AMONG unidentified material kept at the Fish and Wildlife Service Laboratory at Florianopolis, capital of the State of Santa Catarina, were several specimens of the freshwater prawn Macrobrachium. These were identified as M. carcinus and M. acanthurus. The two specimens of M. carcinus, of 200 and 210 mm total length (excluding the second pair of pereiopods, which measured 230 mm), were from Lagoa da Conceicao, a brackish to freshwater lagoon on the Santa Catarina Island. The eight specimens of M. acanthurus of 80–140 mm total length (excluding the second pair of pereiopods, which measured up to 120 mm in length), were from Rio Pinheira (27° 50′ S.), a small river on the mainland, about 3 miles south of the southernmost tip of S. Catarina Island. Local fishermen stated that M. carcinus had occasionally been taken from Rio Pinheira, but this could not be verified.