Though the economic importance of predaceous plant inhabiting mites cannot be at present correctly estimated, the fact they prey on phytophagous mites or insects justifies the researches concerned with them. Phytoseiidae are an important group of these presumably useful mites, while several non mesostigmatid ones have been shown to be effective. The abbreviations used have been defined previously ; the nomenclature of the idiosomal chaetom is that of Hirschmann for the ventral side and that of Athias-Henriot for the dorsal one (with a synonymic table). In the fam. Phytoseiidae, the genus Amblyseius Berlese has been redefined by Chant and by Athias-Henriot on the basis of the setal pattern of the notocephalic portion of the dorsum. Four other ones (Phytoseiulus, Iphiseius, Asperoseius, Proprioseius) exhibit the same pattern, which distinguishes these 5 former genera from Typhlodro-mus and Phytoseius. As the relationships between the 5 former are thought to be closer than that which unites Amblyseius and Typhlo-dromus, Amblyseius is treated as a genus ; this position differs slightly from that of Chant, who considers Amblyseius as a subgenus of Ty-phlodromus. As the species of Amblyseius are numerous, it seemed practically convenient to divide it in species groups ; though the key to the groups (A ben ans, Finlandicus , Cucumeris, Obtusus J is a little complicate, those who have seen many species of the genus could probably admit their individuality intuitively. Among the described species (about 15) of the Cucumeris group, the identities of A. cucumeris (Womersley ex Oudemans) and A. californicus (McGregor) are dubious. In Algéria, 8 species of this group have been found ; they are keyed and adult ♀♂ and nymphs of a new one, A. leucofthaeus, are described. A. reticulatus (Ouds.) has also been taken in Corsica ; the ♂ of A. bellinus (Womersley) is described. A diagnostic table of the 3 known species of the genus Phytoseiulus Evans is proposed which is based on 2 characters, N♀ and the shape of the ♂ventrianal scutum. Five species of actinochitinose entomophagous acari are reported, 3 of them being cheyletid mites. Some remarks about possible economic incidence of Molothrognatus fulgidus Summers and Schlinger (Caligonellidae) and Hemisarcoptes malus (Shimer) (Hemisarcoptidae) are given.