A calcareous nannofossil study of the Paleocene/Eocene Thermal Maximum (PETM) sequence from Ocean Drilling Program Site 1259 on Demerara Rise (western equatorial Atlantic) has revealed a new species, Coccolithus bownii, that peaks just above the boundary. This species thrived in the PETM-related stressed environment and is considered a significant environmental indicator. Based on its ultrastructural characteristics, which are strongly reminiscent of those of the modern Coccolithus pelagicus, the new species is assigned to the genus Coccolithus, instead of Ericsonia, the latter of which is here considered a junior synonym. Two new combinations (Coccolithus insolitus and Coccolithus occidentalis) are validated that were originally published only in electronic media.