Abstract
Structural and behavioural reasons are presented for regarding the Merothripidae, rather than the Aeolothripidae, as the most primitive Thysanoptera. Examination of more than five hundred specimens of Merothrips has resulted in a new interpretation of intraspecific variation and the establishment of eight new synonyms. This genus is regarded as Neotropical with some species widely distributed around the world by man. Keys are provided to the four genera of Merothripidae and to the twelve recent species of Merothrips.