Apparition des Choristitinae (Brachiopodes Spiriferida) au Bashkirien inférieur dans le Bassin de Béchar, Sahara Algérien nord-occidental

The mid-Carboniferous boundary represents a major eustatic and biologic event that strongly affected the brachiopods, especially in the extinction of Serpukhovian Gigantoproductinae, followed during the Bashkirian by the appearance of the Choristitinae. In the Bechar Basin, within the lower member of Tagnana Formation (units Tag. 1A - Tag.1I), the mid-Carboniferous boundary is well established by conodonts and ammonoids of H1 zone at Tag. 1E. The last Gigantoproductinae occur in Tag. 1D, where they are associated with Anthracothyrina, spiriferids devoid of dental adminicula, which are also found at Tag. 1 E. The advent of Choristitinae, with subparallel adminicula, occurs at Tag. 1G, in a new section. The type specimens of « Choristites africanus », recently identified in Paris and Algiers collections, are briefly described, along with the subspecies Alphachoristites (Prochoristites) africanus africanus (Termier and Termier, 1950 ), of imprecise stratigraphic position; A. (P.) africanus menouararensis Legrand-Blain nov. subsp., Tag. 1G, H2/R1 zone, Lower Bashkirian; and A. (P). africanus kermaensis Legrand-Blain nov. subsp., Hassi Kerma Formation, G1-2 zone.