Cenomanian oysters from the Sergipe Basin, Brazil

Cretaceous Research (1999) 20, 747–765Article No. cres.1999.0190, available online at http://www.idealibrary.com on

Cenomanian oysters from the Sergipe Basin,Brazil

Jens Seeling and Peter Bengtson

Geologisch-Palaontologisches Institut der Universitat, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany;e-mail: [email protected]; [email protected]

Revised manuscript accepted 3 August 1999

Cenomanian (mid Cretaceous) oysters from the Sergipe Basin in northeastern Brazil are described, with revisions ofpreviously described forms. Nine genera and subgenera, including eleven species, are distinguished: Rastellum diluvianum(Linne, 1767), Amphidonte (Ceratostreon) reticulata (Reuss, 1846), A. (Ceratostreon) flabellata (Goldfuss, 1833), Exogyra(Costagyra) olisiponensis Sharpe, 1850, Ilymatogyra (Afrogyra) africana (Lamarck, 1801), Rhynchostreon (Rhynchostreon)mermeti (Coquand, 1862), R. (Laevigyra) obliquatum (Pulteney, 1813), R. (Laevigyra) sp., Pycnodonte (Phygraea) vesiculosa (J.Sowerby, 1823), Curvostrea rouvillei (Coquand, 1862) and Ambigostrea sp. No undoubted Turonian oysters are known fromSergipe, although R. (R.) mermeti possibly straddles the Cenomanian–Turonian boundary. This is in sharp contrast with thesituation in the more northerly Brazilian basins, from where several Turonian but no Cenomanian forms have been described.Well-preserved material from Sergipe confirms the close relationship between Exogyra (Costagyra) Vialov and VultogryphaeaVialov. The palaeobiogeographical affinity of the oyster fauna is typically Tethyan with many taxa that are known particularlyfrom the southern Tethys. The inferred palaeoenvironment as implied by the oysters is that of a shallow shelf.

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K W: oysters; taxonomy; Cenomanian; Cretaceous; Sergipe Basin; Brazil.

1. Introduction

The Cenomanian to Coniacian carbonate sequence(Cotinguiba Formation) of the Sergipe Basin, north-eastern Brazil, contains a rich macroinvertebratefauna that is dominated by ammonites and bivalves.Among the bivalves, oysters are abundant and aremostly well preserved, in some beds dominating thefauna. Despite this, little is known about thetaxonomic composition of the oyster faunas. White(1887) described three species from what wassaid to be mid Cenomanian beds: Exogyra conica(J. Sowerby)? [=Rhynchostreon (Laevigyra) obliquatum(Pulteney) herein], Exogyra ostracina (Lamarck)?[=Amphidonte (Ceratostreon) reticulata (Reuss) herein]and Ostrea wegmanniana d’Orbigny?, the latter subse-quently redescribed by Maury (1937) as O. castello-brancoi [here synonymized with Curvostrea rouvillei(Coquand)].

Maury (1937) revised the material of White (1887)and described Lopha syphax (Coquand)? from bedsconsidered to be lower Turonian. Owing to the poorpreservation, the species was not figured. In general,the age of the specimens described by White (1887)

0195–6671/99/020747+19 $30.00/0

and Maury (1937) is uncertain because of impreciselocality indications (Bengtson, 1983). Furthermore,Santos (1962) mentioned an Ostrea sp. from the lowerConiacian and Beurlen (1971) reported Liostreasp. from the Cenomanian. Specimens of Curvostreahave often previously been related to Liostrea, andas C. rouvillei is the only species known from theCenomanian of Sergipe, it is possible that thespecimens of Beurlen (1971) belong to this species.

Bengtson (1983, p. 44) listed three species ofExogyra from the Cenomanian, determined by J.-P.Lefranc as E. (Costagyra) olisiponensis Sharpe, E.(Rhynchostreon) columba (Lamarck) and E. africana(Lamarck). The second species is reassigned here toRhynchostreon (Rhynchostreon) mermeti (Coquand),which is the only species found so far in Sergipe inbeds of Turonian age.

One species, Rastellum diluvianum (Linne), ishere described from uppermost Albian–lowermostCenomanian(?) beds referred to as the RiachueloFormation. Ostrea (Alectryonia) palmetta Sowerby?,Lopha diluviana (Linne)? and Lopha euzebioi Maury,described by White (1887) and Maury (1937),

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748 J. Seeling and P. Bengtson

respectively, from the middle? Albian are heresynonymized with R. diluvianum (Linne).

The aim of this study was to describe theCenomanian oysters of the Sergipe Basin. In additionto the material collected by the authors, the speciesdescribed and figured by White (1887) and Maury(1937) from the basin are revised on the basis ofpublished data. In the available material, nine generaand subgenera, including 11 species, are distin-guished. The stratigraphical ranges, palaeobiogeo-graphical affinities and mode of life of the taxa arediscussed and a palaeoenvironmental interpretation isattempted.

2. Geological setting

The Sergipe Basin is the southern part of the Sergipe–Alagoas Basin in northeastern Brazil, south of the SaoFrancisco River, in the eastern, coastal part of thestate of Sergipe (Figure 1). The basin is one ofnumerous Mesozoic tensional rift basins bordering theSouth Atlantic. It forms a half-graben, open to thesoutheast, and is bounded to the northwest by faults.The thickness of the sedimentary fill ranges between 1and 3 km onshore and reaches 10 km offshore (Ponteet al., 1980). The basin has a regional dip averaging10� to 15� SE (Ojeda & Fugita, 1976). The Cre-taceous sedimentary sequence of the basin is one ofthe most complete among the South Atlantic basins.

The stratigraphical sequence of the basin consists ofthree parts:(1) a non-marine part ranging from Carboniferous toBarremian or Aptian;

(2) a transitional part broadly dated as Aptian, and(3) a marine part from mid or late Aptian to Mioceneor Pliocene in the deepest, offshore parts of the basin.

The marine regime led to deposition of a thick,dominantly carbonate succession, which is subdividedinto the Riachuelo and Cotinguiba formations (Figure1). The Cenomanian–Coniacian Cotinguiba For-mation is composed mainly of fine-grained deep-watercarbonates. It has an average thickness of 200 m andreaches a maximum thickness of over 1000 m (Ojeda& Fugita, 1976). The succession was deposited duringa relative sea-level rise, which caused the drowning ofthe shallow-water carbonate platform of the under-lying Riachuelo Formation (Koutsoukos et al., 1993).The Cotinguiba carbonates were deposited in neriticto upper bathyal environments and indicate moder-ately dysoxic to truly anoxic bottom and well-oxygenated epipelagic conditions (Koutsoukos et al.,1991). A sea-level maximum occurred in the latestCenomanian–earliest Turonian. The middle Turo-nian contains numerous hiatuses in some areas, prob-ably caused by a deceleration of the depositional rate(Bengtson, 1983). For more detailed information onthe evolution of the Cretaceous carbonate sequencesthe reader is referred to Koutsoukos et al. (1993).

Figure 1. Simplified onshore geology of the Sergipe Basin(modified from Koutsoukos & Bengtson, 1993).

Figure 2. Locality map.

3. Material and methods

A significant part of the material was collectedin 1971–1972 and 1977 (Bengtson, 1983). Thismaterial was initially studied by J.-P. Lefranc who,unfortunately, died before the work was completed.His provisional determinations were published byBengtson (1983, pp. 44, 45). Additional material wascollected in 1995 and 1996 by J. Seeling with supportby A. Herrmann, S. Schneider and S. Walter.

A total of 296 specimens from 30 localities (Figure2) were studied. Most of the localities were described

Cenomanian oysters from the Sergipe Basin, Brazil 749

by Bengtson (1983, appendix 1). Four localities arenew (Cruzes 18, Jardim 29, Jardim 30, Jerico 9) andare described in the Appendix.

The species described by White (1887) and subse-quently redescribed by Maury (1937) are revised onthe basis of the descriptions and figured specimens inthese publications.

Figure 3. Stratigraphical distribution of the Cenomanian oysters of the Sergipe Basin. Ammonite zonation after Walter et al.(in press).

4. Biostratigraphy

Bengtson (1983, fig. 5) gave an overview of thehistorical development of age assignments and bio-stratigraphy of the Upper Cretaceous sequence of theSergipe Basin. He established a biostratigraphicalscheme for the Cotinguiba Formation based onammonites. This scheme was refined in subsequentpapers; e.g., by Berthou & Bengtson (1988), Hessel(1988), Smith & Bengtson (1991), Koutsoukos &Bengtson (1993) and Walter et al. (in press). Thescheme of Koutsoukos & Bengtson (1993) comprisesthe biostratigraphical framework for the discussion ofthe distribution of the oyster assemblages describedhere. Recent field work in the Laranjeiras area hasdisclosed the vertical relationships of the key ammo-nite taxa of the Cenomanian–Turonian Vascoceras

harttii–Pseudaspidoceras footeanum Zone of Koutsoukos& Bengtson (1993) and has made it possible toestablish a lowermost Turonian Pseudotissotia sp. Zone(Figure 3). The base of this zone is assumed tocorrelate closely with the proposed Cenomanian–Turonian Global boundary Stratotype Section andPoint (GSSP) (Bengtson, 1996; Walter et al., in press).

Most of the oysters are stratigraphically well pos-itioned on the basis of ammonite datings. Wherenecessary, dating is complemented with other evi-dence such as microfacies analyses (Berthou &Bengtson, 1988), lithostratigraphic correlation orinference on the basis of the geographic position of thelocality (Bengtson, 1983).

The Sergipe specimens derive from Cenomanianbeds (Figure 3), corresponding to the lower part of theCotinguiba Formation. With the exception of oysterfragments in thin sections and a few possible Rhyn-chostreon (Rhynchostreon) mermeti at the base of theTuronian, no oysters were found in the higher part ofthe formation (but see Santos, 1962 for a Coniacianspecimen). The specimens of Rastellum diluvianumdescribed here come from the top of the underlyingRiachuelo Formation and are latest Albian or earliestCenomanian.


