Mitchell.indd 1. INTRODUCTION Radiolitid rudists belonging to the genera Bourno- nia FISCHER, Biradiolites D’ORBIGNY and Thyras- tylon CHUBB are abundant in the Upper Maastrichtian, Titanosarcolites Limestones (Guinea Corn Formation and other formations) of Jamaica. Although there is a large literature on these Jamaican forms (e.g., WHIT- FIELD, 1897; TRECHMANN, 1924; CHUBB, 1956, 1967, 1971), little information on their microstructure, or their detailed stratigraphy has been published. Indeed, there have been few studies on the microstructure of rudists, although those there have been indicate that the microstructures have high taxonomic significance (e.g., AMICO, 1978; STEUBER, 1999). This paper presents Morphology, Microstructure and Stratigraphy of Some Late Cretaceous Radiolitid Rudists from Jamaica Simon F. MITCHELL a detailed study of the morphology, microstructure and stratigraphy of some of these radiolitid rudists, and a revision of some species. 2. GEOLOGY In the Central Inlier of Jamaica (Fig. 1), the Guinea Corn Formation (Titanosarcolites-yielding limesto- nes) forms the middle (marine) portion of the major transgressive–regressive Kellits Sythem (unconform- ity bounded stratigraphic unit) (MITCHELL, in press). These limestones are up to 200 m thick and contain subordinate mudrocks and sandstones (COATES, 1965; MITCHELL, 1999, in press; MITCHELL & GUNTER, 2002). The thickest section through the Guinea Corn Formation is exposed in the Rio Minho between Grantham and Frankfield and can be divided into rhythms up to about 10 m in thickness (MITCHELL, 1999, 2002). Each rhythm consists of a lower clastic unit with diverse infaunal molluscs, a middle clastic/ carbonate unit with diverse corals and/or recumbent antillocaprinid rudists, and an upper part consisting of limestones with abundant radiolitid and antillocaprinid rudists. A bed lettering scheme, with the beds labelled from A to G (Fig. 2) based on the relative proportions of limestone and clastics, was introduced by MITCH- ELL (1999). STEUBER et al. (2002) used Sr-isotope geochronology to suggest a mid to late Late Maastrich- tian age for the Guinea Corn Formation of the Central Inlier, an age that agrees with the few well-determined ages based on other biostratigraphic groups (e.g., sharks – UNDERWOOD & MITCHELL, 2000). 3. METHODOLOGY For this study, rudists were systematically collected from two sections (Fig. 1). Extensive collections were made from the Rio Minho section between Grantham and Guinea Corn (Guinea Corn in Fig. 1) for which a detailed lithostratigraphy has been developed (MITCH- ELL, 1999; MITCHELL & GUNTER, 2002). Addi- tional material was collected from sections at Slippery Rock River, Green River, Logie Green and Pindars Riv- er (Fig. 1). The section at Pindars River (described by COATES, 1965) is important because many of the rud- Geologia Croatica 56/2 149–171 3 Figs. 8 Pls. ZAGREB 2003 Key words: Rudist bivalves, Cretaceous, Maastrich- tian, Taxonomy, Jamaica. Department of Geography and Geology, University of the West Indies, Mona, Kingston, Jamaica; e-mail: smitchell@cwjamaica.com Abstract Radiolitid rudists from the Upper Maastrichtian of Jamaica include genera Bournonia, Biradiolites and Thyrastylon. Three species of Bournonia are recognised, B. cancellata WHITFIELD, B. barretti TRECHMANN and B. thiadensi VERMUNT. B. cancellata evolves into B. barretti by the acquisition of costae on the anterior side. The species of Bournonia are characterised by a distinctive cardinal appa- ratus, a thick inner shell layer, and an outer shell layer composed of cellular microstructure. Two species of Biradiolites are recognised – B. rudissimus TRECHMANN has an outer layer composed of cel- lular microstructure with occasional bands of compact microstructure, particularly in the radial bands, and B. jamaicensis TRECHMANN has a very well organised outer layer with an inner band of cellular microstructure and an outer band of compact microstructure. Biradio- lites and Thyrastylon have a similar dentition, a thin inner layer and similar wall structures in the outer layer. Thyrastylon is distinguished from Biradiolites by the infolding of the radial bands in RV and by the presence of oscules in LV. The evolutionary change from Bo. can- cellata to Bo. barretti, and the first appearance of Bi. jamaicensis are probably useful biostratigraphic markers of the Upper Maastrichtian. 