zones of northern Europe).
The possibility of a basal Upper Maestrichtian age for the upper-
most marine Cretaceous of the Western Interior was not excluded by
Jeletzky. In fact, in his text-figures (1962, text-figs. 1, 2) he extended
the youngest Fox Hills Formation well into the range zone of Belem-
nitella junior (lower Upper Maestrichtian).
Considerable doubt exists as to the position of the base of the
Maestrichtian Stage in the Western Interior sequences. Most workers
follow Jeletzky (in Cobban and Reeside, 1952, p. 1026-1027) in
tentatively placing the lower boundary of the stage at the base of the
zone of Baculites baculus. On the evidence of the ammonites the
boundary could be placed either at the base of the B. baculus zone or
possibly within or at the top of the zone. Jeletzky favored the first
alternative, emphasizing the appearance of certain European Lower
Maestrichtian scaphitid species even though late Campanian Euro-
pean species are also present in the zone of B. baculus and other
typical European Lower Maestrichtian species appear high in or
above the B. baculus zone. Doubt about the stratigraphic ranges of
many of the North American ammonoid species, and lack of docu-
mentation that the North American and European species discussed
by Jeletzky are conspecific (Birkelund, 1965; Waage, 1968) increase
the uncertainties of the proposed correlations between the regions.
Similarly, the position of the boundary between the Lower and
Upper Maestrichtian in the Western Interior is uncertain. Most
workers accept Jeletzky’s (1962, p. 1008) selection of the upper limit
as the top of the range zone of Discoscaphites nebrascensis.
Jeletzky (1960, 1962) placed a lot of weight for an upper Lower
Maestrichtian age for the type Fox Hills Formation on his discovery
FIG. 2. Stratigraphic distribution of the species of the Tenuipteria tegulata
species group in the Upper Cretaceous of North America.
20 POSTILLA
at Hemmoor of an ammonoid fragment which he identified as S. (H.)
nicolleti. Both Birkelund (1965) and Waage (1968) consider the
fragment indeterminable. Waage goes further in showing it to be
morphologically distinct from the true nicolleti of the Western Inte-
rior. After an analysis of the belemnoids, scaphitids and sphenodis-
cids, Waage concludes that an inadequate knowledge of the system-
atics, biostratigraphy, paleoecology and paleogeography of these taxa
in both Europe and North America prevents refined correlations
between the two regions. Of the cephalopods he emphasizes the
potential value of hoploscaphitid ammonoids for correlation at the
intrastage level (see also Birkelund, 1966).
The stratigraphic distribution of the species of Tenuipteria in
Europe and North America tends to support Jeletzky’s correlations.
The equivalved species appear about the same time, latest Cam-
panian, in both regions—at least in Russia and south-central Canada
if the specimen of fibrosa from some 80 feet below the Belanger
Sandstone Member of the Bearpaw Formation (Furnival, 1946,
p. 62), and hence probably below the zone of Baculites baculus, is
correctly identified. The absence of an inequivalved species of
Tenuipteria in the Western Interior of the United States and Canada,
together with the lack of other index taxa, counts against the pres-
ence of Upper Maestrichtian marine beds. Likewise, the occurrence
of the inequivalved 7. argentea in the Prairie Bluff Chalk of the Gulf
Coast is compatible with a correlation with the latest Lower Mae-
strichtian and earliest Upper Maestrichtian.
However, the present inadequate knowledge of the systematics,
biostratigraphy and paleogeography of the species of Tenuipteria,
coupled with the uncertain status of European latest Cretaceous bio-
stratigraphy, negates the possibility of precise correlations. Theoret-
ically, the species need not have isochronous range zones in Europe
FIG, 3. Muscle scar and pallial line impressions for inoceramid species from
the uppermost Cretaceous of the Western Interior of the United States.
3a. Tenuipteria fibrosa (Meek and Hayden). YPM 24037, drawn from the
original of Plate 1, figure 5. The dashed line indicates the position of
edge of the inner shell layer.
3b. “Inoceramus”’ barabini Morton. YPM 24052, Pierre Shale, Converse
County, Wyoming, C. E. Beecher and J. B. Hatcher, collectors.
3c. “Endocostea” typica Whitfield. YPM 24053, Pierre Shale, Converse
County, Wyoming.
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22 POSTILLA
and North America. Assuming that caucasica and tegulatus are con-
specific, and that the correlations are correct, the nonisochroneity of
some range zones would be well documented by the appearance of
caucasica in Russia before the entry of tegulatus in Western Europe
—a difference equivalent to the range zone of Belemnitella lanceolata
(Fig. 1). Even if species are able to spread geographically in a geo-
logically insignificant time interval, the evolution of a species in a
region may involve at least half a million years (Gill and Cobban,
1966), and the migration and establishment of a species may be
prevented by environmental, biological (Briggs, 1967), geological or
hydrographic factors. For example, the later appearance of an
equivalved species of Tenuipteria in Western Europe may be due
largely to environmental control. Until detailed systematic and bio-
stratigraphic studies are completed these arguments tend to be se-
mantic.
