A key to identify the known mature larvae of the South American genera of the family Elmidae is provided. The key includesseven genera presently assigned to the subfamily Larainae and 15 genera assigned to the subfamily Elminae. New distributionaldata for all genera and a checklist of described larvae are also included. The mature larva of Macrelmis saltensis Manzo isdescribed and illustrated for the first time, and compared to other known larvae of the granigera species-group. Distributionalnotes for M. saltensis increase its known range to the north, this being the first citation of the species for Bolivia. Macrelmis isis(Hinton) is also cited for the first time for Bolivia.