Silenis bassleri(Sohn), andKuresaaria gotlandicagen. et sp. n., studied in the present paper are from the Silurian of Gotland. Both belong to the Metacopa for which an emended diagnosis is given and phylogenetic relations of which are discussed. The shape of carapace and the morphology of valves of the described forms suggest that they probably represent two trends of development among Metacopa: respectively thlipsurean and healdiacean.