Possibly the best evidence for the correlation of the Western Inte-
rior sequence comes from the assessment of biostratigraphy and
potassium-argon ages prepared by Gill and Cobban (1966, p. 34—
37). These authors demonstrate that the base of the Baculites baculus
Range Zone, which is correlated with the base of the Lower Mae-
strichtian, is at about 70 million years, and that the Discoscaphites
nebrascensis Range Zone is older than 66 + 2 million years and
estimated to be about 68 million years. Although these dates give a
reasonably good fix for the Western Interior sequence and tend to
place the youngest marine Cretaceous of the Western Interior in the
latest Lower Maestrichtian, correlation with the European stages
remains dependent on classical biostratigraphic methods. Refined
correlation is not possible until radiometric ages are available for
European sequences.
SYSTEMATIC DESCRIPTIONS
Tenuipteria Stephenson 1955 Emend.
SYNONYMY.
Tardinacara Elias, 1931, opp. p. 58, p. 122, 130 (nomen nudum).
Spyridoceramus Heinz, 1932, p. 19 (invalid, no diagnosis).
TYPE SPECIES. By original designation of Stephenson (1955, p. 110),
INOCERAMUS? TEGULATUS SPECIES GROUP 23
Inoceramus argenteus Conrad (1958, p. 329), Owl Creek Formation,
Maestrichtian, Gulf Coast, North America.
DIAGNOSIS. Thin-shelled inoceramid characterized by radial and
concentric plicae, a distinct small anterior auricle and a narrow liga-
ment area, concave in cross section, longitudinally striated, either
lacking ligament pits (fibrosa, the stratigraphically younger tegulata)
or with faint, broad, irregular, weakly impressed pits (stratigraphi-
cally older tegulata, argentea). Muscle scars consist of a posteroven-
trally situated large adductor scar and two anterodorsal byssal-pedal
scars which are joined by a pallial line of discrete scars anterodorsally
but fused ventrally (fibrosa).
EMENDED DESCRIPTION. Equivalved or inequivalved, when the left
valve is the more strongly inflated, small to medium sized with a
distinct anterior ear, usually delimited from the main disc of the
shell, and a flattened, rounded, posterior dorsal margin. Umbones
anterior, moderately projecting on equivalved species, strongly pro-
jecting on the left valve but only slightly projecting on the right valve
of inequivalved species. Shell ornamented by radial and concentric
plicae of variable strength and numbers, usually regular and tending
to produce a distinctive “‘tile-like” pattern, but sometimes with the
radial plicae stronger than the concentric, or vice versa. Along the
crest and ventral flank of the concentric plicae are concentric lamellae
which are dominant on the posterodorsal flank where the plicae are
subdued or absent. Shell thin, of two layers: a thicker, outer prismatic
shell layer which may project well beyond the margin of a thinner,
inner nacreous shell layer (fibrosa, tegulata).
DISCUSSION. The above diagnosis has been made broad to include
species of similar external ornament and shape, but either equivalved
or inequivalved, and having a range of ligament area and muscula-
tion characteristics. In the diagnosis and description species names
in parentheses are given after those features where the morphology
is known from less than three species.
Species included in my broad concept of Tenuipteria are
Tenuipteria tegulata (Hagenow, 1842)
T. fibrosa (Meek and Hayden, 1856a)
T.? caucasica (Dobrov, 1951)
T. argentea (Conrad, 1858)
T.? dobrovi (Jeletzky and Clemens, 1965)
24 POSTILLA
As discussed above, fibrosa and caucasica might be conspecific with
tegulata and dobrovi with argentea. Because of lack of knowledge of
the morphology of their ligament areas, caucasica and dobrovi are
tentatively classed in the genus.
All species included in Tenuipteria differ from Inoceramus in one
or a combination of the internal morphological characteristics.
Future work may show that the equivalved species with a few
very weak or no ligament pits and a partly continuous pallial line
(Tenuipteria tegulata, fibrosa, ?caucasica) should be separated sub-
generically or generically from the inequivalved species with irreg-
ular, weak ligament pits, strongly inflated umbone and the corre-
lated smaller anterior ear and convex anterodorsal margin on the
left valve (argentea, ?dobrovi).
The Turonian genus Didymotis Gerhardt (1897) has a smooth
ligament area lacking pits (Imlay, 1955) and superficially resembles
Tenuipteria in shape, ornament and possession of a thin shell. How-
ever, the equivalved species of Didymotis are oval in shape, have
inconspicuous subcentral umbones and a long, straight dorsal margin,
and lack the distinctive regular “‘tile-like” ornament of Tenuipteria.
On Didymotis irregular, closely spaced, concentric plicae dominate
the few weak, widely spaced, radial plicae that occur only on the
main disc of each valve (Gerhardt, 1897, Pl. 5, figs. 3a,b). The
morphological differences between the genera, and the reasonable
assumption of derivation from different inoceramid stocks at differ-
ent times warrant their treatment as separate taxa. The resemblance
of Didymotis to Tenuipteria is undoubtedly due to convergence,
perhaps dependent on the adoption of a similar mode of life.
