In the present paper Mixogamasus gen. nov., at present monotypical, is defined and its generotype Mixogamasus intermedius n. sp. is described. The following diagnosis is given: an entire dorsal shield with deviations from the normal notocephalic (podonotal) chaetotaxy (19 pairs of setae); the peritremal hield fused with the opisthogastric shield as in Leptogamasus Tragardh sensu ATHIAS 1971; on the pedipalp the two setae on the internal face of the genu are different: the proximal foliate, the distal bifide; the movable digit of the chelicerae has in the female four teeth and in the male two; the female epistome is five pronged while the male s one takes the form of a triangular lobe. The presence or absence of a division of the dorsal shield is considered here as the main character in separating the family in two major subgroups which could be recognized as two subfamilies: Parasitinae and Pergamasinae. Wïthin the Pergamasinae the related genera Mixogamasus gen. nov., Leptogamasus Tragardh sensu ATHIAS 1971 and Phityogamasus (Juvara et Athias) join in the new tribe Leptogamasini.