Complete redescriptions of S. trukense Stone and S. guamense Stone (subgenus Inseliellum Rubtsov) are made based on new material from Micronesia. Holotypes of S. arlecchinum Craig and S. admixtum Craig have been reexamined and new morphological details provided as they are for some other species. Seven new species are described: S. caesariatum, S. fararae, S. hispidum, S. hirticranium, S. joyae, S. pallidicranium, and S. pseudocorium. A new hirticranium subgroup within the castaneum-group, which includes S. pallidicranium, S. hirticranium, S. hispidum, and S. caesariatum, is defined on the basis of numerous elongate cephalic setae and smooth abdominal cuticle in the larvae. Simulium fararae and S. joyae are placed in the castaneum-group and S. pseudocorium in the tahitiense-group. A total of 48 species is now recognized for Inseliellum. Brief comments are made concerning larval habitats, biology, relationships within Inseliellum, and problems with homoplasy.