Balticalcarus archibaldi Simutnik, gen. et sp. n., is described and illustrated based on a female specimen from late Eocene Baltic amber. The new genus is characterized by the absence of a filum spinosum, a "boat"-shaped hypopygium enclosing the ovipositor, reaching far past the apex of the syntergum, the presence of a line of long setae along the entire costal cell of the hind wing, and a transverse line of thickened setae alongside the hyaline spur vein. Moreover, like most previously described Eocene Encyrtidae, the new taxon differs from the majority of the extant ones by a number of morphological features. The new fossil differs from most extant and all known fossil Encyrtidae by its unusually small, thin, smooth (without microsetae) mesotibial spur.
Keywords: Tetracnemini; common ancestor; evolution of Encyrtidae; hypopygium.