Permian pelecypods from Tunisia

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AMERICAN MUSEUM
Novttates

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024

Number 2686, pp. 1-22, figs. 1-23, tables 1-3 October 22, 1979

Permian Pelecypods from Tunisia

DONALD W. BOYD! AND NORMAN D. NEWELL?

| ABSTRACT

Fifteen Late Permian pelecypod species belonging

to 15 genera and 13 families are described from
Tunisia. Shikamaia ? ogulineci, a remarkable am-

pterinopectinid, Denguiria azzouzi, new genus and
new species, is described. A minor element of an

bonychiacean, Gigantocyclus zidensis, a lucinid of
surprisingly modern aspect, and a new species,
Lyroschizodus djemelensis are aes un-
usual elements of the fauna. A new non-byssate

extraordinarily rich assemblage of marine inverte-
brates dominated by _ reef-building calcareous
sponges, the pelecypods show surprisingly little re-
semblance to contemporaneous assemblages of other
areas.

INTRODUCTION

This contribution is devoted to bivalve mol-
luscs of Late Permian age (Guadalupian, as
indicated by associated fusulinaceans and am-
monoids) from southern Tunisia Oe: il). They
were collected as part of a large bio-
Stratigraphic survey involving several ‘scientists
in excursions from 1967 through 1976. The in-
vestigations were undertaken in collaboration
with the Service Géologique de Tunisie. the
Smithsonian Institution, and the American Mu-
seum of Natural History and were aided by
National Science Foundation grants admin-
istered by Dr. William H. Kanes, Director of
the International Geologic Studies Program,
University of South Carolina. The fieldwork
and stratigraphic conclusions are described in a
preliminary publication by Newell et al. (1976)
to which the reader is referred for general in-

formation. Biologic groups other than the pe-
lecypods are being studied and _ published
elsewhere by taxonomic experts and results of
additional fieldwork are being published sepa-
rately by J. Keith Rigby.

The fossiliferous rocks, somewhat more than
800 meters thick, contain a diverse, well-pre-
served fauna dominated by sclerosponges,
fusulinaceans, and algae found primarily in
small limestone bioherms and their marginal
debris (fig. 2). The pelecypods occur mainly in
interreef shales and thin limestone beds. They
belong mainly to endemic species that show
little resemblance to contemporaneous fossils of
Sosio in Sicily, or the Salt Range in Pakistan.
The differences are probably attributable to un-
like physical environments at time of deposi-
tion.

‘Professor of Geology, University of Wyoming, Laramie, Wyoming; Research Associate, American Mu-

seum of Natural History.

2Curator Emeritus, American Museum of Natural History.

Copyright © American Museum of Natural History 1979

ISSN 0003-0082 / Price $1.85

2 AMERICAN MUSEUM NOVITATES NO. 2686

M5 / DJEBEL
C-gy Toujane /
\ Y TEBAGA
rae Nouveau f/
\Teuiane,

Ck TEBAGA
=

-
Medenine

Metameur

Medenine

Fic. 1. Index map showing location of Djebel Tebaga outcrops of Permian strata near Medenine in southern

Tunisia. (From Newell et al., 1976.)

A comprehensive work on Tunisian Permian
fossils was completed recently by Termier et
al. (1977). Our work, together with that of the
other collaborators responsible for the bulk of
our collections, will provide new information
on stratigraphic distribution, morphology and
taxonomy of the fossils. Since the Tunisian
outcrops are readily accessible and contain the
most complete sequence of Permian rocks in
western Tethys they may well serve as a re-
gional stratotype for the Mediterranean region.

Invertebrate paleontology is still plagued by
the introduction and use of specific names for
imperfect, poorly preserved, and isolated speci-
mens. Some of the bivalves described herein
belong to groups with generalized, simple mor-
phologies. Characterization of real populations
by such forms requires good samples that re-
veal diverse characters, preferably including in-

ternal features of musculature and _ hinge.
Furthermore, most pteriomorphians are substan-
tially different on the two sides—the valves are
unequal in form and ornamentation. Both
valves are needed for secure characterization
and identification. Consequently, we have not
ventured definite assignments for a number of
apparently distinctive shells presented here. We
believe that their inclusion is needed for future
analysis of the entire fauna in which they oc-
cur.

The specimens figured herein are deposited
in the collections of the Paleobiology Depart-
ment of the National Museum of Natural His-
tory, Washington, D. C. Duplicates, where
available, are deposited with the Service
Géologique de Tunisie and the American Mu-
seum of Natural History. Most of the mor-
phological terms used here are defined in

1979 BOYD AND NEWELL: PERMIAN PELECYPODS 3

ie Upper Biohermal
ae Complex
~

Saikra

150 Meters

o

EXPLANATION

°_«* Bioherms
Shale
Redbeds

Ez Sandstone

Carbonates
marly or
slabby

Fic. 2. West-East correlation of stratigraphic sections of Permian rocks in the Djebel Tebaga. Djebel Tebaga
Biohermal Complex on the west (e.g., units 5 through 23 of section B) gives way eastward to two tongues
separated by Middle Shaly Facies (e.g., units 9 through 19, section D. From Newell et al., 1976).

Moore (1969, p. 102) and Newell and Boyd
(1975). The terms procrescent and retrocrescent
replace opisthocline and prosocline for reasons
explained elsewhere (Newell and Boyd, 1970,
p. 229).

ACKNOWLEDGMENTS

Our understanding of Permian pelecypods
has been substantially aided by grants from the
National Science Foundation. Mr. G. Robert
Adlington photographed our fossils and Mr.

Frank Lombardi helped us with laboratory
preparation of specimens. Both men are in the
Department of Invertebrates at the American
Museum of Natural History.

We appreciate the courtesy of Doctors Niichi
Nishiwaki, Bruce Runnegar, and Adolph
Seilacher in bringing to our attention papers
relative to the genus Shikamaia. We have also
benefited from discussions of this fossil with
Runnegar and Dr. Thomas Yancey. Dr. Sara
Bretsky helped us to evaluate Gigantocyclus
zidensis. A review of the manuscript by Dr.

4 AMERICAN MUSEUM NOVITATES

John Pojeta, Jr., resulted in numerous improve-
ments in the final version.

SYSTEMATIC DESCRIPTIONS
SUPERFAMILY NUCULACEA GRAY, 1824
FAMILY NUCULIDAE GRAY, 1824
GENUS NUCULOPSIS GIRTY, 1911

Nuculopsis alta (Termier and Termier, 1959)
Figure 3

Nucula alta Termier and Termier, 1959, p. 277, text-
pl. 1, figs. 1-5.

Nucula alta Termier and Termier, 1977, p. 79, pl.
17, fig. 3.

DiaGnosis: Umbo prominent and _ very
strongly opisthogyrate; beak at truncated poste-
rior margin of valve.