The oldest oysters found in the Cotinguiba For-mation are Exogyra (Costagyra) olisiponensis (Sharpe)and Ilymatogyra (Afrogyra) africana (Lamarck), fromthe lower middle Cenomanian Acompsoceras spathi–Dunveganoceras Zone. The overlying Acanthocerasjukesbrownei–Eucalycoceras pentagonum (upper middleCenomanian) and Pseudocalycoceras harpax–Thomelitesaff. sornayi (lower upper Cenomanian) zones haveyielded an assemblage of E. (Costagyra) olisiponensis(Sharpe) and the very abundant I. (Afrogyra) africana(Lamarck) together with rare specimens of Rhynchos-treon (Rhynchostreon) mermeti (Coquand), Amphidonte(Ceratostreon) flabellata (Goldfuss), Pycnodonte (Phy-graea) vesiculosa (Sowerby) and Curvostrea rouvillei(Coquand). All species continue into the upperCenomanian Euomphaloceras septemseriatum Zone. I.(Afrogyra) africana, A. (Ceratostreon) flabellata and E.(Costagyra) olisiponensis disappear in the Vascocerasharttii–Pseudaspidoceras footeanum Zone. Only R. (R.)mermeti, C. rouvillei and P. (Phygraea) vesiculosa occurin this Zone. R. (R.) mermeti is the only speciesthat appears to enter the lowermost TuronianPseudotissotia sp. Zone (Figure 3).

The stratigraphic position of the two species R.(Laevigyra) obliquatum (Pulteney) and A. (Cerato-streon) reticulata (Reuss), originally described by White(1887) and Maury (1937), is uncertain owing toimprecise locality data as discussed below.

5. The species of White (1887) and Maury(1937)

In the material collected by us from the Sergipe Basin,nine species of oysters are distinguished. Besidesthese, only two, presumably Cenomanian species,have previously been described from the basin.

White (1887, p. 33, pl. 2, figs 10–12) figured twocomplete specimens of a species that he identified asExogyra conica (J. Sowerby)? His material was revisedby Maury (1937, pp. 168–171, pl. 6, figs 2–4, usingWhite’s original illustrations) as Exogyra conica(Sowerby). The figured specimens agree in size andoverall appearance with the types of Amphidonte conica(J. Sowerby) and other specimens of the speciesdescribed and figured by different authors. Soares(1963) described a new subspecies from Angola,which he named Exogyra conica pertortumbiformis.Although his material resembles the figured specimensfrom Sergipe, there is no evidence that allows us toclassify our material to subspecies level.

Cox (1940), and more recently Freneix & Viaud(1986) and Aqrabawi (1993), pointed out thatPulteney (1813, May) described the species Chamaobliquata one month before J. Sowerby (1813, June)

described the same species as Chama conica. Althoughthe latter name is well established in the literature,whereas the first has barely been used, Pulteney’sname has priority and conica becomes a junior syno-nym. Malchus (1996) transferred the species A. obli-quatum (Pulteney) to Laevigyra Malchus, which heconsidered to be a subgenus of Rhynchostreon Bayle.Dhondt et al. (1999) maintained his classification. Weagree with this and take the species to be Rhynchos-treon (Laevigyra) obliquatum (Pulteney, 1813).

R. (Laevigyra) obliquatum is known from theAptian? and Albian–Turonian of Europe, the MiddleEast, Africa, India and Brazil. White (1887) andMaury (1937) described their specimens from SantaLuzia in the Estancia area (Figure 2). Maury (1937,p. 171) indicated the horizon as ‘‘probably MiddleAlbian, but this is not proven’’. Following Bengtson(1983, appendix 2) the geographical position of theSanta Luzia outcrops suggests a Cenomanian age.The precise occurrence of this species in the SergipeBasin cannot be established, however, and must beregarded as doubtful at least. This is underscored bythe fact that the species was not found by us at any ofthe localities investigated during our different periodsof field work.

The second previously described species wasassigned by White (1887, p. 31, pl. 2, figs 1–7) toExogyra ostracina (Lamarck)? In her revision ofWhite’s material, Maury (1937, pp. 171–175, pl. 6,figs 1, 9, 14) classified it as Exogyra haliotoidea (J.Sowerby). The species is a typical amphidontoid,however, and should therefore be placed in the genusAmphidonte Fischer de Waldheim, more specifically inthe subgenus Ceratostreon Bayle.

Woods (1913, p. 407) pointed out that Chamahaliotoidea J. Sowerby, 1813 represents a morphotypeof ‘Exogyra’ conica (J. Sowerby, 1813) with a largeattachment area. Therefore, the name Chama haliotoi-dea J. Sowerby, 1813 cannot be applied to the taxonfor which it has traditionally been used (Malchuset al., 1994). The nomenclatorial difficulties in findinga valid name for the species were discussed at lengthby Malchus et al. (1994, pp. 121, 122) and led themto the decision that Exogyra reticulata Reuss, 1846 isthe next available name for the species. For thisreason, the species is here classified as Amphidonte(Ceratostreon) reticulata (Reuss, 1846).

The species closely resembles R. (Laevigyra) obli-quatum, but differs in having a less coiled umbo, lessconvex left valve and more pointed ventral margin. Italso has a larger and longer adductor muscle imprint(Aqrabawi, 1993). Just as for R. (L.) obliquatum, thestratigraphic position of A. (C.) reticulata in theSergipe Basin is uncertain. The species is known from


the Cenomanian–Maastrichtian of Europe, NorthAfrica and Brazil. The specimens of White (1887) andMaury (1937) were from ‘Lastro’ and ‘near BomJesus, Rio Sergipe, Sergipe’, which were both assignedby Maury (1937, p. 175) to the middle Albian. TheLastro locality of different authors corresponds toPraia 9 of Bengtson (1983, appendix 1), which ismainly upper Albian to possibly lower Cenomanian.The frequently-cited locality of Bom Jesus lies in thearea of Laranjeiras 14–17 (Bengtson, 1983, appen-dix 1), which is Vascoceras harttii–Pseudaspidocerasfooteanum and Pseudotissotia sp. zone age (latestCenomanian to earliest Turonian). In this area wefound only R. (R.) mermeti. For this reason, thestratigraphic range of A. (Ceratostreon) reticulataremains uncertain (cf. Bengtson, 1983, table 2).

6. Early Late Cretaceous oysters from otherBrazilian basins

Upper Cretaceous oysters have also been described orreported from other Brazilian basins. Maury (1925,1934) described Ostrea pendenciana Maury, 1925 andO. lagoapiatensis Maury, 1934 from the Potiguar Basin(Rio Grande do Norte). These species were re-described by Beurlen (1964, 1967), who reportedboth species along with O. crenulata Beurlen, 1964,O. jacobi Beurlen, 1964, O. mossoroensis Beurlen,1964, O. cf. owenana Shumard, 1861 and Lopharamicola Beurlen, 1964 from the Turonian of theAcu Formation of the basin. O. pendenciana, O.cf. mesenterica Morton, 1941, Lopha plicatuliformisBeurlen, 1967, L. ramicola, Liostrea cf. delettrei(Coquand, 1862), Pycnodonte cascudoi Beurlen, 1967and P. cf. panda Morton, 1941 were also describedfrom the overlying Turonian–Maastrichtian JandaíraFormation (Beurlen, 1964, 1967). Muniz & Almeida(1988) also reported Lopha ramicola from theCenomanian–Turonian Estiva Formation of the CaboBasin (Pernambuco). Lopha lombardia Dartevelle &Freneix, 1957 was recorded from Cenomanian estu-arine facies of the Itapecuru Formation of theParnaíba Basin (Maranhao) (Klein & Ferreira, 1979).These records of Upper Cretaceous oysters fromthe Brazilian marginal basins were summarized bySimone & Mezzalira (1994).

The oysters from the other basins were only illus-trated through schematic drawings (Beurlen, 1964,1967), which makes taxonomic appraisal difficult.Based on the available figures, most of the taxa ofMaury (1924, 1934) and Beurlen (1964, 1967) areprobably best placed in either Gyrostrea Mirkamalov,1963 or Nicaisolopha Vialov, 1936. According toMuniz & Almeida (1988) L. ramicola shows strong

affinities with Hyotissa semiplana (J. de C. Sowerby,1825), which is today placed in the Pycnodonteinaeand known from the Turonian–Maastrichtian ofEurope (Aqrabawi, 1993). The generic classificationof the two pycnodontid species is uncertain. L. lom-bardi belongs to the group of Oscillolopha syphax(Coquand, 1854), which is known from theSantonian–Campanian of western Africa (Dartevelle& Freneix, 1957).

The oysters described or reported from the otherBrazilian basins differ in several respects from theones described from Sergipe. The latter faunas areCenomanian in age and are strongly dominated byexogyrine forms, whereas the faunas from the otherbasins are all Turonian or younger and contain noexogyrine forms. The incomplete documentation ofthe latter faunas makes further comparison with theSergipe faunas difficult and hampers any reliableinterpretation of the causes of these differences inoccurrence.

7. Biogeography and ecology

The oyster fauna of the Cotinguiba Formation ofSergipe is dominated by genera of the subfamilyExogyrinae (Amphidonte, Exogyra, Ilymatogyra andRhynchostreon). The only representative of the sub-family Palaeolophinae is Rastellum diluvianum fromthe uppermost Riachuelo Formation.

The oyster assemblages are typically Tethyancontaining, in particular, species known from thesouthern Tethys. Pycnodonte (Phygraea) vesiculosa,Amphidonte (Ceratostreon) flabellata and Rastellumdiluvianum are cosmopolitan species, which are wellrepresented, for example, in the northern EuropeanUpper Cretaceous. The Sergipe associations, or atleast parts of them, are characteristic of the middle toupper Cenomanian of the eastern Mediterraneanregion (Jordan, Lebanon, Palestine), northern andnorthwestern Africa (Egypt, Libya, Tunisia, Algeria,Morocco), western and central Africa (Angola,Niger), southern Europe (Portugal, Spain, southernFrance, Sicily) and southern USA (Texas) (Figure 4).

