The taxonomy of two poorly known species of rhizopine crabs, Ceratoplax truncatifrons Rathbun, 1914, and C. fulgida Rathbun, 1914 (Brachyura Linnaeus, 1758: Pilumnidae Samouelle, 1819) is clarified on the basis of the type material from the Philippines. A new species, C. margarita n. sp., is described from Papua New Guinea. It can be distinguished from the above two species (and all congeners) by its carapace, sternal and gonopod characters.
Pilumnidae, Ceratoplax, Papua New Guinea, new species.