DESCRIPTION: Shell very elongate because of
marked prolongation of pre-umbonal portion,
the greatest linear dimension being arbitrarily
taken as basis for measuring length (table 1).
Umbonal flanks steep and slightly concave. Re-
silifer unusually small, separating anterior and
posterior dental series. One left valve 9.4 mm.
long has five teeth behind and 12 in front of
resilifer.

DISTRIBUTION: Long-ranging: Saikra Bioher-
mal Complex (I 12); Djebel Tebaga Biohermal
Complex (J 16-18); Middle Shaly Facies (C 1];
E12, 13).

REMARKS: Our best sample consists of 32
specimens from a single locality, unit 11 of

NO. 2686

Fic. 3. Nuculopsis alta (Termier and Termier).
A. Right valve of articulated specimen from Middle
Shaly Facies (C11), USNM 258949. x3. B. Dorsal
view of same, posterior at top. <3. C. Right valve
from Djebel Tebaga Biohermal Complex (J17),
USNM 258950. x3. D. Interior of same. <3. E.
Left valve from Middle Shaly Facies (C11), USNM
258951. x3. F. Interior of same. x3.

Section C. There are also isolated specimens
from other localities and horizons. All possess

TABLE 1
Dimensions (in Millimeters) of 20 Articulated Shells of Nuculopsis alta from One Bed (C11) of the
Middle Shaly Facies
(Length is greatest dimension of valve; height measured perpendicular to length.)

Length Height Biconvexity
1232 8.8 8.0
12.0 8.5 8.2
11.1 8.1 7.4
10.9 7.4 ded
10.9 7.8 7.1
10.9 7.6 6.9
10.7 7.8 6.9
10.6 7.7 7.0
10.5 7.8 6.8
10.0 7.4 6.2

Length Height Biconvexity
9.9 ee. 6.5
9.8 6.9 6.4
9.7 6.1 5.5
9.4 6.9 5.9
9.2 6.6 5.6
9.0 6.8 5.6
8.8 6.5 5.2
8.8 5.9 5.4
8.3 6.1 4.6

1979 BOYD AND NEWELL: PERMIAN PELECYPODS 5

a smooth inner ventral margin, so we have
referred the species to the Upper Paleozoic
Nuculopsis. The shape of this species is closely
similar to that of the Jurassic genus Nuculoma
and it probably would have been so classed by
us it it had been found in rocks known to be
Jurassic. However, we are not now prepared to
undertake a critical comparison of our species
with that genus. It is worthwhile, however, to
consider Nuculopsis alta as a putative ancestor
of Nuculoma.

SUPERFAMILY NUCULANACEA ADAMS AND
ADAMS, 1858

FAMILY MALLETIIDAE ADAMS AND ADAMS, 1858
GENUS PALAEONEILO HALL AND WHITFIELD, 1869

Palaeoneilo tebagaensis (Termier and Termier,

1959)
Figure 4

Nucula tebagaensis Termier and Termier, 1959, p.
277; text-pl. 1, figs. 6, 7

Palaeoneilo tebagaensis Termier and Termier, 1977,
p. 79-80; text-fig. 37; pl. 17, figs. 1, 2.

DiaGnosis: Elongate shells with length/
height ratio between about 1.62 and 1.83, aver-
aging about 1.7 (table 2). Only external orna-
ment a faint ridge extending backward from the
beak nearly parallel to dorsal margin with inter-

vening area very narrow (0.7 mm. on a valve
13.2 mm. long) and slightly concave.

DESCRIPTION: Prosogyrate beaks well for-
ward of midlength. Ventral margin smoothly
curved, with most ventral point near midlength.
Taxodont dental series extends full length of
dorsal margin, with largest teeth at anterior
end. A right valve 13.2 mm. long has 10 teeth
in front of beak and 40 behind. Inconspicuous
posterior ligament groove extends from beak
about half length of posterior row of teeth.
Adductor scars directly below ends of dental
series. Pallial line not visible.

DISTRIBUTION: Long-ranging: Saikra Bioher-
mal Complex (G 6); Oum El Afia Shale (7?)
(J1); Djebel Tebaga Biohermal Complex (B24;
J5, 17); Middle Shaly Facies (C11; E13, 18,
21-23, 25-28).

REMARKS: A collection of 50 specimens
from E27, in the Middle Shaly Facies, is our
largest sample of this species.

FAMILY NUCULANIDAE ADAMS AND ADAMS, 1858

GENUS PHESTIA CHERNYSHEV, 1951
?Phestia sp.
Figure 5

DESCRIPTION: Small, inflated, slightly
opisthogyrate, taxodont with anterior and ven-

Fic. 4. Palaeoneilo tebagaensis Termier and Termier from Middle Shaly Facies. A. Right valve (E27),
USNM 258981. x2. B. Right valve (E18) with pit resembling resilifer below beak, USNM 258983. x3. C.
Left valve (C11), lacks median pit, USNM 258982, x2. D. Bivalved specimen, dorsal view, USNM 258952.

x2. E. Same specimen, left side view. x2.

ON

AMERICAN MUSEUM NOVITATES

NO. 2686

TABLE 2
Dimensions (in Millimeters) of 20 Articulated Shells of Palaeoneilo tebagaensis from One Bed (E27)
of the Middle Shaly Facies

Length Height Biconvexity Length Height Biconvexity
7.5 4.3 3.6 13.0 8.0 6.8
10.0 5.7 4.7 13.2 8.4 7.4
10.2 5.7 4.8 13.5 7.5 6.3
10.2 5.6 5.0 13.6 7.6 6.9
10.6 6.5 5.5 13.8 8.1 6.7
10.8 6.6 5.8 i4.0 8.6 7.7
11.7 6.7 5.6 14.3 8.7 7.0
12.2 7.4 6.4 14.8 8.8 7.4
12.6 7.5 6.9 15.2 9.2 7.6
12.6 6.9 5.9 15.7 9.5 8.0

Fic. 5. ?Phestia sp. from Djebel Tebaga Bioher-
mal Complex (B24). Bivalved specimen, USNM
258953. A. Dorsal view. X2. B. Left side view.
+ ee

tral margins forming continuous curve connect-
ing anterior end of hinge with posterior
extremity; long dorsal profile behind beak con-
cave. Fine, concentric sculpture except on
broad, steep, flank between posterior ridge and
hinge line. Largest specimen 11.1 mm. long,
7.1 mm. high, 5.9 mm. in biconvexity.

DISTRIBUTION: Djebel Tebaga Biohermal
Complex (J16, 17); Middle Shaly Facies (C11;
E13).

REMARKS: Although it is conventional to re-
fer Permian nuculaniform shells to Phestia on
external resemblance alone, the distinction be-
tween this genus and the Mesozoic Nuculana is
based on internal features. Our qualification of
the assignment of this species to Phestia re-
flects the absence of exposed valve interiors in
our collections.

