We made a comparative analysis of the cytogenetics of spiny rat species of the genus Proechimys collected from several sites of the Madeira River basin (Amazonas State, Brazil) and Jari River valley (Pará State, Brazil). Individuals were assigned to three groups based on diploid and fundamental numbers: 2n = 28, FN = 46 (P. cuvieri and P. gr. longicaudatus); 2n = 38, FN = 52 (Proechimys gr. guyannensis), and 2n = 40, FN = 54 (P. gardneri).
A large number of genera in the tropical fish family Characidae are incertae sedis. Cytogenetic analysis was made of four of these species: Astyanax eigenmanniorum, Deuterodon stigmaturus, Hyphessobrycon luetkenii, and H. anisitsi, collected from various hydrographic basins: hydrographic system from Laguna dos Patos/RS, Tramandaí basin/RS and Tibagi River basin/PR. The first two species were collected in their type locality in the State of Rio Grande do Sul. The 2n = 48 karyotype was observed only in A.