The Collaborative International Dictionary of English v.0.48:

Cyathophylloid \Cy`a*tho*phyl"loid\, n. (Paleon.)
   A fossil coral of the family Cyathophyllid[ae]; sometimes
   extended to fossil corals of other related families belonging
   to the group Rugosa; -- also called cup corals. Thay are
   found in paleozoic rocks.
   [1913 Webster]