Our 30, mainly imperfect, specimens re-
semble juveniles of some of the larger Pennsyl-
vanian species of Phestia (e.g., the Russian P.
ninae Chernyshev). This group is so conserva-

tive that specific assignment cannot be confi-
dently made solely on external characters.

It is interesting that Phestia is rare in Per-
mian faunas of Tethys. ?Phestia subacuta, a
less inflated form from the Salt Range of India,
was described by Waagen (1881) on the basis
of two specimens. Reed (1932) had the same
number at hand when he described the larger
and more acuminate ?P. thompsoni from Kash-
mir.

SUPERFAMILY ARCACEA LAMARCK, 1809
FAMILY PARALLELODONTIDAE DALL, 1898

GENUS PARALLELODON MEEK AND WORTHEN,
1866

Parallelodon sp.
Figure 6

DESCRIPTION: Shell somewhat reduced ante-
riorly. Beak toward anterior end of hinge;
maximum convexity behind beak. Maximum
height near posterior end of shell. Narrow,
closely spaced ligament grooves form obtuse
(168°) chevrons. Transverse teeth beneath beak
bounded by anterior and posterior lateral teeth;
hinge plate broadened posteriorly. Surface
sculpture limited to growth interruptions of two
or three ranks. Largest specimen 21.7 mm.
long, 13.9 mm. high, and 6.2 mm. in convex-
ity.

DISTRIBUTION: Djebel Tebaga Biohermal
Complex (B24); Middle Shaly Facies (C11;
E25, 27).

1979 BOYD AND NEWELL: PERMIAN PELECYPODS 7

Fic. 6. Parallelodon sp. A, B. From Djebel
Tebaga Biohermal Complex (B24). A. Left valve,
USNM 258954. x1. B. Right valve, USNM
258955. <1. C. Left valve interior, from the Middle
Shaly Facies (C11). USNM 258984 x2.

REMARKS: The late Paleozoic arcaceans need
to be revised. The family resemblances are so
strong that there is much uncertainty about cri-
teria for discrimination of genera and species,
and good population samples are scarce.

Several of our six specimens are fragmental
or crushed, and only one exhibits hinge char-
acters. Unlike the Parallelodon specimen fig-
ured by the Termiers (1977, text fig. 38), the
several transverse teeth beneath the beak are
bordered anteriorly by lateral teeth, recalling
Grammatodon. Although shorter and less prom-
inent than their posterior counterparts, the ante-
rior laterals resemble them in being subparallel
to the dorsal margin.

SUPERFAMILY AMBONYCHIACEA MILLER, 1877

FAMILY ALATOCONCHIDAE TERMIER, TERMIER,
AND DE LAPPARENT, 1973

GENUS SHIKAMAIA OZAKI, 1968

Alatoconcha Termier, Termier and de Lapparent,
1973
Tanchintongia Runnegar and Gobbett, 1975

*Shikamaia ogulineci (Kochansky-Devidé,
1978)
Figures 7-14

DiaGNosis: Apical part of keel periphery
forms 90 degree angle with plane of com-

missure. Incurved beaks of articulated valves
nearly in contact. Extensive platform beneath
beak shields apical end of body cavity and is
bordered on anterior edge by prominent collar
around byssal orifice. Duplivincular ligament
area with lightly incised, closely spaced, rec-
tilinear grooves.

DESCRIPTION: Very large, massive shell;
valve folded outward at an acute angle, with
arcuate, flangelike keel separating flattened an-
terior area from reflexed, concave posterior
area. Hinge edentulous. Outer shell layer
coarsely prismatic. Maximum dimension for
full-grown shell estimated at 30 cm.

DISTRIBUTION: Saikra Biohermal Complex
(G16).

REMARKS: This large, aberrant bivalve is
represented by 34 fragments from a thin layer
of shell rubble at the base of unit 16 in section
G. Our specimens, all incomplete and many
extensively abraded, include two articulated
shells, eight left valves, and eight right valves.
The remaining specimens are too fragmentary
to be identified as to valve. We have given the
collection more attention than its quality would
seem to justify because a similar bizarre form
has been independently described and _inter-
preted differently by investigators dealing with
Permian Alatoconcha from Afghanistan (Ter-
mier, Termier and de Lapparent, 1973) and the
similar Tanchintongia from Malaysia (Runnegar
and Gobbett, 1975) and Yugoslavia
(Kochansky-Devidé, 1978). These workers
were also handicapped by inadequate, fragmen-
tary material with the result that their descrip-
tions are incomplete and their interpretations
speculative. We, too, are uncertain as to overall
form and body-shell relationships, but the shell
seems most analogous to that of a myalinid in
which abnormally angular umbonal ridges are
extremely bowed outward from the plane of
commissure.

The most distinctive aspect of the form is
the flangelike character of the arcuate umbonal
keel (fig. 7). This sharp flexure separates two
major parts of the valve. The area in front of
the flange is flat to undulatory, whereas the part
behind is broadly concave. The flanks of the
keel are essentially parallel near its periphery,
with the result that isolated fragments of the
keel as seen in cross section have the aspect of

8 AMERICAN MUSEUM NOVITATES

Body cavity

Edge of flange

Fic. 7. Shikamaia perakensis (Runnegar and
Gobbett). Cross section after Runnegar and Gobbett
(1975). One-third natural size. (Permission of the
publisher).

an isoclinal fold in sedimentary rocks (fig. 8).
The minimal internal space relative to external
surface area in such a situation is illustrated by
measurements of one fragment in which oppos-
ing surfaces of the valve interior are only 6
mm. apart at a point 50 mm. inward from the
flange margin.

A duplivincular ligament area borders the
dorsal margin (fig. 9b). This part of the valve,
in a plane roughly perpendicular to that defined
by the proximal half of the curved umbonal
ridge, is incomplete in all our specimens. Be-
neath the incurved beak, a massive platform
bridges the space between the diverging valve
margins (fig. 9c), thereby shielding the apical
end of the body cavity. This umbonal septum
typically is concave in longitudinal profile
whereas its central part varies from concave to
slightly convex in transverse profile. The re-
semblance of this area to a resilifer is enhanced
- by concave (toward beak) growth irregularities
(fig. 10A).

The anterior edge of the plate is bordered by
an offset, slightly arcuate collar (figs. 9d, 10A,
11). It combines with its counterpart on the
opposite valve to form a spoutlike neck (fig.
11). Collars vary in relief from very prominent
to negligible. Much of this variation may re-
flect vagaries of preservation since the collar
forms a topographic prominence on the rela-
tively flat surface of the valve. The collar has
as much as 2.5 cm. relief in a few specimens
(fig. 12A). It is sheathed by a prismatic layer
which thickens on the inner (toward opposite

NO. 2686

valve) side of the collar, where transverse
striations represent discontinuities between 0.5
mm.-thick growth increments. The rugose
growth pattern exhibited by the inner surface of
the collar together with the presence, on some
specimens, of a shallow groove along the inner
margin of the collar, suggests that the collar
developed in association with a byssus.

