The life history of Deropristis inflata has been demonstrated experimentally. The cercaria is a trichocercous form developing in simple rediae in the marine snail, Bittium alternatum. It enċysts in Nereis virens and the eel, Anguilla rostrata serves as the natural definitive host which becomes infected by eating annelids containing metacercariae.The genus Deropristis and Dihemistephanus sturionis are excluded from the family Acanthocolpidae which is redefined to include for the first time the genera Lepidauchen, Pleorchis, and Pseudolepidapedon. The family Pleorchiidae thereby becomes invalid.It is proposed that the family Allocreadiidae be restricted to include only forms known or believed likely to have ophthalmoxiphidiocercariae with main excretory tubules not reaching the cephalic region of the body before receiving secondary tubules. The Allocreadiidae and Acanthocolpidae are regarded as separate but closely related families.The genus Anallocreadium is reduced to synonymy with Homalometron and the su...