Abstract: A new algal fossil was collected from the lower part of the Lower Cambrian, a Sinian-Cambrian boundary section in Abazhai of Qingzhen County, Guizhou Province. It was discovered in petrographic thin sections of a black laminated chert. The new fossil, Symphysosphaera radialis gen. et sp. nov. is a fossilized muhicellular colony characterized by a surface layer of cells enclosed in an envelope, inner cavity permeated with dark dense mucilage embedded with numerous spherical units. Its difference from all morphs discovered in Precambrian, indicates that the genus may represent member of a new order at the beginning of Cambrian. hs stratigraphic and biological significance merits our attantion.

Key words: Sinian-Cambrian boundary section, Algal fossil, Symphysosphaera Radialis