The part of the shell best represented in our
collection is the apical one-third. By contrast,
our interpretation of the abapical region is
based mainly on one incomplete valve (fig. 13).
In this specimen, the two major surfaces on
either side of the umbonal ridge converge ven-
trally. This is accomplished by posteroventral
warping of the surface that is predominantly
flat in the anterior half of the valve. As a
result, cross-sections of the valve become pro-
gressively constricted abapically. Articulation
of two such valves would produce an abapical
configuration similar to that of the anterior re-
gion of brachiopods with angular fold and sul-
cus, even though the commissure in the
pelecypod coincides with the plane of symme-
try.

Body space was much more restricted than
suggested by external dimensions. As noted
above, space in the hollow keel is very con-
fined. Moreover, umbonal thickening is very
prominent in large valves.

The surface of most of our specimens is
worn. However, an outer gray prismatic layer
is present in places on a few fragments of both
left and right valves (fig. 14). Where the prisms
are 1 or 2 millimeters long and _ perpen-
dicular to the surface, the prismatic layer repre-
sents about one-fifth the wall thickness. Rarely,
the prisms are notably longer and inclined at a
low angle to the valve surface. The remainder
of the wall thickness, as much as several centi-
meters in our thickest fragments, does not ade-
quately retain details of its original
microstructure. Some layering is apparent,
commonly involving shades of gray and brown.

In their interpretation of life orientation of
fossils similar to ours, Runnegar and Gobbett
(1975) envisioned the shell resting on its broad
anterior surface (fig. 7). We think this applies
equally well to the Tunisian species. In this
position, in contrast to the reconstruction of

Fic. 8. Shikamaia ?ogulineci (Kochansky-Devidé). From Saikra Biohermal Complex (G16). A. Polished
surface, cut through umbonal ridge and flange showing hairpin outfolding of shell, USNM 258961. x1. B.
Polished section through thick part of reflexed wall. USNM 258962. x1.

Fic. 9. Shikamaia Pogulineci (Kochansky-Devidé). Interpretation of hinge and adapical part of shell. The
plane of commissure is parallel to the page. Symbols (on left valve): a, umbonal ridge; b, duplivincular
ligament area; c, umbonal septum below beak; d, anterior collar. 2/3.

Fic. 10. Shikamaia ?ogulineci (Kochansky-Devidé). From Saikra Biohermal Complex (G16). A-C. Frag-
ment of left valve, USNM 258956. x %. A. Internal view, commissure parallel with page, beak at upper right;
umbonal septum below beak and marked by lunulate growth lines, bounded at right by byssal trough and
rugose collar. B. Same, rotated 90° to the right; commissure perpendicular to page. Dashed line follows
fracture between exterior (above) and interior (below). Beak at upper right. C. Anterior view of same.

Fic. 11. Shikamaia ?ogulineci (Kochansky-De-
vidé). From Saikra Biohermal Complex (G 16). x %.
A. Apical view of broken fragment of bivalved spec-
imen. Beaks at lower center terminating nearly hori-
zontal umbonal ridges. B. Same specimen, view of
byssal collar. Commissure vertical, beaks at center
of upper margin. USNM 258957.

10

Fic. 12. Shikamaia ?ogulineci (Kochansky-Devidé).
From Saikra Biohermal Complex (G 16). A. Frag-
ment of beak portion of left valve with beak at left
center. Plane of commissure vertical with edge view
of prominent collar below. Extension to the right is
reflexed umbonal ridge and its continuation in the
flange, USNM 258958. x%. B. Another specimen
from the same locality. Inner view of apex, com-
missure parallel to page. Right (anterior) margin is
edge of collar. Central concavity is umbonal septum
with beak at apex, USNM 258959. x%.

1979 BOYD AND NEWELL: PERMIAN PELECYPODS ll

Fic. 13. Shikamaia ? ogulineci (Kochansky-Devidé). From Saikra Biohermal Complex (G 16). A. Abapical
part of right valve broken through flange. anterior surface below. B. Same specimen showing body cavity.

USNM 258960. x %.

Fic. 14. Shikamaia ? ogulineci (Kochansky-Devidé). From Saikra Biohermal Complex (G 16). A. Prismatic
and foliated (?) layers of the shell. SEM photograph, x120. B. SEM photograph, x22.

Kochansky-Devidé (1978), the collars of articu-
lated valves would be directed toward the sub-
strate.

The reflexed winglike form of our specimens
also characterizes four species recently de-
scribed from Permian strata of other countries.
They are Shikamaia akasakaensis from Japan
(Ozaki, 1968), Alatoconcha vampyra from Af-
ghanistan (Termier, Termier and de Lapparent,

1973), Tanchintongia perakensis from Malaysia
(Runnegar and Gobbett, 1975), and T. ogulineci
from Yugoslavia (Kochansky-Devidé, 1978). In
each of the first three papers, a new genus was
created to receive a new species. At the respec-
tive times of writing, Termier and coauthors did
not know of Ozaki’s paper, and Runnegar and
Gobbett had encountered neither that reference
nor the description of the Afghan form. Alato-

12 AMERICAN MUSEUM NOVITATES

concha was said by its authors to be allied to
the Megalodontacea, whereas Tanchintongia
was assigned by its authors to the Am-
bonychiacea. Each of the two groups of inves-
tigators was without knowledge of the other’s
work. Considering the aberrant morphology in-
volved and the poor quality of specimens at
both localities, it is not surprising that the two
investigations resulted in different opinions
concerning taxonomic affinities. Although it is
possible that the Afghan and Malaysian speci-
mens are unrelated, their common geologic
age, biogeographic province, and distinctive
characteristics lead us to believe that they are
congeneric. Some of the differences in the orig-
inal diagnoses probably are artificial. Thomas
Yancey has called our attention to the probable
homology of the distinctive furrow which the
authors of Alatoconcha interpreted as a liga-
ment groove and the authors of Tanchintongia
described as a byssal notch.

Ozaki’s diagnosis of Shikamaia is based on
three fragmental specimens embedded in mas-
sive limestone (Parafusulina zone) from
Akasaka, Japan. He was unable to determine
the phylum represented by his material, but his
illustrations leave no doubt that the shells in
question are closely similar to those described
subsequently from Afghanistan, Malaysia, and
Yugoslavia. The Japanese fossils are bivalved,
large (more that 16 cm. in maximum dimension
and as much as 2 cm. in thickness of shell
wall), and distinguished by a reflexed wall re-
sulting in a broad flange perpendicular to the
commissure. We conclude that Alatoconcha and
Tanchintongia are junior synonyms of
Shikamaia.