A close biogeographic relationship with northwest-ern Africa and Texas during the Cenomanian, asshown by the Sergipe oysters (Figure 5), is confirmedby other benthic macrofossil groups, for exampleechinoids (Smith & Bengtson, 1991). An assemblageof middle to upper Cenomanian oysters includ-ing Exogyra (Costagyra) olisiponensis, Ilymatogyra(Afrogyra) africana and Rhynchostreon (Rhynchostreon)mermeti has also been reported from northern Peru(Dhondt & Jaillard, 1997) (Figure 4). The palaeobio-geographic distribution of oysters in the Cretaceous


Figure 4. Geographical distribution of Ilymatogyra (Afrogyra) africana, Exogyra (Costagyra) olisiponensis and Rhynchostreon(Rhynchostreon) mermeti in the late Cenomanian (after Dhondt, 1992; Malchus, 1996; Dhondt et al., 1999; this paper).Map modified after Dhondt (1992).

Tethys has been summarized by Dhondt (1992),Malchus (1996) and Dhondt et al. (1999). It ispossible that oysters migrated in the early LateCretaceous from northern Africa to the northernSouth Atlantic via the Trans-Saharan Seaway.

In the Cenomanian carbonate sequence of Sergipe,oysters occur in accumulations which generally rep-resent shallow-marine environments. In the lowerTuronian, oysters become scarce or vanish. This mayreflect the fact that, following the Cenomanian–Turonian transgression, conditions became too deepfor oysters. This agrees with results of microfaciesanalyses of the sequence (Berthou & Bengtson, 1988)and of investigations of the echinoid fauna (Seeling,unpublished results). Dhondt et al. (1999) observedthe same situation for the Turonian oysters of NorthAfrica.

With the exception of R. diluvianum and A. (Cera-tostreon) flabellata, all species described herein arerecliners. They rested on, or were partly buried in, softsubstrates without being attached (Stanley, 1970; LaBarbera, 1981). Therefore, the attachment area inmost of the investigated species is very small, or evenabsent, as in R. (R.) mermeti.

There are indications that at least parts of theSergipe oysters represent a transported fauna. Sizedifferentiation of the individuals has been observed atdifferent localities. Thus, in the Japaratuba-Cruzesarea, specimens are generally smaller than in thenearby Timbo-Jardim area and the Tiburcio area inthe south (Figure 2). Size differentiation is possiblythe result of sorting by sedimentary processes.According to Mancini (1978), a transported micro-morph fauna is formed when the smaller individuals ofan assemblage are winnowed out and concentratedseparately. Oysters are strongly inequivalve. Thelower, left valve is heavy, cup-shaped and more dur-able than the upper, right valve, which is thinner,lighter and more fragile. An oyster community buriedin situ, or transported only a short distance, wouldconsist of approximately equal numbers of left andright valves. Transport would be expected to destroyor remove the lighter, more fragile right valves anddeposit the heavier left valves at a shorter distancefrom the original site (Feldmann & Palubniak, 1975).In the Sergipe material, right and left valves are rarelyfound together. The much smaller number of rightvalves in the assemblage is attributed to the fragility


and lower weight as described above. The degree ofdisarticulation, along with abrasion and breakage, is areliable means of determining the relative amount oftransport an oyster or other bivalve has undergonesince death (Boucot et al., 1958). In particular,smaller specimens of P. (Phygraea) vesiculosa, R.(Rhynchostreon) mermeti and I. (Afrogyra) africana arenot found in life position and are mostly disarticu-lated. They are only partly fragmented. In contrast,nearly all larger specimens, mainly of E. (Costagyra)olisiponensis and I. (Afrogyra) africana, are preservedunbroken and articulated. This indicates transportunder high-energy conditions, but of short duration,as abrasion and breakage are usually low.

8. Systematic palaeontology

by Jens Seeling and J.-P. Lefranc1

Oysters are classified mainly on the basis of theirinternal and external shell characters and, in somecases, shell microstructure. Important internal charac-ters are the shape of the ligament area, the umbonal1Universite de Montpellier, France; deceased in 1993.

cavity, outline and location of the posterior adductormuscle scar, and type and presence of chomata.External characters include size, general outline of theshell, tendency and type of coiling of the umbo, shapeand development of the attachment area, and shellornament such as concentric growth lines, radial ribs,folds, nodes and spines (Figure 6). These morpho-logical characters are described and discussed in detailby Stenzel (1971), Malchus (1990) and Aqrabawi(1993).

In recent taxonomic studies of Cretaceous oysters(e.g., Malchus, 1990; Aqrabawi, 1993; Malchus et al.,1994) the microstructure of the shell is used as an aidto classification, in particular at suprageneric level.For this study, and considering the well-preserved andwell-differentiated material at hand, we regard it asadequate to restrict investigation of the shell micro-structure to the genus Rastellum. This is a cementedand highly variable taxon that is difficult to distinguishfrom other groups of the Palaeolophidae on shellmorphology alone. For more comprehensive discus-sions, details of microstructure types and for adescriptive terminology of the shell microstructure ofbivalves and oysters in particular, the reader is referredto Carter (1990) and Malchus (1990, 1998).

In addition to the material from Sergipe, specimenskept at the Technische Universitat (TU) Berlin, theNatural History Museum in London and the InstitutRoyal des Sciences Naturelles in Brussels were studiedfor comparison.

Figure 5. Stratigraphical distribution of Cenomanianoysters in Sergipe (this paper) and North Africa (afterDhondt et al., 1999).

Terminology and abbreviations. The descriptive termi-nology for the external and internal characters of theoyster shell follows that of Stenzel (1971, N1028–N1034) and Malchus (1990, pp. 51–53); that of theshell microstructure follows the terminology ofMalchus (1990) and Aqrabawi (1993). The terminol-ogy for size is based on the height of the leftvalve. Small=<50 mm, medium sized=50–100 mm,large=>100 mm.

Abbreviations: LV=left valve; RV=right valve; H:height=longest distance between dorsal and ventralmargin; L: length=length of test, measured perpen-dicular to the height (H); Hmax/Lmax=height/lengthof largest specimen studied; N=number of measuredspecimens. All measurements are given in mm.

The specimens are kept in the collections of theGeologisch-Palaontologisches Institut, University ofHeidelberg, Germany. Those of White (1887) arehoused in the collection of the Museu Nacional andthe Departamento Nacional da Producao Mineral(DNPM), Rio de Janeiro, Brazil.


Figure 7. a–c, Rastellum diluvianum (Linne, 1767) from Praia 9. a, left valve, internal view (339b.17); b, left valve, externalview; c, right valve, external view (339b.1). All specimens �1. d–g, shell microstructure of R. diluvianum (339b.1c). d,e, umbonal region; f, g, ventral region. Scale bar represents 5 mm.

Figure 6. Internal and external characters and measurements of the oyster shell (modified after Aqrabawi, 1993).

Systematic descriptions

Suborder Ostreina Ferussac, 1822Superfamily Ostreoidea Rafinesque, 1815Family Palaeolophidae Malchus, 1990Subfamily Palaeolophinae Malchus, 1990Genus Rastellum Faujas-St. Fond, 1799

Rastellum diluvianum (Linne, 1767)Figure 7a–f

1767 Ostrea diluviana Linne, p. 1148.1887 Ostrea (Alectryonia) palmetta Sowerby?; White,

p. 29, pl. 1, figs 3–5.1913 Ostrea diluviana Linne, 1767; Woods, pp. 342–

355, text-figs 109, 115, 118, 119, 124, 125.


1937 Lopha diluviana? Linnaeus; Maury, pp. 162,163, pl. 7, fig. 15.

1937 Lopha euzebioi sp. nov; Maury, pp. 158–161,pl. 7, figs 11, 14, 16, 17.

1968 Arctostrea diluviana (Linnaeus); Carter, pp. 463,464, pl. 85, fig. 1.

1982 Lopha diluviana (Linne, 1767); Grundel,pp. 157, 158, pl. 4, figs 6–10.

1986 Rastellum (Rastellum) diluvianum (Linne, 1767);Freneix & Viaud, pp. 50, 51, pl. 6, figs 2, 3.

1993 Rastellum diluvianum (Linne, 1767); Aqrabawi,pp. 93, 94, text-figs 47, e, h–j.

1994 Rastellum diluvianum (Linnaeus, 1767);Malchus et al., pp. 120, 121, pl. 2, figs 3, 5–8.

Material. Six mostly well-preserved single left valvesand one complete specimen, all from locality Praia 9(samples 339b.1a–c, 339b.7, 339b.10, 339b.17).

Description. Medium sized, Hmax=56 mm, Lmax=59 mm. Shell elongated-oval to subrounded, moder-ately to strongly convex, inequivalved, maximumconvexity near anterior flank, which is clearly steeperthan the posterior. Shell thick; attachment area vari-able, but well developed and commonly large, in somespecimens attached with nearly whole LV. Valvescovered with strong, high, sharp ribs; number of ribsand distance of ribbing variable; margins stronglyplicated, folded in a zigzag line, with sharp ends.Ligamental area triangular, adductor muscle imprintoval to kidney-shaped, moderately large, situatedpostero-dorsally.

Discussion. The concept of the oyster group todayreferred to the genus Rastellum has been the topic ofnumerous discussions in the literature. Woods (1913)united the numerous species described under thename Ostrea diluviana, because in his view the char-acters used to distinguish these forms as distinctspecies depend on ecological influences. For moredetailed discussions concerning this topic, the readeris referred to Woods (1913, pp. 342–355), Malchus(1990, p. 106) and Malchus et al. (1994, pp. 120,121).

