Characters: Colonies are flat to hemispherical and up to 2 metres across. They have tusk-like, elongate, closely compacted monocentric corallites. Individual corallites unite only at the base of the colony. Primary septa are very exsert, with long teeth. The exsert primary septa have a spoke-like appearance underwater.
Colour: Uniform grey.
Habitat: Upper reef slopes and lagoons.