Twenty-nine species of Polychaeta collected on, or near, the west coast of Lower California and of Mexico are recorded. Seventeen of them are pelagic. Of these, 10 are heteronereid phases of various Nereidae, in two of which cases (Perinereis monterea and Nereis oligohalina) neither of the heteronereid phases has been described previously. One species recorded (Maupasia caeca) is new to the northeast Pacific.