The main type of forest humus layer known as mull (Muller) seems, as a rule, conditioned by a fauna efficient in keeping down the fungi and maintaining a more bacterial type of decomposition (Muller, 1887; Falck, '23: and Romell, '34). In addition, this fauna may effect an extensive mixing of humus with mineral soil. This is most pronounced in extreme forms of mull such as the crumb mull (Romell and Heiberg, '31 ), inhabited by large earthworms. At least outside Ramann's country, the r6le of earthworms in creating and maintaining a crumb mull type of humus layer has been rather generally accepted after Muller's classical studies (1887). Recently, this has been realized by Ramann's own pupil and successor, Lang ('31). On the other hand, the agents responsible for the formation of less extreme mull forms have remained obscure. Observations reported in the present paper suggest a r6le in the formation of certain mull forms to large myriapods of the American diplopod genus Fonttaria Gray. The findings are believed to have some interest also for animal ecology. Prof. J. W. Bailey, of the University of Richmond, Va., has kindly informed me that most, if not all, work done on myriapods has been systematic in nature, with just a mention, here and there, of feeding habits, etc. In localities with detritus mull (Romell and Heiberg, '31), large diplopods have repeatedly attracted the attention of Professor Heiberg and the writer and particularly of Mr. C. Heimburger, during his extensive field studies in the Adirondacks (Heimburger, '33). Specimens collected by Hfeimburger were kindly determined by Charles H. Blake, of the Boston Museum of Natural History, and by Charles E. Johnson, of the Roosevelt Wild Life Station at the N. Y. State College of Forestry, Syracuse, N. Y. They were found to belong to two species, FoWtaria triniaculata (Wood) and Fonltaria coriacea Koch (see Bollman, p. 123). Both species were described from northeastern United States by Wood, the latter one under the species name corrugatufs. In one particular locality, near North Hudson in the eastern Adirondacks, the largest species, F. triniacuilata, wvas found to be very plentiful and exerting a most striking soil effect. The site is a steep south slope carrying a stand of middle-aged white pine with hardwood undergrowth and a ground vegetation of Heimburger's Dicentra type on a sandy loam rich in lime and showing a brown soil profile. More detailed data are given by Heimburger ('33) under