Distribution and taxonomic contributions to the Ephemeroptera fauna of Mexico and Central America

New records for 16 species of mayflies are reported for Belize, Costa Rica and the Mexican states of Chihuahua, Nuevo Leon and Tamaulipas. The presenc e of Apobaetis indeprensus in Tamaulipas represents a new genus record for Mexico. Fallceon fortipalpus is reported from Tamaulipas, representing the first report in Mexico and first record other than its type locality in Cos ta Rica. Cloeodes excogitatus is reported in Nuevo Leon and Tamaulipas repr esenting the first known locations in Mexico. A new species, Cloeodes waltz i, is described from a distinctive larva collected from the Rio Corona in T amaulipas, Mexico.