Rock boring is a widespread mode of life in pelecypods, occurring in some representatives of eight superfamilies. After a brief review of rock boring mechanisms of the Mytilacea, the systematic position and taxonomy of Corallidomus scobina new name are discussed and evidence is presented for regarding this species as a facultative rock boring mytilacean pelecypod. This is the oldest known (Late Ordovician) occurrence of rock boring by pelecypods in the fossil record.