Tenuipteria fibrosa (Meek and Hayden)
(Plate 1, figs. 1-6; Fig. 3a)
Avicula? fibrosa Meek and Hayden, 1856a, p. 86-87.
Pholadomya fibrosa (Meek and Hayden). Meek and Hayden, 1856b,
pi283:
Pinna fibrosa (Meek and Hayden). Meek, 1864, p. 9.
Avicula (Pseudoptera) fibrosa (Meek and Hayden). Meek, 1873,
p. 489.
Pteria (Pseudoptera) fibrosa (Meek and Hayden). Meek, 1876, p.
INOCERAMUS? TEGULATUS SPECIES GROUP 25
36-37, Pl. 17, figs. 17a—d. Whitfield, 1880, p. 386, Pl. 7, fig. 5.
Whiteaves, 1885, p. 32, Pl. 4, fig. 1.
Inoceramus (Actinoceramus) whitii Toepelman, 1922, p. 63.
Inoceramus (Actinoceramus) fibrosus (Meek and Hayden). Dobbin
and Reeside, 1929, p. 20.
Tardinacara (Pseudoptera) fibrosa (Meek and Hayden). Elias, 1931,
opp. p. 58, p. 124, p. 130. Searight, 1934, p. 4.
Inoceramus (Actinoceramus) fibrosa (Meek and Hayden). Russell,
1940, p. 88.
Inoceramus fibrosus (Meek and Hayden). Landes, 1940, p. 136-137.
Cobban and Reeside, 1952, p. 1020, and correlation chart.
Jeletzky, 1962, p. 1011-1014, Pl. 141, figs. 4-7. Seitz, 1959, p.
123-124 (? synonymous with J. tegulatus Hagenow (1842, p.
559)).
Inoceramus radiatus Kellum, 1962, p. 57, Pl. 5, fig. 17 (non Heine,
1929, p. 105, Pl. 18, figs. 68, 69).
Inoceramus cobbani Kellum, 1964, p. 1006 (new name for J. radiatus
Kellum).
Inoceramus? tegulatus Hagenow, 1842 (non Odum, 1922). Jeletzky,
in Jeletzky and Clemens, 1965, p. 957.
Tenuipteria fibrosa (Meek and Hayden). Speden, 1970, Pl. 8, figs.
11-18; Pl. 9, figs. 1-16.
DESCRIPTION. Specimens 5 to 55 mm long, equivalved, inequilateral,
maximum inflation about mid-height close to anterior margin. Shape
extremely variable, submytiloid to subquadrangular, and rarely al-
most oval. Height, anterior length and width are, respectively, 83 to
100, 8 to 15 and 12 to 27 percent of the length of the outline of the
inner shell layer. Dorsal margin straight, posterodorsal margin
rounded, and the angle subtended at the umbone by the dorsal
margin and the line joining the posteroventral extremity is about 40
to 50 degrees. Umbones prosogyrous, sited near the anterior end of
the straight dorsal margin, not prominent, project only slightly above
the dorsal margin. Anterior auricle distinct, always present, rela-
tively small but of variable size, delimited from the moderately to
strongly inflexed anterodorsal margin by a narrow groove of variable
prominence. When the anterodorsal margin is strongly inturned the
associated groove is deep, and there is a distinct byssal notch and
gape where the groove meets the margin. Otherwise, the byssal notch
and gape are small or indefinite.
26
Ve
255:
na
POSTILLA
PLATE 1
Tenuipteria fibrosa (Meek and Hayden)
YPM 24644; ligament area of a left valve. Note the lack of ligament pits.
YPM A-1140, Locality 115, Protocardia-Oxytoma Assemblage Zone,
Little Eagle lithofacies, Trail City Member, Fox Hills Formation. X1.5.
YPM 24033; the divergence of the outer prismatic layer from the inner
layer dorsally and strong concentric plicae (2), and the striated ligament
area which lacks ligament pits.
YPM A-992, Locality 231, Lower nicolleti Assemblage Zone, Little Eagle
lithofacies, Trail City Member, Fox Hills Formation. Fig. 2 X1, Fig. 3 X2.
. YPM 24039; right valve steinkern with equally strong radial and con-
centric plicae.
YPM A-336, Locality 32, Mobridge Member, Pierre Sale! xaIE
. YPM 24037; right valve steinkern with a posteroventrally situated ad-
ductor scar and two anterior byssal-pedal scars on either side of an umbonal
fracture. The specimen on which Figure 3a is based.
YPM A-3S0, Locality 39, Cucullaea Assemblage Zone, Timber Lake
Member, Fox Hills Formation. X6.
. YPM 24028; left valve steinkern with strong radial plicae.
YPM A-336, Locality 32, Mobridge Member, Pierre Shale. X2.
