The west coast of North America record of the shallow-marine stromboid gastropod genus Rimella Agassiz, 1841 is restudied for the first time in 90 years. This genus comprises a small group of Paleogene gastropods characterized by having an ornamented fusiform shell, a posterior canal ascending the spire, and simple (non-flared) outer lip. Rimella, whose familial ranking has been inconsistent, is placed here in family Rostellariidae Gabb, 1868, subfamily Rimellinae Stewart, 1927. Ectinochilus Cossmann, 1889; Macilentos Clark and Palmer, 1923; Vaderos Clark and Palmer, 1923; and Cowlitzia Clark and Palmer, 1923 are recognized here as junior synonyms of Rimella. Four species are recognized from the west coast of North America: early to middle Eocene Rimella macilenta White, 1889; early Eocene Rimella oregonensis Turner, 1938; middle to late Eocene Rimella supraplicata (Gabb, 1864) new combination, of which Rostellaria canalifer Gabb, 1864, Cowlitizia washingtonensis Clark and Palmer, 1923, and Cowlitzia problematica Hanna, 1927 are recognized here as junior synonyms; and late Eocene Rimella elongata Weaver, 1912.
Rimella was a warm-water gastropod whose earliest known record is of early Paleocene (Danian) age in Pakistan. Other than the west coast of North America, Rimella is found in Eocene strata in western Europe, Turkey, Egypt, Pakistan, southeastern United States, Panama, Peru, and, to a lesser degree, in Trinidad, Columbia, Java, and New Zealand. Global cooling near the end of the Eocene greatly diminished the genus. Its youngest known occurrences are of early Oligocene age in Germany, Italy, England, and Peru.