The specimens of R. diluvianum from Sergipe arerelatively small compared with material from otherareas, for instance Europe, where specimens mayexceed twice the size of the Sergipe material. Forexample, Aqrabawi (1993) gave 150 mm andMalchus et al. (1994) 124 mm as the maximum heightof their specimens.

The shell is moderately to strongly lenticular, with asimply foliated to low-angle cross-foliated microstruc-ture (Figure 7d–f). The laths of a foil are oriented

parallel to subparallel to each other and the foils arenormally subparallel to the exterior shell. Lensesare mainly concentrated on the umbonal region andare filled with micrite or sparite. The shell microstruc-ture of the Sergipe specimens resembles that de-scribed and figured for species of Rastellum from otherareas, for example from Egypt (compare Malchus,1990: Rastellum sp. forma B, p. 107, pl. 25, fig. 4) orfrom Germany and Sweden [compare Aqrabawi,1993: R. diluvianum, p. 93, fig. 12.1, 2; R. carinatum(Lamarck, 1806), p. 94, fig. 13.1, 2].

White (1887) described an Albian species fromthe Sergipe Basin as Ostrea (Alectryonia) palmettaJ. Sowerby? On the basis of this material and aftercomparison with the types of Sowerby, Maury (1937)described the new species Lopha euzebioi. She placedthis species in the group of Lopha syphax (Coquand).The specimens figured by White (1887) and Maury(1937) appear to be conspecific and are better referredto R. diluvianum.

Stratigraphic and geographic distribution. R. diluvianumis widely distributed and occurs in the Valanginian? –Maastrichtian of Europe, North America, Asia, Africaand Brazil. In Sergipe the species has been foundin the uppermost Albian and possibly lowermostCenomanian.

Family Gryphaeidae Vialov, 1936Subfamily Exogyrinae Vialov, 1936Genus Amphidonte Fischer de Waldheim, 1829Subgenus Ceratostreon Bayle, 1878

Amphidonte (Ceratostreon) flabellata (Goldfuss, 1833)Figure 8a–d

1833 Exogyra flabellata Goldfuss, p. 38, pl. 87, fig. 6.1847 Ostrea flabellata Goldfuss; d’Orbigny, p. 717,

pl. 475, figs 1–5.1869 Ostrea flabellata Goldfuss; Coquand, p. 126,

pl. 49, figs 1, 2; pl. 50, figs 1, 2; pl. 52, figs 1–9.1912 Exogyra flabellata Goldfuss; Pervinquiere,

p. 189, pl. 13, figs 6–8.1972 Ceratostreon flabellatum (Goldfuss, 1833);

Freneix, pp. 91, 92, pl. 5, figs 8, 9.1990 A. (Ceratostreon) flabellatum (Goldfuss, 1833);

Malchus, pp. 111–113, pl. 4, figs 4–11; pl. 5,figs 1–7 (with extensive synonymy).

1993 Amphidonte (Ceratostreon) flabellatum (Goldfuss,1833); Aqrabawi, pp. 63, 64, pl. 2, figs 2–5.

Material. Ten moderately to fairly well-preserved,single left valves and complete specimens from locali-ties Cruzes 6, 7, 9, Jardim 19 and Timbo 4 (samples


364.39–364.42, 371.26, 375.57, 375.58, 452.81,452.82, 464.129).

Description. Very small compared with specimens fromother parts of the world, Hmax=28 mm. High oval tocomma-shaped or sickle-like. Shell relatively thick, LVstrongly convex, with a rounded keel, near the anteriormargin, RV slightly convex to nearly flat, with a sharpkeel; ornament of variable radial ribs, some with shorthollow spines, some with only faintly developed ribsor a nearly smooth surface; attachment area distinctand relatively large. Ligamental area narrow, subliga-mental area variable in size from narrow to broad;faint chomata at the periphery of the shell; adductormuscle scar situated postero-dorsally.

Discussion. The specimens closely resemble Am-phidonte (Ceratostreon) flabellata of authors. As dis-cussed above, their small size may be a result ofsorting by transport. Other species [e.g., R. (Rhynchos-treon) mermeti and I. (Afrogyra) africana] from thesame localities are also smaller than average forSergipe. It is not possible to establish whether the lackof ornamentation in some specimens is a result ofabrasion from transport or an expression of naturalvariability. For differentiation from other species andthe view of A. (C.) flabellata as a chronospecies, seediscussion by Malchus (1990).

Figure 8. Amphidonte (Ceratostreon) flabellata (Goldfuss,1833) from Timbo 4. a, left valve, external view; b, leftvalve, internal view (452.81); c, left valve, externalview; d, right valve, external view (452.83). Allspecimens �2.

Nomenclaturally, Amphidonte and Pycnodonte havebeen treated in the literature alternatively as feminineand neuter nouns. In the case of Pycnodonte, Dhondt(1994) pointed out that the suffix -odonte is derivedfrom the Greek odontos, genitive of odontus (tooth),which is a feminine word. Therefore we use the formA. (C.) flabellata. The same applies to Pycnodonte(Phygraea) vesiculosa.

Stratigraphic and geographic distribution. Aptian?,Albian–Cenomanian of Europe, Middle East, North,Central and South Africa, North and Central Americaand Brazil. In Sergipe the species occurs from theAcanthoceras jukesbrownei–Eucalycoceras pentagonumZone (upper middle Cenomanian) to the Pseudocaly-coceras harpax–Thomelites aff. sornayi Zone (lowerupper Cenomanian).

Genus Exogyra Say, 1920Subgenus Costagyra Vialov, 1936

Exogyra (Costagyra) olisiponensis Sharpe, 1850Figure 9a–c

1850 Exogyra olisiponensis Sharpe, p. 185, figs 1, 2.1869 Ostrea olisiponensis Sharpe; Coquand, pl. 45, figs

1–7.1901 Ostrea (Exogyra) olisiponensis Sharpe; Choffat,

p. 16, pl. 4, figs 17–19.1903 Exogyra olisiponensis Sharpe var. duplex Stein-

mann; Paulcke, pl. 15, figs 7, 8.1912 Exogyra olisiponensis Sharpe; Pervinquiere,

p. 174, pl. 13; figs 4, 5, 9.1929 Exogyra olisiponensis Sharpe; Reeside, p. 268,

pls. 65–68; pl. 69, figs 1–4.1958 Exogyra olisiponensis Sharpe; Barber, pp. 21, 22,

pl. 8, fig. 11.1961 Exogyra olisiponensis Sharpe; Soares, pp. 32–34,

pl. 9, fig. 33; pl. 11, fig. 38.1971 Exogyra olisiponensis Sharpe; Collignon, p. 32,

pl. f, fig. 5.1972 Exogyra olisiponensis Sharpe, 1850; Freneix,

pp. 89–91, pl. 5, figs 6, 7.1983 Exogyra (Costagyra) olisiponensis Sharpe;

Lefranc in Bengtson, p. 44.1990 E. (Costagyra) olisiponensis Sharpe; Malchus,

pp. 134–138, pl. 2, figs 1–6 (with extensivesynonymy).

1993 Exogyra (Costagyra) olisiponensis Sharpe, 1850;Aqrabawi, pp. 67, 68, pl. 4, figs 3–5; pl. 5, figs1, 2.

1999 Costagyra olisiponenis (Sharpe, 1850); Dhondtet al., pl. 1, figs 6, 7.


Material. 20 mainly well-preserved, complete speci-mens, and 18 left valves and 5 right valves fromlocalities Jardim 1, 6, 19, Cruzes 1, 2, 3, 5, 6, 7, 8, 11,18, Tiburcio 1, 2, Japaratuba 14 (samples A5.ec1,A5.ec2, CP1329.1–2, 357.46, 359.117, 361.3,361.41, 361.53–54, 364.34, 371.96a–b, 371.98,371.104–105, 371.106a,b, 371.114, 371.116,371.118–121, 371.136, 371.144, 371.160–161,371.172, 372.2, 373.1, 373.ec1, 373.166, 374.7,464x.12, 514.20–22, 514.41, 514.47, 515.4, 618.6).

Description. Medium sized, Hmax=85 mm, high-ovalto subrounded, inequivalve, inequilateral. LV stronglyconvex, inflated, RV only slightly convex. Shell verythick; umbo helicoidally coiled and relatively small,running very close to the commissure line. Attach-ment area variable; ornamentation of LV consists ofscaly growth lamellae traversed by 7–12 radial ribs

with variable interspaces; ribs feebly tuberculated oreven spinose. RV flat to slightly convex, ornamentconsisting of strong scaly growth lamellae, partly tra-versed by short radial ribs. Ligamental area small andhigh; subligamental area large, adductor muscle scarrelatively large, outline oval with a slightly concavedorsal side, situated postero-dorsally.

Figure 9. a–c, Exogyra (Costagyra) olisiponensis Sharpe, 1850. a, b, from Cruzes 6; c from Tiburcio 1. a, left valve; b, rightvalve (371.121); c, left valve (514.47). d–g, Ilymatogyra (Afrogyra) africana (Lamarck, 1801) from Cruzes 6. d, left valve;e, right valve (371.138); f, left valve; g, right valve (371.122). All specimens �1.

Variability. Exogyra (Costagyra) olisiponensis is a veryvariable species. The general outline of the shell seemsto be controlled mainly by the size of the attachmentarea (Malchus, 1990). Malchus (1990) observed thatnearly all long and narrow specimens have small or noattachment areas, whereas the wider and shorterforms have large to very large attachment areas. Thisis also true for the Sergipe specimens. In the case of amissing or very small attachment area, a free andcomplete coiling is possible, and besides this, the keel


is somewhat more strongly developed (Aqrabawi,1993). The variation in shell thickness and ornamentis possibly related to water energy. Strong ribs withtubercles and spines may indicate strong water current(Aqrabawi, 1993). On the other hand, spines mayhave protected the bivalve from sinking into unstablesediments and aided in maintaining its position in asoft substratum, as pointed out by Bottjer (1981) forspecimens of Granocardium bowenae?

