Abstract
In this paper I propose a new subfamily, Riojatrematinae, included in the family Polystomatidae (Carus, 1863) Gamble, 1896, considering the characteristics of Riojatrema bravoae Lamothe, 1963, found in the urinary bladder of Tomodactylus amulae Günther and Bufo simus Schmidt from Tepoztlán, Morelos, México. A diagnosis of the new subfamily is given with a revised key to the subfamilies of Polystomatidae (Carus, 1863 ) Gamble, 1896.