1. an extinct tribe of fossil corals, including numerous species, many of them of large size. they are characteristic of the paleozoic formations. the radiating septs, when present, are usually in multiples of four. see cyathophylloid.

1. an order or other group of sclerodermatous stone-corals, exhibiting tetramerous arrangement of parts and a well-developed corallum, with true thecæ and generally septa and tabulæ; the rugose corals.