The Argas subgenus Secretargas Hoogstraal has previously been based only on A. (S.) transgariepinus White, a parasite of bats and geckos ranging from South Africa to southern Europe and the Near East. Discovery in Madagascar of adults and nymphs of A. hoogstraali Morel and Vassiliades, which was described from larvae only, provides information showing that this species also belongs to the subgenus Secretargas . Both sexes and large and small nymphal instars are described and the larva is redescribed. A. hoogstraali parasitizes 3 species of Oplurus lizards that shelter under stones on slopes that are flooded during the rainy season in the hot, semiarid southwestern area of Madagascar. A related parasite, A. (S.) echinops , new species, is also described from both sexes, large and small nymphs, and larvae. This species infests the Small Madagascar Hedgehog, Echinops telfairi Martin, and is found under larger stones in the same hot, semiarid savannah zone of Madagascar as A. (S.) hoogstraali .