In the first three parts of the present series (Van der Hammen, 1966, 1968, 1969) I have dealt with four species of Opilioacarida, viz., Opilioacarus texanus (Chamberlin & Mulaik), Paracarus hexophthalmus (Redikorzev), Opilioacarus platensis (Silvestri), and Adanacarus arabicus (With). The detailed redescription of Opilioacarus texanus (the first part of the series) constituted the morphological base for the subsequent studies. In the meantime, I completed a glossary of opilioacarid terminology (Van der Hammen, 1976), in which not only terminology, but also notations, measurement, description and orientation of figures are standardized. Consequently the continuation of my series of studies on Opilioacarida is now based on the above-mentioned glossary. After publication of the first papers of the present series, I received opilioacarid material from various parts of the world (among which from India). The greater part of this material was already mentioned in my study of opilioacarid phylogeny (Van der Hammen, 1971). The present paper is the first in which part of the new material is described; it contains redescriptions of species of the genus Panchaetes Naudo, and descriptions of new species of the genus Salfacarus gen. nov. 1) The present series of papers will be completed by two further papers (a revision of the genus Opilioacarus, and a detailed description of all stases of a species of the genus Phalangiacarus Coineau & Van der Hammen, from Gaboon). As far as known, the two genera dealt with in the present paper are geographically separated: Panchaetes is West-African, Salfacarus is now known from East-Africa and Madagascar. In my paper on the phylogeny of Opilioacarida (Van der Hammen,