Postelichus bajaensis Barr and Shepard, new species is described and figured, and its habitat discussed. The first taxonomic key to the males of all seven species of Postelichus Nelson, 1989 is presented with images of the male genitalia. The geographic distributions of the species of Dryopidae occurring on the Baja California Peninsula of Mexico are reviewed. Helichus columbianus Brown, 1931 is reported as a new country record for Mexico and Postelichus immsi (Hinton, 1937) as a new record for Baja California.