Several years ago two new species of the reef-building coral genus Coscinaraea were discovered nearly simultaneously in the extreme eastern and south-western parts of Australia. ... The two new species described below occur at the extreme southern limits of hermatypic corals in eastern and south-western Australia. The most southerly occurrence of Coscinaraea known to this time is at Rundle Island (23°30'S.) on the Great Barrier Reefs (Wells, 155, p. 25, and chart), about 600 miles north of Sydney and where the winter minimum temperatures are about 17°C. The genus has not been previously reported from northwestern or western Australia. In eastern Australia the writer (1955) has noted the occurrence of a few reef coral genera as far south as Sydney: Montipora, Cyphastrea, Turbinaria, Stylocoeniella and Plesiastrea. To this short list is now added Coscinaraea mcneilli n.sp., from Manly Cove and vicinity, in waters where the temperature range is from 12°C in June to 24.5°C in January.