150 Geologia Croatica 56/2 151Mitchell: Morphology, Microstructure and Stratigraphy of Some Late Cretaceous Radiolitid Rudists... ists are embedded in relatively soft mudstones allowing excavation of the cardinal apparatus. Where particular species were common, populations were collected to aid with determining the range of variation within each rudist morphospecies. The terminology of microstruc- tures follows AMICO (1978) and STEUBER (1999). Longitudinal and transverse sections were cut through selected specimens, and the sections polished to show internal features. The polished surfaces were then etched with a 10% solution of HCl for 10 seconds, and allowed to dry. Acetate peels were prepared from the etched surfaces. Negative photographic prints were then developed from the acetate peels. All material, including acetate peels, is deposited in the Geological Museum at the University of the West Indies (UWIGM numbers). Additional material stud- ied is in the American Museum of Natural History (AMNH) in New York, and the Natural History Muse- um (BMNH), London. 4. SYSTEMATIC PALAEONTOLOGY In the following account, long synonymy lists are not given. These are available in other publications (e.g, CHUBB, 1971; ALENCASTER, 1971; STEUBER, 2002). Here, only important synonyms are provided, and these are linked to the morphospecies concepts adopted/developed in this work. Rudist morphospecies are here defined using popu- lations of specimens, where possible, collected from the same level. This provides a more objective method of defining morphospecies that in the published litera- ture where many species have been erected on one or two individuals. When the stratigraphic distribution of populations is examined, a better understanding of the time relationships of morphospecies becomes apparent. Genera are defined on major morphological criteria, species on more subtle criteria. Family RADIOLITIDAE D’ORBIGNY, 1847 Genus Bournonia FISCHER, 1887 Type species: Sphaerulites bournoni DES MOULINS, 1826. Diagnosis: Right valve (RV) conical with relatively thick inner aragonite layer. Outer calcitic layer com- posed of funnel plates with rectangular cells, compact cell layers absent, no cortical layer observed. Surface ornamented with strong costae and intervening furrows. Radial bands represented by more prominent, or flat- tened costae. Prominent, narrow anterior furrow (AF) developed. Left Valve (LV) cap like, or a low cone. Car- dinal apparatus of type A (Pl. 1). Fig. 1 Location of sections in the Central Inlier from which rudists have been collected. Inset, map of Jamaica showing inliers (additional material from the Marchmont and Maldon Inliers). 150 Geologia Croatica 56/2 151Mitchell: Morphology, Microstructure and Stratigraphy of Some Late Cretaceous Radiolitid Rudists... Three Maastrichtian species are recognised in Jama- ica: B. cancellata (WHITFIELD), B. barretti TRECH- MANN and B. thiadensi VERMUNT. Bournonia cancellata (WHITFIELD, 1897) Pls. 1, 2, 3d–f, 4a, c–d v. 1897 Radiolites cancellatus: WHITFIELD, p. 190, pl. 12, fig. 4, pl. 13, figs. 3–7. v. 1924 Biradiolites subcancellatus: TRECHMANN, p. 403, pl. 26, fig. 3. Diagnosis: A species of Bournonia in which the ante- rior side lacks costae. Type specimens: The original material of WHITFIELD (1897) is preserved in the AMNH; it was collected from Logie Green in the Central Inlier. WHITFIELD (1897) figured several specimens, his pl. 13, figs. 3–5 is here selected as lectotype. Material: Extremely abundant material from the A and B Beds of Guinea Corn Formation in the Rio Minho at Grantham. Also abundant specimens from the lowest limestone in the Pindars River Section. Description: RV conical to cylindro-conical. Rang- ing in height up to 14 cm and in diameter up to 7 cm. The external ornament consists of prominent costae which represent downfolds of the funnel plates, the intervening furrows corresponding to upfolds; both are obvious in transverse sections (Pl. 1). The costae number between 7 and 10 and are limited in extent to the ventral, posterior and dorsal sides. The radial bands (posterior band – Pb and ventral band – Vb) are rep- resented by broader costae with flat tops. The anterior side is devoid of longitudinal costae, and bears a single prominent anterior furrow. This furrow corresponds to a prominent downfold of the funnel plates. Growth lines, corresponding to the outer edges of the funnel plates, are well-developed on all aspects; no cortical layer has been seen. Fig. 2 Simplified suc- cession through the Guinea Corn Forma- tion in the Rio Minho between Grantham and Guinea Corn showing bed divisions (after MITCHELL, 1999; MITCHELL & GUNTER, 2002). The boundary between the Middle and Upper C Beds falls within a faulted gap in the section. 