Lenodus variabilis occurs in an interval in the lower to middle Kundan Stage which includes the Arenig-Llanvirn boundary. The lower part of its range constitutes the L. variabilis Zone, the upper part, where it co-occurs with Yangtzeplacognathus crassus, making up the Y. crassus Zone. The conodont faunas of these two consecutive conodont biozones have been investigated in 14 sections from south, south-central and central Sweden, the faunal differences between the areas being mainly expressed in shifts in relative abundance. The taxon which is generally the most abundant, Baltoniodus, has comparable abundance maxima at localities representing shallow parts of the basin as well as in deeper parts, indicating that some environmental factor other than water depth has influenced its distribution. Drepanodus and Protopanderodus rectus prefer areas representing deeper parts of the epicontinental sea. Scalpellodus is most abundant at the sites representing intermediate depths. Semiacontiodus cornuformis was adapted to shallow water and is lacking at levels representing maximum depths, but at some places (for instance in Skĺne) it is replaced by Semiacontiodus davidi.

Key words: conodonts, biostratigraphy, biofacies, ecology, Arenigian, Llanvirnian, Sweden.

Anita Löfgren [anita.lofgren@geol.lu. se], Department of Geology, Lund University, Sölvegatan 13, SE−223 62 Lund, Sweden.