28 POSTILLA
Ornament extremely variable, consisting of concentric and radial
plicae usually of equal size and regular and giving a distinctive “tile-
like” pattern, but sometimes with stronger radial or concentric plicae.
Radial plicae appear at about 5 to 20 mm from the tip of the umbone
and are absent only rarely on specimens longer than 20 mm. Radial
plicae absent from the posterodorsal flank of the valve where the
concentric plicae also weaken and concentric lamellae dominate. A
concentric lamella occurs along the crest or along the dorsal part of
the ventral flank of each concentric plica. Specimens greater than 30
mm in height have about 15 to 30 radial plicae, which are usually
slightly wider than the interspaces, and about 20 to 35 concentric
plicae. Some specimens have irregular broad undulations bearing
three to four of the regular concentric plicae.
Ligament area extends the length of the dorsal margin, inclined
at 30 to 40 degrees to the commissural plane, generally strong con-
cave and almost semicircular in cross-section, or more rarely L-
shaped with a wider, slightly concave dorsal limb and a flat ventral
limb inclined at 60 to 80 degrees to the commissural plane. Surface
of ligament area marked by fine longitudinal striae separated by
much wider shallow grooves; striae stronger on the dorsal part of the
ligament area, often weak or absent on the ventral part. Ligament
area lacks impressed pits, but rare specimens show traces of faint
shallow undulations. In the vicinity of the umbones the dorsal margin
usually strongly overhangs the ligament area.
Posterior adductor scar large, elliptical to pear-shaped, tapering
posterodorsally where deeply impressed at extremity, anterior mar-
gin with an indentation of variable prominence, situated at postero-
ventral extremity of inner shell layer close to its junction with outer
shell layer; rarely preserved. In the umbonal cavity are two antero-
dorsal scars (pedal-byssal retractors), a small oval impression ante-
rior to the line of maximum inflation and a slightly larger subrectan-
gular scar posterior to the line of maximum inflation. Pallial line on
inner shell layer close to junction with outer shell layer, consisting of
a narrow continuous band with irregularly spaced swellings from the
posterior adductor to above mid-height of shell, then continuing as a
series of four to eight small discrete oval or linear impressions. Above
the anterior pedal-byssal scar and close to the dorsal margin are
sometimes seen three to five scars.
Calcitostracum very thin and fragile, observed maximum thickness
0.7 mm, rarely exceeds 0.5 mm, composed of a thick, outer prismatic
INOCERAMUS? TEGULATUS SPECIES GROUP a)
layer and a thin, inner pearly nacreous layer one quarter to one sixth
of the thickness of the outer layer. Outer layer extends considerably
beyond the inner layer, forming a broad flange. Internal surface of
the umbonal cavity is marked by fine irregular striae which approxi-
mately parallel the growth axis. Many specimens have a faint ridge
along a line extending from the dorsal margin posterior to the um-
bone to the anterodorsal end of the posterior adductor.
TYPE SPECIMEN. Lectotype of Avicula? fibrosa Meek and Hayden,
by subsequent designation of Meek (1876, PI. 17, fig. 17a), USNM
460, a steinkern of a right valve, oblique length 34.7 mm. Type
locality: Forks of the Cheyenne River, South Dakota. Stratigraphic
position: Pierre Shale, Early Maestrichtian, Upper Cretaceous.
OCCURRENCE. In the Western Interior of the United States T. fibrosa
occurs in the Pierre Shale and Fox Hills Formation and ranges from
the Baculites baculus zone through to the top of the Timber Lake
Member of the Fox Hills Formation. In the type area of the Fox Hills
Formation it is common only in the Lower and Upper nicolleti as-
semblage zones (Waage, 1961). In south-central Canada it is known
only from the upper part of the Bearpaw Formation (Jeletzky, 1962,
p. 1012; and see Furnival, 1946, p. 62).
DISCUSSION. The description given above is based on specimens from
the Mobridge Member, Pierre Shale, and the Fox Hills Formation in
its type area. The reader is referred to Speden (1970) for additional
illustrations of specimens of fibrosa and data on occurrence. No ac-
count is taken of the morphological variation described for other
samples by Cobban (1964).
Important features of the morphology of T. fibrosa are discussed
below:
a) Shape. The variation in shape is marked. A striking feature of
complete specimens is that the outline of the outer shell layer does
not parallel the outline of the inner shell layer. This divergence is
most marked along the posterior and posteroventral margins, while
the dorsal margin of the ligament area diverges from the dorsal
margin of the inner shell layer by angles of 10 to 25 degrees (PI. 1,
fig. 2). The outline of steinkerns is usually defined by the margin of
the inner shell layer, and all too frequently the thin outer shell layer
breaks off along its junction with the inner layer. Consequently, the
30 POSTILLA
shape based on steinkerns, or even shelled specimens, may be false.
Tenuipteria fibrosa tends to be more oval than is indicated by the
typical mytiloid steinkerns.
