A new subtidal bivalve species, Petricola ramirezi sp. n., is described from specimens collected from among cirripedian communities at Playa El Tabo (33 degrees 27' S, 71 degrees 38' W), central Chile. With a maximum recorded length of 16.3 mm, Petricola ramirezi is one of the smallest species in the genus found in the southeastern Pacific, and it is the fifth species from the subfamily Petricolinae recorded in Chile.