152 Geologia Croatica 56/2 153Mitchell: Morphology, Microstructure and Stratigraphy of Some Late Cretaceous Radiolitid Rudists... Transverse sections of the right valve indicate two well defined layers. The inner layer is up to 2 mm thick, and is represented by calcite spar. This is interpreted to be a replacement fabric after the original aragonitic inner layer. The outer layer is formed of funnel plates showing a quadrangular cellular microstructure; com- pact microstructural elements are lacking. Longitudinal cross-sections show that the funnel plates are orientated upwards, with different degrees of upward extension producing the costae and furrows. Conical tabulae, now represented by calcite menisci, fill the lower part of the body chamber (Pl. 1f). LV ranges from flat to strongly arched. It has a simi- lar microstructure to the RV, with a thick inner arago- nite layer and an outer layer of quadrangular cellular microstructure (Pl. 1e–f). The cardinal apparatus is of type A, and is seen in transverse and longitudinal sections, and also in a specimen excavated from the enclosing matrix (Pls. 1a–d, 3d–f). The teeth of the left valve project deeply into the body cavity of the right valve (Pl. 1e–f). They fit into sockets developed from the inner layer of the right valve (Pl. 1a–d). The teeth are distinctly separated and connected by a strong yolk. The myophores extend from the teeth towards the ventral side, and are broadly parallel to one another (Pl. 1a–d). Posterior myophore (PM) is connected by a narrow neck, and anterior myo- phore (AM) by a wide neck to the teeth (Pl. 1). Specimens occur in weakly conjoined bouquets of up to 10 individuals when found in growth position. However, most specimens occur as isolated, transported or toppled individuals in rudstone beds (MITCHELL, 2002). Discussion: WHITFIELD (1897) and CHUBB (1971) suggested that two anterior furrows may be developed in some specimens. This is considered erroneous here; one furrow represents AF, whereas the other is a crack due to compaction. TRECHMANN (1924) and CHUBB (1971) sepa- rated B. cancellata from B. subcancellata. These spe- cies differ in the relative height of their RVs, B. can- cellata being tall and B. subcancellata short. The type specimen of B. subcancellata has the umbo of the RV broken off. Considering the populations of B. cancel- lata collected from the Guinea Corn Formation during this study, forms similar to B. subcancellata clearly represent extreme morphological variants of B. cancel- lata. B. subcancellata is therefore synonymised with B. cancellata here. Bournonia barretti TRECHMANN, 1924 Pl. 3a–c v. 1924 Bournonia barretti: TRECHMANN, p. 405, pl. 26, figs. 2, 2a. Diagnosis: A species Bournonia in which the anterior side bears from several to many costae. Type: TRECHMANN (1924, pl. 26, figs. 2, 2a) fig- ured a single specimen of Bournonia barretti (BMNH L63227) from the Great River Valley near Catadupa, St. James. This specimen is similar to forms occurring in the Middle C Beds in the Central Inlier, and is here selected as lectotype. Material: Many specimens collected from the Guinea Corn Formation. Forms transitional between B. cancel- lata and B. barretti are common in the Lower C Beds, whereas typical B. barretti has been collected from the Middle C, Upper C, D and G Beds. It is generally rare. Description: RV varies from cylindro-conical to cylin- drical, and is up to 10 cm high and 7 cm in diameter. The dorsal, posterior and ventral sides bear strong cos- tae with prominent furrows between. The anterior side in early examples (Lower C Beds of the Central Inlier) bears a few costae; in later forms (Middle C to G Beds of the Central Inlier) it bears numerous costae. Up to 17 costae may be present in total around the entire shell. When the anterior surface is strongly cemented to a smooth hard substrate (such as a valve of Antillocap- rina or Titanosarcolites), costae are not developed, and the specimen cannot be distinguished from B. cancel- lata. The radial bands are marked by two prominent costae. The anterior furrow is marked by a downfold of the funnel plates between two costae. LV cap like. Specimens usually occur as isolated