Two new genera and three new species of shallow-marine, warm-water gastropods are reported from outcrops of various Cretaceous formations between British Columbia and Baja California. The potamidid Cedrosia pacifica new genus and species is from Turonian strata on Cedros Island, west coast of Baja California, Mexico. It is the earliest potamidid known from the rock record of the Pacific Slope. Alamirifica corona new genus and species, whose suprageneric relationships are uncertain, is from Turonian strata in southern California. The holotype has a round and rimmed aperture most similar to the photine buccinid Neoteron Pilsbry and Lowe, 1932. The holotype also has a pyramidal spire most similar to some fossil cerithioideans traditionally placed in the potamidid Pyrazus Montfort, 1810, but the type species of Pyrazus does not have a pyramidal spire. Future work might reveal that Alamirifica belongs to a new family.
Four other Pacific Slope species are tentatively assigned to Alamirifica: the Aptian A.? harrissi (Allison, 1955); the Coniacian A.? ursa new species; the late Coniacian to early Campanian A.? harveyi (Whiteaves, 1903); and the poorly preserved Turonian Alamirifica? sp.
As presently known, Cedrosia and Alamirifica were endemic to the study area, but they strongly resemble some Old World Tethyan gastropods. The distribution of A.? harveyi lends support to a relatively northern site of deposition for the Nanaimo Group.