The Tunisian species differs from both Af-
ghanistan and Malaysian forms in character and
position of the duplivincular ligament area,
possession of apical platform and bordering
collar, proximity of opposed beaks, and abrupt
lateral expansion of the umbonal ridge away
from the beak. These differences may later
prove to be significant at the generic level, but
the present state of knowledge does not justify
creation of another genus. Pending results of
further study, the Tunisian species is assigned
to Shikamaia.

Our Tunisian material is very similar to the
recently described Yugoslavian species Tanchin-

NO. 2686

tongia ogulineci. Shells from the two areas
share, in addition to generic characters, a
prominent byssal collar, notable flange width at
the apical end, and a very thick prismatic outer
layer. Furthermore, Kochansky-Devidé’s (1978)
illustrations suggest incurved, nearly touching
beaks (her fig. 2), and a probable umbonal
septum (her fig. 3, part 5).

Several differences between the Tunisian and
Yugoslavian specimens give rise to our hesi-
tancy in declaring them conspecific. The Yugo-
slavian byssal furrow appears to be a more
deeply inset trough than its Tunisian counter-
part. Moreover, the furrow’s position on the
byssal collar and its termination at a well-de-
fined aperture are not duplicated on our speci-
mens. The umbonal septum in our largest
specimens is notably concave toward the op-
posing valve. This seems to be different from
the form shown in Kochansky-Devidé’s figure
2c. We see evidence in our specimens of a
duplivincular ligament area with rectilinear
grooves. This should be located along the
lower right margin of Kochansky-Devidé’s fig-
ure 3, part 5, assuming that the striated area
below the byssal furrow in that illustration is an
umbonal septum. Finally, we attribute greater
relief to the abapical half of our shells than that
indicated by Kochansky-Devidé in her figure 3,
part 2. These differences, if real, would justify
recognition of the Tunisian fossils as a separate
species. However, we suspect that a number of
the contrasts simply reflect inadequacies of the
samples and their interpretation.

SUPERFAMILY PTERIACEA GRAY, 1847
FAMILY PTERINEIDAE MILLER, 1877
GENUS LEPTODESMA HALL, 1883

?Leptodesma sp.
Figure 15

Monopteria sp. Termier and Termier, 1977, p. 81,
fig. 39; pl. 17, fig. 4.

DESCRIPTION: Elongated pterioid with dorsal
and ventral margins of posterior half of shell
subparallel to hinge. Beak subterminal. Liga-
ment area broad and flat, with fine striations
parallel to hinge. One or two posterior lateral
teeth.

1979 BOYD AND NEWELL: PERMIAN PELECYPODS 13

DISTRIBUTION: Middle Shaly Facies (E25,
27).

REMARKS: Our sample consists of 15 sepa-
rated valves from a single locality. They are
tightly cemented in skeletal debris, and most
have the interiors exposed. All but one are left
valves, and all have been damaged by abrasion,
compaction, and_ recrystallization. Conse-
quently, the specimens cannot be accurately
measured and are not a good representation of
a population.

The shell is unusually elongate by horizontal
extension of the posterior part after passing
through the usual oblique growth stage char-
acteristic of many pterioids. The beak is well
forward, but not terminal as with Monopteria.
The rather blunt posterior wings probably re-
flect systematic breakage. This conclusion
seems to be confirmed by two associated, ap-
parently juvenile shells, with elongate, strongly
acuminate wings intact.

The striations on the ligament area resemble
growth lines; there is some uncertainty whether
or not they are duplivincular ligament grooves.
In any case, no unequivocal evidence of a re-
silifer has been found. Two specimens display

short, posterior lateral teeth joining the liga-
ment area at a low angle. Unlike Monopteria,
no anterior teeth are present.

Two small valves with the exterior exposed
display papillate ornamentation most conspic-
uous in front of the posterior ridge. Each pa-
pilla is elongate parallel to the growth lines.

FAMILY BAKEVELLIIDAE KING, 1850
GENUS GERVILLIA DEFRANCE, 1820
SUBGENUS CULTRIOPSIS COSSMAN, 1904

Gervillia ?(Cultriopsis) sp.
Figure 16

DESCRIPTION: Small, long-bodied valves
with posteroventral part produced far behind
posterior auricle. Angular posterior ridge arcu-
ate on umbo but rectilinear and parallel to
hinge on main shell body. Two serrate ribs on
front end of left valve extend from beak to
anteroventral margin. Triangular ligament area
exhibits resilifer beneath beak and one or more
additional pits posterior of it. Small peglike
teeth at anterior end of hinge; elongate poste-
rior teeth subparallel to hinge line.

Fic. 15. %Leptodesma sp. from Middle Shaly Facies (E25). A. Interior of right valve retaining posterior
hinge teeth, USNM 258964. x1. B. Left valve with fine papillate ornamentation, USNM 258986. x2. C. Left
valve interior showing entire posterior auricle, USNM 258987. x2. D. Large, imperfect left valve, USNM

258963. x1.

14 AMERICAN MUSEUM NOVITATES

DISTRIBUTION: Middle Shaly Facies (C16;
E25, 27).

REMARKS: The angular posterior ridge is at
mid-height on the long posterior extension of
the valve, resulting in a triangular transverse
section for that part of a valve. Our largest
specimen is 27.5 mm. long and may be in-
complete at the posterior end. The height is
only 6.8 mm., yielding a distinctive length/
height ratio of 4. A narrow but well-differenti-
ated posterior auricle extends between the pos-
terodorsal margin of the ligament area and the
adjacent steep umbonal flank.

The ligament area is asymmetrically triangu-
lar and warped as a result of more rapid shell
addition along the posterior part of the hinge.
The beak is on the anterior side of the triangle
rather than at its apex.

Small anterior teeth, three on the right valve
and two on the left, project perpendicular to the
hinge. The posterior part of the hinge is char-
acterized by slender, rectilinear teeth and sock-
ets with their long axes slightly inclined
anteriorly.

Two ribs at the anterior end of the left valve
are unequal. The anterior one is unobtrusive,
whereas its neighbor rises prominently above
the surrounding surface like a cockscomb.
These ribs are absent on the few right valves
available for study. On a few specimens, the
beak and anterior flank exhibit remnants of a

NO. 2686

fine reticulate pattern formed by radial and con-
centric threads (fig. 16A, B).

In overall form, our specimens resemble En-
sipteria from the Permian of Japan (Nakazawa
and Newell, 1968). However, that monotypic
genus is characterized by a narrow ligament
area bearing a single pit. By contrast, the Tuni-
sian specimens possess triangular ligament
areas. Although convincing ijigament scars can-
not be discerned on most of these, one speci-
men exhibits two or more pits (fig. 16D). On
the basis of this evidence, we interpret the
specimens as bakevelliids, and refer them with
question to Gervillia (Cultriopsis). This sub-
genus of ensiform shells has heretofore been
recognized only in Mesozoic strata.