individuals in growth position. Rarely specimens occur in conjoined bouquets numbering two or three individuals. Discussion: B. cancellata and B. barretti appear to be part of an evolving lineage. B. cancellata occurs in rock-forming abundance in the limestones of the upper A and B Beds. In the Lower C Beds forms with a few weak costae on the anterior side appear, and occur together with forms of typical B. cancellata morphol- ogy. These are here seen as transitional forms between B. cancellata and B. barretti. In the Middle C Beds, Bournonia are rare, but those specimens collected have anterior sides with many costae and are typical of B. barretti; forms similar to B. cancellata are absent. B. barretti occurs sporadically through the Upper C and D Beds, and rarely in the G Beds. ALENCASTER (1971) included B. barretti in the synonomy of B. cardenasensis (BÖSE, 1906). She recorded the latter species from Vega del Paso (locality 30) in the Upper Cretaceous of Mexico. The associated rudist fauna from this locality included Titanosarcolites macgillavryi ALENCASTER, Barrettia monilifera WOODWARD, B. multilirata WHITFIELD and B. gigas CHUBB. In Jamaica, the B. gigas–B. multilirata assemblage is of late Middle to early Late Campanian age (MITCHELL, in press), and B. cardenasensis is therefore older than the late Maastrichtian B. barretti. B. barretti and B. cardenasensis are here considered as homeomorphs. 152 Geologia Croatica 56/2 153Mitchell: Morphology, Microstructure and Stratigraphy of Some Late Cretaceous Radiolitid Rudists... Bournonia thiadensi VERMUNT, 1937 Pls. 3g–h, 4b 1937 Bournonia thiadensi; VERMUNT, p. 271–272, pl. 36, figs. 4–5, text figs. 3e–g. v. 1967 Bournonia tetrahedron: CHUBB, p. 28–29. v. 1971 Bournonia tetrahedron: CHUBB, p. 195, pl. 40, figs. 11–12. Diagnosis: A species of Bournonia with four, five, or rarely six, prominent costae in adults. Type: Type specimens not seen. Material: Moderately rare in the upper Middle C Beds, D Beds and F Beds. A single specimen also from the base of the B Beds. Description: RV conical, up to 6 cm high and 7 cm in diameter. The exterior bears four very prominent costae, two broad costae representing the radial bands, and two acute costae at the ventral and dorsal margins of the flat anterior surface. A further costa may be developed, and sometimes two are seen on the dorsal side. The costae represent downfolds of the funnel plates, the furrows, upfolds. The anterior side is flat and bears the AF, rep- resented by a sharp downfold of the funnel plates. A single transverse section (Pl. 4b) shows that the inner layer of the RV is about 2 mm thick, and the outer layer is composed solely of quadrangular cellular lay- ers; compact layers are absent. The cardinal apparatus is not seen. The LV is cap like, and may bear prominent radial striations. B. thiadensis occurs as isolated individuals, often cemented to valves of other rudists. Discussion: CHUBB’s (1967) species Bournonia tetra- hedron is a juvenile specimen of a Bournonia with four costae. Similar small specimens of Bournonia cemented to hard substrates (usually rudist shells) are not uncom- mon in the upper part of the Guinea Corn Formation. Where such specimens have grown to maturity, they acquire the form of B. thiadensi. Thus, B. tetrahedron is considered a juvenile of B. thiadensi here. Genus BIRADIOLITES D’ORBIGNY, 1850 Type species: Biradiolites canaliculatus D’ORBIGNY, 1850. Diagnosis: Radiolitids with no ligamental infold, radial bands situated in furrows, cardinal apparatus of type B (Pl. 5b), outer layer of RV formed of cellular and com- pact wall structures. Biradiolites rudissimus TRECHMANN, 1924 Pls. 5b–c, 6c–d, 6f 1897 ?Radiolites rudis; WHITFIELD, 189, pl. 11, fig. 4. v. 1924 Biradiolites rudissimus; TRECHMANN, p. 402, pl. 26, figs. 4, 4a, 5. v. 1924 Biradiolites minhoensis; TRECHMANN, p. 402–403, pl. 26, figs. 1, 1a. 1956 Biradiolites forbesi; CHUBB, p. 15–16, pl. 3, figs. 1–2. v. 1971 Biradiolites riograndensis; CHUBB, p. 189, pl. 37, figs. 9–11. Diagnosis: Biradiolites with a broad, flat-topped Vb and a strongly upfolded Pb. Other costae and furrows much reduced. Type: TRECHMANN (1924) figured two specimens of Biradiolites rudissimus from the Railway Cutting at Catadupa, St. James. TRECHMANN’s (1924) pl. 26, fig. 5, is here selected as lectotype. Material: Numerous individuals from the Titanosarco- lites Limestones of Jamaica. Description: A highly variable species of