Royal Irish Academy, May 27. WINIFRED E. FROST: Larval stages of the Euphausiids Nematoscelis megalops and Stylocheiron longicorne taken off the south-west coast of Ireland. The euphausiids form an important part of the fauna of the inshore and deep waters off the south and west coast of Ireland. The present paper deals with the life-histories of two of these animals, the development of which has not previously been described. Sufficient larval stages have been found to give a good idea of the life-history of the organisms and the descriptions make it possible to identify the larvse in the plankton. Some notes are given on the reproductive cycles of the two euphausiids.