FAMILY ISOGNOMONIDAE WOODRING, 1925

GENUS TAMBANELLA NAKAZAWA AND NEWELL,
1968

?Tambanella sp.
Figure 17

DESCRIPTION: Outline rhomboidal without
wings. Beak terminal. Posterior and dorsal mar-
gins form wide (e.g., 140°) angle; dorsal part
of anterior margin reflexed, producing
troughlike area subjacent to beak. Small, con-
cave septum covers apical end of umbonal cav-
ity. Ligament area opisthodetic and

Fic. 16. Gervillia ? (Cultriopsis) sp. A, B from the Middle Shaly Facies (E 27). Left valve USNM 258988.
A. X2. B. Same, enlarged to show ornament. x7. C, D from Middle Shaly Facies (C 16). C. Note the two
ribs and intervening trough at front of shell, USNM 258965. x4. D. Ligament area of same specimen as C,
showing posterior tooth (lower left), two peglike anterior teeth, and two ligament pits. x9.

1979 BOYD AND NEWELL: PERMIAN PELECYPODS 15

multivincular, with pits separated by distances
equal to, or greater than, pit width. One or two
lamellar teeth parallel to valve margin at poste-
rior end of ligament area.

DISTRIBUTION: Djebel Tebaga Biohermal
Complex (B25; J16, 17); Middle Shaly Facies
(Cll, 16; E25, 26).

REMARKS: Of the dozen specimens in our
collection, all but the illustrated one are less
than 16 mm. in maximum dimension. Irreg-
ularly spaced growth lines provide the only
surface sculpture. |

A similar form was illustrated by Termier
and Termier (1959, text-pl. 1, figs. 23, 24) asa
bakevelliid. They subsequently (1977, p. 82)
reassigned it to Waagenoperna of the Isog-
nomonidae. Our specimens have more widely
spaced ligament pits than does the valve illus-
trated by the Termiers. Furthermore, they did
not report dentition, whereas our material ex-
hibits posterior teeth. We are referring our
specimens with hesitation to Tambanella, a
genus currently represented by a single species
from the Permian of Japan. The uncertainty
arises from lack of unequivocal evidence for a
cardinal tooth in our specimens, and from ap-

Fic. 17. ?7Tambanella sp. A. Interior of large
right valve from Djebel Tebaga Biohermal Complex
(B 25). Posterior part of the hinge is missing,
USNM 258966. x2. B. Right valve from Djebel
Tebaga Biohermal Complex (J 16), USNM 258967.
x2. C. Interior of a small right valve from Middle
Shaly Facies (C 16) showing posterior lateral teeth,
USNM 264362. x3.

parent absence of an apical septum in the Jap-
anese material.

SUPERFAMILY PECTINACEA RAFINESQUE, 1815
FAMILY PTERINOPECTINIDAE NEWELL, 1938
GENUS DENGUIRIA, NEW GENUS

ETyMoLoGy: Denguir, a prominent hill in
the southern Djebel Tebaga, southern Tunisia.

TYPE SPEcIES: Monotypic.

Dracnosis: Adult right valve lacks byssal
notch. Otherwise like Dunbarella.

Denguiria azzouzorum, new species
Figure 18

HoLoTYPE: USNM 264364.

ETYMOLoGy: Named in honor of Ahmed and
Azzedine Azzouz, of Tunis, who greatly facili-
tated work leading to discovery of this species.

DIAGNOsIs: Orbicular, retrocrescent shells
with weakly differentiated anterior auricles and
flattened posterior auricles; beaks well forward.
Very low ligament area extends full length of
hinge; sharply incised duplivincular grooves di-
verge at very obtuse angles below beak. Hinge
edentulous. Radial ribs crossed by closely
spaced growth threads on both valves.

DisTRIBUTION: Middle Shaly Facies (E27).

REMARKS: This thin-shelled pectinacean is
systematically flattened by compaction and our
10 fragmental specimens have been crushed
against the irregular surface of a thin layer of
skeletal debris. Nevertheless, the umbonal cav-
ity is not crushed and the original convexity
was probably quite low in both valves. Costae
of left valves are narrower and more regular
than those of right valves. Costae increase dur-
ing growth by intercalation on left valves. In-
crease in right valves is probably by
bifurcation, as in Dunbarella, but preservation
is too poor to allow a definite conclusion.

FAMILY AVICULOPECTINIDAE MEEK AND
HAYDEN, 1864
GENUS ANNULICONCHA NEWELL, 1938
Annuliconcha sp.
Figure 19B

REMARKS: We have a single specimen, an
imperfect left valve, representing this distinc-

16 AMERICAN MUSEUM NOVITATES

NO. 2686

Fic. 18. Denguiria azzouzorum, new genus and new species from Middle Shaly Facies (E27). A. Right
valve, the holotype, interior showing duplivincular ligament area and lack of a byssal notch, USNM 264363.
x3. B. Right valve exterior showing lack of a byssal notch, USNM 264364. x3. C. Left valve, USNM

264365. x2.

tive genus. The surface ornament includes ra-

dial and concentric threads as well as a

prominent series of beaded concentric ridges.
DISTRIBUTION: Middle Shaly Facies (C11).

GENUS STREBLOPTERIA M’COY, 1851

2Streblopteria sp.
Figure 19A

REMARKS: The single specimen representing
this taxon is a right valve 26.4 mm. high. It is
slightly procrescent and has a small posterior
auricle, a prominent anterior auricle, and a nar-
row and deep byssal notch. The evenly convex
valve surface lacks radial ornament but is
marked by innumerable, somewhat irregular
growth threads. This aspect is unlike the
smooth surface typical of Streblopteria valves.

DISTRIBUTION: Djebel Tebaga Biohermal
Complex (J17).

GENUS CLARAIA BITTNER, 1901

?Claraia posidoniformis Termier and Termier,
1977

Figure 20

Claraia ? posidoniformis Termier and Termier, 1977,
p. 82; pl. 16, fig. 10.

DESCRIPTION: Suborbicular, retrocrescent
valves with long, straight hinge line and slight
convexity. Anterior (small) and _ posterior
(large) auricles of left valve weakly differenti-
ated. Subjacent anterior and posterior marginal

sinuses very shallow. Radial ribs and fine con-
centric growth threads as in Claraia stachei.

DISTRIBUTION: Saikra Biohermal Complex
(112); Middle Shaly Facies (E27).