The great variability in E. (C.) olisiponensis has ledto splitting of the taxon into different ‘species’ and‘varieties’. These varieties are based on differentdevelopment of ribs, spines and the scalyness of thegrowth lamellae. The varieties are linked by tran-sitional forms. Malchus (1990) discussed this pointin detail. Paulcke (1903) figured a specimen, whichhe named ‘var. duplex’ Steinmann. He distinguishedthis variety from the typical form by its short radialribs on the right valve. However, these ribs arepseudo-ribs caused by an undulating commissureline, where the ribs of the left valve touch thecommissure shelf (Malchus, 1990). The majority ofthe Sergipe specimens belong to this morphologicalvariety.

Discussion. Exogyra (Costagyra) olisiponensis showstypical features that are not found in other species ofthe genus (straight chomata, which encircle the wholevalve, relict chomata, strong ribs, pseudo-ribs andhollow spines). Some of these features can be foundin species of Amphidonte (Ceratostreon), but this sub-genus is distinguished by its twisted umbo and smallersize (Malchus, 1990). Aqrabawi (1993) pointed outthe similarity with E. (Exogyra) italica (Seguenza,1882), but E. (C.) olisiponensis is smaller, has a morerounded outline and a less helicoidally twisted umbo(Aqrabawi, 1993). For differentiation from otherexogyrine oysters, see the detailed discussion ofMalchus (1990).

One complete, very well-preserved specimen of E.(C.) olisiponensis (514.47; Figure 9c) from the upperCenomanian of southern Sergipe, gives cause for adiscussion of the relationships of the (sub)generaCostagyra Vialov and Vultogryphaea Vialov. Originally,Vialov (1936) regarded Vultogryphaea as a subgenus ofFatina Vialov, 1936. Stenzel (1971) synonymized thelatter with the ostreid genus Sokolowia Bohm, 1933.The available material of Vultogryphaea was veryscarce, poorly preserved and lacked diagnostic inter-nal characters (Stenzel, 1971, p. N1125). But owingto the features of the ligament area and the develop-ment of the umbo, Stenzel (1971) believed Vultogry-phaea to be an exogyrine oyster. This was accepted bysubsequent authors (e.g., Badve, 1981; Freneix &

Viaud, 1986; Malchus et al., 1994; Cooper, 1995).Nevertheless, the generic position and the systematicorigin of this genus gave cause for discussion. Freneix& Viaud (1986) regarded Vultogryphaea as a synonymof Costagyra, but did not discuss the synonymy.Malchus (1990) pointed out that in 1878, Bayle hadplaced Vultogryphaea in Rhynchostreon. On the basis ofshell microstructure, Aqrabawi (1993) consideredVultogryphaea a subgenus of Amphidonte.

In its outline, its external characters, with very well-preserved, strongly developed hollow spines, and itsoverall appearance, specimen 514.47 would seem tobe a typical representative of Vultogryphaea. But with-out doubt it is an E. (Costagyra) olisiponensis, especiallyconsidering its co-occurrence with many ‘typical’specimens of this species. It appears that the ornamen-tation normally found in E. (C.) olisiponensis is a resultof incomplete preservation, due to the fragility of thespines. Thus, the present specimen seems to supportthe view of Freneix & Viaud (1986). Even if, for adefinite decision about the synonymy of the (sub)gen-era, more material needs to be studied, the materialfrom Sergipe seems to indicate that Vultogryphaeaeither had its origin in, or is a synonym of, Costagyra.

Stratigraphic and geographic distribution. Middle lowerCenomanian–upper Cenomanian, lower? Turonianof the Mediterranean Tethys, including Europe andAfrica, also from south-east Central Asia and fromNorth and South America (Brazil, Peru). The mainoccurrence is in the upper Cenomanian (Malchus,1990). In Sergipe the species is found in the middleand upper Cenomanian.

Genus Ilymatogyra Stenzel, 1971Subgenus Afrogyra Malchus, 1990

Ilymatogyra (Afrogyra) africana (Lamarck, 1801)Figure 9d–g

1801 Gryphaea africana Lamarck, p. 399, pl. 189, figs5, 6.

1862 Ostrea auressensis Coquand, p. 233, pl. 22, figs12, 13.

1869 Ostrea africana Lamarck; Coquand, p. 134,pl. 39, figs 5, 6; pl. 55, figs 10–12.

1903 Exogyra reissi Steinmann; Paulcke, p. 271,pl. 15, figs 5, 6.

1918 Exogyra delettrei (Coquand); Greco, p. 10, pl. 2,figs 7, 8.

1943 Ostrea (Exogyra) africana Lmk.; Schneegans,p. 99, pl. 1, fig. 13.

1983 Exogyra africana (Lamarck); Lefranc inBengtson, p. 44.


1990 I. (Afrogyra) africana (Lamarck, 1801) ‘formacrassa’; Malchus, pp. 121–124, pl. 7, figs 6, 8,9, 11, 12, 14–20; pl. 8, figs 1–3.

1993 Ilymatogyra (Afrogyra) africana (Lamarck,1801); Aqrabawi, pp. 70, 71, pl. 2, figs 6–11;pl. 3, figs 1–3.

1999 Ilymatogyra africana (Lamarck, 1801); Dhondtet al., pl. 1, figs 1, 2.

Material. 154 mainly well-preserved single and doublevalved specimens from localities Cruzes 6, 11, Jardim1, 10, 16, 19, Jerico 3, 9, Praia 3, Tiburcio 1 (samplesA5.a1–a15, 116.89, 335.1, 361.1–2, 361.12, 371.12–14, 371.17, 371.23, 371.27–28, 371.31–33, 371.52,371.59, 371.61, 371.65–68, 371.70–71, 371.73–77,371.79–82, 371.85, 371.87–93, 371.97, 371.101–102, 371.107–112, 371.115, 371.117, 371.122–129,371.131–135, 371.137–141, 371.145–146, 371.148–150, 371.152–159, 371.162–165, 371.167, 371.170–171, 371.173–174, 384.11–17, 384.19, 464.128,512.a1–a5, 512.15, 514.23–25, 620.7–8, 657.a1–a24).

Description. Small to medium sized, Hmax=53 mm.Oval to elongated-oval, partly obliquely drop-like.Inequivalve and inequilateral; LV commonly stronglyconvex; RV flat or slightly convex. Umbo weakly tohelicoidally twisted, with a tendency to uncoiling;attachment area mostly small; keel blunt to roundedand well developed; LV ornamented with regular,mostly scaly or smooth growth lamellae, RV coveredwith dense, fine growth squamae. Ligament arealonger than high, relatively large, normally ophistogy-rate; subligamental area small; adductor muscle scarkidney-shaped.

Variability. Malchus (1990) differentiated two var-ieties of Ilymatogyra (Afrogyra) africana, which henamed ‘forma typica’ and ‘forma crassa’. The latter islarger, broader in relation to the height of the shell,less convex, has a sharper keel and is covered with veryscaly growth lamellae. He pointed out that the twovarieties in Egypt are tied to different facies. ‘Formatypica’ occurs in clay- and silt-rich marls, whereas‘forma crassa’ occurs in sandy marls and marly lime-stones. The two forms are possibly ecophenotypes(Malchus, 1990). All the specimens from Sergipecorrespond to ‘forma crassa’ sensu Malchus (1990).There, as well as in Egypt, ‘forma crassa’ occurs incarbonate-rich sediments.

Discussion. The species resembles Exogyra delettrei(Coquand) sensu Greco (1918), but differs from typi-cal E. delettrei by the stronger twisting of the umbo and

narrower interspaces of the growth lamellae on theright valve. In Algeria and Tunisia, transitional formsexist (Malchus, 1990). It is possible that E. delettreirepresents another ecological variation of I. (Afrogyra)africana (Malchus, 1990). E. reissi Steinmann,described by Paulcke (1903), is also an I. (Afrogyra)africana ‘forma crassa’.

Figure 10. a, b, Rhynchostreon (Rhynchostreon) mermeti(Coquand, 1862) from Tiburcio 1. a, left valve; b, leftvalve, posterior view (514.42). c, d, Rhynchostreon (Lae-vigyra) sp. from Japaratuba 14. c, left valve; d, leftvalve, posterior view (618.12). All specimens �1.

Stratigraphic and geographic distribution. Middle andupper Cenomanian of southern Europe, North Africa,Niger, Madagascar, Middle East, South and CentralAmerica.

Genus Rhynchostreon Bayle, 1878Subgenus Rhynchostreon Bayle, 1878

Rhynchostreon (Rhynchostreon) mermeti (Coquand,1862)Figure 10a, b

1862 Ostrea mermeti Coquand, p. 234, pl. 23, figs3–5.

1958 Exogyra columba (Lamarck); Barber, p. 21,pl. 8, figs 3, 4.

1972 Rhynchostreon columbum (Lamarck) mermeti(Coquand, 1862); Freneix, p. 89, pl. 5, figs 4, 5.

1983 Exogyra (Rhynchostreon) columba (Lamarck);Lefranc in Bengtson, p. 44.


1990 Rhynchostreon mermeti (Coq., 1862); Malchus,pp. 128–131, pl. 8, figs 15–17; pl. 9, figs 1–21(with extensive synonymy).

1993 Rhynchostreon mermeti (Coquand, 1862);Aqrabawi, pp. 74, 75, pl. 3, figs 4–12.

1999 Rhynchostreon mermeti (Coquand, 1862);Dhondt et al., pl. 1, fig. 4.

Material. 27 incomplete, fairly well- to well-preservedleft valves from localities Laranjeiras 2, 16, Cruzes 3,7–9, Timbo 4, Jardim 9, Tiburcio 1 (samples 252.11,282.r1, 357.49, 360.29, 361.r1, 364.35–38, 375.53–56, 452.75–77, 452.79–80, 462.22–25, 514.40,514.42, 514.r1–r3).

