TWO very remarkable new types of Canadian Cretaceous dinosaurs are described by Mr. Barnum Brown in the first and last of a consecutive series of three papers published in vol. xxxiii., pp. 530-65, of the Bull. Amer. Mus. Nat. Hist. The first of the triad is devoted to Anchiceratops, a member of the horned group (Ceratopsia) from the Edmonton beds of Alberta, characterised by the great size of the knobs bordering the nuchal flange, and the pair of large oval vacuities by which the latter is pierced. Special interest attaches to this type from the fact that it serves to explain the mode of origin of the ceratopsian flange. In the smaller and less specialised type represented by Monoclonius the supra-occipitals form a pair of hook-like opposing processes on the hind border of the upper surface of the skull, leaving a mushroom-shaped interval between them, and a pair of very large vacuities in the skull-roof. In Anchiceratops the supra-occipital processes have united in the middle line, where only a remnant of a central fontanelle is left, while the vacuities in the lateral portion of the cranial roof are very much smaller. Finally, in Triceratops, which is both the largest and latest member of the whole group, all vacuities have disappeared from the cranial roof and the nuchal flange attains its maximum development.