REMARKS: Our collection includes two-dozen
fragments of this enigmatic form. Most are left
valves, all but one from the same collecting
site (112), and all are exposed on the surfaces
of seams of fibrous calcite, varying from 2
mm. to 2 cm. in thickness. The unusual devel-
opment of the fibrous calcite, resulting in dupli-
cate images on opposite surfaces of a crust, is
similar to an occurrence involving Lower Tri-
assic Claraia in Idaho (Boyd and Newell,
1976).

The genus Claraia has long been considered
to be a good indicator of Early Triassic age for
enclosing deposits. However, Claraia is now
known in association with a Permian fauna in
Kashmir (Nakazawa, 1977) so that we agree
with the Termiers that it may be reasonably
considered in the present situation.

One good left valve demonstrates rib in-
crease by intercalation. Left valve auricles
stand out not because of topographic differ-
entiation, but because they lack the prominent
radial ribs that cover the rest of the valve. The
posterior auricle of the right valve appears sim-
ilar to its left valve counterpart. One right
valve exhibits a narrow, anterior, subauricular
notch parallel to the hingeline. Poor preserva-
tion of the specimen and absence of other right
valves with the critical area preserved make it
impossible to be sure that the notch is an origi-

1979 BOYD AND NEWELL: PERMIAN PELECYPODS 17

Fic. 19. 2Streblopteria sp. and Annuliconcha sp. A. Right valve of ?Streblopteria sp. from Djebel Tebaga
Biohermal Complex (J 17), USNM 258968. x2. B. Annuliconcha sp. Left valve. From Middle Shaly Facies

(C 11), USNM 258969. x2.

Fic. 20. ?Claraia posidoniformis Termier and
Termier from Saikra Biohermal Complex (I 12). A.
Latex replica of exterior of left valve, USNM
258985. x1. B. Right valve, inner surface of outer
layer showing byssal notch. USNM 264366. x1.

nal feature of the specimen. Other reasons for
uncertainty in the generic assignment include
the strong ornamentation, the poorly developed
anterior auricle of the left valve, and a weak
posterodorsal, subauricular sinus.

SUPERFAMILY TRIGONIACEA LAMARCK, 1819
FAMILY SCHIZODIDAE NEWELL AND BOYD, 1975
GENUS SCHIZODUS DE VERNEUIL AND
MURCHISON, 1884
Schizodus cf. S. pinguis Waagen, 1881
Figure 21

DESCRIPTION: Large (e.g., 48 mm. high)
shell with hinge of schizodian grade (Newell

and Boyd, 1975, p. 77). Slightly carinate poste-
rior ridge bounds concave corselet.

DISTRIBUTION: Saikra Biohermal Complex
(G17).

REMARKS: This form is represented by a
dozen fragmental specimens from one collect-
ing site. They are too incomplete and abraded
to allow an adequate species characterization.
Overall form and lack of surface relief other
than the slightly raised crest of the posterior
ridge suggest that the Tunisian specimens are
conspecific with S. pinguis from the upper
Productus Limestone of the Salt Range. The
posterior ridge is less strongly carinate, and the
outline less trigonal, than is the case with S.
canalis from the western United States.

FAMILY TRIGONIDAE LAMARCK, 1819

GENUS LYROSCHIZODUS NEWELL AND BOYD,
1975

Lyroschizodus djemelensis, new species
Figure 22

Myophoria sp. Termier and Termier, 1959, p. 278;
text-pl. I, fig. 25.

Cardinia sp. Termier and Termier, 1959, p. 278;
text-pl. II, figs. 1-4.

Astartella gemmifera Termier and Termier, 1977
[partim], p. 85, text-figs. 43b, c; pl. 17, figs.
8-10.

18 AMERICAN MUSEUM NOVITATES

NO. 2686

Fic. 21. A right valve of Schizodus cf. S. pinguis Waagen from the Saikra Biohermal Complex (G 17),
USNM 258970. A. Exterior. Note carinate posterior ridge. <1. B. Interior. x1. C. Enlargement of hinge.
Schizodian hinge grade, with ligament groove and nymph on right. Posterior tooth damaged. 3.

HoLotyrPe: USNM 258972.

ETYMOLOGy: The trivial name is from the
village of Halg el Djemel.

DIAGNOSIS: Posterior ridge indistinct; liga-
ment groove broad, troughlike; imbricating,
conspicuous rugae formed by growth interrup-
tions.

DESCRIPTION: Small, oval shells with pros-
ogyrate beaks located slightly anterior to mid-
length. Maximum convexity behind beak, on
broadly rounded posterior ridge. Dorsal margin
slopes gently downward behind beak, but more
steeply in front of beak, resulting in relatively
sharply curved anterior margin and a higher,
somewhat truncate posterior margin. Corselet
slightly flatter than the adjacent surface, but not
sharply defined. Two ranks of concentric sur-
face relief produced by fine concentric ridges
superimposed on shinglelike growth incre-
ments. Ligament groove broad (as much as 0.6
mm.), troughlike, with length about equal to
distance from beak to distal end of major tooth.
Dentition schizodian, major teeth bulbous; ma-
jor sockets three-fourths floored. In three speci-
mens the average length/height ratio is 1.10;
height/convexity ratio, 3.10; ratio length/partial

length (distance from beak to anterior ex-
tremity), 2.54. Largest specimen: length, 18
mm, height, 16 mm, biconvexity, 10 mm, par-
tial length, 7 mm.

DISTRIBUTION: Saikra Biohermal Complex
(G6, 16; 112); Oum El Afia Shale (?) (B1; F4):
Middle Shaly Facies (C11; E13, 25, 27): Djebel
Tebaga Biohermal Complex (B23, 24; C18;
J18).

REMARKS: Following a smooth juvenile stage
at the umbones, the first growth interruption
forms a rugosity at a height ranging between
3.5 mm. and 6.0 mm. in different shells. In
some valves, minor concentric ridges appear
before the first growth interruption; in others,
the first minor ridge appears just ventral to the
first ruga. The rugae, or growth imbrications,
are spaced from 0.5 mm. to 2.5 mm. Valves 15
mm. high possess from eight to 11 rugae. Al-
though much less conspicuous, the minor con-
centric ornament is more consistent in form and
spacing. The minor ridges are from 0.1 mm. to
0.2 mm. wide, with intervening troughs of
comparable width.

