LAUSR

Abstract Two hundred and seventy-eight specimens of fossil bivalves were collected from the Tuwaiq Mountain Limestone (Callovian) and the Hanifa Formation (Oxfordian), Central Saudi Arabia. Of all the outcrops studied, the Khashm al Qaddiyah contains the richest assemblage of the bivalves (49%), as regards variety and frequency; followed by Dirab (27%), Jabal al Abakkayn (13%) and Maashabah (11%). Twenty bivalve species have been identified and systematically described. They belong to fourteen genera, twelve families and nine orders. Among these species, six Callovian species; Grammatodon ( Cosmetodon ) elongatum (J. Sowerby, 1824), Limea ( Pseudolimea ) duplicata (Sowerby, 1827), Liostrea multiformis (Koch and Dunker, 1837), Actinostreon marshi (Sowerby, 1814), Eopecten velatus (Goldfuss, 1833) and Ceratomya striata (Sowerby, 1815) and four Callovian–Oxfordian taxa; Musculus ( M. ) somaliensis (Cox, 1935), Actinostreon erucum (Defrance, 1821), Pholadomya ( Ph. ) deltoidea Sowerby, 1827 and Ph. ( Ph. ) socialis Morris and Lycett, 1854 were reported for the first time from the Jurassic deposits of Saudi Arabia. Paleobiogeographically, the studied bivalve assemblage has a dominantly Tethyan character and shows close relationships with Europe, East Africa, India and Iran. In addition, there are considerable links with the Middle East, North Africa and China. No endemic species were recorded from the studied sections.