Because of the wide variation in shape shown by fibrosa, and the
nonparallelism of the outlines of the outer and inner shell layers,
only gross measurements are given in the above description.
b) Ornament. The Fox Hills “populations” are characterized by
extremely variable ornament. Normally, the radial and concentric
plicae are of almost equal strength, although the concentric ornament
is commonly stronger than the finer and more regular radial plicae.
Specimens with strong radial sulci, which closely resemble the lecto-
type, are present in many collections from all assemblage zones but
are more common in the Mobridge Member of the Pierre Shale along
the Moreau River (YPM A-336). The radial plicae are very weak on
some small specimens, particularly those in collections from the
Timber Lake Member, Fox Hills Formation. However, this weak-
ness may be related to the factor of size.
The pattern of ornament shown by the Fox Hills “populations”
covers the third and fourth ‘“‘forms” of Cobban (1964, i.e. those with
“concentric and radial sculpture . . . of about equal strength, and a
final form in which the concentric sculpture dominates”. It should
be stressed that the individual specimens may have very strong or
very weak radial plicae. The range of variation of ornament in a
single collection at a locality prevents positive placing in either of
Cobban’s “forms”, at least until they are more fully documented.
Ornament studies ideally should be based on external moulds or
the original shell surface and not on steinkerns, which are often all
that a paleontologist has to study. In the case of the Fox Hills sam-
ples the narrow radial plicae are notably more subdued on the
steinkern than on the external mould or shell surface
c) Ligament area. The ligament area is basically smooth and lacks
the incised, transverse, rectangular ligament pits characteristic of the
genus [noceramus. Rare specimens show traces of faint shallow un-
dulations on the floor of the ligament area. These, however, are ir-
regular and cannot be compared with the ligament pits of Inocera-
mus. Odum (1922) records the presence of similar faint undulations
on his specimens of 7. tegulata from the White Chalk of Denmark
and shows the presence of small ligament pits on the dorsal half of
the ligament area of a specimen from M@gens Klint (1922, fig. 6).
According to Birkelund (letter of February 2, 1966), the specimen
INOCERAMUS? TEGULATUS SPECIES GROUP 31
with ligament pits from Méens Klint is stratigraphically older than
the specimens from Aalborg which lack pits.
Small but distinct pits occur on the dorsal part of the ligament
area of specimens of Inoceramus cf. barabini Morton (YPM 24452,
24055), labeled as from Converse County, Wyoming, Pierre Shale
(Campanian), C. E. Beecher and J. B. Hatcher, collectors, held in
the Division of Invertebrate Paleontology, Peabody Museum of Nat-
ural History, Yale University. On these specimens the pits are
smaller and less definite toward and under the umbones (Speden,
1970). Derivation of the fibrosa type of pitless ligament area by de-
generation from a typical Inoceramus ligament area with pits is
suggested by these observations.
d) Musculation. Musculation is rarely described for species of
Inoceramus, largely because of the lack of impression of the scars
into the thin shell and the poor preservation of specimens. The ad-
ductor scar of fibrosa is also hard to find for the above reasons, and
also because it is sited so close to the posteroventral margin of the
inner shell layer, a portion of the shell often broken or not collected.
A search of the literature indicates that the musculation of species
classed in Inoceramus consists characteristically of a pallial line of
discrete scars and a posterior adductor scar sited in a submedial posi-
tion (see Jones and Gryc, 1960, p. 159). Kauffman (1965) has
recently recognized three types of muscle scar patterns in Cretaceous
species of Inoceramus. One category includes that of T. fibrosa as
described above. Other Upper Cretaceous “Jnoceramus’’ species
have a musculation pattern similar to that of fibrosa, but with a
pallial line consisting solely of discrete scars and generally with small
scars extending in a line across the posterodorsal part of the shell. A
specimen (YPM 24052) of the “Inoceramus” barabini complex
and two specimens (YPM 24053) labeled “Endocostea typica
Whitf.”, all from ‘““Converse County, Wyoming, Pierre Shale”, C. E.
Beecher and J. B. Hatcher, collectors, have this type of pattern (Figs.
3b,c; see also Speden, 1970).
Species of recent isognomiid genera (Isognomon, Melina) have a
very similar pattern of muscle scars, with two small byssal-pedal
scars in an anterodorsal position, but the large adductor scar is
usually in a more subcentral position on the inner shell layer and is
joined to the anterior of the two anterodorsal scars by a line of
discrete small pallial scars. The possession of similar musculation
patterns supports the close relationship between the isognomiid and
32 POSTILLA
inoceramid stocks postulated on stratigraphic and other morpholog-
ical grounds by many workers (Cox, 1940; Hayami. 1960). In the
case of fibrosa the resemblance is probably secondary and due to
convergence through the adoption by an inoceramid stock of an epi-
faunal mode of life similar to that of Jsognomon.
