The pectinid bivalve genus Neithea is an important indicator for understanding the Cretaceous biogeographic relationships between the Tethyan Realm and peripheral regions. However, its records in the Northeast Pacific have been scarce and Neithea (Neithea) grandicosta Gabb is the only known species from this area, though its stratigraphic range and morphology are poorly known. Recently collected specimens of N. (N.) grandicosta from the Hauterivian and Upper Aptian parts of the Budden Canyon Formation in northern California are described in detail. It is possible that the stratigraphic distribution of Neithea in the Northeast Pacific is also restricted to the Lower Cretaceous as it is in the Northwest Pacific. It can be considered that the demise of the Tethyan biota and following origination of endemic fauna in the post-Aptian Cretaceous occurred not only in the Northwest Pacific, but also in the Northeast Pacific. The stratigraphic distribution of the non-rudist Tethyan bivalves and other Tethyan biota in the Northeast Pacific is an important clue for understanding major mid-Cretaceous biogeographic changes in the entire North Pacific.