Biradiolites. RV up to 15 cm in diameter and 11 cm high. The RV is conical and ranges from narrow, tall cones (Radiolites rudis- or Biradiolites minhoensis-like forms) to broad, low cones. The margin of the RV is usually irregular, and may be devoid of costae and furrows other than for the radial bands. The radial bands are strongly marked and very distinctive. Vb is characterised by a sunken, flat, square-topped upfold, and is broad. Pb is narrower, convex and strongly upfolded. The apertural surface may bear plications and/or vascular impressions. Transverse sections of RV show a thin inner layer (less than 0.5 mm thick), and an outer layer formed largely of quadrangular, cellular microstructure with occasional irregular compact layers (Pl. 5b–c). Compact layers are often best developed adjacent to the radial bands. The cardinal apparatus is of type B (Pl. 5b). The teeth are relatively close together and fit into sockets in the RV. They are connected by a yoke that forms a small accessory cavity between the cardinal apparatus and the inner layer of the RV. The myophores form two arcs extending towards the ventral side (Pl. 5b). LV cap-like, with a raised central portion (Pl. 6c), and a flat brim that extends across the apertural surface. This brim is usually broken away, although vestigaes are sometimes preserved (e.g., at the top of Pl. 6c). B. rudissimus occurs as isolated individuals, or in small conjoined bouquets numbering up to three indi- viduals. Discussion: A great deal of confusion surrounds the relationship between Radiolites rudis WHITFIELD and 154 Geologia Croatica 56/2 155Mitchell: Morphology, Microstructure and Stratigraphy of Some Late Cretaceous Radiolitid Rudists... Biradiolites rudissimus TRECHMANN. The type and only specimen of R. rudis is in AMNH, and is embed- ded in a hard limestone matrix. Consequently, the form of the radial bands cannot be determined. The general morphology of the RV resembles narrow specimens of B. rudissimus, but in the absence of details of the radial bands the specimen must be regarded as indeterminate. R. rudis is therefore questionably placed in the synony- my list of B. rudissimus here. Biradiolites minhoensis TRECHMANN has a shape typical of conical specimens of B. rudissimus, but with rather smooth radial bands. Similar specimens with smooth radial bands do occur in large populations of B. rudissimus (e.g., a population taken from rhythm D1 in the Central Inlier), and since B. rudissimus has page preference, B. minhoensis is placed in synonymy here. In describing Biradiolites forbesi and B. rudissimus, CHUBB (1971, p. 188) stated that “[it] appears there is little… to differentiate between the two species”, and B. forbesi is placed in synonymy here. B. riograndensis CHUBB also has similar radial bands to B. rudissimus, and falls within the range of collected populations. Biradiolites jamaicaensis TRECHMANN, 1924 Pls. 5a, 5d–e, 6a–b, 6e v. 1924 Biradiolites jamaicensis; TRECHMANN, p. 404, pl. 24, figs. 5, 5a, 6, 6a, 7. v. 1967 Biradiolites robinsoni; CHUBB, p. 27. v. 1971 Biradiolites robinsoni; CHUBB, p. 187, pl. 36, figs. 1–3. Diagnosis: Biradiolites with strong stellate transverse sections, well-organised thick cellular and compact lay- ers, and a double costa in the interband. Type: TRECHMANN (1924) figured three specimens of B. jamaicensis. His pl. 24, figs. 5, 5a is the most typical, and is here designated as lectotype. Material: Abundant material from the Guinea Corn Formation and elsewhere in the Titanosarcolites Lime- stones of Jamaica. Description: RV cylindrical, straight, twisted or gently arched. Diameter up to 4 cm, length up to 25 cm. RV bears between 7 and 12 strong angular costae, includ- ing the two costae in the interband. Minor, longitudinal ridges may be developed on some costae. The cross section ranges from triangular to square to broadly rounded. Pb and Vb are marked by flat bands on either side of the prominent double costae of the interband (Pls 5a, 6a–b, 6e). The surface of RV is smooth. Transverse sections indicate a very well structured wall of the RV. The inner layer is very thin (less than 0.5 mm). The outer layer is divided into an inner por- tion with quadrangular cellular layers and an outer portion of compact layers (Pl. 5a, 5e). The compact lay- ers correspond to the strongly upturned margin of the funnel plates (Pl. 5d). Cardinal apparatus similar to B. rudissimus. LV with a central raised portion, and