Important, relatively recent publications that warrant mention include texts on each class (Lewis 1981, on centipedes; Hopkin and Read 1992, on millipedes). Information on the North American fauna in the latter was updated by Shelley (1996). Other works include a generic-level classification of the Diplopoda with distributional information and nomenclatural notes (Hoffman 1980); illustrated keys to orders and families of New World millipedes (Hoffman 1990, Hoffman et al. 1996) and centipedes in the north-central states (Summers 1979); and a key to worldwide orders and families of centipedes (Mundel 1990). Checklists of North American and Central American millipede species (Chamberlain and Hoffman 1958, Loomis 1968) contain useful distributional information but are outdated; efforts are underway to update them. There is also a survey of cave millipedes in the United States (Shear 1969), which contains an illustrated key to families and genera, and valuable discussions on the latter; it has been supplemented by numerous works, most recently by Hoffman and Lewis (1997) on cave species in Indiana. Faunistic studies with keys to millipede species are available for eastern Canada (Shelley 1988) and central North Carolina (Shelley 1978, Filka and Shelley 1980), and ones without keys are available for Michigan (Snider 1991) and western Canada and Alaska (Shelley 1990a); there is also a faunistic study of Illinois centipedes that was subsequently updated (Summers et al. 1980, 1981). Older publications that are still useful include one by Bailey (1928) on New York centipedes species. Finally, there is an illustrated key to orders and families of centipedes and millipedes in Canada and the adjacent United States (Kevan and Scudder 1989), but it contains internal flaws and should be disregarded (Shelley 1990b).