The principles of comparing the jaws of the fossil and Recent polychaetes are here discussed. A Jurassic jaw apparatus is described and assigned to the Recent genus Ophryotrocha. Other jaws of polychaetes not having composite apparatus are assigned to Recent genera Glycera and ?Goniada. It has been found that the Paranereites, a scolecodont genus common in the Mesozoic, is a synonym of the genus Glycera. Other scolecodonts, considered by some authors as ancestors of the Recent genera Nereis and Glycera, are not closely related to these polychaetes. The generic assignment of the Mesozoic scolecodonts, usually included in the genus Goniada, is not certain. It has also been found that the Mesozoic polychaetes are moooe closely rela.ted to the Recent rather than the Palaeozoic genera.