Since the comprehensive taxonomic work on Brazilian Simuliidae by Shelley et al. (2010) we have discovered variations in characters of two species S. minusculum Lutz and S. oyapockense Floch and Abonnenc of the subgenus Psaroniocompsa. Variations in adult thoracic pattern and pupal gill configuration are described for S. minusculum and based on these a new form for the population of Chapada das Guimarães is created. The variation in pupal cocoon form from typical slipper-shaped to the rarer shoe-shaped form in the same population of S. oyapockense s.l. in Brazil confirms S. sanchezi as a junior synonym of this species. A redescription of the larva of S. minusculum is also provided.