Deposition of the Sama Formation in the northeastern part of the Central Asturian Coal Basin most probably started in late Lower or early Upper Moscovian time and continued into the Myachkovian; a conclusion based wholly on investigation of the genus Hemifusulina. The Hemifusulina specimens occur all in siltstones and shales with a varying amount of lime, which apparently are the type of sediments laid down in conditions in which this genus could thrive. In the Sama Formation three Hemifusulina zones have been distinguished. A lower zone with H. ex gr. moelleri Raus. at the very base of this formation, a middle zone containing H. ex gr. communis Raus. and H. ex gr. dutkevichi (Putrya) and an upper zone with H. ex gr. graciosa (Lee). The lower zone contains H. hispanica (Gübler) (= Fusulina cylindrica var. hispanica Gübler, 1943); the upper zone contains the new species H. mosquiterensis.