The original material of 3 type species is described, and additional specimens belonging to these 3 genera including some of Ectenonotus like the type but from Nevada, and another species from Newfoundland; some of Pseudomera like the type but from Nevada, and a new species from Newfoundland; some of Pliomerops from New York State. The genus Pliomera is briefly discussed, and the new genus Colobinion proposed for a Newfoundland species which may be allied to Pseudocybele. Special attention is paid to ventral sutures and the hypostome. It is suggested that the Pilekia group and Diaphanometopus do not belong in Pliomeridae and a new diagnosis of the family given. The remarkable similarity between pliomerid species in the early Middle Ordovician of Nevada and Newfoundland supports the correlation based on brachiopods proposed by Cooper.