The British form recognized under this designation appears to have been first recorded and figured from this country by J. de C. Sowerby (16, pl. lvii, fig. 30), who named it Asaphus or Trinucleus (?). He remarks “that no trace of the position of the eyes remains on the cast, which is also the case with the genus Trinucleus, Murchison”. This form was afterwards allocated by Salter to Phacops (Trimerocephalus) lœvis (Münst.) (13, p. 16, pl. i, figs. 5–7; 14, p. 1, pl. ix, figs. 1–5). Phillips had previously named the same species Calymene lœvis, Münst. (8, p. 129, pl. lv, fig. 250), a determination which both Salter (13, p. 16) and M'Coy (6, p. 404) showed to be at fault. This was complicated by the fact that Münster (7, pl. x, fig. 6; 7a, pl. v, fig. 4) had described two different forms under the same specific name, Trinucleus ? lœvis and Calymene lœvis, the latter of which Salter (13, p. 18) correctly adjudged to be a synonym of Phacops granulatus (Münst.) (Calymene auct.) (7a, pl. v, fig. 3). M'Coy had previously noted the identity of C. lœvis, Münst., with Calymene granulata of the same author, but assigned it to his genus Portlockia (6, p. 404).