<i>Biradiolites</i> from the Yigeziya Formation of the Southwestern Tarim Basin

Abstract

Two Biradiolites species described from the Yigeziya Formation of the southwestern Tarim Basin are revised. The Maastrichtian Biradiolites boldjuanensis is small and pipe-like species that is usually preserved as clusters or bouquets. Although it was considered to be endemic to Central Asia, similar specimens are abundant in Maastrichtian of other Tethyan regions. Biradiolites minor specimens have no relationship with the genus Biradiolites because their ventral and posterior bands are protruding ridges and interband is depressed broad groove. This species is comparable with the Campanian-Maastrichtian eastern Arabian species Glabrobournonia arabica , by the character of smooth outer shell layer in right valve, and simple radial bands and ridges on margin of each shell flank, but it differs from the latter species in size and the shape of left valve. This study will be a supportive tool for the establishment and reconstruction of the palaeogeographic connection between Central Asia and other Tethyan regions.