Abstract
The fauna and correlations of the beds with Illaenus crassicauda (Wahl.) and Tallinnella dimorpha Öpik (lower Middle Ordovician), originally called »Flagkalk» by Törnquist (1883), are discussed. For these beds, that appear to be contemporaneous with the Uhaku stage of Estonia, the name Crassicauda stage is proposed.

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