Among the fishes of the Lower Lias of Lyme Regis, Dorsetshire, described by Egerton from imperfect evidence, is the genus Osteorachis, with the single species, O. macrocephalus. The original description and figure are so unsatisfactory that nothing beyond the name of the fish is quoted even in Zittel's “Handbuch” (vol. iii, p. 230), while this bears an appended query; and the author's definition of the genus is certainly much too vague to admit of any precise determination of its systematic relationships. Under these circumstances it is of interest to return to a consideration of the fish in the light of more recently discovered specimens, which seem to the present writer to comprise not only examples of the trunk but also, at least, one satisfactory head.