Revision of acritarchs and prasinophyte algae from the lower Silurian of Belgium

Abstract. The type acritarch and prasinophyte algal material of Stockmans & Willière (1963), from the Silurian of the Courtrai region, Belgium, has been re-examined. Revised descriptions for the holotypes of several type species are given, which detail the greater morphological diversity recognized. Four new combinations are proposed (Buedingiisphaeridium parveroquesi, Dictyotidium deflandrei, Helosphaeridium echinodermum and Multiplicisphaeridium pentagonale). Micrhystridium? radians is provisionally retained, although it is probable that this species should be referred to a new, unrecognized genus (it possesses a pylome and spinose, simple and branched processes). The synonymy of Diexallophasis denticulata and Diexallophasis remota (proposed by Playford, 1977) is rejected, as the latter has broader-based and more robust processes. The generic assignment of Diexallophasis mucronata is confirmed. Several of the taxa proposed by Stockmans & Willière have been re-illustrated to show clearly the features of taxonomic importance. These descriptions and illustrations will enable the reliable recognition of these taxa in contiguous sections elsewhere, and will help to form the basis of future population studies.