COMPARISONS. Seitz (1959) suspected that T. tegulata Hagenow (not
of @dum) might be synonymous with T. caucasica Dobrov and T.
fibrosa Meek and Hayden, but he stressed the need for further study
of better preserved and more abundant specimens before his pro-
posed synonymies could be accepted as valid. Jeletzky (1962), using
the concept of tegulata Hagenow as an inequivalved species, syn-
onymized caucasica Dobrov with fibrosa Meek and Hayden. In 1965
Jeletzky (Jeletzky and Clemens, 1965) accepted tegulata Hagenow as
being an equivalved, morphologically variable species and synony-
mized fibrosa and caucasica under tegulata Hagenow.
Seitz considered that T. fibrosa differs from T. tegulata Hagenow in
having growth lamellae which are convex ventrally across the raised
nodular radial plicae, whereas they are convex dorsally on T. tegula-
ta. On specimens of fibrosa from the Fox Hills Formation, South
Dakota, the growth lamellae and striae may be concave or convex
dorsally across the raised radial plicae, and an individual lamella may
have both orientations along its length On most specimens the sec-
ond order concentric costate ornament has a straight or slightly con-
vex ventral trace. Only on specimens where a very nodular pattern
is produced by strong radial and concentric plicae do the lamellae
have a convex dorsal trace. The growth lamellae on specimens of T.
dobrovi available to me have an irregular trace, while a specimen of
T. tegulata (the original of @dum, 1922, fig. 5) does not show clearly
the concentric lamellate ornament across the radial plicae on the
main disc of the valve. On the posterodorsal flank the lamellae are
irregularly undulating. Although the difference between tegulata
Hagenow and fibrosa noted by Seitz is unlikely to be of specific rank,
additional data on the consistency of orientation of the trace of these
lamellae across the radial plicae are required to confirm my opinion.
The few specimens and illustrations of tegulata Hagenow and
caucasica available to the writer indicate, as suggested by Seitz
(1959) and Jeletzky and Clemens (1965), that the three equivalved
species tegulata, fibrosa and caucasica might be synonymous. The
three “species” include forms with a wide variation of shape and
INOCERAMUS? TEGULATUS SPECIES GROUP 33
similar ornament. Specimens of fibrosa greater than 30 mm in height
have about 15 to 30 radial raised plicae and about 20 to 35 concentric
plicae (see p. 28). @dum’s (1922, fig. 5) specimen of segulata
Hagenow has an indefinite number of radial plicae and about 25
concentric plicae, while those of caucasica figured by Dobrov (1951)
have about 10 to 30 radial and 20 to 35 concentric plicae.
Cobban (1964), in his recognition of his ornament groups, has
emphasized the variation in strength of radial and concentric plicae.
Our present knowledge is insufficient to permit the synonymizing
of the three species. Detailed studies are required of the stratigraphic
and biogeographic variation of adequate samples of the European
species such as are being undertaken by Cobban (1964) for the
North American 7. fibrosa.
Tenuipteria argentea (Conrad)
(Plate 2, fig. 7; Plate 3, figs. 1-6)
Inoceramus argenteus Conrad, 1858, p. 329, Pl. 34, fig. 16.
Inoceramus costellatus Conrad, 1858, p. 329, Pl. 34, fig. 12.
Inoceramus argenteus Conrad. Stephenson and Monroe, 1940, p.
280, Pl. 10, figs. 8, 9.
Tenuipteria argentea (Conrad). Stephenson, 1955, p. 111, Pl. 16,
figs. 4-9.
REDESCRIPTON. Species of moderate size, specimens from about 10
to 65 mm long, inequilateral, inequivalved, umbones prosogyrous.
Right valve slightly to moderately inflated, the umbone barely
projecting above the dorsal margin, the anterior auricle small and
distinct. Left valve strongly inflated with a prominent umbone pro-
jecting above the dorsal margin, anterior auricle small. Posterodorsal
margin of each valve rounded.
Valves ornamented by radial plicae, strongest on the right valve,
which divide by gemmation on the center of the disc, become wider
ventrally and are separated by narrower interspaces Radial plicae
number about 25 to 30 on the left valve (N = 4) and 26 to 33 on the
right valve (N = 4). Posterodorsal third of the shell and the antero-
dorsal margin lack radial plicae. Radial plicae crossed by regular
weak concentric plicae which are accentuated by a prominent growth
34
1,
POSTILLA
PLATE 2
Tenuipteria tegulata (Hagenow)
2, 3. MMH 1816; the original of @dum, 1922, fig. 5, a left valve steinkern
with shell dorsally showing anterior ear, slightly projecting umbone, and a
longitudinally striated ligament area which lacks ligament pits. Aalborg,
Lower Maestrichtian. (Plaster cast NZGS-WM 8956). Figs. 1, 2 X3;
Fig. 3 X1.
Tenuipteria dobrovi (Jeletzky)
. MMH 1814; poorly preserved left valve, the original of @dum, 1922,
figs. 1, 2. “Dania” at Mariager, Upper Maestrichtian. (Plastic cast NZGS-—
WM 8957). X1.
. MMH collection 1965/694; left valve steinkern. Limhamn, Scania, Sweden,
Upper Maestrichtian. X1.
