Nucella demouthae n. sp. is a new muricid described from the late Miocene part of the Wilson Grove Formation in Sonoma County, central California. It is distinguished from other modern and fossil California Nucella by its small size with faint to moderately strong  radial sculpture, and its thickened and recurved outer lip with two denticles in the aperture. This rocky shore predatory gastropod has been found only at Bloomfield Quarry, north of the town of Bloomfield in Sonoma County, in the lowest part of the Wilson Grove Formation, which has been dated between 9.3 and 6.2 Ma, this time period falling within the late Miocene “Jacalitos” California provincial molluscan stage.