The placement of the tribe Gastropini within the subfamily Gymnomyzinae, with the tribe Gymnomyzini as a sister-group, is supported. Validity for two genera Gastrops Williston and Notacanthina Macquart (senior synonym of Beckeriella Williston) is maintained. Particular characters of their proboscis, ventral receptacle and the male terminalia are presented. A key to species and habitus photographs of selected species of Gastrops and Notacanthina are provided. The following new combinations are proposed: Notacanthina clypeata (Lizarralde de Grosso, 1986), comb. nov., N. fasciata (Mathis & Grimaldi, 2000), comb. nov., N. filipina (Lizarralde de Grosso, 1994), comb. nov., N. gigas (Lizarralde de Grosso, 1986), comb. nov., N. longiventris (Lizarralde de Grosso, 1990), comb. nov., N. maculata (Mathis & Grimaldi, 2000), comb. nov., N. magnicornis (Cresson, 1934), comb. nov., N. paragigas (Lizarralde de Grosso 1991a), comb. nov., N. parapendicornis (Lizarralde de Grosso, 1992), comb. nov., N. pendicornis (Cresson, 1934), comb. nov., N. pseudoclypeata (Lizarralde de Grosso, 1991), comb. nov., N. schildi (Cresson, 1934), comb. nov., N. wirthi (Lizarralde de Grosso, 1998), comb. nov. N. brasiliensis (Lizarralde de Grosso, 1998) is treated as an invalid name of N. wirthi (Lizarralde de Grosso, 1998).