a brim extend- ing across the apertural face. The thin brim is often broken away. Occurs as ramifying masses and well-defined bou- quets of up to 100 or more individuals (MITCHELL, 2002). Discussion: CHUBB (1967) erected B. robinsoni for a short, curved form. The type specimen is missing (Edward ROBINSON, pers. comm., 2000), although a cast of it is in the BMNH. This specimen shows the typical radial bands of B. jamaicensis, and B. robinsoni is placed in synonymy here. Genus Thyrastylon CHUBB, 1956 Type species: Radiolites adhaerens WHITFIELD, 1897. Diagnosis: A radiolitid with no ligamental infold, quadrangular cellular and compact layers in the outer layer of RV, type B cardinal apparatus, radial bands par- tially infolded into the shell layer of the RV, and oscules developed in the LV. Thyrastylon adhaerens (WHITFIELD, 1897) Pls. 7, 8 v. 1897 Radiolites adhaerens; WHITFIELD, p. 188– 189, pl. 10, fig. 1, pl. 12, fig. 1. Diagnosis: As for genus (but see discussion). Type: WHITFIELD (1897) figured several specimens of Radiolites adhaerens. No lectotype is currently selec- ted, pending revision of TRECHAMNN’s (1924) and CHUBB’s (1956, 1971) species concepts. Material: Abundant material from the Titanosarcolites Limestones of Jamaica. Description: RV cylindrical to conical, up to 10 cm long and 7 cm in diameter. Margin broadly rounded and irregular, with radial bands marked by wide or narrow furrows. Aperture with radial plications and/or vascular impressions. Transverse cross sections of the RV show a thin inner layer (less than 0.5 mm) and an outer layer formed mainly of quadrangular cellular microstructure with occasional bands of compact microstructure (Pl. 7c). Compact shell layers are particularly developed around the infolded radial bands (Pl. 7d). Longitudinal sections show the upward projecting funnel plates, with occasional layers of compact microstructure, which is also concentrated adjacent to the infolded radial bands (Pl. 8a–b). The cardinal apparatus is type B as in B. rudissimus (see CHUBB, 1971). 154 Geologia Croatica 56/2 155Mitchell: Morphology, Microstructure and Stratigraphy of Some Late Cretaceous Radiolitid Rudists... The LV is cap like, with a central raised/domed sec- tion and a wide thin brim that extends across the aper- tural face. The LV has two oscules developed above the radial bands (CHUBB, 1956, 1971). Specimens occur as weakly to strongly attached elevators or clingers. Sometimes in bouquets number- ing up to 20 or more individuals. Discussion: TRECHMANN (1924) erected two further species, Biradiolites coryi and Biradiolites semiannu- losus, that CHUBB (1956) placed in Thyrastylon. The distinction between these ‘species’ is remarkably diffi- cult in many of the collected specimens. A full revision of the genus using populations is needed to sort out the species concepts in this genus. Many of the features of Thyrastylon resemble those of B. rudissimus. The genus differs in the infolding of the radial bands and the development of oscules in the LV. 5. STRATIGRAPHY The distribution of the Maastrichtian rudists discussed in this paper, together with similar forms from the San- tonian and Campanian of Jamaica is shown in Fig. 3. This demonstrates that Bo. cancellata-like, Bo. thiaden- si-like and Bi. rudissimus-like forms occur over extend- ed ranges. In continuous sections, in would probably be difficult to separate these ‘species’, which undoubt- edly represent lineages. The evolutionary change from Bo. cancellata to Bo. barretti, and the first appearance of Bi. jamaicensis are probably useful biostratigraphic markers of the Upper Maastrichtian. Acknowledgements Many thanks to Gavin C. GUNTER who collected some of the specimens from western Jamaica illustrated in this paper. Many thanks to Shakira KHAN for print- ing the negative prints. Thanks to Thomas STEUBER and Gloria ALENCASTER for help with obtaining lit- erature, and to Stefan GÖTZ and Tvrtko KORBAR for valuable comments on the original manuscript. 6. REFERENCES ALENCASTER, G. (1971): Rudistas del Cretacico Superior de Chiapas [Upper Cretaceous rudists from Chiapas – in Spanish].– Paleontologia Mexicana, 34, 1–91. AMICO, S. (1978): Recherches sur la structure du test des Radiolitidae [Study of the shell structure of radiolitidae – in French].– Traveaux du Laboratoire de Géologie Histo- rique et de Paléontologie, 8, 1–131. Fig. 3 Stratigraphy of radiolitid rudists from the Upper Cre- taceous of Jamaica. JM = Jerusalem Mountain occur- rences, A–G = Beds in Guinea Corn Formation; the gap between JM and A–G is not known at outcrop. 