Palaeoersachus bicarinatus gen. et sp. n. is described from Eocene Baltic amber. The species seems to be most closely related to the extant Neotropical genus Ersachus Erichson, 1847. Potential synapomorphies of the two genera are the presence of pronotal carinae and hypomera with a pronounced internal border. The systematic position of Ersachus and Palaeoersachus gen. n. is discussed; apparently, they do not belong to the subfamilies Limnichinae or Cephalobyrrhinae, as stated by previous authors. Both genera are tentatively regarded as Limnichidae incertae sedis.