. MMH collection 1965/693; left valve steinkern. Limhamn, Scania, Sweden,
Upper Maestrichtian. (Plaster casts NZGS-WM 9238). X1.
Tenuipteria argentea (Conrad)
. USNM Cat. No. 159947; left valve, incomplete. Topotype, USGS Locality
707, USNM 20661, Owl Creek, Mississippi, Maestrichtian. X2.
36 POSTILLA
PLATE 3
Tenuipteria argentea (Conrad)
1. USNM Cat. No. 159948; an incomplete bivalved specimen. X1.5.
2. USNM Cat. No. 159949; right valve showing lack of radial plicae on the
posterior flank. X1.5.
3. USNM Cat. No. 159947; left valve ligament area showing weak ligament
pits. X2.
4. USNM Cat. No. 159948; left valve of specimen of Figure 1. X1.5.
5, 6. USNM Cat. No. 159950; right valve showing ornament and ligament
area with more strongly incised ligament pits and distinct anterior auricle.
Bige Sel. 3. Fig? 6eX3.
All specimens are topotypes from USGS Locality 707, USNM collection
20661, Owl Creek, Mississippi, Owl Creek Formation, Maestrichtian.
iy BRE,
38 POSTILLA
lamella developed along the crest of each plica. Concentric plicae
closely spaced on umbonal 10 mm of shell, on the dorsal flanks and
along the ventral margins of adult specimens, but number about one
per millimeter on the main disc of the shell. The intersection of radial
and concentric plicae produces a distinctive tile-like pattern of shal-
low rectangular depressions.
Ligament area more or less flat, bearing two to five shallow sub-
rectangular or subtrigonal ligament pits; that under the umbone the
largest, and sometimes consisting of two fused pits. Pits and inter-
spaces crossed by fine striae extending the length of the ligament
area. Ligament area of the right valve inclined at about 20 to 30
degrees to the plane of the commissure, and that of the left valve
inclined at about 60 to 80 degrees
Muscle scars unknown. Shell very thin; shell of the main disc at-
taining a maximum thickness of about 0.5 mm, consisting of a thick,
inner nacreous lamellar layer (0.4 mm) and a very thin, outer pris-
matic layer (0.1 mm).
TYPE SPECIMEN. Neotype, USNM 124102, here designated, a topo-
typic left valve shell showing the ligament area, the original of
Plate 16, figure 6 of Stephenson (1955), USGS 6464. Type locality:
Owl Creek, three miles northeast of Ripley, Tippah County, Missis-
sippi (E 1% Sec. 7, T.4 S, R.4 E). Stratigraphic position: Owl Creek
Formation, Maestrichtian.
Stephenson (1955) presumed that the holotype was lost, and this
was confirmed subsequently by Richards (1968). Conrad (1858) did
not record the number of species he studied, but apparently no syn-
types are present in the collection of the Academy of Natural Sci-
ences, Philadelphia. Consequently, one of the topotypic specimens
studied by Stephenson when he established the genus is selected as
a neotype.
DISCUSSION. The above redescription is based on the examination
of about 60 specimens, mostly incomplete and slightly crushed, in
collections held by the United States National Museum, catalogue
numbers USGS 6875 (N=6), USNM 20612 (N=22) and USNM
20661 (N=31), kindly forwarded to the writer by the courtesy of
Dr. Erle G. Kauffman.
Measurements taken from the best specimens in these collections
are given in Table 1. Because the measurements are based on the
outline of the inner shell layer they should be accepted with caution.
INOCERAMUS? TEGULATUS SPECIES GROUP
39
TABLE 1. Measurements of specimens (in mm) of Tenuipteria argentea (Conrad).
Length of
Half Anterior dorsal
No. Valve Length Height width length margin DUPM*
USNM 20661 right a 32 7.0 4.6 = —
es left 29) 30 14.0 3.0 18 4.5
~ left 65 62 14.0 15.0 41 —
left 15 13 2.0 2.5 12 —
Bs right ra | 26 7.0 4.0 18 —
‘a right 25 DS 6.0 5.0 22 =
20612 left 39 42 18.5 6.0 28 6.5
< right 40 41 10.0 6.0 — —
USGS 6875 right 31 28 5.0 6.0 24 —
3 right 49 45 7.0 9.0 33 —
*Distance the umbone of the left valve projects above the dorsal margin
ligament area.
of the
COMPARISONS. Dobrov (1951, p. 164) was the first to suggest the
presence in the latest Cretaceous of North America of the in-
equivalved group of “Jnoceramus tegulatus”. Tenuipteria dobrovi
Jeletzky (1965) externally closely resembles T. argentea in having
a strongly inflated left valve and a flattish right valve, with both
valves ornamented by regular to subregular radial and concentric
plicae and concentric lamellae.
