Parts I to III of the paper describe faunas of fossil fish from different horizons of the Los Angeles Basin. Part I. Collections of fish fossils were made at a number of localities on the west side of Sepulveda Canyon, Santa Monica Mountains, California. The fishes occur in hard siliceous sandstone and shale of the lower Modelo formation (Upper Miocene). Eighteen families and twenty genera are represented. The assemblage suggests a marine neritic subtropical fauna, living at a depth of 100 to 200 m. Part II. The diatomaceous shale of the Upper Modelo formation yielded an abundance of fossil fish at localities near Van Nuys along the northern rim of the Santa Monica Mountains. Strata containing fish remains interfinger with barren layers of volcanic ash, sandstone, and mudstone. The restricted fauna of a bathypelagical environment is represented by nine genera. Nearly all are present with a great many specimens. A fauna transitional between the Upper and Lower Modelo is found in platy shale conformably underlying the Upper Modelo. Part III. Fossil fish have been found in marine deposits of late middle to early Upper Miocene age (Altamira shale) on the coast of the Palos Verdes Hills, near San Pedro, California. A subtropical shallow sea is indicated as the place of deposition of this particular assemblage. The fauna of the Altamira shale is yet incompletely known, and fishes are also present in the overlying Valmonte member of the Monterey formation. Part IV. The herringlike fishes of the California Miocene are reviewed. This type of fish is the most common in the Miocene deposits. The clupeoid fishes have undergone considerable changes in the California sea since Miocene. Part V. Represents a study of the Zaphlegidae, a family of the Scombroidei belonging to the first division of the suborder, the Trichiuriformes. The family, evidently extinct, was related to the Gempylidae and lived in offshore deeper water. The reasons for its extinction were possibly climatic changes toward the end of the Miocene. Part VI. Gives a complete revision of the fish fauna from the diatomaceous earth of Lompoc, Santa Barbara County, California. The fauna comprises 31 families, 39 genera, and 42 species. It represents a harmonious assemblage that accumulated in a warm-temperate coastal sea of 25 to 50 fathoms depth, half a mile away from shore. Greater similarity existed between the fish faunas of the Pacific and Atlantic Coast of America during the Miocene than at present. A relatively great number of fish forms has become extinct in the California sea since Miocene times. Bathypelagical types were established best. Local changes probably caused the extinction of most of these types.