156 Geologia Croatica 56/2 157 BÖSE, E. (1906): La fauna de moluscos del Senoniano de Cárdenas, S.L.P. [The mollusc fauna of the Senonian of Cardenas, S.L.P. – in Spanish].– Boletín del Instituto Geo- lógico de México, 24, 1–92. CHUBB, L.J. (1956): Thyrastylon, a new rudists genus from the Upper Cretaceous of Guatemala, the Antilles, and Persia, with a discussion of the function of rudists oscules and pillars.– Palaeontographica Americana, 4/27, 33–49. CHUBB, L.J. (1967): New rudist species from the Cretaceous rocks of Jamaica.– Journal of the Geological Society of Jamaica, 9, 24–31. CHUBB, L.J. (1971): Rudists of Jamaica.– Palaeontographica Americana, 7, 161–257. COATES, A.G. (1965): A new section in the Maastrichtian Guinea Corn Formation near Crawle River, Clarendon.– Journal of the Geological Society of Jamaica (Geonotes), 7, 28–33. FISCHER, P. (1887): Manuel de conchyliologie et de paléonto- logie conchyliogique ou histoire naturelle des mollusques vivants et fossils [Manual of shell and shell paleontology and natural history of Recent and fossil molluscs – in French].– F. Savy, Paris, 1369 p. MITCHELL, S.F. (1999): Stratigraphy of the Guinea Corn Formation (Upper Cretaceous) at its type locality bet- ween Guinea Corn and Grantham (northern Clarendon, Jamaica).– Journal of the Geological Society of Jamaica, 33, 1–12. MITCHELL, S.F. (2002): Palaeoecology of corals and rudists in mixed volcaniclastic–carbonate small-scale rhythms (Upper Cretaceous, Jamaica).– Palaeogeography, Palaeoclimatology, Palaeoecology, 186, 237–259. MITCHELL, S.F. (in press): Sedimentary and tectonic evolu- tion of central Jamaica.– In: BARTOLINI, C., BURKE, K., BUFFLER, R., BLICKWEDE, J. & BURKART, B. (eds.): Mexico and the Caribbean Region: Plate Tectonics, Basin Formation and Hydrocarbon Habitats.– American Association of Petroleum Geologists Memoir. MITCHELL, S.F. & GUNTER, G.C. (2002): Biostratigraphy and taxonomy of the rudist Chiapasella in the Titanosar- colites Limestones (Maastrichtian) of Jamaica.– Cretace- ous Research, 23, 473–487. DES MOULINS, C. (1826): Essai sur les sphérulites qui existent dans les collections de MM. F. Jouannet, member de l’Académie royale des Sciences, belle Lettres et Arts de Bordeaux, et Charles des Moulins; et considerations sur la familie à laquelle ces fossils appartiennent [Essay on the Dherulites in the collection of MMF Jouannet, member of the Royal Academy of Sciences, beautiful Let- ters and Arts of Bordeaux, and Charles des Moulins and consideration on the families to which these fossils belong – in French].– Bulletin d’Histoire Naturelle de la Société Linnéenne de Bordeaux, 1, 148–303. PLATE 1 Bournonia cf. cancellata (WHITFIELD), forms with a few weak costae on anterior side, Lower C Beds, Guinea Corn a – UWIGM.RUD.3003.3; b–e – UWIGM.RUD.2003.171–174, respectively; f – UWIGM.RUD.2003.2. a–d Transverse sections cut at various levels and angles through the cardinal apparatus. e–f Longitudinal sections. Camera lucida drawings, outer layer structure simplified. Black, aragonitic inner layer of left valve; dark grey, arag- onitic inner layer of right valve; light greys calcitic outer layers of left and right valves; dotted, epifornal corals. PM, posterior myophore; AM, anterior myophore; Pb, posterior band; Vb, ventral band; AF, anterior furrow. Note intense boring (Entobia isp.) in upper part of aragonitic inner layer of left valve in f. 156 Geologia Croatica 56/2 157Mitchell PLATE 1 I' b AF 158 Geologia Croatica 56/2 159 D’ORBIGNY, A. (1847): Sur les brachiopods ou palliobran- chs [On the brachiopods and pallialbranchs – in Fren- ch].– Comptes rendus hebdomadaires des Séances de l’Académie des Sciences, 25, 266–269. D’ORBIGNY, A. (1850): Paléontologie Francaise, Terrains Crétacés. Vol. 4, Brachiopodes [Paleontology of France, Cretaceous rocks. Vol. 4, Brachiopods – in French].– Ber- trand, Paris, 105–328. STEUBER, T. (1999): Cretaceous rudists of Boeotia, central Greece.– Special Papers in Palaeontology, 61, 229 p. STEUBER, T. (2002): Depository item 2002022, List of occurrences of rudist bivalves (Hippuritoidea) in the Ame- ricas. Plate tectonic control on the evolution of Cretaceous platform-carbonate production.– Geology, 30, 259, 71 p. STEUBER, T., MITCHELL, S.F., BUHL, D., GUNTER, G. & KASPER, H.U. (2002): Catastrophic extinction of Caribbean rudist bivalves at the Cretaceous–Tertiary boundary.