A new non-encrusting species of Aulopora is described from the Middle Devonian of southwest England. Its colonial form is reconstructed from serial sections using a computer program. These sections also allow the description of protocorallite ontogeny and the formation of offsets in the new species. For comparison, aspects of ontogeny and astogeny were investigated in some other auloporids: protocorallite ontogeny and colony form in ‘Plexituba’? cucullina; increase in Aulopora serpens and Aulocystis sp. cf. A. amica. Most reptant auloporids show a more or less constant angle of offsetting to the parent, but in ‘P.’? cucullina, the interoffset angle decreases with each successive increase event in the colony. The phylogenetic significance of the auloporids is reassessed on the basis of these new data on protocorallite ontogeny and increase. □Tabulata, auloporids, ontogeny, astogeny, phylogeny, Devonian.