Quelques graptolites du Silurien superieur du Sahara septentrional

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Abstract
A detailed study of graptolites from two oil wells south of Laghouat, Algeria, permits a precise subdivision of the upper Silurian from the upper Wenlock to the upper Ludlovian. The upper Wenlockian is characterized by Sardinian forms unknown in northern Europe. The eight species described from this age are similar to Moroccan and Bohemian faunas and indicate that during that time the connection with the northern European seas, although slight, had not yet been cut. In the lower Ludlovian the communication between the seas was normal as indicated by the similarities with the faunas of America, northern Europe, and the USSR. Eight species are described which have been recognized previously in Bohemia, Great Britain, and America. The middle Ludlovian fauna is sparse but recognizable as a Bohemian fauna. Three species and a new variety--Monograptus aequabilis n. var.--are described. The upper Ludlovian fauna is correlative with zone egamma of central Europe. Five species are described, including Monograptus sp. (sub-hercynicus n. sp.?).

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