Bryanites graeffii sp. n. is described from Samoa based on a single male specimen collected between 1862–1870 that was recently discovered in the Muséum national d’Histoire naturelle, Paris. Cladistic analysis based on 127 morphological characters from 49 exemplars of the carabid beetle tribe Platynini in the Austral-Pacific region, places the new species as adelphotaxon to Bryanites samoaensis Valentine, type species of the genus Bryanites Valentine, 1987. Bryanites comprises, along with Vitagonum Moore, 1998 of Fiji and Ctenognathus Fairmaire, 1843 of New Zealand, a clade that diverged early in the evolutionary history of Pacific platynine Carabidae. Bryanites graeffii exhibits very large body size among taxa of Platynini—16.2 mm standardized body length—with the genus characterized by vestigial flight wings and metathoracic apomorphies that are associated with flight-wing loss. Along with Blackburnia Sharp, 1878 of Hawaii, the origins of Bryanites, Vitagonum, and Ctenognathus are hypothesized to date to the Miocene, with their radiations beginning long before the origins of the geographically widespread, flight-capable species of Metacolpodes Jeannel, 1948 that colonized numerous island systems across the western Pacific. Given the numerous platynine taxa collected by extensive biotic surveys of Samoa during the first quarter of the 20th Century, the absence of any specimens of B. graeffii since the initial collection of the unique holotype prior to 1871 suggests that this species may be extinct. Such extirpation of large platynine carabid beetles has also been documented for Hawaii, where the time of extinction of seven Blackburnia species represented only by subfossil fragments coincides with the time of human colonization and attendant introduction of the Pacific rat, Rattus exulans (Peale).