The posterior cardinal tooth and ligament
nymph of the right valve are parts of the same

1979 BOYD AND NEWELL: PERMIAN PELECYPODS 19

Fic. 22. Lyroschizodus djemelensis, new species. A. Right valve from Middle Shaly Facies (E 27).
Posterior tooth forms thickened anterior edge of nymph. Major socket floored, paratype USNM 258971. x2.
B. Holotype, a left valve from Middle Shaly Facies (E 27). Narrow ligament nymph lacks associated tooth,
USNM 258972. x2. C. Dorsal view of articulated valves, anterior on right, from Middle Shaly Facies (E 13).
Elongate cavity behind beaks is ligament area, paratype USNM 258973. x2. D. Right valve of shell shown in
fig. C, illustrating both major and minor concentric ridges. X2. E. Dorsal view of articulated shell, anterior on
right, from Saikra Biohermal Complex (G 6). Abraded area behind beaks. Absence of well-defined posterior
ridge is typical of species, paratype USNM 258974. x2. F. Right valve of shell shown in figure E. Subcircular
outline is typical of this species. Minor concentric ornament not well preserved. x2.

ridge but the narrower nymph of the left valve
lacks an associated tooth. Muscle scars are
poorly defined in the specimens at hand but the
two adductors appear to be subequal. There is a
suggestion of an anterior retractor imprinted at
the anteroventral end of the hinge plate, next
to, but partly separated from, the subjacent ad-
ductor scar.

Several specimens illustrated by Termier and
Termier (1959, 1977) appear to be representa-
tives of Lyroschizodus djemelensis. In their
1959 paper, these include a left valve illustrated
as Myophoria sp. (their text-pl. 1, fig. 25) and
several specimens assigned to Cardinia sp.
(their text-pl. 11, figs. 1-4). In 1977, the Termi-
ers reassigned all these specimens to Astartella
gemmifera, a species first described in the 1959
contribution. As illustrated in that paper (text-
pl. Il, figs. 10-13), A. gemmifera differs from
Lyroschizodus djemelensis 1n possessing more
ornate, beaded ornamentation and in exhibiting
a series of interlocking denticles along the inner
ventral margin. Lateral teeth, lacking in L.
djemelensis, are said to be present in A. gem-

mifera (Termier and Termier, 1977, p. 85).
However, several of the specimens illustrating
A. gemmifera in the 1977 paper appear to us to
represent L. djemelensis. The likely candidates
include their text-figures 43b and c, and figures
8 to 10 on plate 17.

Our collection consists of 28 calcareous
specimens, most of them articulated and de-
formed by compaction. Hinge features are illus-
trated by three left valves and four right valves.
The species is assigned to Lyroschizodus be-
cause of its ornamentation and hinge char-
acters.

SUPERFAMILY LUCINACEA FLEMING, 1828
FAMILY LUCINIDAE FLEMING, 1828

GENUS GIGANTOCYCLUS TERMIER AND TERMIER,
1977

The original description of this monotypic
genus did not include observations on the hinge
and muscles needed to characterize it. Conse-
quently, we are revising it here from our more
ample collection.

20

DIAGNOsIs: Shell subcircular and large for a
lucinoid. Hinge edentulous; nymph long and
narrow. Surface sculpture limited to concentric
growth imbrications. Closely similar only to the
Cenozoic Anodontia Link from which it differs
in having a much broader anterior than poste-
rior adductor.

Gigantocyclus zidensis Termier and Termier,
1977
Figure 23
Incertae sedis Termier and Termier, 1959, p. 280;
text-pl. Il, fig. 8.
Gigantocyclus zidensis Termier and Termier, 1977, p.
84-85; text-fig. 42.

DIAGNOSIS: Compressed shell with max-
imum convexity centrally located. Anterior ad-
ductor scar strongly divergent from pallial line,
with maximum dimension twice that of poste-
rior scar.

DESCRIPTION: Shell prosogyrate; narrow,
slightly concave escutcheon behind beak. Ex-
ternal surface relief formed by growth irreg-
ularities of two ranks, with the coarser
imbrications from 2 to 4 mm. apart.

DISTRIBUTION: Djebel Tebaga Biohermal
Complex (B 25a).

REMARKS: Our collection includes a dozen
valves with interiors exposed although ones
with sharply defined muscle scars are rare.

AMERICAN MUSEUM NOVITATES

NO. 2686

Only one valve in our collection demonstrates
unequivocally the distinctive configuration of
the anterior adductor scar. The only accessory
scar we have identified is that of the posterior
pedal retractor, located at the anterodorsal mar-
gin of the posterior adductor scar.

Sharply delineated anterior and posterior
dorsal areas typical of many modern lucinids
(Bretsky, 1976, p. 227) are not present on the
Tunisian shells.

The long, narrow nymph is accentuated ven-
trally by a bordering shallow groove. The hinge
plate of the left valve exhibits a broad, low
mound expanding posteroventrally from the
beak, and separated from the proximal part of
the nymph by a furrow. Although these fea-
tures suggest weak dentition, appropriate coun-
terparts are absent across the plane of
commissure. The posterior furrow is opposed
on the right valve by a comparable furrow, and
the ill-defined mound is opposite a featureless
platform beneath the beak of the right valve.
The concave dorsal margin in front of the beak
bears a faint inward-projecting ridge, equally
prominent in both valves. Considering the vari-
ability of each of these features and the lack of
opposed positive and negative relief, the shell
is best described as edentulous. In this respect,
and in its form, it resembles Cenozoic lucinids
of the genus Anodontia (table 3).

TABLE 3
Dimensions (in Milimeters) of 11 Valves of Gigantocyclus zidensis from One Unit (B25a) in the Djebel
Tebaga Biohermal Complex
(Partial length = length from beak to anterior extremity; beak-nymph = distance from beak to distal end

of nymph.)
Length Height Convexity Partial Length Beak-Nymph
(Left Valves)
75 66 11 23 33
72 61 — 26 27
71 57 9 27 28
71 56 9 — —
69 56 9 23 33
61 50 — — —
(Right Valves)
78 60 10 — —
74 59 7 19 31
71 56 8 17 30
61 47 7 23 26
56 47 4 a =

1979 BOYD AND NEWELL: PERMIAN PELECYPODS 21

Fic. 23. Gigantocyclus zidensis Termier and Termier from Djebel Tebaga Biohermal Complex (B 25). A.
Anterior half of left valve, exhibiting irregularly spaced concentric growth ridges, USNM 258975. x4. B.
Weathered exterior of left valve. Note very faint umbonal ridge, USNM 258976. x%. C. Enlarged hinge of
left valve shown in fig. E. <2. D. Interior of right valve, USNM 258978. x1. E. Interior of a complete left
valve, USNM 258977. x1. F. Interior of left valve with unusually well-defined pallial line and muscle scars.
Anterior adductor scar diverges posteroventrally from pallial line, USNM 258979. x1. G. Interior of dorsal
part of left valve, USNM 258980. x1.

22 AMERICAN MUSEUM NOVITATES

LITERATURE CITED

Boyd, D. W., and Newell, N. D.

1976. Diagenetic image reversal in a Triassic
pelecypod. Contributions to Geology, Uni-
versity of Wyoming, vol. 14, pp. 65-68.

Bretsky, S. S.

1976. Evolution and classification of the Lu-
cinidae (Mollusca; Bivalvia). Palaeon-
tographica Americana, vol. 8, no. 50, pp.
219-337.

Kochansky-Devidé,

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