A revised superfamily Arcacea contains the family Arcidae, subfamilies Arcinae, Anadarinae, and Litharcinae (new), and the family Noetiidae, subfamilies Noetiinae and Striarcinae. Litharca lithodomus (Sowerby), illustrated and described in detail, isa boring form,
living on the open seacoast, ranging from Manta, Ecuador, to Cabo Blanco, Peru.  A record from Panama is questioned. Anadara (Larkinia) grandis (Broderip and Sowerby) ranges from Magdalena Bay, Lower California, and the Gulf of California to Sechura Bay, Peru. It is an ecologi- cally restricted form, temperature controlled, living in mud flats in estuaries and embayments. Some paleoecological inferences based on the species are questioned.