Through a review of older type collections and identifications of undescribed collections, using a broad species definition, the Devonian succession is divided into 10 assemblages. The names of many species are revised. With the exception of the Pragian, all stages of the system are represented by one or more assemblages. The ranges of important taxa are plotted and shown to be relatively short and diagnostic of the 10 intervals. In the absence of conodonts in the reef facies, stromatoporoids offer a supplementary method of correlation. Many species occurring in Canada can be recognized in the stromatoporoid faunas of the former Soviet Union, China, Europe, and Australia.