The Gryphaeidae, common name the foam oysters or honeycomb oysters, are a family of marine bivalve mollusks, and are a kind of true oyster. This family of bivalves is very well represented in the fossil record, however the number of living species is very few.All species have shells cemented to a substrate. Shells are considered brittle, inequivalve, with the left, lower (cemented) valve convex and the right (upper, non-cemented) valve flat or slightly concave.