Specimens of the large, shallow-marine, volutid gastropod Volutoderma Gabb, 1877, herein recognized only from strata of Late Cretaceous (Coniacian through early Maastrichtian) age in British Columbia, Washington, California, and Baja California have commonly been identified as Volutoderma averillii (Gabb, 1864). This review of available specimens assigns them to two genera: Volutoderma and Longoconcha Stephenson, 1941.
Twelve species, nine of them new, comprise three morphologic lineages of Volutoderma, i.e., 1) “Typical” includes V. querna n. sp., V. averillii (Gabb), V. blakei n. sp., V. jalama n. sp., V. perissa n. sp., and possibly Volutoderma? n. sp.; 2) “Angelica” includes V. angelica n. sp., V. elderi n. sp., and V. ynezae n. sp.; and 3) “Magna” includes V. santana Packard, V. magna Packard, and perhaps V.? antherena n. sp. A new species of Longoconcha, L. eumeka, is the first Pacific Slope record of this genus, which has a Gulf Coast and Tethyan Old World distribution. A smaller volutid, Retipirula Dall, 1907 is endemic to the study area and was formerly known only from its type species R. crassitesta (Gabb, 1869) of Paleocene age. Two new Retipirula are reported: R. calidula of latest Maastrichtian age and R. pinguis of Paleocene age.
Only the Volutoderma lineage containing V. averillii has been found north of San Francisco. Recovery of rudist bivalves from formations yielding Volutoderma suggests that these volutes were warm-temperate to subtropical gastropods. Co-occurrences of these gastropods and rudistids may aid in placing the warm-temperate/subtropical boundary during the Late Cretaceous.