The classification of Pluteus into three sections on the structure of the cuticle of the pileus and the type of pleurocystidia appears justified. Section Celluloderma for North America contains twenty-four species and varieties and is subdivided on the presence or absence of pileocystidia into subsections Mixtini and Celluloderma. Two species and one variety are described as new. Keys of the North American species of the section Celluloderma are given. Photogaphs of basidiocarps and line drawings of microscopic characters are included. Differences in color of the vacuolar pigment were found to be important for delineating species. Shape and size of cystidia, and spore and shape of basidiocarp, and texture of the surface of pileus are regarded as secondary. Although the species occur on rotting wood all attempts to obtain cultures from tissue transplants failed, and none of the attempts to germinate spores were successful. This is contrary to growth studies of wood inhabiting fungi generally and seems to indicate some sort of special ecological adaption on the part of this genus. The family Volariaceae appears to be relatively isolated in the Agaricales and not related closely to the Amanitaceae.