– Geology, 30, 999–1002. TRECHMANN, C.T. (1924): The Cretaceous limestones of Jamaica and their Mollusca.– Geological Magazine, 61, 25–410. UNDERWOOD, C.J. & MITCHELL, S.F. (2000): Serrato- lamna serrata (Agassiz) (Pisces, Neoselachii) from the Maastrichtian (Late Cretaceous) of Jamaica.– Caribbean Journal of Earth Science, 34, 25–30. VERMUNT, L.W.J. (1937): Cretaceous rudistids of Piñar del Rio, Cuba.– Journal of Paleontology, 11, 261–275. WHITFIELD, R.P. (1897): Descriptions of species of Rudistae from the Cretaceous rocks of Jamaica, W. I., collected and presented by Mr. F. C. NICHOLS.– Bulletins of the American Museum of Natural History, 9, 185–196. Manuscript received March 04, 2003. Revised manuscript accepted November 04, 2003. PLATE 2 a–c Three views of conjoined specimens of Bournonia cancellata (WHITFIELD), bed 15 upper, upper A Beds, Guinea Corn, UWIGM.RUD.2002.89. Anterior furrow (AF) obvious in b. 158 Geologia Croatica 56/2 159Mitchell PLATE 2 c b 1cm - 160 Geologia Croatica 56/2 161 PLATE 3 a–c Bournonia barretti TRECHMANN, Lower C Beds (upper part), Slippery Rock River, UWIGM.RUD. 2002.90. d–f Cardinal apparatus of Bo. cancellata, lowermost limestone, Pindars River Section, UWIGM.RUD.2003.1. g–h Bo. thiadensi VERMUNT, F Beds, Green River, UWIGM.RUD.2002.73. Vb, ventral band; Pb, posterior band. 160 Geologia Croatica 56/2 161Mitchell PLATE 3 1 em - Vb 162 Geologia Croatica 56/2 163 PLATE 4 a, c Transverse section of Bournonia cf. cancellata (same as Pl. 1b); b Transverse section of Bo. thiadensi, Marchmont Inlier, UWIGM.58CA34; d Longitudinal section of Bo. cf. cancellata (same as Pl. 1e). Negative prints of acetate peels. Scale bar = 1 cm; a and b show the inner aragonitic layer, and the outer calcitic layer composed of quadrangular cell structure; c, detail showing quadrangular cell structure in outer shell layer; d, showing the very thick aragonitic inner layers of the left and right valves, and the massive aragonite of the cardinal structure; note the closely spaced funnel plates in the outer layer. Aragonite of inner layer replaced by calcite. 162 Geologia Croatica 56/2 163Mitchell PLATE 4 164 Geologia Croatica 56/2 165 PLATE 5 a, e Transverse section of Biradiolites jamaicensis TRECHMANN, uppermost limestone, Pindars River, UWIGM.RUD.2001.114; note the well developed compact (co) and cellular (ce) structure of the outer shell layer. b, c Transverse section of Bi. rudissimus TRECHMANN, Rhythm D1, Guinea Corn, UWIGM.RUD.2001.114; b shows the cardinal structure, and alternation of compact (co) and cellular (ce) microstructure in the outer shell layer; c, detail showing compact (co) shell structure in Pb. d Longitudinal section of Bi. jamaicensis, upper part Lower C Beds, Guinea Corn, UWIGM.RUD.2002.96; note that the compact (co) shell structure corresponds to the strongly vertical upturned part of the funnel plates. Scale bar = 1 cm. Pb, posterior band; Vb, ventral band. Negative prints of acetate peels. 164 Geologia Croatica 56/2 165Mitchell PLATE 5 166 Geologia Croatica 56/2 167 PLATE 6 a, b Biradiolites jamaicensis TRECHMANN, Middle C Beds, Guinea Corn, UWIGM.RUD.2001.50; c–d Bi. rudissimus TRECHMANN, Marchmont Inlier, UWIGM.RG.2001.109.MM15 (collected by Gavin GUN- TER and SFM); e Bi. jamaicensis, Logie Green, UWIGM.RUD.2001.147; f Bi. rudissimus, Rhythm D1, Guinea Corn, UWIGM.RUD.2001.117, split showing body cavity. Pb, posterior band; Vb, ventral band. 166 Geologia Croatica 56/2 167Mitchell PLATE 6 f 1 em - 168 Geologia Croatica 56/2 169 PLATE 7 a–b Thyrastylon adhaerens (WHITFIELD); a, Lower C Beds, Guinea Corn, UWIGM.RUD.2002,143; b, UWIGM.RG.2001.96.MM16, Marchmont Inlier (collected by Gavin GUNTER); c–d T. adhaerens [form approaching T. coryi (TRECHMANN)], Middle C Beds, Guinea Corn, UWIGM.RUD. 2002.104. Pb, posterior band; Vb, ventral band. 168 Geologia Croatica 56/2 169Mitchell PLATE 7 b 1 em 170 Geologia Croatica 56/2 171 PLATE 8 a, b Longitudinal section of Thyrastylon adhaerens (WHITFIELD) cut through a radial band showing compact (co) and cellular (ce) microstructure, D Beds, Guinea Corn, UWIGM.RUD.2003.175; c, d Detail of c: transverse section showing infolded radial bands showing compact (co) and cellular (ce) micro- structure, Middle C Beds, Guinea Corn, UWIGM.RUD.2002.91. Scale bar = 1 cm. Negative prints of acetate peels. 170 Geologia Croatica 56/2 171Mitchell PLATE 8 d 172 Geologia Croatica 56/2