Cupedidae, the most species-rich family of the archaic suborder Archostemata, were abundant, diverse and widespread in the Mesozoic, yet little is known about the early evolution and biogeography. This stems, in part, from a lack of exceptionally preserved fossils from the Mesozoic and of formal phylogenetic study of both extant and extinct taxa. Here we describe and illustrate a new fossil from mid-Cretaceous Burmese amber, and provide a phylogeny combining both fossils and all known extant genera of Archostemata. A dataset of 43 ingroup taxa and four outgroup taxa based on 110 morphological characters was analysed under parsimony. The results indicate that Priacma LeConte and Paracupes Kolbe, as well as the Cretaceous genera Barbaticupes Jarzembowski et al. and Mallecupes Jarzembowski et al., together form a sister clade to the rest of Cupedidae. Priacma megapuncta sp.n. is attributed to the relict North American Priacma by the presence of distinct subtruncate elytral apices, lateral elytral margins with two rows of sharp teeth, and peculiar fixing epipleural folds near the elytral apices. Our discovery of the first fossil species of Priacma in Burmese amber reveals the antiquity and wider distribution of the genus in the late Mesozoic. This published work has been registered in ZooBank, .