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<div>Radiolitid rudists from the Upper Maastrichtian of Jamaica include</div><div>genera Bournonia, Biradiolites and Thyrastylon. Three species of</div><div>Bournonia are recognised, B. cancellata WHITFIELD, B. barretti</div><div>TRECHMANN and B. thiadensi VERMUNT. B. cancellata evolves</div><div>into B. barretti by the acquisition of costae on the anterior side. The</div><div>species of Bournonia are characterised by a distinctive cardinal apparatus, a thick inner shell layer, and an outer shell layer composed of cellular microstructure. Two species of Biradiolites are recognised</div><div>– B. rudissimus TRECHMANN has an outer layer composed of cellular</div><div>microstructure with occasional bands of compact microstructure,</div><div>particularly in the radial bands, and B. jamaicensis TRECHMANN</div><div>has a very well organised outer layer with an inner band of cellular</div><div>microstructure and an outer band of compact microstructure. Biradiolites</div><div>and Thyrastylon have a similar dentition, a thin inner layer and</div><div>similar wall structures in the outer layer. Thyrastylon is distinguished</div><div>from Biradiolites by the infolding of the radial bands in RV and by</div><div>the presence of oscules in LV. The evolutionary change from Bo. cancellata to Bo. barretti, and the first appearance of Bi. jamaicensis are</div><div>probably useful biostratigraphic markers of the Upper Maastrichtian.</div>