Dolomitic limestones containing abundant stromatolites at the base of the Paleozoic sedimentary series of the Taoudenni syncline in the western Sahara (French West Africa) are Cambrian in age. The stromatolites are calcareous concretions whose formation was due to the action of algae and possibly also of bacteria. In the case of Collenia, genera and species refer to the structure formed, not to the organism responsible for the formation. Forms assigned to Conophyton exhibit a regularity indicating a homogeneous group, which may be of stratigraphic significance.