Recent publications present diverse opinions concerning the classification and taxonmy of the Trematoda. Dollfus (1958b) adopted the system of Faust and Tang (1936), recognizing three subclases: Monogenea, Digenea, and Aspidogastrea. Baer and Euzet (1961) removed the Monogenea from the Trematoda and regarded the group as a separate and independent class in the phylum Platyhelminthes, while Baer and Joyeux (1961) restricted the Trematoda to three subclases: Aspidogastrea, Digenea, and Didymozoidea. Stunkard (1962) presented a new arrangement and restored the terminology of Burmeister (1856) but revised the status of the Aspidobothrea. The class Trematoda was divided into two subclasses, Pectobothridia and Malacobothridia. The Pectobothridia contain two orders, Monopisthocotylea and Polyopisthocotylea; the Malacobothridia contain two orders, Aspidodothrea and Digenea. Morphological and development data are presented to support the opinion that the polystomes should be retained in the Trematoda; that the Did...