Abstract
The zonal scheme proposed in 1971, mainly for the french sequences, is slighthy modified in order to improve thecorrelations: 1, inside the NW european province, where several charts have been proposed, which were based on different ammonites-groups; 2, with the Western Tethys. A new “Fluitans” Subzone is introduced to avoid the confusions which have risen due to the difficult interpretation of the index Pleydellia aalensis (voir note 1, p. 11). The Dispansum Zone is now adopted because its base is a good marker; the range of the Insigne Subzone is thus reduced. All the horizons of the Bifrons Zone are now indexed on the Hildoceras sequence of species. In the mediterranean province, Hammatoceras bonarellii has been choosen to replace Osperlioceras rivierense for the part of the succession where the difficulties of correlation are the worst. The synchronism of the boundaries is often questionnable. This problem has led to the use of local indexes as Hammatoceras speciosum and Hildaites levisoni..
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