Description. Relatively small for the species. Althoughthe specimens are not complete, the L:H ratio agreeswith that given by Malchus (1990) for his R. mermeti‘forma minor’. Measurements: N=13; Hmax=36 mm; L:H=0.85. Elongated oval to subrounded;LV strongly convex. Surface ornamented with fineradial ribs, traversed by fine concentric growth lineswhich may become lamellose towards the ventralmargin. Some shells are smooth, which may be due topreservation; some specimens with radial sulcus sepa-rating the stronger convex middle part of the shellfrom the less arched posterior parts. Umbo relativelysmall, helicoidally coiled, nearly orthogyral; attach-ment area absent. Ligament and subligament areanarrow and small; chomata not visible.

Variability. Malchus (1990) differentiated two var-ieties of R. mermeti in his Egyptian material, ‘formaminor’ and ‘forma typica’. The material from Sergipecorresponds in its measured L:H ratio and its overallappearance to ‘forma minor’. For differentiation ofthese varieties, see Malchus (1990, p. 130).

Discussion. The great similarities between Rhynchos-treon (Rhynchostreon) mermeti and R. (R.) suborbicu-latum (Lamarck) make it difficult to separate thesespecies, especially when dealing with small specimens,as in Sergipe. This has led to intensive discussions inthe literature. Freneix (1972) and Freneix & Viaud(1986) treated R. mermeti as a subspecies of R. subor-biculatum. In contrast, Malchus (1990) and Aqrabawi(1993) regarded them as independent species on thebasis of two clearly distinct European (R. suborbicula-tum) and Tethyan (R. mermeti) extremes. Generally,R. (R.) suborbiculatum is larger and more convex, has arelatively smaller, less twisted umbo and a smoothsurface (Aqrabawi, 1993). Cooper (1995) describedR. suborbiculatum from the Cenomanian of southeastAfrica. He based his determination on the absence of

ornamentation, but he only examined a single internalmould, which is not sufficient for reliable differentia-tion from R. (R.) mermeti. Whereas the ornamentedspecimens from Sergipe are typical R. (R.) mermeti,the smooth ones resemble R. (R.) suborbiculatum.Their lack of ornamentation may be a result of abra-sion during transport or of natural variability. How-ever, this character seems not to be sufficient to dividethe Sergipe specimens into two species.

Small specimens of R. (R.) mermeti are also difficultto distinguish from R. (R.) plicatulum (Lamarck). Asthese forms occur together in the upper Cenomanian,and in these horizons the specimens of R. (R.) sub-orbiculatum are predominantly small, they are takento be conspecific by some authors (e.g., Freneix &Viaud, 1986).

Stratigraphic and geographic distribution. The species iswidely distributed in the Cenomanian–Turonian ofthe southern Tethys. It is known from southernEurope (southern Italy, Sicily, Portugal), the MiddleEast, Afghanistan, northern Africa (Morocco, Algeria,Egypt), Nigeria, Madagascar and South America(Peru, Brazil). In Sergipe the species occurs from theupper middle Cenomanian to possibly the lowerTuronian.

Subgenus Laevigyra Malchus, 1990

Rhynchostreon (Laevigyra) sp.Figure 10c, d

Material. One incomplete left valve from localityJaparatuba 14 (sample 618.12).

Description. Small, H=37.5 mm. Elongated oval. LVstrongly convex and strongly inequilateral; postero-dorsal area slightly concave. Ventral margin not pre-served. Surface smooth; umbo small, with very smallattachment area; keel situated posteriorly, well definedin the early growth stages, becoming indistinct ven-trally; shell thin. Internal characters not preserved.

Discussion. The specimen shows great similarities withspecimens of R. (Laevigyra) luynesi (Lartet, 1872) inthe collection of Malchus at the TU Berlin (Py 981,Py 982), and is therefore attributed to this subgenus.

Stratigraphic and geographic distribution. The subgenusR. (Laevigyra) is known from the Albian?, Ceno-manian to upper? Maastrichtian of the Middle East(Jordan, Palestine), North Africa (Egypt, Algeria),Europe (France, Netherlands) and the USA (WesternInterior, Gulf States) (Malchus, 1996). In Sergipe thespecies is found in the uppermost Cenomanian.


Subfamily Pycnodonteinae Stenzel, 1959Genus Pycnodonte Fischer de Waldheim, 1835Subgenus Phygraea Vialov, 1936

Pycnodonte (Phygraea) vesiculosa (J. Sowerby, 1823)Figure 11a–c

1823 Gryphaea vesiculosa Sowerby, p. 93, pl. 369.1913 Ostrea vesiculosa (Sowerby, 1823); Woods,

p. 374, pl. 54, fig. 1; pl. 55, figs 10–14.1990 P. (Phygraea) vesiculosum (Sowerby, 1823);

Malchus, pp. 145, 146, pl. 2, figs 2–7 (withextensive synonymy).

1993 Pycnodonte (Phygraea) vesiculosum (Sowerby,1823); Aqrabawi, pp. 79, 80, pl. 5, figs 15, 16.

Material. 37 well-preserved left valves and 6 rightvalves from localities Cruzes 11, 6, Timbo 4, Jardim7, 9, 19, 10 (samples 361.p1–p5, 371.16, 371.18,371.20, 371.22, 371.24, 371.29–30, 371.34, 371.63,371.69, 371.83–84, 452.78, 458.5, 462.15–22,464.p1–14, 620.9–10).

Description. Small, Hmax.=22 mm. Suboval to subcir-cular; LV strongly convex, RV flat to slightly concave.LV normally with clearly developed posterior sulcus,surface almost smooth, with only faintly developed

growth lines; umbo relatively small, subcircular,slightly ophistogyrate to orthogyrate; attachment areasmall or absent, RV smooth, only covered with faintgrowth lines. Ligamental area small, subtriangular,longer than high; adductor muscle scar rounded,postero-centrally situated.

Discussion. All specimens of Pycnodonte (Phygraea)vesiculosa from Sergipe are small. As mentionedbefore, this also applies to other oyster species in thebasin. With the exception of size, the specimensresemble closely P. (P.) vesiculosa as described in theliterature.

P. (P.) vesicularis (Lamarck) differs from this speciesin its larger size and different stratigraphic distribution(Campanian–Maastrichtian). The differentiation fromother species of the subgenus has been extensivelydiscussed by Freneix & Viaud (1986) and Malchus(1990).

Stratigraphic and geographic distribution. Aptian?,Albian–Cenomanian of Europe, Africa the MiddleEast, India, Brazil. In Sergipe the species occurs in themiddle and upper Cenomanian.

Family Ostreidae Rafinesque, 1815Subfamily Liostreinae Malchus, 1990Genus Curvostrea Vialov, 1936

Curvostrea rouvillei (Coquand, 1862)Figure 12a–d

1862 Ostrea rouvillei Coquand, p. 232, pl. 22, figs8–10.

1869 Ostrea rouvillei Coquand; Coquand, p. 89,pl. 21, figs 3–6; pl. 24, figs 7–11.

1887 Ostrea wegmanniana d’Orbigny?; White, p. 28,pl. 3, figs 14–18.

1912 Liostrea rouvillei (Coquand); Pervinquiere,p. 168.

1918 Liostrea Rouvillei (Coquand); Greco, p. 4, pl. 1,figs 6, 8–11.

1937 Ostrea castellobrancoi sp. nov.; Maury, pp. 154–157, pl. 7, figs 1–5.

1971 Curvostrea rediviva (Coquand); Stenzel, N1168,fig. J142, 1, 2.

1972 Liostrea rouvillei (Coquand, 1862); Freneix,p. 97, text-fig. 10A–D.

1990 Curvostrea rouvillei (Coq., 1862); Malchus,pp. 154, 155, pl. 14, figs 1–7, 16 (with extensivesynonymy).

Figure 11. a–c, Pycnodonte (Phygraea) vesiculosa ( J.Sowerby, 1823); a, b, from Cruzes 6; c, from Jardim19. a, left valve, external view; b, left valve, internalview (371.83); c, left valve, external view (464.p1).d, Ambigostrea sp. from Tiburcio 1 (514.3). Allspecimens �2.

Material. Ten mostly well-preserved single and doublevalved specimens from localities Cruzes 6, Timbo 4,


Tiburcio 1, Jardim 29, 30 (samples A8.c1, A8.c2,371.52, 452.c, 514.c1–514.c6).

Description. Small, Hmax=39 mm. Elongated oval,tongue-shaped, flat, plate-like or slightly curved with adrop-like outline. Shell thin, only slightly inequivalve;LV flat to slightly convex, smooth surface, partly withweakly developed growth squamae; RV less convexto slightly concave, weakly developed growth lines;umbo small, narrow; attachment area small. Ligamentarea small, triangular.

Discussion. Ostrea rouvillei and O. rediviva, describedby Coquand (1862) and separated on account of theirstratigraphic positions, are now considered synony-mous (Malchus, 1990). They are closely related to,and possibly conspecific with, Curvostrea bourguignati(Coquand). Large, plate-shaped, flat specimensmay be better referred to C. tevesthensis (Coquand)(Malchus, 1990). The species may also be conspecificwith Liostrea oxiana Romanowski (Malchus, 1990).C. heinzi (Peron & Thomas) is more convex, has morestrongly developed chomata and a different strati-graphic distribution (Coniacian–Santonian). There issome similarity with Indostrea indica Chiplonkar &Badve, 1976, but this species has larger, well-developed chomata, which cover the whole interiorof the shell (Malchus, 1990). White (1887) described

O. wegmanniana d’Orbigny?, 1843 from the SantaLuzia area in Sergipe. His specimens were later re-described by Maury (1937) and on the basis of thismaterial she described the new species O. castello-brancoi. The two species are here synonymized withC. rouvillei, as the description by Maury (1937) for O.castellobrancoi does not seem to warrant differentiationfrom C. rouvillei.

