The Lower Devonian ostracoderm Phialaspis symondsi differs sufficiently from the type species of the Traquairaspididae, Traquairaspis campbelli , to place it within a separate family, the Phialaspididae. This family also includes Toombsaspis pococki comb, nov., T. sabrinae comb. nov. and Munchoaspis denisoni comb, nov. The Traquairaspididae includes Traquairaspis campbelli and Rimasventeraspis angusta comb. nov. A new reconstruction of the carapace of Phialaspis symondsi is given and, from an examination of immature plates,
a possible mode of growth is outlined. Likely feeding and respiratory mechanisms are discussed. A new form of jet-aided steering is proposed for phialaspidid ostracoderms.