A new chewing louse genus and species belonging to the Philopteridae, namely, Palmaellus inexpectatus n. gen., n. sp., is described. The new genus is distinguished from the other ischnoceran genera hitherto described by its peculiar characters of the dorsal anterior head plate with 2 postero-lateral projections, pterothorax and abdomen with scarce chaetotaxy, male genitalia with simple mesomere and paramere lacking inner digitiform projection, and the genital region of female with postero-vulvar plates bearing setae. It is a parasite of the trumpeters, an avian family endemic to South America's Amazon Basin.