Stratigraphic and geographic distribution. Cenomanian–Santonian of North and Central Africa, the MiddleEast, Europe, India, Brazil. In Sergipe the speciesoccurs in the middle to uppermost Cenomanian.

Genus Ambigostrea Malchus, 1990

Ambigostrea sp.Figure 11d

Material. One incomplete left valve from localityTiburcio 1 (sample 514.3).

Description. Small; the specimen is incomplete, butpart of the ventral margin is preserved and the esti-mated height lies between 20 and 25 mm. Trigonallyovate, with rounded ventral margin. The LV is nearlyflat and covered with numerous fine, narrow, radialsimple or dichotomous ribs; shell thin. Internalcharacters are not preserved.

Discussion. On account of the description given above,this specimen is placed in the genus Ambigostrea,which was introduced by Malchus (1990). Owing tothe poor preservation and lack of internal characters, aspecies designation is not possible; however, the out-line, overall appearance and rib pattern show affinitywith A. dominici Malchus, 1990. Specimens of A.dominici from Egypt kept in the Malchus collection atthe TU Berlin can be compared with the Sergipematerial.

Figure 12. a–d, Curvostrea rouvillei (Coquand, 1862) fromJardim 30. a, left valve; b, right valve (A8.c1); c, leftvalve; d, right valve (A8.c2). All specimens �1.

Stratigraphic and geographic distribution. Middle–lowerupper Cenomanian of southern Sergipe, Brazil. Thepossibly conspecific A. dominici is known from theupper Cenomanian of Egypt.

Acknowledgements

JS thanks Simone Walter, Achim Herrmann andStefanie Schneider (all Heidelberg) for fieldassistance, and especially Nikolaus Malchus(Berlin) and Annie V. Dhondt (Brussels) for helpfuldiscussions on taxonomic matters. PB thanks SuzanaBengtson (Heidelberg), Diogenes de Almeida


Campos (DNPM, Rio de Janeiro) and Petrobras SA(Aracaju and Rio de Janeiro) for field and logisticassistance. We thank Annie V. Dhondt (Brussels) andAndrew B. Smith (London) for careful and construc-tive reviewing of the manuscript. The photographicwork was carried out by K. Will and the preparation ofthe specimens by K. Riedelsberger (both Heidelberg).The field work was financed by the Swedish NaturalScience Research Council, NFR, grant nos G2320,G3475 (PB) and by the German Academic ExchangeService, DAAD (JS). The part of the work concerningthe Cenomanian–Turonian boundary was carriedout with financial support by the German ResearchCouncil, DFG, grant no. Be 1382/9. This is acontribution to IGCP Project 381 ‘South AtlanticMesozoic Correlations’.

References

Aqrabawi, M. 1993. Oysters (Bivalvia–Pteriomorphia) of the UpperCretaceous rocks of Jordan: palaeontology, stratigraphy andcomparison with the Upper Cretaceous oysters of northwestEurope. Mitteilungen aus dem Geologisch-Palaontologischen Institutder Universitat Hamburg 75, 1–136.

Badve, R. M. 1981. Remarks on the fossil genus VultogryphaeaVyalov (Pelecypoda: Mollusca) with description of a new speciesfrom Cretaceous beds of South India. Proceedings of the IndianAcademy of Science, Animal Sciences 90, 351–355.

Barber, W. 1958. Upper Cretaceous Mollusca from north-easternNigeria. Records of the Geological Survey of Nigeria (for 1956),14–37.

Bengtson, P. 1983. The Cenomanian–Coniacian of the SergipeBasin, Brazil. Fossils and Strata 12, 1–78.

Bengtson, P. (compiler) 1996. The Turonian stage and substageboundaries. In Proceedings of the ‘Second International Symposiumon Cretaceous Stage Boundaries’, Brussels 8–16 September 1995 (edsRawson, P. F., Dhondt, A. V., Hancock, J. M. & Kennedy,W. J.), Bulletin de l’Institut Royal des Sciences Naturelles de Belgique,Sciences de la Terre 66, Supplement, 69–79.

Berthou, P.-Y. & Bengtson, P. 1988. Stratigraphic correlation bymicrofacies of the Cenomanian–Coniacian of the Sergipe Basin,Brazil. Fossils and Strata 21, 1–88.

Beurlen, K. 1964. A fauna do calcario Jandaıra da regiao deMossoro (Rio Grande do Norte). Colecao Mossoroense, Serie C 13,1–215 (Editora Pongetti, Rio de Janeiro).

Beurlen, K. 1967. Geologia da regiao de Mossoro. Colecao Mosso-roense, Serie C 18, 1–168 (Editora Pongetti, Rio de Janeiro).

Beurlen, K. 1971. A paleontologia na geologia do Cretaceo noNordeste do Brasil. Anais da Academia Brasileira de Ciencias,Suplemento 43, 89–101.

Bottjer, D. J. 1981. Structure of Upper Cretaceous chalk benthiccommunities, southwestern Arkansas. Palaeogeography, Palaeo-climatology, Palaeoecology 34, 225–256.

Boucot, A. J., Brace, W. & DeMar, R. 1958. Distribution ofbrachiopod and pelecypod shells by currents. Journal of Sedimen-tary Petrology 28, 321–332.

Carter, R. M. 1968. Functional studies on the Cretaceous oysterArctostrea. Palaeontology 11, 458–485.

Carter, J. G. (compiler) 1990. Glossary of skeletal biomineraliz-ation. In Skeletal biomineralization: patterns, processes and evolution-ary trends, Volume 1 (ed. Carter, J. G.), pp. 609–671 (VanNostrand Reinhold, New York).

Choffat, P. 1886–1902. Recueil d’etudes paleontologiques sur lafaune cretacique du Portugal. Volume I: Series 1–4. Commissiondu Service Geologique du Portugal, 1–171.

Collignon, M. 1971. Gasteropodes et Lamellibranches du Sahara.Annales de Paleontologie 57, 145–202.

Cooper, M. R. 1995. Exogyrid oysters (Bivalvia: Gryphaeoidea)from the Cretaceous of southeast Africa. Part 1. Durban MuseumNovitates 20, 1–48.

Coquand, H. 1862. Geologie et paleontologie de la region sud de laprovince de Constantine, 343 pp. (Arnaud, Marseille).

Coquand, H. 1869. Monographie du genre Ostrea. Terrain cretace,215 pp. (Bailliere et fils, Paris).

Cox, L. R. 1940. Cretaceous mollusca described by R. Pulteney inthe second edition of Hutchins’s history of Dorset. Proceedings ofthe Malacological Society of London 24, 121–128.

Dartevelle, E. & Freneix, S. 1957. Mollusques fossiles du Cretacede la cote occidentale d’Afrique du Cameroun a l’Angola. II.Lamellibranches. Annales du Musee Royal du Congo Belge, Seriein-8�, Sciences Geologiques 20, 1–271.

Dhondt, A. V. 1992. Palaeogeographic distribution of CretaceousTethyan non-rudist bivalves. In New aspects on Tethyan Cretaceousfossil assemblages (eds Kollmann, H. A. & Zapfe, H.), Schriften-reihe der Erdwissenschaftlichen Kommissionen der O} sterreichischenAkademie der Wissenschaften 9, 75–94.

Dhondt, A. V. 1994. Upper Cretaceous bivalves from Tercis,Landes, SW France. Bulletin de l’Institut Royal des SciencesNaturelles, Sciences de la Terre 63, 211–259.

Dhondt, A. V. & Jaillard, E. 1997. Cretaceous bivalves fromEcuador and northern Peru. Gaea Heidelbergensis 4, 117–118.

Dhondt, A. V., Malchus, N., Boumaza, L. & Jaillard, E. 1999.Cretaceous oysters from North Africa: origin and distribution.Bulletin de la Societe Geologique de France 170, 67–76.

Feldmann, R. M. & Palubniak, D. S. 1975. Palaeoecology ofMaastrichtian oyster assemblages in the Fox Hills Formation.Geological Association of Canada, Special Paper 13, 211–233.

Freneix, S. 1972. Les Mollusques bivalves cretaces du bassin cotierde Tarfaya (Maroc meridional). Notes et Memoires du ServiceGeologique du Maroc 228, 49–255.

Freneix, S. & Viaud, J.-M. 1986. Huıtres du Cretace superieur duBassin de Challans-Commequiers (Vendee): biostratigraphie,taxonomie, paleobiologie. Bulletin Trimestriel de la Societe Geo-logique de Normandie et des Amis du Museum du Havre 73, 13–79.

Goldfuss, A. 1833. Petrefacta Germaniae, II, 68 pp. (Arnz & Co.,Dusseldorf).

Greco, B. 1918. Fauna cretacea dell’Egitto raccolta dal Figari Bey.Parte terza: Lamellibranchiata (cont. e fine). Fasc. 2� Lamelli-branchi del Turoniano e del Cenomaniano. PalaeontographicaItalica, Memorie di Palaeontologia 24, 1–58.

Grundel, J. 1982. Ostreen (Bivalvia) aus der sachsischen Ober-kreide II. Abhandlungen des Staatlichen Museums fur Mineralogieund Geologie zu Dresden 31, 151–161.

Hessel, M. H. R. 1988. Lower Turonian inoceramids from Sergipe,Brazil: systematics, stratigraphy and palaeoecology. Fossils andStrata 22, 1–49.

Klein, V. C. & Ferreira, C. S. 1979. Paleontologia e estratigrafia deuma facies estuarina da Formacao Itapecuru, Estado do Mara-nhao. Anais da Academia Brasileira de Ciencias 51, 523–533.

Koutsoukos, E. A. M. & Bengtson, P. 1993. Towards an integratedbiostratigraphy of the Aptian–Maastrichtian of the Sergipe Basin,Brazil. Documents du Laboratoire de Geologie de Lyon 125, 241–262.

