The original intent of this study was to reinvestigate and confirm the validity of thirteen species of Podocotyle reported from Dillon Beach, California. Eight species were described by Park (1937) and five described by Johnson (1949-unpublished). Among these species basic similarities were evident in such features as: cirrus sac, seminal vesicle, body shape, extent and distribution of vitellaria, which indicated the possibility of conspecificity. Because four of these species (Podocotly blennicottusi, P. california, P. pedunculata, and P. pacifica) were also reported from fishes of the Pacific Northwest coast by Ching (1960), Pratt and McCauley (1961), Arai (1969), and Hall and Pratt (1969), it was decided to expand the investigation to include these forms and other Podocotyle spp, from coastal areas of the world in an attempt to determine the number of valid species and introduce and improved method of species determination within this group. Some 489 tide pool fish, representing 23 species, were collected and examined at the Pacific Marine Station, Dillon Beach, California, between July 1969 and August 1970. Specimens of Pococotyle, obtained by the investigator, were augmented by material from previous collections in that area.