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Llandovery and early Wenlock conodont faunas show high diversity and rapid evolution, and conodonts provide a valuable biostratigraphic tool for this interval. Wenlock, Ludlow and Downtonian faunas are of lower diversity and variability, but, with the exception of the lower Ludlow, abundances are fairly high and several species are useful in local correlation. The local geographic distribution of conodonts is affected by facies variation, and this is particularly marked in the upper Llandovery and lower Wenlock. Geographic restrictions on distribution are also evident on an international scale, and of the ten conodont zones defined in the Silurian of Europe only four (the celloni, amorphognathoides, sagitta and eosteinhornensis Zones) have been identified in Britain. However, several species that are of value in Britain have been widely recognized, and with further work, the promise shown by eonodonts for international correlation should be fulfilled.
