A new feather mite genus Armophyllodes gen. n. (Proctophyllodidae: Proctophyllodinae) is established based on two new species, Armophyllodes gracilis sp. n. (type species) and A. robustus sp. n., described from the Olivaceous flatbill, Rhynchocyclus olivaceus (Temminck) (Passeriformes: Tyrannidae), in Panama. The new genus is related to the Nycteridocaulus generic group and clearly differs from other genera in having the strongly sclerotized lateral parts of coxal fields II in both sexes, the epigynum fused with the inner tips of epimerites IIIa in females, and vestigial terminal lamellae in males. The fusion of the epigynum with epimerites is an extremely rare character state in the subfamily Proctophyllodinae; among other known members of this subfamily, it was previously known only in females of Anisophyllodes pipromorphae Atyeo, 1967. In contrast to the subfamily Pterodectinae, in all representatives of which the fusion of the epigynum with epimerites is complete and these sclerites constitute a uniformly sclerotized arch-like structure, in the two species of the genus Armophyllodes and in An. pipromorphae, the traces of fusion between these sclerites are clearly distinct. This gives evidence that the fusion of the epigynum with epimerites in pterodectines and proctophyllodines originated independently.