Fifteen jaw apparatuses of polychaetes from the Ordovician and Silurian of the Mielnik boring on the Bug are described. They include eight known species, three species identified to the generic level and four new species: Mochtyella duplicidentata n. sp., M. fragilis n. sp.; M. multilamellata n. sp. and Skalenoprion bugensis n. sp. The Ordovician assemblage of polychaetes differs fundamentally from the Silurian one and is much richer. The genera Rhytiprion Kielan-Jaworowska, Polychaetura Kozlowski, Ramphoprion Kielan-Jaworowska, Kalloprion Kielan-JaWorowska, Leptoprion Kielan-Jaworowska and Pistoprion Kielan-Jaworowska are known from the Ordovician only, while Paulinites Lange is most common in the Silurian deposit