The Collaborative International Dictionary of English v.0.48:

Rugosa \Ru*go"sa\, n. pl. [NL. See Rugose.] (Paleon.)
   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.
   [1913 Webster]