The diagnostic characters of the group of brachiopods centered about "Orthis testudinaria Dalman" [Ordovician to Devonian] have been reexamined in an attempt to remedy the serious deficiencies evident in the current classification of the group. The cardinalia, ventral muscle field and radial ornament are critically discussed from the functional as well as the morphological aspects. Nineteen genera are considered valid and placed in the family Dalmanellidae Schuchert emended. Idiorthis, Crassiorina, Mesodalmanella, Elsaella, Dalejina, Soudleyella, and Cristiferina are placed in synonymy with Dalmanella, Cryptotyris, Howellites, Heterorthina, Menacella, Onniella, and Paucicrura respectively. A rediscription of the type species of Dalmanella is given.