PARNAHIBA, a river of Brazil, rises near the 10th degree of S. Lat., and flows northward to the Atlantic, separating the provinces of Piauí and Maranhão. Its whole length is more than 700 miles, for a great part of which it is navigable. It falls into the sea by several mouths, forming a delta about 5 miles broad. Its chief affluents are the Gurgua from the E., and the Balsas from the W.