Koutsoukos, E. A. M., Destro, N., Azambuja Filho, N. C. de &Spadini, A. R. 1993. Upper Aptian–Lower Coniacian carbonatesequences in the Sergipe Basin, northeastern Brazil. In Cretaceouscarbonate platforms (eds Simo, T., Scott, B. & Masse,J. P.), American Association of Petroleum Geologists, Memoir 56,127–144.

Koutsoukos, E. A. M., Mello, M. R. & Azambuja Filho, N. C. de1991. Micropalaeontological and geochemical evidence of mid-Cretaceous dysoxic-anoxic environments in the Sergipe Basin,northeastern Brazil. In Modern and ancient continental shelf anoxia(eds Tyson, R. V. & Pearson, T. H.), Geological Society, London,Special Publication 58, 427–447.


La Barbera, M. 1981. The ecology of Mesozoic Gryphea, Exogyraand Ilymatogyra (Bivalvia: Mollusca) in a modern ocean. Paleo-biology 7, 510–526.

Lamarck, J. B. de 1801. Systeme des animaux sans vertebres. Classepremiere. Les Mollusques, 51–142 (Paris).

Malchus, N. 1990. Revision der Kreide-Austern (Bivalvia: Pterio-morphia) A}gyptens (Biostratigraphie, Systematik). Berliner Geo-wissenschaftliche Abhandlungen, A 125, 1–231.

Malchus, N. 1996. Palaeobiogeography of Cretaceous oysters (Bi-valvia) in the western Tethys. Mitteilungen aus dem Geologisch-Palaontologischen Institut der Universitat Hamburg 77, 165–181.

Malchus, N. 1998. Multiple parallel evolution and phylogeneticsignificance of shell chambers and chomata in the Ostreoidea(Bivalvia). In Bivalves: an eon of evolution—palaeobiological studieshonoring Norman D. Newell (eds Johnston, P. A. & Haggart,J. W.), pp. 393–407 (University of Calgary Press, Calgary).

Malchus, N., Dhondt, A. V. & Troger, K.-A. 1994. Upper Cre-taceous bivalves from the Glauconie de Lonzee near Gembloux(SE Belgium). Bulletin de l’Institut Royal des Sciences Naturellesde Belgique, Sciences de la Terre 64, 109–149.

Mancini, E. A. 1978. Origin of micromorph faunas in the geologicrecord. Journal of Paleontology 52, 311–322.

Maury, C. J. 1925. Fosseis terciarios do Brasil, com descripcao denovas formas cretaceas. Servico Geologico e Mineralogico do Brasil,Monographia 4, 1–711.

Maury, C. J. 1934. Fossil invertebrata from northeastern Brazil.Bulletin of the American Museum of Natural History 67, 123–179.

Maury, C. J. 1937. O Cretaceo de Sergipe. Servico Geologico eMineralogico do Brasil, Monographia 11, 1–283.

Muniz, G. C. B. & Almeida, J. A. C. de 1988. Contribuicao aoconhecimento da idade do calcario de Ipojuca, Formacao Estiva,Bacia do Cabo, Pernambuco. Anais do XXXV Congresso Brasileirode Geologia, Belem, 1988, pp. 2371–2375 (Sociedade Brasileirade Geologia, Belem).

Ojeda, H. A. O. & Fugita, A. M. 1976. Bacia Sergipe/Alagoas:geologia regional e perspectivas petrolıferas. Anais do XXVIIICongresso Brasileiro de Geologia, Porto Alegre, 1974, 1, pp. 137–158 (Sociedade Brasileira de Geologia, Sao Paulo).

Orbigny, A. d’ 1843–1847. Paleontologie francaise: description desmollusques et rayonnes fossiles de France. Terrain cretaces III, Lamel-libranches, 807 pp., 489 pls (G. Masson, Paris).

Paulcke, W. 1903. U} ber die Kreide-Formation in Sudamerika undihre Beziehungen zu anderen Gebieten: I. Theil. Neues Jahrbuchfur Mineralogie, Geologie und Palaontologie, Beilageband 17, 252–312.

Pervinquiere, L. 1912. Eutudes de paleontologie tunisienne: II. Gastero-podes et Lamellibranches des terrains cretaces. Direction generaledes travaux publics, Carte geologique de la Tunisie, 338 pp.(Paris).

Ponte, F. C., Fonseca, J. R. & Carozzi, A. V. 1980. Petroleumhabitats in the Mesozoic–Cenozoic of the continental margin ofBrazil. In Facts and principles of world petroleum occurrence (ed.Miall, A. D.), Canadian Society of Petroleum Geologists, Memoir 6,857–886.

Pulteney, R. 1813. Catalogues of the birds, shells and some of the morerare plants of Dorsetshire from the new enlarged edition of Mr.Hutchin’s history of that county, 108 pp. (London). [non vidimus]

Reeside, J. B., Jr 1929. Exogyra olisiponensis Sharpe and Exogyracostata Say in the Cretaceous of the Western Interior. UnitedStates Geological Survey, Professional Paper 154/1, 267–271.

Santos, M. E. C. M. 1962. Novos lamelibranquios do calcarioSapucari, Estado de Sergipe. Anais da Academia Brasileira deCiencias 34, 32–33.

Schneegans, D. 1943. Invertebres du Cretace superieur duDamergou (Territoire du Niger). In Etudes stratigraphiques etpaleontologiques sur le Bassin du Niger (eds Arambourg, C.,Joleaud, L., Lambert, R. & Schneegans, D.), Bulletin de laDirection des Mines 7, 87–167.

Sharpe, D. 1850. On the secondary district of Portugal which lieson the north of the Tagus. Quarterly Journal of the GeologicalSociety of London, Proceedings 6, 135–195.

Simone, L. R. L. de & Mezzalira, S. 1994. Fossil molluscs of Brazil.Universidade de Sao Paulo, Instituto de Geologia, Boletim 11, 1–202.

Smith, A. B. & Bengtson, P. 1991. Cretaceous echinoids fromnorth-eastern Brazil. Fossils and Strata 31, 1–88.

Soares, A. F. 1961. Lamelibranquios do Cretacico da regiao deBenguela-Cuio (Angola). Boletim dos Servicos de Geologia e Minas,Angola-Portugal 4, 5–56.

Soares, A. F. 1963. Sobre os lamelibranquios cretacicos da regiaoBenguela-Cuio. Memorias e Notıcias 55, 1– 22.

Sowerby, J. 1813. The mineral conchology of Great Britain, vol. 1,236 pp. (Benjamin Meredith, London).

Sowerby, J. 1823. The mineral conchology of Great Britain, vol. 4,160 pp. (Benjamin Meredith, London).

Stanley, S. M. 1970. Relation of shell form to life habits of theBivalvia (Mollusca). Geological Society of America, Memoir 125,1–296.

Stenzel, H. B. 1971. Oysters. In Treatise on invertebrate paleontology,Part N, Volume 3, Mollusca 6, Bivalvia (ed. Moore, R. C.), pp. N953–1224 (Geological Society of America, Boulder and Univer-sity of Kansas, Lawrence).

Vialov, O. S. 1936. Sur la classification des huıtres. Academie desSciences de l’URSS, Comptes Rendues (Doklady), New series 4/13,N.1 (105), 17–20.

Walter, S., Herrmann, A. & Bengtson, P. (in press). Stratigraphyand facies analysis of the Cenomanian–Turonian boundary suc-cession in the Japaratuba area, Sergipe Basin, Brazil. Journal ofSouth American Earth Sciences.

White, C. A. 1887. Contribuicoes a paleontologia do Brazil.Archivos do Museu Nacional do Rio de Janeiro 7, 1–273.

Woods, H. 1913. A monograph of the Cretaceous Lamellibranchiaof England. Palaeontographical Society, London 2, 1–473.

Appendix

Four new localities are described herein, following the systemintroduced by Bengtson (1983). The main meridian for theUTM coordinates (Universal Transverse Mercator) is 39�W ofGreenwich.

CRUZES 18UTM 8 824 750 N/724 250 ETopographical map sheet: SC.24-Z-B-V Japaratuba. Geologicalmap sheet: SC.24-Z-B-V-1 Carmopolis.Section at Petrobras well-site CP-1329. Altitude c. 20 m.Lithology: Cotinguiba Formation, Sapucari Member. 3 m of hard,compact, grey Laranjeiras limestones, overlain by light grey, loose,marly material.Fossils: Sparse Exogyra (Costagyra) olisiponensis, plicatulids.

JARDIM 29UTM 8 822 790 N/727 730 ETopographical map sheet: SC.24-Z-B-V Japaratuba. Geologicalmap sheet: SC.24-Z-B-V-1 Carmopolis.Section on hillside facing NNE. Altitude c. 25 m.Lithology: Cotinguiba Formation, Sapucari Member. Yellowish,coquinoid Laranjeiras limestones, overlain by hard, compactLaranjeiras limestones.Fossils: Ammonites abundant, bivalves, especially inoceramids andoysters abundant in some horizons; gastropods and echinoidspresent.

JARDIM 30UTM 8 823 130 N/727 550 ETopographical map sheet: SC.24-Z-B-V Japaratuba. Geologicalmap sheet: SC.24-Z-B-V-1 Carmopolis.Section on hillside facing NE. Altitude c. 20 m.Lithology: Cotinguiba Formation, Sapucari Member. Nodular,hard, yellowish Laranjeiras limestones.Fossils: Ammonites, echinoids; in the upper part a horizon withabundant Curvostrea rouvillei is exposed.


JERICOu 9UTM 8 823 350 N/724 150 ETopographical map sheet: SC.24-Z-B-V Japaratuba. Geologicalmap sheet: SC.24-Z-B-V-1 Carmopolis.Section at Petrobras well-site CP-1173, facing NE. Altitude c. 10 m.

Lithology: Cotinguiba Formation, Sapucari Member. Cream tolight brown limestones.Fossils: Oysters [Ilymatogyra (Afrogyra) africana], other bivalves,e.g., plicatulids, pectinids; ammonites (Dunveganoceras sp.).