Summary
This paper is a contribuition to the qualitative survey of the filamentous desmids from two lakes, lago Cristalino and lago São Sebastião in the northern State of Amazonas, Brasil. Samples were gathered montnly during one year. The material collected was identified to totaling 13 infrageneric taxa, all of which were described in every morphological detail possible. They were also given measurements and the illustrations needed for the taxonomic identification of each of the 13 taxa. Comments about every named taxon are included. An artificial key based on fundamental morphological and vegetative characteristics was prepared for the identifications of the genera, species, varieties, and named taxonomic formae documented in the text. One map and one plate containing 18 figures complement the text. A larger number of desmid genera were observed to occur in lago Cristalino than in lago São Sebastião. The genera commonly occuring in both lakes were: Desmidium, Hyalotheca, Sphaerozosma and Spondylosium. The genera Bambusina and Groenbladia only occurred in lago Cristalino.