A combination of molecular, biogeographic and morphological data indicates that the eastern Pacific species Felimare ghiselini is a synonym of F. californiensis, also recorded from this region. However, a disjunct population from Peru, previously considered to be F. ghiselini, represents a distinct species, formally described herein as F. sechurana. Although previous work recognized that F. californiensis had a disjunct range with populations on the Pacific coast of North America and in the Gulf of California, the synonymization with F. ghiselini extends the range of this species into the southern part of the Gulf of California and also to Clipperton Island. Consequently, F. californiensis can now be stated to be common in the southern Gulf of California, minimizing concerns about the conservation status of this species. A latitudinal gradient in morphology is discussed. Speciation between F. californiensis and F. sechurana is hypothesized to be the result of dispersal of members of an ancestral population across the tropical eastern Pacific during the repeated periods of glaciation during the Pleistocene, followed by isolation. These results are consistent with a pattern of antitropical speciation that may have shaped biodiversity patterns across the eastern Pacific Ocean.