Males of Ornitocheyletia hallae from pigeon are described and an analysis made on a number of structures of gnathosoma of both sexes. The habitat of Ornitocheyletia hallae is skin of pigeons where only epidermis is affected by the mites transforming its stratum, corneum to a spongy layer of exfoliated horny flakes combined with serous exudations. The cheliceral apoteles can only reach down to the uppermost layer of corium. The transformed horny layer is attacked by an actinomycet, J.Vlicromonospora chalcea, and a mutualistic interrelationship is suggested to exist between this microorganism and the mite; with its proteolytic enzymes the microorganism may decompose the high organic components of the horny layer to products which the mite can assimilate directly. Modified cheliceral setae (’scrapers’) are looked upon as an adaptive mode to transport decomposed products into the mouth and the bipectinate empodia of the ambulacra may serve to disentangle the claws from the filaments of Micromonospora chalcea.