Examination of specimens of Tenuipteria argentea in three col-
lections held by the United States National Museum, Washington
(catalogue numbers USGS 6875 and USNM 20612 and 20661),
three left valves of T. dobrovi from the late Maestrichtian of Den-
mark, and illustrations indicates that the valves of these species are
very similar in size and shape. Each species has left valves with
height to length ratios of about one. Tenuipteria argentea has height
to length and half width to length ratios for left valves of 0.87 to
1.14 (N = 5) and 0.22 to 0.47 (N = 3), respectively; for T.? dobrovi
the ratios are 1.00 to 1.20 (N = 3) and 0.23 to 0.34 (N = 4), re-
spectively. Because of the inadequate numbers of specimens these
values can be taken only as an indication of similarity.
On both T. argentea and dobrovi the radial plicae are most dis-
tinct on the central and anterior part of the valve and are weak or
lacking on the broad posterior ear. Replicas of two left valves of
dobrovi from the Maestrichtian of Denmark, NZGS—WM 8957 (the
40 POSTILLA
original of @dum, 1922, figs. 1, 2; height = 46 mm; PI. 2, fig. 4) and
NZGS-WM (height 43 mm; PI. 2, fig. 6), have 17 and 23 radial
plicae and about 37 and 29 concentric plicae, respectively. Photo-
graphs of a left and a right valve of argentea figured by Stephenson
(1966, Pl. 16, figs. 4, 6) suggest the presence of about 18 radial
plicae; the concentric plicae could not be counted. Topotypes of
argentea from Owl Creek, Mississippi, in collection Cat. No. 20661
held by the U.S. National Museum, have 25 to 30 radial plicae on
the left valve (N — 4) and 26 to 33 on the right valve (N = 4). These
valves, which are 20 to 41 mm high, have about one concentric plica
per millimeter on the main disc, i.e. about 25 to 45 per valve.
The close external similarity of T. dobrovi and argentea suggests
that they may be conspecific and congeneric. However, the ligament
area of dobrovi has not been described or illustrated. Until the inter-
nal morphology of dobrovi and the external morphology of both
species are more fully known, the synonymy of the two species is
uncertain though possible.
LITERATURE CITED
Aliev, M. M., 1958, Inotseramy melovykh otlozhenii SSSR: Akad. Nauk
Azerbaidzhanskoi SSSR Izv., 1957, no. 3, p. 47-61. (Reprinted in Inter-
nat. Geol. Cong., 20th, Mexico 1956, sec. 7, Paleontologia, taxonomia y
evolucion, p. 123-137 [1958]).
Aliev, R. A. 1960, K Paleontologicheskoy Kharakteristike Verkhnego Mela
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Upper Cretaceous in South-east Caucasus]: Akad. Nauk SSSR Doklady,
v. 131(2), p. 378-379. (Am. Geol. Inst. translation, 1961, p. 295—296a).
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1965, Ammonites from the Upper Cretaceous of West Greenland:
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1966, Die Entwicklung der jiingsten Scaphiten und ihre stratigraphische
Bedeutung Gebiet: Deutsche geol. Gesell. Ber. [Berlin], Wiss. A, Geologie
Palaontologie, v. 11, no. 6, p. 737-744.
Briggs, J. C., 1967, Dispersal of tropical marine shore animals: Coriolis param-
eters or competition: Nature, v. 216, no. 5113, p. 350.
Cieslinski, Stefan, 1960, Biostratygrafia i zasieg form przewodrich g6rnej
kredy W Polsce [Biostratigraphy and extent of index forms in the Upper
Cretaceous of Poland]: Kwartalnik geologiczny [Warsaw], v. 4, no. 2,
p. 432-441. (English summary)
Cobban, W. A., 1964, Evolution of two Upper Cretaceous mollusks, in U.S.
Geol. Survey Mem., Paleontologia Indica, ser. 9, v. 3, pt. 3, 157 p.,
——— and Reeside, J. B., Jr., 1952, Correlation of the Cretaceous forma-
INOCERAMUS? TEGULATUS SPECIES GROUP 41
tions of the western interior of the United States: Geol. Soc. America
Bull., v. 63, p. 1011-1043.
Conrad, T. A., 1858, Observations on a group of Cretaceous Fossil Shells,
found in Tippah County, Miss., with descriptions of fifty-six new species:
Acad. Nat. Sci. Philadelphia Jour., ser. 2, v. 3, p. 323-336, pls. 34, 35.
Cox, L. R., 1940, The Jurassic lamellibranch fauna of Kuchh (Cutch): India
Geol. Survey Mem., Paleontologia Indica, ser. 9, v. 3, pt. 3, 157 p.,
10 pls.
1955, Proposed determination of the nominal species to be accepted
as the type species of the genus “Jnoceramus” Sowerby (J.), 1814 (Class
Pelecypoda) and proposed addition of that name to the “Official list of
generic names in Zoology”: Zool. Nomenclature Bull., v. 11, p. 239-245.
Dobbin, C. E., and Reeside, J. B., Jr., 1929, The contact of the Fox Hills and
Lance formations: U.S. Geol. Survey Prof. Paper 158, p. 9-25.
Dobrov, S. A., 1951, Gruppa Inoceramus caucasicus sp. n.—Inoceramus
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